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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]

[Display omitted] • Excited-state level and nature can be readily tuned by the species and number of donor. • The mono-substituted donor slightly increases 1LE and significantly improves 3LE. • 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 (1LE) and local-excited triplet (3LE) 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]

Modulating charge transfer (CT) interactions between donor and acceptor molecules may give rise to unique dynamic changes in physicochemical properties, exhibiting great importance in supramolecular chemistry and materials science. In this work, we demonstrate the first instance of reversible photomodulation of donor-acceptor (D-A) CT interaction in the solid state.Pyridinium-based chromophore featuring π-conjugated D-A structures can not only function as a good electron acceptor to undergo photoinduced electron transfer (ET) or engage in intermolecular CT interaction, but also exhibit unique dual emission depending on the excitation wavelengths. The rotatable C-C single bonds within D-A pairs enhance the tunability of molecular structure. Through the synergy of a photoinduced ET and an excited-state conformational change, the intermolecular CT interaction can be switched on and off by alternate light irradiation to enables reversibly modulation of the affinity between donor and acceptor molecules, accompanied by visual color switching and fluorescence on-off as feedback signals., (© 2024 Wiley‐VCH GmbH.)

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.

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 BF2-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]

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]

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.

• 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]

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]

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

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]

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]

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]

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.

Highlights: [•] Ground-state projected bond orders. [•] Bond-covalency index in excited-states. [•] Criterion of maximum separation in density matrix spectrum. [ABSTRACT FROM AUTHOR]

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]

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]

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]