194 results on '"excited-state"'
Search Results
2. Temperature Evolution of Two-State Lasing in Microdisk Lasers with InAs/InGaAs Quantum Dots.
- Author
-
Makhov, Ivan, Ivanov, Konstantin, Moiseev, Eduard, Fominykh, Nikita, Dragunova, Anna, Kryzhanovskaya, Natalia, and Zhukov, Alexey
- Subjects
- *
QUANTUM dots , *INDIUM gallium arsenide , *HIGH temperatures , *NUMERICAL functions , *CRITICAL temperature , *WHISPERING gallery modes , *SUPERCONDUCTING transitions - Abstract
One-state and two-state lasing is investigated experimentally and through numerical simulation as a function of temperature in microdisk lasers with Stranski–Krastanow InAs/InGaAs/GaAs quantum dots. Near room temperature, the temperature-induced increment of the ground-state threshold current density is relatively weak and can be described by a characteristic temperature of about 150 K. At elevated temperatures, a faster (super-exponential) increase in the threshold current density is observed. Meanwhile, the current density corresponding to the onset of two-state lasing was found to decrease with increasing temperature, so that the interval of current density of pure one-state lasing becomes narrower with the temperature increase. Above a certain critical temperature, ground-state lasing completely disappears. This critical temperature drops from 107 to 37 °C as the microdisk diameter decreases from 28 to 20 μm. In microdisks with a diameter of 9 μm, a temperature-induced jump in the lasing wavelength from the first excited-state to second excited-state optical transition is observed. A model describing the system of rate equations and free carrier absorption dependent on the reservoir population provides a satisfactory agreement with experimental results. The temperature and threshold current corresponding to the quenching of ground-state lasing can be well approximated by linear functions of saturated gain and output loss. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
3. Theoretical studies on the excited-state properties of di(pyridinyl)methanone-based emitters with efficient thermally activated delayed fluorescence.
- Author
-
Zou, Ya-tong, Ding, Xiang, Xiao, Xuan, Yang, Ji-feng, Ou, Li-hui, Jin, Jun-ling, Gao, Ying, and Wu, Yong
- Subjects
DELAYED fluorescence ,SPIN-orbit interactions ,NUMBERS of species ,INTRAMOLECULAR proton transfer reactions - Abstract
[Display omitted] • Excited-state level and nature can be readily tuned by the species and number of donor. • The mono-substituted donor slightly increases
1 LE and significantly improves3 LE. • The different nature between S 1 and T 1 induces strong spin–orbit coupling. • Fast reverse intersystem crossing rates for the designed emitters. The excited-state properties of seven thermally activated delayed fluorescence (TADF) emitters with di(pyridinyl)methanone acceptor were investigated using DFT and TD-DFT methods. The results indicate that the species and number of donors strikingly impact the excited-state nature. The mono-substituted donor increases the local-excited singlet (1 LE) and local-excited triplet (3 LE) contribution, promoting the radiative decay processes and strengthening spin–orbit coupling (SOC) between S 1 and T 1 states. The decreased charge transfer (CT) contribution of S 1 gives rise to a much smaller Δ E ST , and the mixed CT-LE nature of T 1 guarantees the strong SOC for the designed emitters 1 – 4 and 6 , endowing them with high reverse intersystem crossing rates. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
4. The Study of Excited-State Intramolecular Charge Transfer in Organic Molecules and the Development of a Novel Sub-Micron Sampling and Offline Chemical Analytical Technique
- Author
-
Cohen, Trevor Elijah
- Subjects
Physical chemistry ,Excited-State ,Indigo ,Molecules ,Organic ,REMPI ,TELD - Abstract
A molecule’s ability to survive upon irradiation is intrinsically tied to how quickly it can release the energy it has absorbed, as prolonged excitation leads to damaging reactions with its surroundings. To probe how unique structural moieties of various biomolecules and organic dye molecules mechanistically relax after photoexcitation in a solvent-free environment, Resonance Enhanced Multi-Photon Ionization (REMPI) was used. REMPI is a powerful spectroscopy technique that describes photon events involving two to three photons sequentially absorbed by the sample to excite and ionize the molecule of interest along various trajectories. These spectroscopic studies employ lasers ranging from the UV-IR with either picosecond or nanosecond pulse width to analyze the absorption spectrum, tautomeric structure, and the excited-state dynamics of the molecules. In collaboration with theoretical calculations modelling the excited-state potential energy surface and dynamics, it becomes possible to draw conclusions on how electronically and structurally a molecule relaxes.Upon excitation, a molecule can utilize various mechanisms to reach the ground state. For example, the canonical nucleobases utilize fast internal conversion to reach conical intersections leading back to the ground state. A study of the alternative nucleobase, isocytosine, was performed comparing its dynamics to guanine and cytosine. Another relaxation mechanism used is excited-state intramolecular hydrogen, proton, and charge transfer (ESIHT, ESIPT, and ESICT respectively), which describes the movement of a charge or hydrogen atom from a donor to acceptor site. This process produces new photoproducts, each with new available relaxation pathways to the ground state. Intramolecular charge and atom transfer are typically ultrafast processes and are too fast to measure with the picosecond laser systems available but are slowed by several orders of magnitude when quantum tunneling is involved. Measurements of the photoproducts post transfer can also provide insight into the mechanism. These studies focus on how various structural moieties in organic dyes, nucleosides, and polypeptides and substituents such as methylation, deuteration, halogenation, and changes in secondary structure affect the rate of excited-state intramolecular transfer. Selective placement of the substituent groups at or near the transfer site provides precise control of the dynamics that when combined with theoretical calculations can develop detailed models of the mechanism. REMPI is a powerful chemical characterization tool that provides both highly specific mass, absorption, and structural information of a sample. However, the technique cannot distinguish spatial features on the surface of the sample material. The development of a novel sub-micron sampling technique, Tip Enhanced Laser Desorption (TELD), is described below. TELD is an off-line sampling process in which a sample is first imaged with an AFM, then a laser is focused and fired at the probe desorbing the surface beneath it, and then the vaporized material is collected and redeposited onto a new substrate for further analysis. Separation of the sampling and chemical characterization techniques results in independent optimization of the samples collected depending on the analytical technique chosen. Detailed experiments into various parameters of the technique such as laser power, number of pulses fired, tip material, and the forced applied between the tip and surface providing insight into the underlying mechanism of energy transfer.The synthesis and characterization of InGaN multi-quantum wells and the lasing wavelength of the material was also studied. Pumping of the material with a 355 nm pulsed laser revealed a pumping threshold of 1.5 MW/cm2 and a lasing wavelength of 568 nm, a spectral region previously not producible with semi-conducting laser materials.
- Published
- 2023
5. Temperature Evolution of Two-State Lasing in Microdisk Lasers with InAs/InGaAs Quantum Dots
- Author
-
Ivan Makhov, Konstantin Ivanov, Eduard Moiseev, Nikita Fominykh, Anna Dragunova, Natalia Kryzhanovskaya, and Alexey Zhukov
- Subjects
two-state lasing ,quantum dots ,microdisks ,ground-state ,excited-state ,temperature ,Chemistry ,QD1-999 - Abstract
One-state and two-state lasing is investigated experimentally and through numerical simulation as a function of temperature in microdisk lasers with Stranski–Krastanow InAs/InGaAs/GaAs quantum dots. Near room temperature, the temperature-induced increment of the ground-state threshold current density is relatively weak and can be described by a characteristic temperature of about 150 K. At elevated temperatures, a faster (super-exponential) increase in the threshold current density is observed. Meanwhile, the current density corresponding to the onset of two-state lasing was found to decrease with increasing temperature, so that the interval of current density of pure one-state lasing becomes narrower with the temperature increase. Above a certain critical temperature, ground-state lasing completely disappears. This critical temperature drops from 107 to 37 °C as the microdisk diameter decreases from 28 to 20 μm. In microdisks with a diameter of 9 μm, a temperature-induced jump in the lasing wavelength from the first excited-state to second excited-state optical transition is observed. A model describing the system of rate equations and free carrier absorption dependent on the reservoir population provides a satisfactory agreement with experimental results. The temperature and threshold current corresponding to the quenching of ground-state lasing can be well approximated by linear functions of saturated gain and output loss.
- Published
- 2023
- Full Text
- View/download PDF
6. Solvent effects on excited-state relaxation dynamics of paddle-wheel BODIPY-Hexaoxatriphenylene conjugates: Insights from non-adiabatic dynamics simulations†.
- Author
-
Chen, Wen-Kai, Cui, Ganglong, and Liu, Xiang-Yang
- Subjects
SOLVENTS ,CHARGE transfer ,PHOTOINDUCED electron transfer ,BAND gaps ,EXCITED states ,ELECTRONIC structure - Abstract
Understanding the excited state dynamics of donor-acceptor (D-A) complexes is of fundamental importance both experimentally and theoretically. Herein, we have first explored the photoinduced dynamics of a recently synthesized paddle-wheel BODIPY-hexaoxatriphenylene (BODIPY is the abbreviation for BF
2 -chelated dipyrromethenes) conjugates D-A complexes with the combination of both electronic structure calculations and non-adiabatic dynamics simulations. On the basis of computational results, we concluded that the BODIPY-hexaoxatriphenylene (BH) conjugates will be promoted to the local excited (LE) states of the BODIPY fragments upon excitation, which is followed by the ultrafast exciton transfer from LE state to charge transfer (CT). Instead of the photoinduced electron transfer process proposed in previous experimental work, such a exciton transfer process is accompanied with the photoinduced hole transfer from BODIPY to hexaoxatriphenylene. Additionally, solvent effects are found to play an important role in the photoinduced dynamics. Specifically, the hole transfer dynamics is accelerated by the acetonitrile solvent, which can be ascribed to significant influences of the solvents on the charge transfer states, i.e. the energy gaps between LE and CT excitons are reduced greatly and the non-adiabatic couplings are increased in the meantime. Our present work not only provides valuable insights into the underlying photoinduced mechanism of BH, but also can be helpful for the future design of novel donor-acceptor conjugates with better optoelectronic performance. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
7. Editorial: Advances in Density Functional Theory and Beyond for Computational Chemistry
- Author
-
Wei Hu and Mohan Chen
- Subjects
density functional theory ,low-scaling algorithms ,machine learning ,excited-state ,high-performance computing ,Chemistry ,QD1-999 - Published
- 2021
- Full Text
- View/download PDF
8. Effect of water on excited‐state double proton transfer in 7‐azaindole‐H2O complex: A theoretical study.
- Author
-
Yi, Jiacheng and Fang, Hua
- Subjects
- *
INTRAMOLECULAR proton transfer reactions , *PROTON transfer reactions , *PROTONS , *HYDROGEN bonding , *WATER - Abstract
The dynamics of excited‐state double proton transfer (ESDPT) depending on hydrogen bonding of water molecules to the mediating water were studied at the TD‐M06‐2X/6‐31+G(d, p) level. The additional H‐bonding accepting (aW) or donating (dW) water had an effect on the mechanism of ESDPT. The double proton transfer occurred in an asynchronous but concerted protolysis or solvolysis pattern dependence on the aW or dW, respectively. The aW or dW stabilized the corresponding protolysis or solvolysis mechanism, respectively. The extra aW and dW would increase the asynchronicity of proton transfer. The bridging water in ESDPT process needed only one single H‐bond accepting or donating solvent molecule relying on the protolysis or solvolysis mechanism energetically. The specific vibrational modes in the 7AIW‐aW, 7AIW‐dW, and 7AIW‐aW‐dW complexes red‐shifted due to aW or dW. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
9. Excited-State Intramolecular Proton Transfer: A Short Introductory Review
- Author
-
Hem C. Joshi and Liudmil Antonov
- Subjects
tautomerism ,proton transfer ,excited-state ,spectroscopy ,Organic chemistry ,QD241-441 - Abstract
In this short review, we attempt to unfold various aspects of excited-state intramolecular proton transfer (ESIPT) from the studies that are available up to date. Since Weller’s discovery of ESIPT in salicylic acid (SA) and its derivative methyl salicylate (MS), numerous studies have emerged on the topic and it has become an attractive field of research because of its manifold applications. Here, we discuss some critical aspects of ESIPT and tautomerization from the mechanistic viewpoint. We address excitation wavelength dependence, anti-Kasha ESIPT, fast and slow ESIPT, reversibility and irreversibility of ESIPT, hydrogen bonding and geometrical factors, excited-state double proton transfer (ESDPT), concerted and stepwise ESDPT.
- Published
- 2021
- Full Text
- View/download PDF
10. Theoretical insights into the excited-state intermolecular hydrogen bonding dynamics of PRODAN derivative in toluene solution.
- Author
-
Zhao, Dan, Liu, Yang, Zhang, Xin, Gao, Jiawei, Liu, Shixin, and Zhao, Zhen
- Subjects
- *
HYDROGEN bonding , *EXCITED state chemistry , *TIME-dependent density functional theory , *FRONTIER orbitals , *MOLECULAR structure , *ELECTRON density - Abstract
• Excited state chemistry of PRODAN derivative 1a-toluene compound was studied by TDDFT. • Hydrogen bonds formed by PRODAN derivative 1a in toluene are enhanced in excited state. • PRODAN derivative 1a experiences the local excitations in toluene. The density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to get insights into the properties of PRODAN derivative in toluene at both ground as well as excited states. On the basis of molecular structure analysis, spectra comparisons and electron density studies, we confirm that the intermolecular hydrogen bond in PRODAN derivative-toluene complex is strengthened upon the photoexcitation. Frontier molecular orbitals exhibited the similar electron density distributions in HOMO and LUMO, suggesting that the PRODAN derivative 1a experiences the local excitations in toluene. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
11. Halogen substituent effect on the water-assisted excited-state tautomerization of 2, 7-diazaindole-H2O complex in aqueous solution: A theoretical study.
- Author
-
Fang, Hua
- Subjects
- *
DIPYRRINS , *AQUEOUS solutions - Abstract
Abstract We studied the ESPT process in the 2-DAI-H 2 O complex theoretically for the first time, and compared the kinetics of 2-DAI-H 2 O with those features of 7-DAI-H 2 O. The substituted effect on the dynamics of excited-state double proton transfer in 2-DAI-H 2 O and 7-DAI-H 2 O clusters in water were also investigated at the TD-M06-2X/6-311+G(d, p) level. In this work, 2,7-DAI-H 2 O is also expressed as 2-DAI-H 2 O and 7-DAI-H 2 O, in which correspond to different ESPT reactions and generate two tautomers (N 2 H form and N 7 H form). In both the 2-DAI-H 2 O and 7-DAI-H 2 O complexes, ESPT processes happened in a concertedly but asynchronously protolysis pathway. The ESPT process preferred to occur in the 7-DAI-H 2 O complex due to its lower barrier height. For the 3-X-2-DAI-H 2 O and 3-X-7-DAI-H 2 O (X = H, F, Cl, Br) complexes, the replacement of halogen atom did not influence the ESPT mechanism. However, the replacement of halogen atom changed the structural parameters evidently, reduced the barrier height up to 4–5 kcal/mol, and enlarged the asynchronicity of ESPT apparently. ∆(R 1 +R 2) values in the 3X-2-DAI-H 2 O and 3X-7-DAI-H 2 O complexes have linear correlation to the ZPE-corrected ESPT barrier height linearly. Graphical Abstract Unlabelled Image Highlights • ESPT in the 2-DAI-H 2 O and 7-DAI-H 2 O complexes occurred in a concertedly but asynchronously protolysis mechanism. • The excited-state double proton transfer in the 2,7-DAI-H 2 O complex preferred to happen between N 1 H and N 7 H isomers. • Halogen substituted had no effect on the ESPT mechanism, but enlarged the asynchronicity of proton transfer and reduced the ESPT barrier height. • The changes in the sum of N 1 -O 11 and O 11 -N 2 (O 11 -N 7) distances were linear dependence on the ZPE-corrected barrier height. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
12. Nitrostyrene‐Modified 2‐(2‐Hydroxyphenyl)benzothiazole: Enol‐Emission Solvatochromism by ESICT‐ESIPT and Aggregation‐Induced Emission Enhancement.
- Author
-
Niu, Yahui, Wang, Rong, Shao, Panlin, Wang, Yuxiu, and Zhang, Yanrong
- Subjects
- *
SOLVATOCHROMISM , *INTRAMOLECULAR charge transfer , *INTRAMOLECULAR proton transfer reactions , *HYDROGEN bonding , *ELECTROPHILES , *ELECTRON donors - Abstract
Excited‐state intramolecular charge transfer (ESICT) and excited‐state intramolecular proton transfer (ESIPT) are two competitive reactions that occur in the excited states of organic dyes that contain intramolecular hydrogen‐bonds and electron acceptors and donors. Determining the mechanisms of these processes is key to understanding their multiple emission features, as the manner in which these processes interact can be modulated by modifying the dye structure. In addition, donor–π–acceptor (D–π–A) molecules often suffer from aggregation‐induced quenching. Herein, we report the synthesis of three nitrophenyl‐modified 2‐(2‐hydroxyphenyl)benzothiazole (HBT) derivatives, HBT‐s‐NO2, HBT‐d‐NO2, and HBT‐t‐NO2, which have C−C, C=C, and C≡C bonds between their HBT and nitrophenyl moieties, respectively. Compared with the enol emissions from HBT‐s‐NO2 and HBT‐t‐NO2, that from HBT‐d‐NO2 exhibits outstanding solvatochromism owing to consecutive ESICT‐ESIPT. In addition, X‐ray diffraction reveals that despite the highly planar and polar nature of HBT‐d‐NO2, which is strongly H‐aggregated, it exhibits highly efficient fluorescence. Hence, this study provides new insight into the design of ESICT/ESIPT‐coupled systems and for engendering planar dipolar molecules with excellent emission properties in the solid state. Enol emission: Conjugation of nitrophenyl and 2‐(2‐hydroxyphenyl)benzothiazole moieties through a C=C bond, but not through C−C or C≡C bonds, facilitates outstanding enol‐emission solvatochromism owing to consecutive excited‐state intramolecular charge transfer and excited‐state intramolecular proton transfer, with resulting excellent emission performance in the solid state. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
13. DFT/TDDFT methods analysis of ESIPT process in a series of 7-hydroxy-1-indanone derivates and new dyad design.
- Author
-
Lei, Yuan-Qing, Xi, Jian-Ying, Guo, Hao, and Jia, Ran
- Abstract
Abstract In this work, DFT/TDDFT methods were utilized to have an analysis on the excited-state intramolecular proton transfer (ESIPT) in a series of 7-hydroxy-1-indanone derivates. By comparison of the relative energy in first excited state of each isomer, it is concluded that the direction of ESIPT is decided by the stability of isomer, which may be tuned by the change of conjugation pattern. Based on the results above, a strategy was proposed to control the ESIPT process, in which a dyad was designed by combining the derivate and dithienylethene together. Through the photoisomerization of dithienylethene, the excited group involved in excitation will make an effective shift, which, could act as a switch for the ESIPT process. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
14. Ultrafast structural changes direct the first molecular events of vision
- Author
-
Thomas Gruhl, Tobias Weinert, Matthew Rodrigues, Christopher J Milne, Giorgia Ortolani, Karol Nass, Eriko Nango, Saumik Sen, Philip J M Johnson, Claudio Cirelli, Antonia Furrer, Sandra Mous, Petr Skopintsev, Daniel James, Florian Dworkowski, Petra Båth, Demet Kekilli, Dmitry Ozerov, Rie Tanaka, Hannah Glover, Camila Bacellar, Steffen Brünle, Cecilia M Casadei, Azeglio D Diethelm, Dardan Gashi, Guillaume Gotthard, Ramon Guixà-González, Yasumasa Joti, Victoria Kabanova, Gregor Knopp, Elena Lesca, Pikyee Ma, Isabelle Martiel, Jonas Mühle, Shigeki Owada, Filip Pamula, Daniel Sarabi, Oliver Tejero, Ching-Ju Tsai, Niranjan Varma, Anna Wach, Sébastien Boutet, Kensuke Tono, Przemyslaw Nogly, Xavier Deupi, So Iwata, Richard Neutze, Jörg Standfuss, Gebhard FX Schertler, and Valerie Panneels
- Subjects
basis-sets ,Multidisciplinary ,software ,energy-storage ,dynamics ,Photobiology ,isomerization ,rhodopsin ,excited-state ,retinal chromophore ,counterion displacement ,Visual system ,crystallography ,X-ray crystallography - Abstract
Vision is initiated by the rhodopsin family of light-sensitive G protein-coupled receptors (GPCRs). A photon is absorbed by the 11-cis retinal chromophore of rhodopsin, which isomerizes within 200 femtoseconds to the all-trans conformation, thereby initiating the cellular signal transduction processes that ultimately lead to vision. However, the intramolecular mechanism by which the photoactivated retinal induces the activation events inside rhodopsin remains experimentally unclear. Here we use ultrafast time-resolved crystallography at room temperature to determine how an isomerized twisted all-trans retinal stores the photon energy that is required to initiate the protein conformational changes associated with the formation of the G protein-binding signalling state. The distorted retinal at a 1-ps time delay after photoactivation has pulled away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space. Notably, the very early structural motions in the protein side chains of rhodopsin appear in regions that are involved in later stages of the conserved class A GPCR activation mechanism. Our study sheds light on the earliest stages of vision in vertebrates and points to fundamental aspects of the molecular mechanisms of agonist-mediated GPCR activation., 視覚に関わるタンパク質の超高速分子動画 --薄暗いところで光を感じる仕組み--. 京都大学プレスリリース. 2023-03-23.
- Published
- 2023
15. Theoretical study on the substituent effect of halogen atom at different position of 7-azaindole-water derivatives: relative stability and excited-state proton-transfer mechanism.
- Author
-
Yi, Jiacheng and Fang, Hua
- Subjects
- *
HALOGENS , *AZAINDOLE derivatives , *EXCITED states , *PROTON transfer reactions , *SUBSTITUTION reactions - Abstract
We have theoretically investigated the substituted effect on the first excited-state proton-transfer process of nX7AI-H2O (n = 2~6, X = F, Cl, Br) complex at the TD-M06-2X/6-31 + G(d, p) level. Here X is the substituted halogen atom, and n value denotes the substituted position of X, such as C2, C3, C4, C5, or C6. For the substituted 7-azaindole clusters, 6X7AI-H2O molecule is the most stable structure in water. The replacement of halogen atom X does not affect the characters of the HOMO and LUMO, but influence the S0 → S1 adiabatic transition energies of nX7AI-H2O (n = 2~6, X = F, Cl, Br). Our calculated results show that the double proton transfer occurs in a concerted but asynchronous protolysis pathway no matter which H atom is replaced by halogen atom. The halogen substitution changes the structural parameters evidently and leads to amply the asynchronousity during the proton-transfer process. The ESPT barrier height increases or decreases due to the halogen atom and substituted position. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
16. Effect of different alkyl groups on excited-state tautomerization of 7AI-azaindole-H2O: A theoretical study.
- Author
-
Yi, Jiacheng and Fang, Hua
- Subjects
- *
TAUTOMERISM , *AZAINDOLES , *ALKYL group , *PROTON transfer reactions , *ADIABATIC processes - Abstract
The effect of substituted alkyl groups at different substituted position on the first excited-state proton transfer of nR7AI-H 2 O (n = 2–6; R = CH 3 , C 2 H 5 , CF 3 ) complexes were theoretically investigated at the TD-M06-2X/6–31 + G(d, p) level. Here n value denoted the substituted position C n of R group. The replacement of alkyl R group had no effect on the features of HOMO and LUMO, but influenced the S 0 → S 1 adiabatic transition energies of the nR7AI-H 2 O complex. Through computation, we found that the double proton transfer took place in a concerted but asynchronous protolysis pattern regardless of substituted group R and substituted position in the nR7AI-H 2 O complex. The vibrational-mode specific nature of ESPT was verified. The alkyl group R changed the geometrical parameters of TS, and resulted in enlarging/narrowing the asynchronousity of ESPT. The ESPT barrier height was also affected by the substituted group and position. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
17. Theoretical study on excited-state multiple proton-transfer process of 7-azaindole with ammonia and mixed water-ammonia: Stepwise or concerted?
- Author
-
Fang, Hua and Jiang, Yanxialei
- Subjects
- *
AZAINDOLES , *PROTON transfer reactions , *AMMONIA analysis , *GAS phase reactions , *ELECTRON configuration , *EXCITED states - Abstract
A detailed study of the excited-state tautomerization of 7AI-(NH 3 ) n (n = 1, 2), 7AI-H 2 O-NH 3 and 7AI-NH 3 -H 2 O complex in the gas phase were investigated at the CASSCF(10, 9)/6-31G(d, p) level theoretically. The effect of dynamic electron correlation on the barrier height and reaction energy was considered by MRPT2. The excited-state double proton transfer in 7AI-NH 3 takes place in a concerted but asynchronous protolysis pathway. However, the triple proton transfer in 7AI cluster along the H-bonded ammonia dimer prefers a two-step process with a distinct intermediate. Each proton transfer step was a concerted but asynchronous path. The formation of H-bonded chain consisting of mixed water-ammonia affected the excited-state proton transfer mechanism. With the stabilization effect of the second solvent molecule, the first solvent molecule with large or small proton-accepting ability made the ESTPT occur in a stepwise or concerted pattern. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
18. Photochemistry and Photophysics of Coordination Compounds: Rhenium
- Author
-
Kirgan, Robert A., Sullivan, B. Patrick, Rillema, D. Paul, Balzani, Vincenzo, editor, and Campagna, Sebastiano, editor
- Published
- 2007
- Full Text
- View/download PDF
19. Nonlinear Dynamics of Exclusive Excited-State Emission Quantum Dot Lasers Under Optical Injection
- Author
-
Zai-Fu Jiang, Zheng-Mao Wu, Elumalai Jayaprasath, Wen-Yan Yang, Chun-Xia Hu, and Guang-Qiong Xia
- Subjects
quantum dot lasers ,excited-state ,nonlinear dynamics ,optical injection ,Applied optics. Photonics ,TA1501-1820 - Abstract
We numerically investigate the nonlinear dynamic properties of an exclusive excited-state (ES) emission quantum dot (QD) laser under optical injection. The results show that, under suitable injection parameters, the ES-QD laser can exhibit rich nonlinear dynamical behaviors, such as injection locking (IL), period one (P1), period two (P2), multi-period (MP), and chaotic pulsation (CP). Through mapping these dynamic states in the parameter space of the frequency detuning and the injection coefficient, it can be found that the IL occupies a wide region and the dynamic evolution routes appear in multiple forms. Via permutation entropy (PE) calculation to quantify the complexity of the CP state, the parameter range for acquiring the chaos with high complexity can be determined. Moreover, the influence of the linewidth enhancement factor (LEF) on the dynamical state of the ES-QD laser is analyzed. With the increase of the LEF value, the chaotic area shrinks (expands) in the negative (positive) frequency detuning region, and the IL region gradually shifts towards the negative frequency detuning.
- Published
- 2019
- Full Text
- View/download PDF
20. [Ru(bpy)3]2+∗ revisited. Is it localized or delocalized? How does it decay?
- Author
-
Dongare, Prateek, Myron, Brent D.B., Wang, Li, Thompson, David W., and Meyer, Thomas J.
- Subjects
- *
ELECTRON spin , *LIGANDS (Chemistry) , *EXCITED states , *CHARGE transfer , *ELECTRON configuration - Abstract
The issue of localization/delocalization of electron spin density in Metal-to-Ligand Charge Transfer (MLCT) excited states of [Ru(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine) has been debated for almost four decades. Localization/delocalization of MLCT excited states specifically addresses the question regarding electron configuration in the excited state and whether the excited electron in the dπ 5 π ∗1 excited state was localized on one ligand, [Ru III (bpy)(bpy − )] 2+∗ , or delocalized over all three, [Ru III (bpy − 1/3 ) 3 ] 2+∗ . This contribution outlines the results of a detailed meta-analysis of available experimental data to delineate the factors that govern how the excited state electron density evolves over the time from excitation until final excited state equilibration. Given the nature of the analysis, a number of interwoven issues are discussed in this article. A cohesive evaluation of the existing data leads to a detailed mechanistic understanding of the events that accrue following excitation of [Ru(bpy) 3 ] 2+ . The results of the meta-analysis are both remarkably systematic and consistent with existing theories of dynamic processes. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
21. Hydrogen-bonded channel-dependent mechanism of long-range proton transfer in the excited-state tautomerization of 7-hydroxyquinoline: a theoretical study.
- Author
-
Fang, Hua and Kim, Yongho
- Subjects
- *
HYDROGEN bonding , *PROTON transfer reactions , *EXCITED state chemistry , *HYDROXYQUINOLINE , *QUANTUM mechanics , *METHANOL - Abstract
The first excited-state proton transfer (ESPT) in 7-hydroxyquinoline (7HQ) mediated by water and methanol molecules in a nonpolar solution was studied by quantum mechanical calculations. The multiple proton transfer through a hydrogen-bonded channel consisting of two or three hydroxyl molecules occurs in a concerted and asynchronous pathway. When the H-bonded channel molecules are water or methanol, proton transfer takes place in a solvolytic or protolytic fashion, respectively. The barrier height of the ESPT depends on the basicity of the H-bonded channel. The predicted barrier height is 2.97 kcal/mol lower with two CHOH than with two HO since monomeric methanol is more basic than monomeric water in heptane and DPE. The ESPT barrier heights are 3-4 kcal/mol lower with three H-bonded molecules than with two. The rate constants and KIEs for the ESPT of 7HQ-(ROH) (ROH = HO, CHOH) were calculated and compared to the experimental values. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
22. Time-dependent density functional theory study on the excited-state hydrogen-bonding characteristics of polyaniline in aqueous environment.
- Author
-
Zhang, Yahong, Duan, Yuping, and Liu, Jin
- Subjects
- *
TIME-dependent density functional theory , *HYDROGEN bonding , *POLYANILINES , *ELECTRONIC excitation , *OSCILLATOR strengths - Abstract
A theoretical study was carried out to study the excited-state of hydrogen-bonding characteristics of polyaniline (PANI) in aqueous environment. The hydrogen-bonded PANI-H 2 O complexes were studied using first-principles calculations based on density functional theory (DFT). The electronic excitation energies and the corresponding oscillator strengths of the low-lying electronically excited states for hydrogen-bonded complexes were calculated by time-dependent density functional theory (TDDFT). The ground-state geometric structures were optimized, and it is observed that the intermolecular hydrogen bonds C N ⋯ H O and N H ⋯ O H were formed in PANI-H 2 O complexes. The formed hydrogen bonds influenced the bond lengths, the charge distribution, as well as the spectral characters of the groups involved. It was concluded that all the hydrogen-bonded PANI-H 2 O complexes were primarily excited to the S1 states with the largest oscillator strength. In addition, the orbital transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) involved intramolecular charge redistribution resulting to increase the electron density of the quinonoid rings. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
23. Excited-state molecular dynamics simulation based on variational quantum algorithms.
- Author
-
Hirai, Hirotoshi
- Subjects
- *
MOLECULAR dynamics , *METASTABLE states , *EXCITED states , *ALGORITHMS - Abstract
We propose an excited-state molecular dynamics simulation method based on variational quantum algorithms at a computational cost comparable to that of ground-state simulations. We utilize the feature that excited-states can be obtained as metastable states in the restricted variational quantum eigensolver calculation with a hardware-efficient ansatz. To demonstrate the effectiveness of the method, molecular dynamics simulations are performed for the S1 excited-states of H 2 and CH 2 NH molecules. The results are consistent with those of the exact adiabatic simulations in the S1 states, except for the CH 2 NH system, after crossing the conical intersection, where the proposed method causes a nonadiabatic transition. [Display omitted] • An excited-state MD scheme based on variational quantum algorithms is presented. • Excited states can be obtained as metastable states by VQE calculations. • Excited-state MD simulations based on the VQE result in "diabatic" simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Excited-states and spectroscopic properties of superoxide anion: a theoretical study including spin–orbit coupling.
- Author
-
Liu, Hui, Shi, Deheng, Sun, Jingfeng, and Zhu, Zunlue
- Subjects
- *
EXCITED states , *SUPEROXIDES , *SPIN-orbit interactions , *HAMILTONIAN mechanics , *BOUND states - Abstract
The potential energy curves (PECs) of 24 Λ–S electronic states of superoxide anion (O2−), which correlated with the first dissociation channel, were calculated using a high-accuracy internally contracted multireference configuration interaction (icMRCI) methodology with the Davidson correction in conjunction with the correlation-consistent basis sets. The core electron correlation and scalar relativistic corrections as well as basis set extrapolation were included. The spin–orbit coupling was also taken into account by using the state interaction approach with the Breit–Pauli Hamiltonian. The PECs of 54 Ω states generated from the 24 Λ–S states were constructed and described in detail. The spectroscopic constants of the seventeen Λ–S and 37 Ω bound states were evaluated and the vibrational properties of some weakly bound states were predicted. Comparing with the available experimental and theoretical data shows that the computational strategy employed is suitable and highly accurate for this system. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
25. Recombination and regeneration dynamics in FeNHC(<scp>ii</scp>)-sensitized solar cells
- Author
-
Edoardo Marchini, Roberto Argazzi, Philippe C. Gros, Mohamed Darari, Carlo Alberto Bignozzi, Stefano Caramori, Rita Boaretto, Luca Lazzarin, Università degli Studi di Ferrara (UniFE), Laboratoire Lorrain de Chimie Moléculaire (L2CM), and Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
EXCITED-STATE ,PE4_12 ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,PE4_15 ,7. Clean energy ,01 natural sciences ,Redox ,Catalysis ,Materials Chemistry ,[CHIM]Chemical Sciences ,ComputingMilieux_MISCELLANEOUS ,INTERFACIAL CHARGE SEPARATION ,Chemistry ,Regeneration (biology) ,Metals and Alloys ,Ambientale ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Dye-sensitized solar cell ,LIGHT ,Chemical engineering ,Ceramics and Composites ,TIO2 ,PHOTOSENSITIZATION ,COMPLEXES ,0210 nano-technology ,Recombination - Abstract
Recombination and regeneration dynamics in Fe-NHC-sensitized DSSCs revealed incomplete injection and the detrimental effect of photoinjected electron recapture by the I3-form of the redox electrolyte on performance. Importantly, the use of additives in the electrolyte allowed the best efficiency ever recorded for an iron-based DSSC to be reached.
- Published
- 2020
26. Quantum self-consistent equation-of-motion method for computing molecular excitation energies, ionization potentials, and electron affinities on a quantum computer
- Author
-
Ayush Asthana, Ashutosh Kumar, Vibin Abraham, Harper Grimsley, Yu Zhang, Lukasz Cincio, Sergei Tretiak, Pavel A. Dub, Sophia E. Economou, Edwin Barnes, and Nicholas J. Mayhall
- Subjects
Coupled-cluster method ,construction ,Chemical Physics (physics.chem-ph) ,Quantum Physics ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics - Chemical Physics ,excited-state ,FOS: Physical sciences ,propagator ,General Chemistry ,chemistry ,Quantum Physics (quant-ph) - Abstract
Near-term quantum computers are expected to facilitate material and chemical research through accurate molecular simulations. Several developments have already shown that accurate ground-state energies for small molecules can be evaluated on present-day quantum devices. Although electronically excited states play a vital role in chemical processes and applications, the search for a reliable and practical approach for routine excited-state calculations on near-term quantum devices is ongoing. Inspired by excited-state methods developed for the unitary coupled-cluster theory in quantum chemistry, we present an equation-of-motion-based method to compute excitation energies following the variational quantum eigensolver algorithm for ground-state calculations on a quantum computer. We perform numerical simulations on H-2, H-4, H2O, and LiH molecules to test our quantum self-consistent equation-of-motion (q-sc-EOM) method and compare it to other current state-of-the-art methods. q-sc-EOM makes use of self-consistent operators to satisfy the vacuum annihilation condition, a critical property for accurate calculations. It provides real and size-intensive energy differences corresponding to vertical excitation energies, ionization potentials and electron affinities. We also find that q-sc-EOM is more suitable for implementation on NISQ devices as it is expected to be more resilient to noise compared with the currently available methods. Department of Energy (DOE) [DE-SC0019199]; NSF [1839136]; Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory (LANL) [20200056DR]; National Nuclear Security Administration of the U.S. Department of Energy [89233218CNA000001] Published version This research was supported by the Department of Energy (DOE). E. B. and N. J. M. acknowledge Award No. DE-SC0019199, and S. E. E. acknowledges support from the NSF, award number 1839136. A. A. would like to thank Dr Luke Bertels for helpful discussions. The authors thank the Advanced Research Computing (ARC) facility at Virginia Tech for the computational infrastructure. A. K., Y. Z., L. C., S. T., and P. A. D. are thankful for the support from the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory (LANL) under project number 20200056DR. LANL is operated by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy (contract no. 89233218CNA000001).
- Published
- 2022
- Full Text
- View/download PDF
27. Characterizing the Solvated Structure of Photoexcited [Os(terpy)2]2+ with X-ray Transient Absorption Spectroscopy and DFT Calculations.
- Author
-
Xiaoyi Zhang, Pápai, Mátyás, Møller, Klaus B., Zhang, Jianxin, and Canton, Sophie E.
- Subjects
- *
ELECTRONIC structure , *INTERFACIAL bonding , *PHOTOEXCITATION , *ELECTRODES , *X-ray spectra - Abstract
Characterizing the geometric and electronic structures of individual photoexcited dye molecules in solution is an important step towards understanding the interfacial properties of photo-active electrodes. The broad family of "red sensitizers" based on osmium(II) polypyridyl compounds often undergoes small photo-induced structural changes which are challenging to characterize. In this work, X-ray transient absorption spectroscopy with picosecond temporal resolution is employed to determine the geometric and electronic structures of the photoexcited triplet state of [Os(terpy)2]2+ (terpy: 2,21:61,211-terpyridine) solvated in methanol. From the EXAFS analysis, the structural changes can be characterized by a slight overall expansion of the first coordination shell [OsN6]. DFT calculations supports the XTA results. They also provide additional information about the nature of the molecular orbitals that contribute to the optical spectrum (with TD-DFT) and the near-edge region of the X-ray spectra. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
28. Theoretical study on excited-state proton transfer via hydrogen-bonded ethanol (EtOH) wire for 7AI in the gas phase.
- Author
-
Fang, Hua
- Subjects
- *
GROUND state energy , *PROTONS , *ETHYL group , *ELECTRON configuration , *METHYL groups - Abstract
Systematic studies of the excited-state tautomerization in the 7-azaindole–(EtOH)n (n = 1, 2) complexes in the gas phase were theoretically investigated. Structures and energies for reactant, transition state and product were computed at the CASSCF levels with the 6-31G(d,p) and 6-311G(d,p) basis sets. The barrier heights and reaction energies were corrected by the second-order multireference perturbation theory (MRPT2) to consider the dynamic electron correlation. The excited-state double-proton transfer in 7AI–EtOH occurs in a concerted but asynchronous mechanism. Similarly, such paths are also found in the two transition states during the excited-state triple-proton transfer of 7AI–(EtOH)2 complex. One path is that the proton from the pyrrole ring moved first to ethanol, and the other path is that the ethanol proton moved first to pyridine ring. The CASSCF level with the MRPT2 correction clearly showed that the former path was much preferable to the latter. The preferable barrier height for the 7-azaindole–(EtOH)2 complex was 4.3 kcal/mol with the zero-point energy correction. Additionally, the effect on the substitution of the ethyl group for the methyl group in the 7AI–(MeOH)n (n = 1, 2) was discussed. The replacement of the methyl group by the ethyl group obviously increased the barrier height and the asynchronousity of proton transfer in the 7AI–(EtOH)2 complex and had little effect on the 7AI–(EtOH) complex. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
29. Quasiparticle scattering, lifetimes, and spectra using the GW approximation
- Author
-
Vigil-Fowler, Derek Wayne
- Subjects
Condensed matter physics ,Materials Science ,Theoretical physics ,bandstructures ,excited-state ,first principles ,many-body perturbation theory ,materials design ,particle lifetimes - Abstract
Computer simulations are an increasingly important pillar of science, along with exper-iment and traditional pencil and paper theoretical work. Indeed, the development of theneeded approximations and methods needed to accurately calculate the properties of therange of materials from molecules to nanostructures to bulk materials has been a great tri-umph of the last 50 years and has led to an increased role for computation in science. Theneed for quantitatively accurate predictions of material properties has never been greater,as technology such as computer chips and photovoltaics require rapid advancement in thecontrol and understanding of the materials that underly these devices. As more accuracy isneeded to adequately characterize, e.g. the energy conversion processes, in these materials,improvements on old approximations continually need to be made. Additionally, in orderto be able to perform calculations on bigger and more complex systems, algorithmic devel-opment needs to be carried out so that newer, bigger computers can be maximally utilizedto move science forward.In this work we discuss our endeavors to improve approximations and algorithms to an-swer the challenge of better describing material properties. After an introduction to defineand discuss all the important concepts that appear later, we first discuss the calculation ofso-called satellite properties in the photoemission spectra (PES) of doped graphene. Whilethe GW approximation accurately produces the quasiparticle energies across a range ofmaterials from nanostructures and molecules to bulk metals and semiconductors, it doesnot accurately produce the satellite properties seen in PES experiments. We find that amore advanced treatment of the Green’s function, the cumulant expansion, is needed toadequately describe the satellite properties of doped graphene on SiC. In addition to thismore advanced Green’s function treatment, a novel technique is devised for including thescreening due to the SiC substrate on which the doped graphene is placed. This more ad-vanced treatment of the substrate is also crucial for obtaining agreement with experiment.Next, we show how the cumulant expansion can be used to accurately predict the ARPESspectra of bulk Si and the time-domain capacitance spectra of two-dimensional electrongases (2DEGs) in semiconductor quantum wells, with both the quasiparticle and satellitefeatures given correctly (unlike in GW theory, in which only the quasiparticle propertiesare predicted accurately). We then discuss carrier lifetimes from the GW approximationin bulk Si and GaAs, showing how theory can provide access to detailed microscopic in-formation that could be of use in designing more efficient photovoltaics. In chapter 6, wediscuss the effect of the pseudopotential approximation on excited-state GW calculations.Finding a small amount of error due to the use of nodeless pseudowavefunctions when us-ing pseudopotentials, we are able to understand the tendency of GW calculations that usepseudowavefunctions to overestimate the band gap in many common semiconductors. Wequantify this error and suggest improved techniques for applications where this error istoo large. In the last section on research, we discuss the effect of self-consistency in GWcalculations. Chapter 7 is on computational algorithm development, and there we discusssome algorithmic advances made in improving the BerkeleyGW code. A technique for bet-ter distributing the data during the calculation of the inverse dielectric matrix is discussedand shown to give very good performance improvements, especially for the large systemsthat are becoming increasingly common. Other small improvements that allow for a moreaccurate calculation of quasiparticle lifetimes are also discussed. Finally, a few appendicesare included for completeness.
- Published
- 2015
30. Supramolecular Construction of Cyanide-Bridged Re I Diimine Multichromophores
- Author
-
Kirill Yu. Monakhov, Antonio Doménech-Carbó, Antti J. Karttunen, Igor O. Koshevoy, Elena V. Grachova, Kristina S. Kisel, Alexei S. Melnikov, Valentin Semenov, and Sergey P. Tunik
- Subjects
CARBONYL-COMPLEXES ,SPECTROSCOPIC PROPERTIES ,Cyanide ,Supramolecular chemistry ,EXCITED-STATE ,Crystal structure ,010402 general chemistry ,01 natural sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,CRYSTAL-STRUCTURE ,Physical and Theoretical Chemistry ,Triphenylphosphine ,ta116 ,MULTIPLE EMISSIONS ,Diimine ,DENSITY-FUNCTIONAL METHODS ,010405 organic chemistry ,LUMINESCENT RE(I) ,0104 chemical sciences ,RHENIUM(I) TRICARBONYL COMPLEXES ,Crystallography ,chemistry ,Excited state ,PHOTOPHYSICAL PROPERTIES ,Phosphorescence ,COORDINATION POLYMERS ,Derivative (chemistry) - Abstract
The reactions of labile [Re(diimine)(CO)3(H2O)]+ precursors (diimine = 2,2′-bipyridine, bpy; 1,10-phenanthroline, phen) with dicyanoargentate anion produce the dirhenium cyanide-bridged compounds [{Re(diimine)(CO)3}2CN)]+ (1 and 2). Substitution of the axial carbonyl ligands in 2 for triphenylphosphine gives the derivative [{Re(phen)(CO)2(PPh3)}2CN]+ (3), while the employment of a neutral metalloligand [Au(PPh3)(CN)] affords heterobimetallic complex [{Re(phen)(CO)3}NCAu(PPh3)]+ (4). Furthermore, the utilization of [Au(CN)2]−, [Pt(CN)4]2–, and [Fe(CN)6]4–/3– cyanometallates leads to the higher nuclearity aggregates [{Re(diimine)(CO)3NC}xM]m+ (M = Au, x = 2, 5 and 6; Pt, x = 4, 7 and 8; Fe, x = 6, 9 and 10). All novel compounds were characterized crystallographically. Assemblies 1–8 are phosphorescent both in solution and in the solid state; according to the DFT analysis, the optical properties are mainly associated with charge transfer from Re tricarbonyl motif to the diimine fragment. The energy of this p...
- Published
- 2019
31. Inverted energy gap law for the nonradiative decay in fluorescent floppy molecules: larger fluorescence quantum yields for smaller energy gaps
- Author
-
Maria A. Izquierdo, Begoña Milián-Medina, Junqing Shi, Sangyoon Oh, Soo Young Park, Daniel Roca-Sanjuán, Johannes Gierschner, and Theoretical Chemistry
- Subjects
MECHANISM ,DERIVATIVES ,010405 organic chemistry ,Chemistry ,Band gap ,SURFACES ,Organic Chemistry ,Solid-state ,EXCITED-STATE ,SUBSTITUTION ,Conical intersection ,CONICAL INTERSECTION ,010402 general chemistry ,01 natural sciences ,Fluorescence ,AGGREGATION-INDUCED EMISSION ,0104 chemical sciences ,Fluid solution ,CHEMISTRY ,Law ,NANOPARTICLES ,Molecule ,DEACTIVATION ,Quantum ,Energy (signal processing) - Abstract
A data survey on experimental fluorescence quantum yields of (multi)substituted dicyano-distyrylbenzenes in fluid solution evidences that non-radiative decay increases with the Franck-Condon energy (E-FC), being opposite to the conventional energy gap law. Quantum-chemistry indicates that this is controlled by access to the conical intersection (CI) following the Bell-Evans-Polanyi principle as a first-step approximation for this family of molecules; the variations in E-FC among the different compounds are found to be decisive, while those of E-CI are estimated to be weaker or even enhancing the effect. The current findings may have significant consequences for the design of molecules for organic solid state emitters.
- Published
- 2019
32. Ultrafast X-ray Spectroscopy of Haem Proteins
- Author
-
Camila Bacellar and Majed Chergui
- Subjects
carbon-monoxide ,molecular-dynamics ,resolved resonance raman ,nitric-oxide ,transient absorption ,x-ray emission spectroscopy ,General Medicine ,General Chemistry ,x-ray absorption spectroscopy ,structural dynamics ,heam proteins ,cytochrome-c ,protein excited state dynamics ,ultrafast dynamics ,hydrogen-sulfide ,geminate recombination ,excited-state - Abstract
In this article we revisit our recent picosecond and femtosecond X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) experiments, probing the ultrafast electronic and geometric evolution of photoexcited haem proteins, namely ferrous Nitrosyl Myoglobin (MbNO) and ferric Cytochrome c (Cyt c). We show through these two examples, combined with results from ultrafast optical spectroscopy, the universal behavior of the excited state dynamics of ferric and ferrous complexes. Regardless of the type of ligand, its dissociation or lack thereof, or the metal oxidation state, the photoexcited system relaxes through a cascade of excited spin states leading to formation of a high spin state, which in the case of the haem is a domed porphyrin.
- Published
- 2022
33. Excited-State Intramolecular Proton Transfer: A Short Introductory Review
- Author
-
Liudmil Antonov and Hem Chandra Joshi
- Subjects
Models, Molecular ,spectroscopy ,Proton ,proton transfer ,Pharmaceutical Science ,Excited state intramolecular proton transfer ,Electrons ,02 engineering and technology ,Review ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Analytical Chemistry ,lcsh:QD241-441 ,lcsh:Organic chemistry ,Drug Discovery ,excited-state ,Physical and Theoretical Chemistry ,Ions ,Excitation wavelength ,Chemistry ,Hydrogen bond ,Organic Chemistry ,Hydrogen Bonding ,021001 nanoscience & nanotechnology ,Tautomer ,Salicylates ,0104 chemical sciences ,tautomerism ,Chemistry (miscellaneous) ,Excited state ,Intramolecular force ,Molecular Medicine ,Quantum Theory ,Thermodynamics ,Protons ,0210 nano-technology ,Salicylic Acid ,Hydrogen - Abstract
In this short review, we attempt to unfold various aspects of excited-state intramolecular proton transfer (ESIPT) from the studies that are available up to date. Since Weller’s discovery of ESIPT in salicylic acid (SA) and its derivative methyl salicylate (MS), numerous studies have emerged on the topic and it has become an attractive field of research because of its manifold applications. Here, we discuss some critical aspects of ESIPT and tautomerization from the mechanistic viewpoint. We address excitation wavelength dependence, anti-Kasha ESIPT, fast and slow ESIPT, reversibility and irreversibility of ESIPT, hydrogen bonding and geometrical factors, excited-state double proton transfer (ESDPT), concerted and stepwise ESDPT.
- Published
- 2021
34. A theoretical study on water-assisted excited state double proton transfer process in substituted 2,7-diazaindole-H2O complex
- Author
-
Fang, Hua
- Published
- 2020
- Full Text
- View/download PDF
35. Thienyl/phenyl bay-substituted perylenebisimides: Intersystem crossing and application as heavy atom-free triplet photosensitizers
- Author
-
Ayhan Elmali, Daniel Escudero, Ahmet Karatay, Jianzhang Zhao, Yuqi Hou, Zhijia Wang, and Farhan Sadiq
- Subjects
Technology ,Engineering, Chemical ,General Chemical Engineering ,Materials Science ,Substituent ,Quantum yield ,EXCITED-STATE ,02 engineering and technology ,Triplet state ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Perylenebisimide ,DENSITY-FUNCTIONAL THEORY ,Electron transfer ,chemistry.chemical_compound ,ENERGY-LEVELS ,Engineering ,CHARGE-TRANSFER ,Thiophene ,Materials Science, Textiles ,ELECTRON-TRANSFER ,Singlet state ,SINGLET OXYGEN GENERATION ,ACTIVATED DELAYED FLUORESCENCE ,BASIS-SETS ,PERYLENE ,Science & Technology ,Chemistry ,Singlet oxygen ,Process Chemistry and Technology ,Intersystem crossing ,021001 nanoscience & nanotechnology ,Delayed fluorescence ,0104 chemical sciences ,Chemistry, Applied ,PHOTON UP-CONVERSION ,Excited state ,Physical Sciences ,0210 nano-technology - Abstract
Different perylene-3,4:9,10-bis(dicarboximide) (abbreviated as perylenebisimides, or simply PBI) compounds (MT-PBI, DT-PBI, MP-PBI and DP-PBI) with thienyl and phenyl substituents at the bay position were prepared to study the effect of substitution on the photophysical properties, especially the intersystem crossing (ISC) efficacy. We found that the derivative with a monothienyl substituent (MT-PBI) shows efficient ISC (singlet oxygen quantum yield ΦΔ = 72%) and longer triplet state lifetime (τT = 64.4 μs) as compared to reference compounds (derivative with monophenyl substituent at bay position, MP-PBI, ΦΔ = 23% and τT = 48.5 μs). Theoretical computations reveal that the ISC efficiency is dependent on the magnitude of the spin orbit couplings (SOC) between the singlet and triplet excited states, and the SOC matrix element is up to 2 cm−1 for compound showing the highest ISC efficiency. Femtosecond transient absorption spectra show the ISC rate constant of 8 × 109 s−1 for MT-PBI, and no charge transfer exists. Photo-driven electron transfer was observed with the PBI derivatives in the presence of sacrificial electron donor triethanolamine (TEOA), and reversible formation of PBI radical anion (PBI−•) was observed, which shows absorption in the range of 600 nm–800 nm and 900 nm–1000 nm. Delayed fluorescence (P-type) in MT-PBI was also observed (τT = 31.0 μs). These finding are useful for the design of PBI-derived heavy atom-free compounds to be used as triplet photosensitizers.
- Published
- 2021
36. Investigation of Luminescent Triplet States in Tetranuclear Cu$^{I}$ Complexes: Thermochromism and Structural Characterization
- Author
-
Sophie Steiger, Willem Klopper, Daniel Volz, Jasmin M. Busch, Martin Nieger, Florian R. Rehak, Stefan Bräse, Markus Gerhards, Pit Boden, Patrick Di Martino-Fumo, Oliver Fuhr, and Department of Chemistry
- Subjects
Chemistry & allied sciences ,116 Chemical sciences ,Infrared spectroscopy ,Halide ,EXCITED-STATE ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Catalysis ,chemistry.chemical_compound ,BLUE ,Cu-I complexes ,Pyridine ,luminescence ,COPPER-IODIDE CLUSTERS ,Spectroscopy ,theoretical calculations ,Coordination Chemistry | Hot Paper ,Thermochromism ,SPECTROSCOPY ,Full Paper ,010405 organic chemistry ,DINUCLEAR ,Organic Chemistry ,PHOSPHORESCENCE ,General Chemistry ,Full Papers ,0104 chemical sciences ,X-ray diffraction ,Crystallography ,FTIR spectroscopy ,CuI complexes ,chemistry ,ddc:540 ,LIGANDS ,Phosphorescence ,Luminescence ,EMISSION ,FLUORESCENCE THERMOCHROMISM ,Methyl group - Abstract
To develop new and flexible CuI containing luminescent substances, we extend our previous investigations on two metal‐centered species to four metal‐centered complexes. These complexes could be a basis for designing new organic light‐emitting diode (OLED) relevant species. Both the synthesis and in‐depth spectroscopic analysis, combined with high‐level theoretical calculations are presented on a series of tetranuclear CuI complexes with a halide containing Cu4X4 core (X=iodide, bromide or chloride) and two 2‐(diphenylphosphino)pyridine bridging ligands with a methyl group in para (4‐Me) or ortho (6‐Me) position of the pyridine ring. The structure of the electronic ground state is characterized by X‐ray diffraction, NMR, and IR spectroscopy with the support of theoretical calculations. In contrast to the para system, the complexes with ortho‐substituted bridging ligands show a remarkable and reversible temperature‐dependent dual phosphorescence. Here, we combine for the first time the luminescence thermochromism with time‐resolved FTIR spectroscopy. Thus, we receive experimental data on the structures of the two triplet states involved in the luminescence thermochromism. The transient IR spectra of the underlying triplet metal/halide‐to‐ligand charge transfer (3 m/XLCT) and cluster‐centered (3CC) states were obtained and interpreted by comparison with calculated vibrational spectra. The systematic and significant dependence of the bridging halides was analyzed., Highly luminescent! The synthesis and an in‐depth photophysical characterization of highly luminescent tetranuclear CuI complexes are presented. For these promising candidates for organic light‐emitting diodes, a pronounced luminescence thermochromism with clearly separated emission bands is observed. The corresponding excited state structures are determined by applying temperature‐dependent time‐resolved step‐scan FTIR spectroscopy in combination with DFT calculations.
- Published
- 2021
37. Fundamental Characterization, Photophysics and Photocatalysis of a Base Metal Iron(II)‐Cobalt(III) Dyad
- Author
-
Wojciech Gawelda, Lukas Burkhardt, Lennart Schmitz, Ahmet Kertmen, Michal Nowakowski, Marina Huber‐Gedert, Regine Herbst-Irmer, Adam Neuba, Tae-Kyu Choi, Natalia Lindner, Roland Schoch, Jacek Kubicki, Matthias Bauer, and UAM.Departamento de Química
- Subjects
Absorption spectroscopy ,Evolution ,Population ,Water Reduction ,Base Metal Complexes ,Proton Reduction ,Photochemical Hydrogen-Production ,Excited-State ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,Bipyridine ,chemistry.chemical_compound ,Iron(Ii) Complexes ,Dyads ,Pincer Dicarbene Complexes ,Photosensitizer ,Singlet state ,Photocatalysis ,Spectroscopy ,education ,education.field_of_study ,Full Paper ,010405 organic chemistry ,Organic Chemistry ,General Chemistry ,Química ,Full Papers ,Time-Resolved Spectroscopy ,Copper-Based Photosensitizers ,0104 chemical sciences ,Homogeneous Catalysis ,chemistry ,Absorption band ,ddc:540 ,Time-resolved spectroscopy ,Heterocyclic Carbene Complexes ,Visible-Light - Abstract
Chemistry - a European journal 27(38), 9905 - 9918 (2021). doi:10.1002/chem.202100766, A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4���-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal-to-ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the $^{3}$MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a $^{3}$MC state. Attachment of cobaloxime to the iron photosensitizer increases the $^{3}$MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two-component system, consisting of the iron photosensitizer and Co(dmgH)$_2$(py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems., Published by Wiley-VCH, Weinheim
- Published
- 2021
38. Characterizing the Solvated Structure of Photoexcited [Os(terpy)2]2+ with X-ray Transient Absorption Spectroscopy and DFT Calculations
- Author
-
Xiaoyi Zhang, Mátyás Pápai, Klaus B. Møller, Jianxin Zhang, and Sophie E. Canton
- Subjects
X-ray transient absorption spectroscopy ,excited-state ,osmium polypyridyl complex ,Organic chemistry ,QD241-441 - Abstract
Characterizing the geometric and electronic structures of individual photoexcited dye molecules in solution is an important step towards understanding the interfacial properties of photo-active electrodes. The broad family of “red sensitizers” based on osmium(II) polypyridyl compounds often undergoes small photo-induced structural changes which are challenging to characterize. In this work, X-ray transient absorption spectroscopy with picosecond temporal resolution is employed to determine the geometric and electronic structures of the photoexcited triplet state of [Os(terpy)2]2+ (terpy: 2,2′:6′,2″-terpyridine) solvated in methanol. From the EXAFS analysis, the structural changes can be characterized by a slight overall expansion of the first coordination shell [OsN6]. DFT calculations supports the XTA results. They also provide additional information about the nature of the molecular orbitals that contribute to the optical spectrum (with TD-DFT) and the near-edge region of the X-ray spectra.
- Published
- 2016
- Full Text
- View/download PDF
39. Evidence for octupole collectivity in Pt-172
- Author
-
Ertoprak, A., Cederwall, B., Qi, C., Aktas, O., Doncel, M., Hadinia, B., Liotta, R., Sandzelius, M., Scholey, C., Andgren, K., Back, T., Badran, H., Braunroth, T., Calverley, T., Cox, D. M., Cullen, D. M., Fang, Y. D., Ganioglu, E., Giles, M., Gomez Hornillos, M. B., Grahn, T., Greenlees, P. T., Hilton, J., Hodge, D., Ideguchi, E., Jakobsson, U., Johnson, A., Jones, P. M., Julin, R., Juutinen, S., Ketelhut, S., Khaplanov, A., Kumar Raju, M., Leino, M., Li, H., Liu, H., Matta, S., Modamio, V., Nara Singh, B. S., Niikura, M., Nyman, M., Ozgur, I., Page, R. D., Pakarinen, J., Papadakis, P., Partanen, J., Paul, E. S., Petrache, C. M., Peura, P., Rahkila, P., Ruotsalainen, P., Saren, J., Sorri, J., Stolze, S., Subramaniam, P., Taylor, M. J., Uusitalo, J., Valiente-Dobon, J. J., Wyss, R., and Department of Chemistry
- Subjects
COEXISTENCE ,NUCLEI ,SPECTROMETERS ,MOMENTS ,SHAPES ,INSTABILITY ,116 Chemical sciences ,EXCITED-STATE ,MASS ,114 Physical sciences ,TRANSITION ,GAMMA-RAY SPECTROSCOPY - Abstract
Excited states in the extremely neutron-deficient nucleus Pt-172 were populated via Ru-96(Kr-78, 2p) and Mo-92(Kr-83, 3n) reactions. The level scheme has been extended up to an excitation energy of approximate to 5MeV and tentative spin-parity assignments up to I-pi = 18(+). Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negativeparity band. The lowestmember of this negative-parity structure was firmly assigned spin-parity 3(-). In addition, we observed an E3 transition from this 3(-) state to the ground state, providing direct evidence for octupole collectivity in Pt-172. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3(-) state as a collective octupole-vibrational state.
- Published
- 2020
40. H-He collision-induced satellite in the Lyman alpha profile of DBA white dwarf stars
- Author
-
Grégoire Guillon, John F. Kielkopf, Roberto Linguerri, Majdi Hochlaf, Siyi Xu, Ivan Hubeny, Muneerah Mogren Al Mogren, N. F. Allard, Bilel Mehnen, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Astronomy [Louisville], University of Louisville, Gemini Observatory, parent, Laboratoire Interdisciplinaire Carnot de Bourgogne [Dijon] (LICB), Université de Bourgogne (UB)-Université de Technologie de Belfort-Montbeliard (UTBM)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Instrumentation, Simulation et Informatique Scientifique (COSYS-LISIS), Université Gustave Eiffel, King Saud University [Riyadh] (KSU), and University of Arizona
- Subjects
ATOMIC DATA ,LINE: PROFILE ,Ab initio ,chemistry.chemical_element ,BASIS-SET ,LINE ,EXCITED-STATE ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Spectral line ,Physics - Atomic Physics ,WHITE DWARF ,0103 physical sciences ,Radiative transfer ,ABSORPTION ,Astrophysics::Solar and Stellar Astrophysics ,AB-INITIO CALCULATION ,Physics::Atomic Physics ,ELECTRONIC-TRANSITION MOMENT ,010306 general physics ,STARS: ATMOSPHERE ,010303 astronomy & astrophysics ,Helium ,Line (formation) ,POTENTIAL-ENERGY CURVE ,Physics ,[PHYS]Physics [physics] ,BALMER-ALPHA ,White dwarf ,Astronomy and Astrophysics ,MOLECULAR DATA ,Potential energy ,Dipole ,chemistry ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,ATOMIC PROCESS ,SHAPE ,[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph] ,Atomic physics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
The spectra of helium-dominated white dwarf stars with hydrogen in their atmosphere present a distinctive broad feature centered around 1160~\AA\/ in the blue wing of the Lyman-$\alpha$ line. It is extremely apparent in WD 1425+540 recently observed with HST COS. With new theoretical line profiles based on ab initio atomic interaction potentials we show that this feature is a signature of a collision-induced satellite due to an asymptotically forbidden transition. This quasi-molecular spectral satellite is crucial to understanding the asymmetrical shape of Lyman-$\alpha$ seen in this and other white dwarf spectra. Our previous work predicting this absorption feature was limited by molecular potentials that were not adequate to follow the atomic interactions with spectroscopic precision to the asymptotic limit of large separation. A new set of potential energy curves and electronic dipole transition moments for the lowest electronic states of the H--He system were developed to account accurately for the behavior of the atomic interactions at all distances, from the chemical regime within 1~\AA\/ out to where the radiating H atoms are not significantly perturbed by their neighbors. We use a general unified theory of collision-broadened atomic spectral lines to describe a rigorous treatment of hydrogen Lyman-$\alpha$ with these potentials and present a new study of its broadening by radiative collisions of hydrogen and neutral helium. These results enable ab initio modeling of radiative transport in DBA white dwarf atmospheres., Comment: 9 pages, 7 figures
- Published
- 2020
41. Uncovering Structure-Property Relationships in Push-Pull Chromophores: A Promising Route to Large Hyperpolarizability and Two-Photon Absorption
- Author
-
Anna Spalletti, Cosimo G. Fortuna, Alessio Cesaretti, Fausto Elisei, Paolo Foggi, and Benedetta Carlotti
- Subjects
Materials science ,Solvatochromism ,Hyperpolarizability ,02 engineering and technology ,Chromophore ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Two-photon absorption ,Acceptor ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Intramolecular charge-transfer ,nonlinear-optical properties ,N-methylpyridinium salts ,excited-state ,pyridinium salts ,Chemical physics ,Intramolecular force ,Ultrafast laser spectroscopy ,Physical and Theoretical Chemistry ,0210 nano-technology ,Absorption (electromagnetic radiation) - Abstract
In this investigation, we report the first hyperpolarizabilities and two-photon absorption cross sections of a large series of 12 push–pull cationic chromophores. All of these dyes show a dipolar acceptor+–π–donor structure, where the nature of the donor and acceptor units and π-bridge was synthetically tuned to allow insightful comparisons among the molecules. The hyperpolarizability was obtained through a solvatochromic method, by exploiting the rare negative solvatochromism exhibited by the investigated compounds. The two-photon absorption cross sections were determined through two-photon excited fluorescence measurements by means of a tunable nanosecond laser system for sample excitation. The nonlinear optical properties were discussed relatively to the photoinduced intramolecular charge transfer occurring in these donor–acceptor systems, investigated by femtosecond transient absorption experiments. We found a strong increase in hyperpolarizability upon increasing the molecular conjugation. Unexpectedly, the hyperpolarizability is almost unaffected by an increase in donor/acceptor strength and intramolecular charge transfer degree. Differently, the two-photon absorption cross sections of these dyes are enhanced by an increase in both molecular conjugation and intramolecular charge transfer efficiency. Several recent literature works have reported at the same time scattered information about the hyperpolarizability and two-photon absorption of small organic molecules. Our investigation is, to the best of our knowledge, the first attempt to uncover detailed structure–property relationships for these two nonlinear optical properties. Our results represent a promising route to achieve large hyperpolarizability and two-photon absorption in push–pull dyes and may drive the design of new efficient nonlinear optical materials.
- Published
- 2020
42. Carbazole-Perylenebisimide Electron Donor/Acceptor Dyads Showing Efficient Spin Orbit Charge Transfer Intersystem Crossing (SOCT-ISC) and Photo-Driven Intermolecular Electron Transfer
- Author
-
Antonio Toffoletti, Antonio Barbon, Xue Zhang, Jianzhang Zhao, Noreen Rehmat, and Zafar Mahmood
- Subjects
Materials science ,Electron donor ,EXCITED-STATE ,Photochemistry ,law.invention ,chemistry.chemical_compound ,Electron transfer ,ACCEPTOR ,law ,BODIPY ,Ultrafast laser spectroscopy ,Materials Chemistry ,Triplet state ,Electron paramagnetic resonance ,SINGLET OXYGEN ,General Chemistry ,Acceptor ,Intersystem crossing ,TRIPLET-TRIPLET ANNIHILATION ,TIME-RESOLVED EPR ,UP-CONVERSION ,LOW-POWER ,PHOTOSENSITIZERS ,GENERATION ,chemistry ,Ground state - Abstract
Perylenebisimide-carbazole (PBI–Cz) dyads were prepared to study charge-recombination (CR) induced intersystem crossing (ISC) in electron donor/acceptor dyads. The distance and the mutual orientation of the perylenebisimide (PBI) and carbazole (Cz) moieties were varied to study their effect on photophysical properties. Steady state and time-resolved optical spectroscopies show that electronic coupling between the electron donor and acceptor is negligible at the ground state. The fluorescence of the PBI moiety is strongly quenched in the dyads, and a larger separation between the donor and the acceptor results in less fluorescence quenching. The Gibbs free energy changes of the electron transfer and the energy level of the charge transfer state were studied using the electrochemical and optical spectra data. The singlet oxygen quantum yields (ΦΔ) are up to 72% for dyads with the shortest separation between the donor and the acceptor. Nanosecond transient absorption spectra confirmed the formation of the PBI-localized long lived triplet state (the lifetime is up to 190 μs). Notably non-orthogonal dyads show efficient spin orbit charge transfer (SOCT-ISC), which is different from the previously proposed orthogonal molecular structure for SOCT-ISC. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy shows that all three dyads give the same electron spin polarization of eae/aea, and thus the radical pair ISC (RP ISC) mechanism is excluded, which is different from the previously reported PBI-phenothiazine analogues. Efficient and reversible transformation of dyads to their radical anion was observed in the presence of sacrificial electron donor triethanolamine in an inert atmosphere with photo-irradiation.
- Published
- 2020
43. Ground-state projected covalency index of the chemical bond.
- Author
-
Szczepanik, Dariusz W. and Mrozek, Janusz
- Subjects
GROUND state (Quantum mechanics) ,COVALENT bonds ,CHEMICAL bonds ,EXCITED state chemistry ,SEPARATION (Technology) ,DENSITY matrices - Abstract
Highlights: [•] Ground-state projected bond orders. [•] Bond-covalency index in excited-states. [•] Criterion of maximum separation in density matrix spectrum. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
44. A twisted tale: measuring viscosity and temperature of microenvironments using molecular rotors
- Author
-
Aurimas Vyšniauskas, Marina K. Kuimova, and Engineering & Physical Science Research Council (EPSRC)
- Subjects
MEMBRANE-FLUIDITY ,DYNAMICS ,CHEMICAL-REACTIONS ,MEMBRANE VISCOSITY ,EXCITED-STATE ,02 engineering and technology ,Molecular rotors ,Physics, Atomic, Molecular & Chemical ,010402 general chemistry ,INNER MEMBRANE ,01 natural sciences ,Chemical reaction ,PROBES ,ACTIVATION ,INTRAMOLECULAR-CHARGE-TRANSFER ,Viscosity ,DEPENDENCE ,0307 Theoretical and Computational Chemistry ,LIVING CELLS ,Physical and Theoretical Chemistry ,Microscale chemistry ,0306 Physical Chemistry (incl. Structural) ,Science & Technology ,Chemical Physics ,Chemistry, Physical ,Physics ,LIPID-MEMBRANES ,FLUORESCENT THERMOMETER ,021001 nanoscience & nanotechnology ,LIVE CELLS ,DIFFUSION ,0104 chemical sciences ,Chemistry ,MOBILITY ,Chemical physics ,Excited state ,Physical Sciences ,0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics ,AEROSOL-PARTICLES ,0210 nano-technology - Abstract
Measuring viscosity and temperature on the microscale is a challening yet very important task, in materials sciences and in biology alike. In this perpsective we review and discuss fluorescent microviscosity sensors, termed ‘molecular rotors’, that offer a convenient way of measuring microscopic viscosity and sometimes may even be used to measure microscopic temperature in addition to viscosity. We discuss how temperature in combination with various solvent properties can affect microviscosity measurements and we review possible action mechanisms that make molecular rotors sensitive to multiple parameters of their environment. Overall, we reveal a complicated, yet exciting, behaviour of molecular rotors at different viscosity, temperature and solvent properties on the microscale and how this behaviour can be explained and exploited.
- Published
- 2018
45. THEORETICAL INVESTIGATION OF SUBSTITUTION EFFECT ON THE PROTON TRANSFER MECHANISM IN 3-MERCAPTO-PROPENETHIAL.
- Author
-
RAISSI, HEIDAR, FARZAD, FARZANEH, and FARSI, HOSSEIN
- Subjects
- *
SUBSTITUTION reactions , *PROTON transfer reactions , *CHEMICAL derivatives , *GAS phase reactions , *EXCITED state chemistry , *HYDROGEN bonding , *NATURAL orbitals , *THERMODYNAMICS - Abstract
We present detailed theoretical studies of the proton transfer (PT) in the 3-Mercapto-propenethial (MP) and in some of its derivatives. The effect of substitution on the transition state structures corresponding to the PT in R2 or Rl(3) positions is studied by using B3LYP/6-311++G** level of theory in gas phase and water solution. The following substituents have been taken into consideration: CI, F, OH, SH, OCH3, SCH3, CHO, NO., CCH and OCF3. For the different derivatives of 3-MP, we have computed geometries and potential energy curves for the intramolecular PT in their ground. Also, the excited-state properties of intramolecular hydro-gen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. The 7r-electron derealization parameter (Q) and HOMA index as a geometrical indicator of a local aromaticity are investigated. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolec-ular interactions. The results of analysis by Quantum theory of "Atoms in Molecules" and NBO method fairly support the DFT results. Correlations between the PT reaction barrier versus topological parameters, ν(S-H) and γ(S--H) are also probed. The obtained results showed a strong influence of the R substituent on the PT reaction barrier changes. Numerous correlations between topological, geometrical, thermodynamic properties and energetic parameters were also found. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
46. Excited-state properties of the 16kDa red carotenoid protein from Arthrospira maxima
- Author
-
Chábera, Pavel, Durchan, Milan, Shih, Patrick M., Kerfeld, Cheryl A., and Polívka, Tomáš
- Subjects
- *
CAROTENOIDS , *BACTERIAL proteins , *CYANOBACTERIA , *BILAYER lipid membranes , *SOLVENTS , *HYDROGEN bonding , *ABSORPTION (Physiology) - Abstract
Abstract: We have studied spectroscopic properties of the 16kDa red carotenoid protein (RCP), which is closely related to the orange carotenoid protein (OCP) from cyanobacteria. Both proteins bind the same chromophore, the carotenoid 3′-hydroxyechinenone (hECN), and the major difference between the two proteins is lack of the C-terminal domain in the RCP; this results in exposure of part of the carotenoid. The excited-state lifetime of hECN in the RCP is 5.5ps, which is markedly longer than in OCP (3.3ps) but close to 6ps obtained for hECN in organic solvent. This confirms that the binding of hECN to the C-terminal domain in the OCP changes conformation of hECN, thereby altering its excited-state properties. Hydrogen bonds between the C-terminal domain and the carotenoid are also absent in the RCP. This allows the conformation of hECN in the RCP to be similar to that in solution, which results in comparable excited-state properties of hECN in solution. The red-shift of the RCP absorption spectrum is most likely due to aggregation of RCP induced by hydrophobic nature of hECN that, when exposed to buffer, stimulates formation of assemblies minimizing contact of hECN with water. We suggest that the loss of the C-terminal domain renders the protein amphipathic, containing both hydrophobic (the exposed part of hECN) and hydrophilic (N-terminal domain) regions, and may help the RCP to interact with lipid membranes; exposed hECN can penetrate into the hydrophobic environment of the lipid membrane, possibly to provide additional photoprotection. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
47. Effect of temperature on the fluorescence emission of 2H-chromen-2-one derivative in non-polar and polar solvents
- Author
-
Evale, Basavaraj G., Hanagodimath, S.M., and Kulkarni, Manohar V.
- Subjects
- *
BENZOPYRANS , *FLUORESCENCE , *TEMPERATURE effect , *EXCITED state chemistry , *ACTIVATION (Chemistry) , *FORCE & energy , *SOLVENTS , *RADIATIONLESS transitions - Abstract
Abstract: The effect of temperature (293–333K) on the fluorescence emission of 4-(5-methyl-3-phenyl-benzofuran-2-yl)-6-chloro-2H-chromen-2-one (MPBClC) is recorded in non-polar (1,4-dioxane, and toluene), and polar (butanol and DMSO) solvents. It is found that there is no shift in the position of fluorescence maxima, but the intensity decreases with increase in temperature, which depends on the polarity of the solvent. A mechanism of fluorescence quenching with rise in temperature is discussed in terms of the relative location of lowest 1(ππ ⁎) and 3(nπ ⁎) states, and the energy difference between them. The change in temperature brings about a change in the probabilities of radiative and non-radiative transition. The radiationless deactivation of excited-state in the absence of quencher is temperature-dependent and its thermal activation energy has been determined. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
48. Fluorescence quenching phenomena facilitated by excited-state hydrogen bond strengthening for fluorenone derivatives in alcohols
- Author
-
Liu, Yu-Hui, Zhao, Guang-Jiu, Li, Guang-Yue, and Han, Ke-Li
- Subjects
- *
FLUORESCENCE , *EXCITED state chemistry , *HYDROGEN bonding , *ALCOHOLS (Chemical class) , *DENSITY functionals , *BAND gaps , *INTERNAL conversion (Nuclear physics) - Abstract
Abstract: Spectroscopic studies on benzo[b]fluorenone (BF) solvatochromism in several aprotic and alcoholic solvents have been performed to investigate the fluorescence quenching by hydrogen bonding and proposed a weaker ability to form intermolecular hydrogen bond of BF than fluorenone (FN). In this work, the time-dependent density functional theory (TD-DFT) method was used to study the excited-state hydrogen bonding of both FN and BF in ethanol (EtOH) solvent. As a result, it is demonstrated by our theoretical calculations that the hydrogen bond of BF–EtOH complex is almost identical with that of FN–EtOH. Moreover, the fluorescence quantum yields of FN and BF in the alcoholic solvent is efficiently dependent on the energy gap between the lowest excited singlet state (fluorescent state) and ground state, which can be used to explain the fluorescence quenching by the excited-state hydrogen bond strengthening. [Copyright &y& Elsevier]
- Published
- 2010
- Full Text
- View/download PDF
49. Theoretical studies on the structural and optical properties of a series of Os(II) diimine complexes [Os(N∧N)(CO)2I2] (N∧N=2,2′-bipyridine(bpy), 4,4′-di-tert-butyl-2,2′-bipyridine(dbubpy), 4,4′-dichlorine-2,2′-bipyridine(dclbpy))
- Author
-
Wu, Yu-Hui, Pan, Qing-Jiang, Zhou, Xin, Xia, Bao-Hui, Liu, Tao, and Zhang, Hong-Xing
- Subjects
- *
BIPYRIDINE , *ION exchange (Chemistry) , *CHARGE transfer , *DENSITY functionals - Abstract
Abstract: The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(N∧N)(CO)2I2] (N∧N=2,2′-bipyridine (bpy) (1), 4,4′-di-tert-butyl-2,2′-bipyridine (dbubpy) (2), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) (3)) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539nm for 1–3, respectively, were attributed to the admixture of the [dxy (Os)→π∗(bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I)→π∗(bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687nm also have the 3MLCT/3LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H→ t-Bu→Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
50. Effects of conjugation in length and dimension on two-photon properties of fluorene-based chromophores.
- Author
-
Nguyen, Kiet A., Day, Paul N., and Pachter, Ruth
- Subjects
- *
BIOCONJUGATES , *PHYSICAL & theoretical chemistry , *PHOTONS , *FLUORENE , *METHANE - Abstract
We report calculated two-photon (TPA) absorption spectra based upon results obtained from quadratic response time-dependent density functional theory for fluorene-based donor-π-acceptor molecules. Coulomb attenuated functionals with a long-range exchange contribution are applied to predict TPA excitation energies and cross-sections. Observed spectra are explained, and the effects of conjugation and multibranching on the TPA spectra are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.