Search

Time‐dependent density functional theory (TD‐DFT) and multiconfigurational second‐order perturbation theory (CASPT2) are two of the most widely used methods to investigate photoinduced dynamics in DNA‐based systems. These methods sometimes give diverse dynamics in physiological environments usually modeled by quantum mechanics/molecular mechanics (QM/MM) protocol. In this work, we demonstrate for the uridine test case that the underlying topology of the potential energy surfaces of electronic states involved in photoinduced relaxation is similar in both electronic structure methods. This is verified by analyzing surface‐hopping dynamics performed at the QM/MM level on aqueous solvated uridine at TD‐DFT and CASPT2 levels. By constraining the dynamics to remain on ππ* state we observe similar fluctuations in energy and relaxation lifetimes in surface‐hopping dynamics in both TD‐DFT and experimentally validated CASPT2 methods. This finding calls for a systematic comparison of the ES potential energy surfaces of DNA and RNA nucleosides at the single‐ and multi‐reference levels of theory. The anomalous long excited state lifetime at the TD‐DFT level is explained by nπ* trapping due to the tendency of TD‐DFT in QM/MM schemes with electrostatic embedding to underestimate the energy of the ππ* state leading to a wrong ππ*/nπ* energetic order. A study of the FC energetics suggests that improving the description of the surrounding environment through polarizable embedding or by the expansion of QM layer with hydrogen‐bonded waters helps restore the correct state order at TD‐DFT level. Thus by combining TDDFT with an accurate modeling of the environment, TD‐DFT is positioned as the standout protocol to model photoinduced dynamics in DNA‐based aggregates and multimers. [ABSTRACT FROM AUTHOR]

Cluster B12C4N8 has a broad application prospect. It is of great significance for investigating the properties of cluster B12C4N8 under the external electric field. The dipole moment, energy gap and infrared spectrum of cluster B12C4N8 molecule under external electric field (0–30 V/nm) are studied with density functional theory at B3LYP/6-31G(d) level. The dipole moment increases almost linearly from 0.87838 to 30.79096 Debye and the energy gap decreases continuously. Meanwhile, the ultraviolet-visible absorption spectra, the excitation wavelength, the excitation energy, oscillator strength and real space representation of hole and electron distributions of first ten excited states of cluster B12C4N8 under the external electric field are also studied with the time-dependent density functional theory at B3LYP/6-31G(d) level. It is found that the absorption peak of cluster B12C4N8 occurs blue shift. The excitation energy decreases significantly as the external electric field increases from 0 to 15 V/nm, increases as the external electric field increases from 15 to 20 V/nm, and decreases almost linearly as the external electric field increases from 20 to 30 V/nm. The results can offer an important reference to use external electric Fifield to tune the properties of cluster B12C4N8. [ABSTRACT FROM AUTHOR]

The rationality of the minimum electrophilicity principle (MElP) as a companion of minimum polarizability principle and maximum hardness principle is studied for simple diatomic, triatomic, and tetratomic molecules. The applicability is further justified considering organic molecules (e.g., pyrene and acridine yellow) are known for their photophysical properties and accordingly their excited state properties. Single excitation CI (CIS) and time‐dependent density functional theory (TDDFT) are employed to study the excited state reactivity. Two types of excitations, namely vertical and adiabatic, are considered. Processes involving conservation and change in spin multiplicity are included during excitation. The general trend is that the molecules are less electrophilic in the ground state than those in the corresponding excited states. It is found that adiabatic excitation validates the principle even for the triplet ground state molecules undergoing an excitation where spin multiplicity gets altered. The TDDFT method explains the validity of the MElP augmenting the CIS method. This study echoed the MElP during molecular electronic excitation. [ABSTRACT FROM AUTHOR]

The formulations and performances of spin‐restricted ensemble‐referenced KS and mixed‐reference spin‐flip time‐dependent density functional theory incorporating strong correlations into density functional theories are documented. As a result of balanced dynamic and nondynamic correlation, they are capable of describing strongly correlated challenging systems including diradicals, bond dissociation, conical intersections, doubly excited states, and so on, overcoming the limitations of current density functional theories. [ABSTRACT FROM AUTHOR]

The ground and lowest singlet excited state geometries of selected (para -C5H4X)Ir(PH3)3 iridabenzene complexes (para -substituent = NH2, OMe, Me, H, F, Cl, CCl3, CF3, NO2) are optimized using the MPW1PW91 procedure employing the LanL2DZ(Ir) and 6-311G(d, p) (C, H, N, O, P, F, Cl, P) basis sets. The excited state is generated using the time-dependent density function method. The effects of electron-donating groups and electron-withdrawing groups on the energy, atomization energy, rotational constants, and frontier orbital energies in the first singlet excited state (S1) of iridabenzene are investigated and compared to those of the ground state (S0). The Ir–C and Ir–P bonds in the studied molecules are analyzed by electron localization function and localized-orbital locator methods. The correlations between the Ir-C and Ir–P bond distances, electron localization function, and localized-orbital locator values Hammett constants (σp) and dual parameters (σI and σR) are given for the two studied states. The para -delocalization index is used for investigation of the aromaticity of the studied complexes. [ABSTRACT FROM AUTHOR]

In this study, the effects of the external electric field (EEF) on osmabenzyne in the ground (S0) and first excited singlet (S1) states are investigated using the hybrid density functional MPW1PW91. The first singlet excited state is determined by the time-dependent density functional theory. Variations in the structure, dipole moment, electronic spatial extent, and aromaticity of the title complex are compared in the presence and absence of EEF. In addition, rotation constants, electron-donating (ω–) and electron-accepting (ω+) powers are calculated. The para-delocalization index is used to investigate the aromaticity in these systems. [ABSTRACT FROM AUTHOR]

The luminescent properties 1‐(9‐antryl)butane‐1,3‐dione (1) have been investigated by means of time resolved and steady state luminescence. The results have been analyzed via the method of time‐dependent density functional theory (TD DFT). It has been shown that for compound 1 there are two forms of enol, A and B, which differ in the position of the luminescence bands. For compound 1 in polar solvents, the dual luminescence has been detected: the structured band of 420 nm and the wide diffuse band at 530 nm. In nonpolar solvents, only a broad band at 530 nm was observed. A long‐wavelength band at 530 nm was attributed to the processes of Excited‐State Intramolecular Proton Transfer (ESIPT) and Twisted Intramolecular Charge Transfer (TICT). For compound 1 in acetone, the intensity of the short‐wavelength band of the enol B increased along with the temperature increase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methylation on the isomerizable alkene bond of plant sunscreen sinapates is first performed. • The critical role of molecular planarity breaking on accelerating this nonradiative process is highlighted. • This work provides a facile strategy to modulate the isomerization dynamics of photoswitches, proteins and sunscreens. E-Z photoisomerization constitutes the footstone of photosensitive proteins, molecular photoswitches and sunscreens and is believed to be controlled by photoinduced intramolecular charge transfer. In this work, we have made methylation on isomerizable alkene bond of plant sunscreen sinapate esters to break the coplanarity between phenol ring and C C double bond in ground state. Femtosecond transient absorption spectroscopy combined with time-dependent density functional theory calculations determine that this molecular planarity breaking triggers an immediate excited-state C C double bond twisting and thus accelerates the isomerization by more than one order of magnitude. These results highlight the role of molecular geometry on isomerization dynamics. [ABSTRACT FROM AUTHOR]

Issue concerning accurate prediction of the reverse intersystem crossing rate (kRISC) is critical for developing novel efficient thermally activated delayed fluorescence (TADF) materials. In this contribution, the kRISC rates from the lowest excited triplet T1 state to the lowest excited singlet S1 state were evaluated for five donor‐π‐acceptor‐type pyrimidine‐based TADF emitters using the semiclassical Marcus theory. Both the singlet‐triplet energy difference (ΔEST) and spin–orbit coupling (V) between the S1 and T1 states were investigated by performing the density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) calculations. In addition, their fluorescence emission wavelengths (λem) were also calculated at the TD‐DFT level. The predicted kRISC and λem values are found to reproduce well the available experimental findings. The present results reveal that the kRISC rates of molecules possessing the unsymmetrical diphenyl pyrimidine acceptor core are calculated to be slightly larger than those of their analogues with the symmetrical diphenyl pyrimidine. In addition, introducing two tert‐butyl groups into the 2,7‐positions of the donor moiety of the latter is also an effective method for increasing kRISC when designing TADF emitters. Such a difference is related to the nature of the T1 excited state. A more remarkable charge‐transfer (CT) contribution to the state can achieve a smaller ΔEST, leading to a more efficient RISC process, and consequently a shorter delayed fluorescence lifetime as observed experimentally. © 2019 Wiley Periodicals, Inc. Five molecules exhibiting the TADF behavior were studied theoretically. Calculations reveal that a remarkable charge‐transfer contribution to the T1 excited state can achieve a smaller singlet‐triplet energy difference. This leads to a more efficient reverse intersystem crossing process. [ABSTRACT FROM AUTHOR]

Abstract A series of inexpensive and water-soluble fluorescent dihydro-[1,2,4]triazolo [4,3- a ]pyridin-2-ium-carboxylates (Safirinium dyes) have been synthesized and characterized by UV–Vis, IR, 1H- and 13C NMR spectroscopic techniques as well as by single crystal X-ray analysis. Significantly lower fluorescence quantum yields were determined in aprotic polar solvent (DMF). The photophysical properties of zwitterions and hydrochlorides were rationalized theoretically. A combined experimental and DFT/TD-DFT study of absorption and emission spectra have been performed. The calculations were carried out within the vertical non-equilibrium approximation or the state-specific approach using conventional (APFD, B3LYP and PBE0) and long-range-corrected hybrid functionals (CAM-B3LYP and ωB97XD) by means PCM and SMD solvation models. We have found that global hybrid functionals (GH) fail for charge transfer excited states in which charge is moved from the substituent to the heteroaromatic system, while the long range corrected functionals deliver consistent estimates, especially within the state-specific PCM modeling framework. The long-range-corrected hybrid functionals (RSH) were also found to be the most efficient in reproducing the emissive properties of the dyes. Highlights • A series of inexpensive and water-soluble fluorescent Safirinium dyes have been synthesized. • The photophysical properties of the dyes were rationalized theoretically with TD-DFT methods. • The long-range-corrected hybrid methods were found to be the most efficient in reproducing the photo-physical properties. [ABSTRACT FROM AUTHOR]

Singlet and triplet excited-state properties of a single poly- p -phenylenevinylene (PPV) chain are studied using the Pariser-Parr-Pople-Peierls (P-P-P-P) model combined with the configuration interaction singles (CIS) formalism. The analytic CIS energy gradient is derived using the coupled perturbed Hartree-Fock (CPHF) equations in order to perform excited-state geometry optimizations. According to whether the diagonal elements of transition density matrices being zero or not, all excited states can be classified into two types: type I with nonzero diagonal elements, and type II with zero diagonal elements. In general, type I excited states can be directly generated upon photoexcitation, and there is high probability to find the electron and the hole very close to each other. While type II excited states cannot be directly generated upon photoexcitation, and there is high probability to find the electron and the hole far to each other. Using the parameters developed for this model, we examine the energy levels, oscillator strengths, optical absorption spectrum, and optimized excited-state geometries of the excited states at low energies, and they are consistent with other theoretical work very well. This work provides a new perspective on the excited-state properties of conjugated polymers. [ABSTRACT FROM AUTHOR]

In this work, the time-dependent density functional theory (TDDFT) method was performed to investigate the electronic spectra and charge transfer in excited states of firefly luciferin anion (NRO - ) in aqueous solution. A novel electronic spectral blue-shift (usually red-shift) phenomenon of NRO - was observed due to the significant influence of intermolecular hydrogen bonds between firefly luciferin anion and water molecules. We theoretically demonstrated that the excited-state intermolecular hydrogen bond weakening is confirmed by the increase of hydrogen bond length and decrease of hydrogen bond binding energy from our optimized ground-state and excited-state geometric conformations of the hydrogen-bonded NRO - –H 2 O complex. The hydrogen bond weakening behavior could also be indicated by photoinduced charge transfer from the carboxyl group to the planar part of NRO - in the excited state. Furthermore, we pointed out that the electronic spectral blue-shift should be ascribed to the intermolecular hydrogen bond weakening in this electronic excited state. The weakened hydrogen bonding interaction in the excited state would induce smaller downshift for the excited-state energy level than that for ground-state energy level. As a result, the energy gap between the excited state and ground state becomes larger, which means that the spectral peak corresponding to the electronic excited state will shift to the blue induced by the excited-state hydrogen bond weakening dynamics. [ABSTRACT FROM AUTHOR]

In this work, the excited-state intermolecular hydrogen bonding interactions, photoinduced charge transfer, and vibrational spectroscopic properties of deprotonated deoxyadenosine monophosphate [dAMP-H] − anion in aqueous solution were investigated by the DFT/TDDFT method. The intermolecular hydrogen-bonded model complexes [dAMP-H] − –nH 2 O ( n = 0, 1, 2, 3, 4) in both the ground state and electronic excited state were first discussed. Analysis of frontier molecular orbitals reveals an intramolecular charge transfer (ICT) state for [dAMP-H] − –nH 2 O ( n = 0, 1, 2) complexes in which charge transfer occurs from the phosphate group to the base. However, it becomes a locally excited (LE) state for [dAMP-H] − –nH 2 O ( n = 3, 4) complexes, which only locates on the adenine moiety. The excited energies of the first excited state of [dAMP-H] − –nH 2 O ( n = 0, 1, 2, 3) increase gradually during the introduction of water molecules, but decreases with the fourth water molecule at adenine site. The fourth water molecule has little influence on the structure but significant to the photoexcitation. Upon electronic excitation, stretching vibration frequencies of N H and O H of hydrogen bonds: N 5 H 10 ⋯ O 9 , O 9 H 19 ⋯ O 10 and O 10 H 21 ⋯ O 3 are red-shifted. The excited-state bond lengths of these hydrogen bonds are also shortened. Therefore, the total intermolecular hydrogen bonding interaction at the base moiety is significantly strengthened in the electronic excited state. [ABSTRACT FROM AUTHOR]

[Display omitted] • The excited-state properties of three hydroxyanthraquinone compounds from the Marine Crinoid Pterometra venusta were studied by TDDFT. • After the excitation procession the pull shrinkage deformation about the middle ring is slightly stronger in HAQ3 than HAQ1 and HAQ2. • For S 0 → S 1 excitation, HAQ1 and HAQ2 is the local excitation of π-π*, while HAQ3 presents S 0 → S 1 as n-π*charge transfer excitation characteristic. Three natural hydroxyanthraquinone compounds HAQ (1–3) extracted from the Marine Crinoid Pterometra venusta. In order to identify their photochemical and electronic excited state properties of them, the theoretical research of optoelectronic properties have been studied. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, UV- absorbance and fluorescence emission spectra of HAQ (1–3) had been calculated. The results show that calculated spectra are very consistent with the experimental data. For S 0 → S 1 excitation, HAQ1 and HAQ2 are the local excitation of π-π*, while HAQ3 presents S 0 → S 1 as n-π*charge transfer excitation characteristic. [ABSTRACT FROM AUTHOR]

This study presents an efficient algorithm to search for the poles of dynamic polarizability to obtain excited states of large systems with nonlocal excitation nature. The present algorithm adopts a homogeneous search with a constant frequency interval and a bisection search to achieve high accuracy. Furthermore, the subtraction process of the information about the detected poles from the total dynamic polarizability is used to extract the undetected pole contributions. Numerical assessments confirmed the accuracy and efficiency of the present algorithm in obtaining the excitation energies and oscillator strengths of all dipole-allowed excited states. A combination of the present pole-search algorithm and divide-and-conquer-based dynamic polarizability calculations was found to be promising to treat nonlocal excitations of large systems. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The effect of electrochemical degradation on Magnéli phase Ti 4 O 7 anode combined with UV irradiation on the removal of PFOS was systematically evaluated in the present study. A synergistic effect of electrolysis and UV irradiation rather than a simple additive effect for PFOS degradation was demonstrated experimentally and theoretically. The short wavelength irradiation within 400 nm is the main contribution to enhance the electrochemical degradation of PFOS, while the initial pH of the solution has little effect on the PFOS degradation. The increase of current density accelerates the removal of PFOS either by electrolysis treatment or the joint process. The time-dependent density functional theory (TD-DFT) calculation indicates that the synergistic effect of the electrolysis and UV irradiation is most likely due to the involvement of the excited PFOS induced under UV irradiation in the electrochemical reaction. This study provides the first mechanistic explanation for the electrochemical degradation of PFOS enhanced by UV irradiation. [Display omitted] • PFOS degradation by electrolysis on Ti 4 O 7 anode combined with UV irradiation was studied. • A synergistic effect exists between electrolysis and UV irradiation for PFOS degradation. • TD-DFT calculation elucidates the synergistic mechanism of electrolysis and UV irradiation. • Excited PFOS induced by UV reduces the anodic potential required for electrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of exchange–correlation functionals on charge-transfer excited states is tested. • The explicit solvent model gives a reasonable description of the electronic structure based on the QM/MM approach. • Red-shifts of the emission peak with increasing solvent polarity was reproduced in the theoretical calculations. ABSTRAC:A typical thermally activated delayed fluorescence (TADF) molecule, 3DPyM-pDTC was investigated theoretically in terms of geometric structure, absorption and emission spectra, and luminescence rates. The result of different XC functionals, the implicit and explicit solvent models on calculating geometries, and electron structures of the excited states were compared comprehensively. It's found that time-dependent density functional theory (TDDFT) with the PBE0 functional could give a rational description of the electron structure of 3DPyM-pDTC employing the explicit solvent model based on QM/MM. Red-shifts of the emission peak with increasing solvent polarity was reproduced. The TADF properties in the solid phase reproduced well. [ABSTRACT FROM AUTHOR]

So far, coumarin dyes have been extensively studied with various means to understand their photophysical behaviors and properties. Here, our performing time-dependent density functional theory calculation is aimed at exploring the excited-state hydrogen bonding dynamics of coumarin 153 (C153) in protic ethanol (EtOH) solvent. The calculated results suggest that the excited-state hydrogen bond CO⋯HO between CO group and OH group in the C153-EtOH complex is strengthened, and the S0 → S1 transition of the complex corresponds to the highest occupied molecular orbital (HOMO) hopping to the lowest unoccupied molecular orbital (LUMO). The excited-state hydrogen bond strengthening has been further confirmed by its larger binding energy in the S1 state than in the S0 state. In addition, because of the formation of the hydrogen bond CO⋯HO, a red shift of about 7 nm occurs in the electronic spectra of the C153-EtOH complex, which is in good accordance with the experiment result. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Theoretical chemistry provides a panel of powerful tools to investigate the geometries and electronic properties of excited states. However, it is necessary to benchmark the accuracy of existing models to determine the range of their applicability and accountability. In the present work, the performance of two related methodologies in this context, symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent double-hybrid density functional theory (TD-DHDFT), is compared in detail for the calculation of absorption and fluorescence energies of small organic molecules and π-conjugated heteroaromatic compounds. Pragmatically, for the SAC-CI calculations the singles and doubles linked excitation operators are considered in the wave functions. On the other hand, for the TD-DHDFT calculations the linear-response Tamm–Dancoff formalism has been imposed. The considered DH density functionals include the approximations from both families of adjusted and non-adjusted models. Our numerical data reveal that of the tested adjusted DHs, B2-PLYP performs the best, while among the category of non-adjusted approximations the PBE0-DH functional outperforms others. Furthermore, the DH density functionals show deviations less than those obtained from SAC-CI method. Putting all the results together, the B2-PLYP and B2GP-PLYP functionals are found to be superior for overall performance. Altogether, the present contribution and recent efforts in this arena point out that besides the ground-state properties the DH approximations have also unquestionably entered into the field of excited-state calculations, where the DHDFT again comes into play and further evidence on the quality of the corresponding models is pronounced. [ABSTRACT FROM AUTHOR]

We present an efficient real-time time-dependent density functional theory (TDDFT) method for large-scale accurate simulations of electron–nucleus dynamics, as implemented in the time dependent ab-initio package (TDAP). By employing a local basis-set presentation, we are able to simulate systems of large size (∼500 atoms) and for long electronic propagation time (∼300–500 fs) with less computation cost while maintaining relatively high accuracy. We show several quintessential examples, such as photoabsorption spectra of dye-sensitized TiO 2 nanowire, proton transfer coupled nonradiative relaxation of eumelanin constituents, electron injection and electron–hole recombination in dye solar cells, hole-transfer dynamics between MoS 2 /WS 2 interlayer heterojunction, and solvent effects on electron dynamics. Our method is demonstrated to have superiority over available methods in dealing with interesting excited state characteristics of complex systems involving dynamics of electrons and atoms. [ABSTRACT FROM AUTHOR]

A comparison of excited state and electroluminescent properties between Pt(C^N^N)Cl and Pt(N^C^N)Cl complexes has been done with Time-Dependent Density Functional Theory (TDDFT), [C^N^N = 6-phenyl-2,2-bipyridine, N^C^N = 1,3-di(2-pyridyl)benzene]. The substituent effect of fluorine ligands on eight tridentate cyclometalated Pt(C^N^N)Cl complexes has been investigated, which includes electronic density variation between ground states and excited states, absorption and emission spectra, quantum yields and radiative lifetime. In addition, one dimeric form of Pt(C^N^N)Cl complex has been investigated. [ABSTRACT FROM AUTHOR]

6-Aminophenanthridine (6AP) and its derivatives show important biological activities as antiprion compounds and inhibitors of the protein folding activity of the ribosome. Both of these activities depend on the RNA binding property of these compounds, which has been recently characterized by fluorescence spectroscopy. Hence, fundamental insights into the photophysical properties of 6AP compounds are highly important to understand their biological activities. In this work, we have calculated electronic structures and optical properties of 6AP and its three derivatives 6AP8CF3, 6AP8Cl, and 6APi by density functional theory (DFT) and time-dependent density functional theory (TDDFT). Our calculated spectra show a good agreement with the experimental absorption and fluorescence spectra, and thus, provide deep insights into the optical properties of the compounds. Furthermore, comparing the results obtained with four different hybrid functionals, we demonstrate that the accuracy of the functionals varies in the order B3LYP > PBE0 > M062X > M06HF. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fluoride-sensing mechanism of a fluorescent sensor is theoretically confirmed. • Calculated VTEs are in good agreements with experimental spectra. • Fluoride-sensor complex undergoes an ESPT process with a relatively high potential barrier. • ESPT alleviates the steric hindrance in the sensor and enlarges the conjugated system. • ESPT process leads to the red-shifted fluorescence upon the addition of fluoride. An understanding of the excited-state process and the sensing mechanism for specific anions can be helpful for the design and synthesis of fluorescent sensors in analytical chemistry and biotechnology. Here, we theoretically investigated the fluorescent response mechanism of a reported acylhydrazone-based fluorescent sensor (Soft Matter , 2019, 15, 6690) for fluoride recognition using the time-dependent density functional theory approach. At the M06/TZVP/SCM level, the vertical excitation energies, which were calculated based on the ground state and first singlet-state geometries of the sensor molecule, agreed well with the experimental ultraviolet–visible and fluorescence spectra. Therefore, the time-dependent density functional theory method was considered reasonable and effective. According to the frontier orbital analysis and an excited-state potential energy scan, we proposed an excited-state proton transfer mechanism for the sensor-fluorine complex, where the steric hindrance leads to a high potential barrier. The excited-state proton transfer process facilitates sensor molecule deprotonation, alleviates its steric hindrance effect and expands its conjugated system. As a result, the fluorescence emission band of the sensor molecule was red-shifted significantly with the addition of fluoride anion. Based on this fluorescence difference, the sensor could be used for fluoride anion identification. This work provides a strategy to study sensor–analyte interactions in the excited state and offers an approach to tune the fluorescence emission wavelength of sensor molecules in anionic environments. [ABSTRACT FROM AUTHOR]

A two new compounds with potential biologically active were synthesized: ethyl 4-(2H-4,6-dimethyl-3-oxo-2,3-dihydroisothiazolo [5,4-b] pyridin-2-yl) butanoate and ethyl 4-(2H-4,6-dimethyl-2,3-dihydroisothiazolo [5,4-b] pyridin-3-yloxy) butanoate. The structures of all of the newly formed compounds were identified by elemental analysis, FTIR and H NMR. Their optical properties were studied in ethanol and n-hexane by UV-Vis absorption and fluorescence spectroscopy. The ground-state and excited-state properties were investigated using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) methods. The results showed differences between emission spectra in ethanol and n-hexane solution (solvatochromism) for both new compounds. [ABSTRACT FROM AUTHOR]

The intermolecular hydrogen bonding dynamics between the functionalized activated carbons (AC) and ethyl mercaptan (ETM) were investigated using DFT and TDDFT methods, respectively. The ground-state and excited-state structures, electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states for the functionalized ACs and their hydrogen-bonded complexes I, II, III and IV were calculated. It is demonstrated that the stability trend of forming hydrogen-bonded complexes is I > II and III > IV, which coincides with the results from the interaction energies calculation EHB. Moreover, according to Zhao's rule on the excited hydrogen bonding dynamics, it is found that the hydrogen bonds in the complexes I, II and III are significantly strengthened, with the excitation energy of a related excited state being red shifted, the hydrogen bond interactions can facilitate ETM adsorption onto AC-COOCO, AC-CCC and AC-CO, respectively. The intermolecular hydrogen bond of complex IV in the excited state is noteworthily weakened, in which the excitation energy of a related excited state is blue shifted. Therefore, the hydrogen bond interaction in complex IV is against ETM adsorption onto AC-OH in the excited state. The photoexcitation for complex IV should be controlled during the absorption process. [ABSTRACT FROM AUTHOR]

Highlights: [•] The excited-state nature of the ion-pair formed between 6-hydroxyquinoline and trimethylamine in polar solvents has been studied. [•] Both of the contact ion-pair and solvent separated ion-pair exist following the ESPT reaction. [•] The polarity of solvents could effectively facilitate the formation of the solvent separated ion-pair. [Copyright &y& Elsevier]

The time-dependent density functional theory method was performed to investigate the excited-state hydrogen-bonding dynamics of N-(2-hydroxyethyl)-1,8-naphthalimide (2a) and N-(3-hydroxyethyl)-1,8-naphthalimide (3a) in methanol (meoh) solution. The ground and excited-state geometry optimizations, electronic excitation energies, and corresponding oscillation strengths of the low-lying electronically excited states for the complexes 2a + 2meoh and 3a + 2meoh as well as their monomers 2a and 3a were calculated by density functional theory and time-dependent density functional theory methods, respectively. We demonstrated that the three intermolecular hydrogen bonds of 2a + 2meoh and 3a + 2meoh are strengthened after excitation to the S1 state, and thus induce electronic spectral redshift. Moreover, the electronic excitation energies of the hydrogen-bonded complexes in S1 state are correspondingly decreased compared with those of their corresponding monomer 2a and 3a. In addition, the intramolecular charge transfer of the S1 state for complexes 2a + 2meoh and 3a + 2meoh were theoretically investigated by analysis of molecular orbital. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A series of heteroleptic cyclometalated Ir(III) complexes for organic (OLEDs) application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, the electronic structures, the lowest-lying singlet absorptions and triplet emissions of Ir(dfppy)2(tpip), Ir(tfmppy)2(tpip), and theoretically designed models of Ir(ppy)2(tpip) were investigated with the density functional theory (DFT)-based approaches, where ppy = 2-phenylpyridine, dfppy = 4,6-difluorophenylpyridine, tfmppy = 4-trifluoromethylphenylpyridine, and tpip = tetraphenylimidodiphosphinate. Their structures in the ground and their excited states have been optimized at the DFT/Becke 3-parameter Lee Yang Parr (B3LYP)/Los Alamos National Laboratory 2-double-z (LANL2DZ) and time-dependent DFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy transfer mechanism together with the advantage of low efficiency roll-off for these complexes also can be analyzed here. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Firstly locate a more reasonable structure for the product of DHADC reacted with CN−. • A new fluorescence quenching mechanism for DHADC has been proposed. • Photo-induced hydrogen bonding variations have been explored. In this work, we investigated the fluorescence mechanism of the probe (E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide (DHADC) for both Zn2+ and CN− by using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Utilizing the constructed potential energy curves both in the ground and excited states as a function of the distance of N2···H1, the proton transfer process of DHADC has been explored. According to the calculated spectra, another more reasonable structure of DHADC-CN for the product of DHADC responding to CN− has been proposed. All of the simulated absorption and emission spectra in this work are in agreement well with those in the experiment. Furthermore, the excited state decay picture and the fluorescence quenching mechanism of DHADC , as well as the fluorescence mechanism for Zn2+ and CN− have been fully explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fluorescent sensing mechanism for hydroxyl radicals is obtained by TD-DFT. • Calculated VTEs well agree with UV–Vis and fluorescent spectra of the probe. • TICT process of the probe is responsible for its weak fluorescence. • Different FMOs lead to different fluorescent properties of the probe and its oxidation product. Due to the relevance to excited-state processes, sensing mechanisms of fluorescent probes were difficult to study directly by experimental methods. This work investigated theoretically the sensing mechanism of a reported bifunctional fluorescent probe to detect intracellular hydroxyl radicals and their environmental viscosity (J. Am. Chem. Soc. 2019, 141, 18301). Calculations were performed at the B3P86/TZVP/SMD level using density functional theory and time-dependent density functional theory. The transition from the ground-state (S 0) to the first singlet excited state (S 1) was calculated to have the largest oscillation strength for the probe. The wavelength that corresponded to the S 0 -S 1 vertical excitation energy (427 nm) agreed well with the maximum absorption band at 400 nm in the ultraviolet–visible spectra. Theoretical results showed that the probe had two distinct geometries in the S 0 and S 1 states, respectively. This difference was caused by the different distributions of frontier molecular orbitals that were involved in the S 0 -S 1 transition and corresponds to a twisted intramolecular charge transfer. The S 1 -state potential energy curve of the probe molecule confirmed that the twisted intramolecular charge transfer could proceed spontaneously with a potential barrier of only 12.20 kJ/mol. This result provided an irradiative approach for the probe molecule to dissipate the S 1 -state energy, which explained its fluorescence quenching. In contrast, the hydroxyl oxidation reaction changed frontier molecular orbitals of the probe molecule, which made its S 1 state a local S 1 state with a strong fluorescence emission. Precisely due to the mechanism, the hydroxyl radicals could be detected by changes in the fluorescence signal of the probe molecule. [ABSTRACT FROM AUTHOR]

The series of heteroleptic cyclometalated Ir(III) complexes for organic light-emitting display application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of Ir-(pmb)3 and theoretically designed models Ir-(Rpmb)2pic were investigated with density functional theory (DFT)-based approaches, where pmb = phenyl-methyl-benzimidazolyl, pic = picolinate, and R = H/F. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. The mobility of holes and electrons were studied computationally based on the Marcus theory. Calculations of ionization potentials were used to evaluate the injection abilities of holes into these complexes. The reasons for the higher electroluminescence efficiency and phosphorescence quantum yields in Ir-(Rpmb)2pic than in Ir-(pmb)3 have been investigated. The designed moleculars are expected to be highly emissive in pure-blue region. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods were performed to investigate the electronic excited-state hydrogen bonding dynamics of the hydrogenbonded complex formed by BHC-nicotinamide (BHCN) and methanol (MeOH). The ground-state geometry optimizations, electronic transition energies, corresponding oscillation strengths of the low-lying electronically excited states, and the optimized S1 excited-state geometry for the isolated BHCN and MeOH monomers, the hydrogen-bonded BHCN-MeOH dimers, and BHCN-2MeOH trimer complexes have been calculated by using the DFT and TDDFT methods, respectively. We have demonstrated that the intermolecular hydrogen bond C10=O14···H40−O39−Me is weaker than C16=O17···H46−O45−Me in the hydrogen-bonded dimers and trimer no matter whether in the ground state or the excited state. In addition, our results are consistent with the relationship between the electronic spectral shifts and excited-state hydrogen bonding dynamics: hydrogen bond strengthening can induce the relative electronic spectra redshift, whereas a blueshift will be induced. In addition, we focused our attention on the frontier molecular orbital and the results could reasonably explain the hydrogen bond strengthening or weakening mechanism. [ABSTRACT FROM AUTHOR]

Intramolecular and intermolecular hydrogen bonding in electronic excited states of calixarene building blocks bis(2-hydroxyphenyl)methane (2HDPM) monomer and hydrogen-bonded 2HDPM-HO complex were studied theoretically using the time-dependent density functional theory (TDDFT). Twenty-four stable conformations (12 pairs of enantiomers) of 2HDPM monomer have been found in the ground state. From the calculation results, the conformations 1a and 1b which both have an intramolecular hydrogen bond are the most stable ones. The infrared spectra of 2HDPM monomer and 2HDPM-HO complex in ground state and S state were calculated. The stretching vibrational absorption band of O − H group in the monomer and complex disappeared in the S state. At the same time, a new strong absorption band appeared at the C=O stretching region. From the calculation of bond lengths, it indicates that the O − H bond is significantly lengthened in the S state. However, the C − O bond is drastically shortened upon electronic excitation to the S state and has the characteristics of C=O band. Furthermore, the intramolecular hydrogen bond O − H · · · O of the 2HDPM monomer and the intermolecular hydrogen bonds O − H · · · O and O − H · · · O of 2HDPM-HO complex are all shortened and strengthened in the S state. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The structure, spectral properties and the hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine have been studied by using quantum chemical methods. The time-dependent density functional theory (TD-DFT) and the singly excited configuration interaction (CIS) methods are employed to optimize the excited state geometries of isolated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine in both the gas and solvent phases. The solvent phase calculations are performed using the polarizable continuum model (PCM). The absorption and emission spectra are calculated using the time-dependent density functional theory (TD-DFT) method. The results from the TD-DFT calculations reveal that the excitation spectra are red shifted relative to absorption in aqueous medium. These changes in the transition energies are qualitatively comparable to the experimental data. The examination of molecular orbital reveals that the molecules with a small H→L energy gap possess maximum absorption and emission wavelength. The relative stability and hydrogen bonded interactions of mono and heptahydrated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine have been studied using the density functional theory (DFT) and Møller Plesset perturbation theory (MP2) implementing the 6-311++G(d,p) basis set. The formation of strong N-H...O bond has resulted in the highest interaction energy among the monohydrates. Hydration does not show any significant impact on the stability of heptahydrated complexes. The atoms in molecule (AIM) and natural bonding orbital (NBO) analyses have been performed to elucidate the nature of the hydrogen bond interactions in these complexes. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this work, the time-dependent density functional theory (TD-DFT) method was used to study the electronic excited-state dynamics of the hydrogen-bonded p-Cresol-NH-HO complex. The intermolecular hydrogen bonds O-H···N and C-O···H were demonstrated by the optimized geometric structure of the hydrogen-bonded p-Cresol-NH-HO complex. The infrared spectra (IR spectra) of the hydrogen-bonded p-Cresol-NH-HO complex in the ground and excited states were also calculated by using the density functional theory (DFT) and TD-DFT methods. It is demonstrated that hydrogen bond O-H···N can be strengthened while hydrogen bond C-O···H is weakened upon photoexcitation to the S state. The significant changes of the hydrogen bond from the calculated bond lengths in different electronic states can be observed. In addition, the spectral shifts of the stretching vibrational mode of the hydrogen-bonded O-H group in different electronic states are accounted for the hydrogen bond changes in the S state too. [ABSTRACT FROM AUTHOR]

Experimental absorption and emission spectra of benzoaza-18-crown-6-containing styryl dye and its complexes with Li, Na, and Ca are recorded. It is found that complexation causes large hypsochromic shifts of the long-wave absorption band of the dye. In addition, the spectra of Li and Na complexes exhibit an additional band or a shoulder with λ virtually coinciding with the absorption band of the free dye. Complexation also enhances the fluorescence of the dye. Simulating the structure and electronic spectra of the dye and its complexes with Li, Mg, Na, and Ca by DFT and TD DFT allowed us to explain these effects. It is found that cation coordination breaks the conjugation of the crown ether nitrogen with the chromophore, thus reducing the effective chromophore size, and the positive charge of the cation simultaneously decreases the donor nature of the amino group. This explains large hypsochromic shift of the long-wave absorption band. It is found that Li and Na complexes can form two types of conformers, with and without cation-nitrogen bond. The conformers with the cation-nitrogen bond exhibit a very strong blue shift of the absorption maximum, while the absorption spectra of the complexes without cation-nitrogen bond are almost unshifted relative to the spectra of the free dye. The ground-state recoordination of the cation in the macrocycle cavity involves the change between these two forms. Recoordination is promoted by the interaction of the cation with solvent molecules. This explains the presence of the additional long-wave band or shoulder in the spectra of the complexes. Cation-induced fluorescence enhancement is explained by the changes in the excited-state structure of the free dye and its complexes. The free dye changes its structure from the 'quinoid' form in the ground state to the 'benzenoid' form in the excited state, thus facilitating the rotation of the alkoxyaminophenyl group and causing near-degeneracy of the potential energy surfaces of the ground and excited states. This results in rapid nonradiative deactivation and fluorescence quenching. Complexation with cations reverses the dye structure to the 'benzenoid' form in the ground state and to the 'quinoid' form in the excited state thus preventing alkoxyaminophenyl group from rotation, which results in fluorescence enhancement. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (S0) states, the electronic structures of first singlet excited (S1) states are rather delocalized. The electron-donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S0 → S1 absorption energies and S1 → S0 emission energies of 2TV derivatives. The NO2- and NH2-substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro-substituted 2TV exhibit noticeable red shifts as the medium polarity increases. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Coumarins are well-known laser dyes in the blue-green region and studies on their electronic spectroscopy are important for understanding of their solvatochromic properties. A theoretical research of the various properties of the ground (S0) and first excited states (S1) of coumarin 6 in different solvents, including absorption and emission spectra, is presented here. Four isomers of coumarin 6 are investigated and compared. The excited-state geometries were optimized at the CIS level of theory whereas for the ground state, the HF and B3LYP levels of theory were applied. The geometric relaxation between the S0 and S1 states was examined and explained in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. The absorption and emission spectra in various solvents were calculated using the time-dependent density functional theory in combination with the polarized continuum model, and the results are in very good agreement with experimental measurements. [Copyright &y& Elsevier]

Abstract: The lower singlet excited states for 4′-N-dimethylamino-3-hydroxyflavone (DMA3HF) have been investigated. Theoretical calculations have been performed by using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with 6-31G(d,p) basis set have been used to compute transition energies. Ground-state geometries are optimized by using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d,p) basis set. The first excited state geometries are optimized by using configuration interaction all single-excitations methods with 6-31G(d,p). Vertical absorption energy and excited state electronic dipole moments calculations show that the singlet excited states S1 of the normal of DMA3HF has the character of a large charge separation and effective charge transfer. Calculated emission energies for both the normal and tautomer show a large Stokes shift between the absorption and fluorescence maxima. The present calculations suggest that DMA3HF appears dual fluorescence in gas phase. Our results obtained explain the strong ‘dual-fluorescence’ feature that involves the excited-state intramolecular proton transfer and charge transfer of DMA3HF. [Copyright &y& Elsevier]

Abstract: Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulphonate) (PSS) has been widely used in light-emitting devices as hole transport layer and in photovoltaic devices as hole-collecting layer. In the present study, various quantum chemical calculations were carried out for the investigation of low-lying excited states of ethylenedioxythiophene (EDOT), and styrenesulphonic acid. The lowest adiabatic transition energies were calculated using configuration interaction singles method. The time-dependent density functional theory was also applied for the calculation of the vertical excitation energies. Differential self-consistent-field-based density functional theory method is well known to show good performance for the geometry of excited state and hence it was also applied to study of the first singlet excited state. In addition to the calculation of the monomer, the electronic properties of PEDOT were calculated by periodic density functional theory method and the result is in good agreement with the experimental observation. [Copyright &y& Elsevier]

The geometrical optimization of Oxophosphorus triazatetrabenzcorrole (POTBC) has been studied at Density Functional Theory (DFT) level using various basis sets. The results at Hartree–Fock (HF) level were used for comparison. The results calculated at the HF and B3LYP levels are very different. The geometry at B3LYP level has Cs structure while at HF level it has no symmetry. The structure at the DFT level is reliable because DFT includes an electron correlation correction. The HOMO-1 of POTBC is separated from HOMO-2 by a large gap. As a result the excited states of POTBC can be interpreted by the Gouterman''s four-orbital model. It has been proved by TDDFT calculations of the excited states of POTBC. It can be concluded that the structure of POTBC is similar to that of phthalocyanine (Pc), while its orbital energies are similar to porphyrin''s [Copyright &y& Elsevier]

• Sensing mechanism of a fluorescent probe for thiols was theoretically confirmed. • Both S 0 and S 1 geometries are analyzed for the probe and its thiol complexes. • Calculated spectra are in good agreements with the reported reference. • Photoisomerization process could explain the weak fluorescence of the probe. The sensing mechanism of a reported fluorescence probe for cysteine, homocysteine and glutathione (Yin et al., 2018) has been investigated by time-dependent density functional theory. Experimental absorption and emission spectra of the probe before and after thiol addition were reproduced well by theoretical calculations, which validated the rationality of the method. Optimized geometries showed that the probe molecule had distinctly different geometries in its ground and excited states. It corresponded to the photoisomerization process and explained the weak fluorescence of the probe molecule. Moreover, by the potential energy curve scan, photoisomerization was further confirmed to be a spontaneous process with a barrier that barely existed. Frontier orbital analysis indicated that this photoinduced isomerization of the probe molecule derived from the antibonding character for lowest unoccupied molecular orbital at its C C double bond. In contrast, probe-thiol complexes exhibited similar geometries in their ground and excited states, which was responsible for the strong fluorescence of the probe with thiols. Due to distinct excited-processes, the probe can be used to sense thiols by monitoring the fluorescent change. [ABSTRACT FROM AUTHOR]

Y6 is a new type of non-fullerene acceptor, which has led to power conversion efficiencies of single-junction polymer solar cells over 17% when combined with a careful choice of polymeric donors. However, the excited state characteristics of Y6, which is closely correlated with its opto-electronic applications, are not clear yet. In this work, we studied the excited state properties of the Y6 solution and Y6 film, by using steady-state and time-resolved spectroscopies as well as time-dependent density functional theory (TD-DFT) calculations. UV-Vis absorption and fluorescence simulation, natural transition orbitals (NTOs) and hole-electron distribution analysis of Y6 solution were performed for understanding the excitation properties of Y6 by using TD-DFT calculations. The lifetimes of the lowest singlet excited state in Y6 solution and film were estimated to be 0.98 and 0.8 ns, respectively. Combining the exciton lifetime and photoluminescence (PL) quantum yield, the intrinsic radiative decay lifetimes of Y6 in the solution and film were estimated, which were 1.3 and 10.5 ns for the Y6 solution and film, respectively. Long exciton lifetime (~0.8 ns) and intrinsic radiative decay lifetime (~10.5 ns) of Y6 film enable Y6 to be a good acceptor material for the application of polymer solar cells. [ABSTRACT FROM AUTHOR]

Seventeen singlet excited states of ethylene have been calculated via time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the geometries of 11 excited states were optimized successfully. The local vibrational mode theory was employed to examine the intrinsic C=C/C–H bond strengths and their change upon excitation. The natural transition orbital (NTO) analysis was used to further analyze the C=C/C–H bond strength change in excited states versus the ground state. For the first time, three excited states including π y ′ → 3s, π y ′ → 3p y and π y ′ → 3p z were identified with stronger C=C ethylene double bonds than in the ground state. [ABSTRACT FROM AUTHOR]

The hydrogen bonding between ammonia (NH 3) and a two-dimensional material 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP)-4,4′-diphenyl-butadiynebis (boronic acid) (DPB) covalent organic framework (HHTP-DPB COF) in its electronically excited state was investigated using density functional theory and time-dependent density functional theory. The formation of the hydrogen bonding changed the luminescence mechanism of the material, which was confirmed by analysis of the frontier molecular orbitals and the corresponding electronic configurations. The comparison of the properties of hydrogen bonds in the ground state (S 0) and excited state (S 1) revealed that in the S 1 state the hydrogen bonds were strengthened, which was adverse to the radiation transition process, and resulting in the weakening of the fluorescence intensity. After the introduction of NH 3 , the fluorescence rate constant of the COF was decreased and the internal conversion rate constant was increased. Therefore, these findings indicated that HHTP-DPB COF has great application prospects for detecting the indoor air pollutant NH 3. [ABSTRACT FROM AUTHOR]

• Excited state chemistry of PRODAN derivative in methanol solvent was studied by TDDFT. • Intermolecular hydrogen bonds of PRODAN-3a-MeOH are enhanced in S 1 state. • For PRODAN-3a-MeOH, the S 1 state involves the intermolecular charge transfer. The role of intermolecular hydrogen bond of PRODAN derivative is investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT). Geometry analysis demonstrated that the intermolecular hydrogen bonds are enhanced in S 1 state. The red-shift phenomenon of fluorescence spectrum and IR spectrum as well as the energy of intermolecular hydrogen bond further confirm the intermolecular hydrogen bond strengthening in excited state. PRODAN-3a-MeOH has been electronically excited to S 1 which is a local excitation. The small change of electron density occurred the interaction region of intermolecular can directly influence the intermolecular hydrogen bonding in S 1 state. [ABSTRACT FROM AUTHOR]

• Novel tungsten-containing organometallic complexes are synthesized. • Dual fluorescence emissions are originated from LL and LMCT excited states. • Femtosecond transient absorption is used to explain charge transfer in organometallic complexes. In this work, we first designed and synthesized two tungsten-containing organometallic complexes MeNOON and MeNOOO with novel dual fluorescence emissions. Moreover, the combined femtosecond ultrafast spectroscopy and time-dependent density functional theory (TDDFT) method has been performed to investigate the excited-state dynamics of MeNOON and MeNOOO complexes. It is distinctly demonstrated that dual fluorescence emissions of tungsten-containing organometallic complexes are originated from the localized-on-ligand (LL) and ligand-to-metal charge transfer (LMCT) excited states, respectively. Furthermore, the ultrafast LMCT process has been measured by the femtosecond spectroscopy. [ABSTRACT FROM AUTHOR]

Boron subphthalocyanine chloride has been extensively studied by experimentalists and computational chemists due to its unique optical and electronic properties. It has been practical to modify the optical and physical properties of subphthalocyanine through axial, peripheral, and center substitutions or ring expansion. However, there have been few investigations on the substitution of central boron atom. In the present work, a new metal-substituted (center substitution of boron atom) series of boron subphthalocyanine chloride (metal = Fe, Co, Ni, Cu, and Zn) are theoretically designed utilizing modern density functional theory. The optimized results of this series in gas phase and with polarizable continuum model show that they may be chemically stable, and the predicted order of the stability of MSubPC is Fe>Cu>Ni>Co>Zn. Also, this new series of MSubPC molecules all becomes more non-planar and has much smaller dipole moments, which imply that they may be feasible for blend with organic acceptors. The HOMO-LUMO energy gaps of MSubPC (M=Co, Ni, Cu) are smaller than that of subPC. Furthermore, the wavelength of simulated absorption peaks of ZnSubPC and NiSubPC is red-shifted with respect to prototype subPC molecule in the visible region, and FeSubPC has noticeably stronger absorption strength than subPC because its excitation involves more orbital transitions and d electrons. The work here shows a new way to design photoelectric materials based on subphthalocyanine with center metal substitution. Unlabelled Image • MSubPC (M=Fe, Co, Ni, Cu, and Zn) may be chemically stable, and the predicted order of the stability of MSubPC is Fe>Cu>Ni>Co>Zn. • This new series of MSubPC molecules all becomes more non-planar and has much smaller dipole moments than subPC. • The HOMO-LUMO energy gaps of MSubPC (M=Co, Ni, Cu) are smaller than that of subPC. • FeSubPC has noticeably stronger absorption strength than subPC. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) and time-dependent density functional theory (TDDFT) were performed to investigate the ground state and excited state hydrogen-bonding dynamics of flavonoid in hydrogen donating aqueous solution. We demonstrated that the intermolecular hydrogen bond C=O•••H-O between flavonoid and water molecules is significantly strengthened in the electronically excited-state upon photoexcitation of the hydrogen-bonded complex. The radiationless deactivation via intramolecular proton transfer in excited state (ESIPT) can be facilitated by the hydrogen bond strengthening in the excited state. At the same time, quantum yields of the excited-state deactivation via fluorescence are correspondingly decreased. The total fluorescence of flavonoid in polar protic solvents can be drastically quenched by hydrogen bonding. As a consequence, we propose a fluorescence modulation mechanism by hydrogen bonding to explain fluorescence emissions of flavonoid in hydrogen- bonding solvents and no hydrogen-bonding solvents. Given that water molecules have anomalous properties that are different from other small organic molecules that form hydrogen bonds with flavonoids, this theoretical study has reference significance for the development of in vivo probes. Hopefully, the newly proposed mechanism can inspire experimentalists to develop and synthetic non-toxic high signal-to-noise ratios without the need to wash fluorescent probes for individual targets in vivo. Unlabelled Image • Hydrogen bond is strengthened from S0 to S1 in aqueous solution. • Strengthening hydrogen bond facilitate ESIPT. • A stronger hydrogen bond makes a lower electronic state energy level. • The enhancement of ESIPT promotes fluorescence quenching. [ABSTRACT FROM AUTHOR]