On the role of intramolecular vibrational energy redistribution in infrared multiphoton excitation of polyatomic molecules

A model approach conceived to account for the processes of intramolecular vibrational energy redistribution (IVR) in the course of infrared multiphoton excitation (IRMPE) of polyatomic molecules is considered.     

Dynamical correlation between quantum entanglement and intramolecular energy in molecular vibrations:An algebraic approach

The dynamical correlation between quantum entanglement and intramolecular energy in realistic molecular vibrations is explored using the Lie algebraic approach. The explicit expression of entanglement measurement can be achieved using algebraic operations. The common and different characteristics of dynamical entanglement in different molecular vibrations are also provided. The dynamical study of quantum entanglement and intramolecular energy in small molecular vibrations can be helpful for controlling the entanglement and further understanding the intramolecular dynamics.     

Phonon-assisted excitation energy transfer in photosynthetic systems

The phonon-assisted process of energy transfer aiming at exploring the newly emerging frontier between biology and physics is an issue of central interest.This article shows the important role of the intramolecular vibrational modes for excitation energy transfer in the photosynthetic systems.Based on a dimer system consisting of a donor and an acceptor modeled by two two-level systems,in which one of them is coupled to a high-energy vibrational mode,we derive an effective Hamiltonian describing the vibration-assisted coherent energy transfer process in the polaron frame.The effective Hamiltonian reveals in the case that the vibrational mode dynamically matches the energy detuning between the donor and the acceptor,the original detuned energy transfer becomes resonant energy transfer.In addition,the population dynamics and coherence dynamics of the dimer system with and without vibration-assistance are investigated numerically.It is found that,the energy transfer efficiency and the transfer time depend heavily on the interaction strength of the donor and the high-energy vibrational mode,as well as the vibrational frequency.The numerical results also indicate that the initial state and dissipation rate of the vibrational mode have little influence on the dynamics of the dimer system.Results obtained in this article are not only helpful to understand the natural photosynthesis,but also offer an optimal design principle for artificial photosynthesis.     

Symmetry-adapted tensorial formalism to model rovibrational and rovibronic spectra of molecules pertaining to various point groups

We present a short review on the tensorial formalism developed by the Dijon group to solve molecular spectroscopy problems. This approach, originally devoted to the rovibrational spectroscopy of highly symmetrical species (spherical tops) has been recently extended in several directions: quasi-spherical tops, some symmetric and asymmetric tops, and rovibronic spectroscopy of spherical tops in a degenerate electronic state. Despite its apparent complexity (heavy notations, quite complex mathematical tools), these group theoretical tensorial methods have a great advantage of flexibility: a systematic expansion of effective terms for any rovibrational/rovibronic problem up to a given order is automatically generated. Inclusion of all possible interaction terms for any polyad scheme is therefore easy. This makes such an approach suitable for many types of molecular problems, not only the most symmetric ones.     

Theoretical investigation on the excited state intramolecular proton coupled charge transfer phenomenon for a novel fluorophore

We theoretically investigate the excited state behaviors of the novel fluorophore tetraphenylethene‐2‐(2′‐hydroxyphenyl)benzothiazole (TPE‐HBT), which was designed based on the intersection of TPE and HBT, using density functional theory and time‐dependent density functional theory methods. Compared with previous experimental results about fluorescence peaks, our calculated results are in good agreement with experimental data, which further confirms that the theoretical level we used is reasonable. Furthermore, our results confirm that the excited state intramolecular proton transfer (ESIPT) process happens upon photoexcitation, which is distinctly monitored by the infrared spectra and the potential energy curves. In addition, the calculation of highest occupied molecular orbital and lowest unoccupied molecular orbital reveals that the electron density change of proton acceptor because of the intramolecular charge transfer (ICT) process in the S₁ state induces the ESIPT. Moreover, the transition density matrix is worked out to facilitate deeper insight into the ESIPT coupled ICT process. It is hoped that the present work not only elaborates the ESIPT coupled ICT phenomenon and corresponding mechanisms for the TPE‐HBT but also may be helpful to design and develop new materials and applications involved in TPE‐HBT systems in future.     

Vibration-assisted coherent excitation energy transfer in a detuned dimer

The important role of high-energy intramolecular vibrational modes for excitation energy transfer in the detuned photosynthetic systems is studied. Based on a basic dimer model which consists of two two-level systems(pigments)coupled to high-energy vibrational modes, we find that the high-energy intramolecular vibrational modes can enhance the energy transfer with new coherent transfer channels being opened when the phonon energy matches the detuning between the two pigments. As a result, the energy can be effectively transferred into the acceptor. The effective Hamiltonian is obtained to reveal the strong coherent energy exchange among the donor, the acceptor, and the high-energy intramolecular.A semi-classical explanation of the phonon-assisted mechanism is also shown.     

Manifestation of intramolecular proton transfer in imidazole in the electronic-vibrational spectrum

Electronic-vibrational spectra of both imidazole (I) and the intermediate molecular structure (II) in the intramolecular proton transfer process N₁H(I) → N₃H(III) have been calculated and analyzed theoretically. The geometries of the molecular structures of I and II in the first ππ* excited state were determined using semi-empirical correlations and the method of hybridized atomic orbitals. The difference in their spectra indicates that the intramolecular proton-transfer mechanism with imidazole (I ↔ III) tautomeric conversion can be identified by electronic-vibrational spectroscopy. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 164–169, March–April, 2008.     

Breakdown of the reduction of the rovibrational Hamiltonian: The case of SO2F2

The ground state rotational spectrum of the near-spherical top molecule S¹⁸O₂F₂ (sulfuryl fluoride) has been measured from 50 to 700 GHz. As for the parent isotopologue, S¹⁶O₂F₂ [K. Sarka, J. Demaison, L. Margulès, I. Merke, N. Heineking, H. Bürger, H. Ruland, J. Mol. Spectrosc. 200 (2000) 55-64], it was necessary to use a non-reduced Hamiltonian in order to obtain a satisfactory fit. It was possible to determine six quartic centrifugal distortion constants (instead of five for a standard asymmetric top) and five sextic constants (one of them not existing in the reduced Hamiltonian) could also be determined. This ground state level has also been analysed thanks to a tensorial formalism developed in Dijon. Only two tensorial sextic constants are fixed to zero, all others have been adjusted. Although S¹⁸O₂F₂ is less spherical than S¹⁶O₂F₂, the analysis was more difficult. It is partly due to the fact that S¹⁸O₂F₂ is oblate whereas S¹⁶O₂F₂ is prolate. The experimental quartic centrifugal distortion constants were found in good agreement with those calculated from the force field, confirming the correctness of the analysis.     

Photo-induced intramolecular electron transfer and intramolecular vibrational relaxation of rhodamine 6G in DMSO revealed by multiplex transient grating spectroscopy

Photo-induced intramolecular electron transfer （PIET） and intramolecular vibrational relaxation （IVR） dynamics of the excited state of rhodamine 6G （Rh6G＋） in DMSO are investigated by multiplex transient grating. Two major compo- nents are resolved in the dynamics of Rh6G＋. The first component, with a lifetime τTPIET = 140 fs-260 fs, is attributed to PIET from the phenyl ring to the xanthene plane. The IVR process occurring in the range ZIVR = 3.3 ps-5.2 ps is much slower than the first component. The PIET and IVR processes occurring in the excited state of Rh6G＋ are quantitatively determined, and a better understanding of the relationship between these processes is obtained.     

氢分子振动态与铯分子基态碰撞中转动-振动能量转移

利用受激拉曼泵浦将H2激发到v=1,J=3态,研究了H2(1, 3)态与Cs2分子碰撞(1, 3)态的弛豫及Cs2(X1+g)振动态的激发过程。利用相干反斯托克斯拉曼散射(CARS)检测H2的振转态分布,由CARS峰值得到密度比[H2(1, 3)]/[H2(0, 3)]和[H2(1, 1)]/[H2(1, 3)],由H2(v=0)振转态的Boltzmann分布确定H2(0, 3)的密度,由此得到[H2(1, 3)]和[H2(1, 1)]态的密度。激光诱导荧光光谱(LIF)确定被碰撞激发的Cs2(X1+g, v=11-15)各态。利用单模半导体激光作瞬时光吸收,对于v= 11, 12, 13, 14和15,积分吸收系数(单位：106cm-1s-1)分别是6.5,7.9,7.0,6.1和4.7,结合H2(1, 3)的密度,得到H2(1, 3)Cs2(X1+g, v)的转移速率系数,对于v=11-15,分别是(单位：10-13cm-1s-1)1. 40. 6,1.70. 7,1.50. 6,1.30.5和1.00. 4。利用吸收线Doppler增宽测量分别得到了Cs2(X1+g, v=11-15)的平动能。     

氢分子振动态与铯分子基态碰撞中转动-振动能量转移

利用受激拉曼泵浦将H2激发到v=1,J=3态,研究了H2(1, 3)态与Cs2分子碰撞(1, 3)态的弛豫及Cs2(X1+g)振动态的激发过程。利用相干反斯托克斯拉曼散射(CARS)检测H2的振转态分布,由CARS峰值得到密度比[H2(1, 3)]/[H2(0, 3)]和[H2(1, 1)]/[H2(1, 3)],由H2(v=0)振转态的Boltzmann分布确定H2(0, 3)的密度,由此得到[H2(1, 3)]和[H2(1, 1)]态的密度。激光诱导荧光光谱(LIF)确定被碰撞激发的Cs2(X1+g, v=11-15)各态。利用单模半导体激光作瞬时光吸收,对于v= 11, 12, 13, 14和15,积分吸收系数(单位：106cm-1s-1)分别是6.5,7.9,7.0,6.1和4.7,结合H2(1, 3)的密度,得到H2(1, 3)Cs2(X1+g, v)的转移速率系数,对于v=11-15,分别是(单位：10-13cm-1s-1)1. 40. 6,1.70. 7,1.50. 6,1.30.5和1.00. 4。利用吸收线Doppler增宽测量分别得到了Cs2(X1+g, v=11-15)的平动能。     

Quenching of the fluorescence of solutions of complex molecules by nonradiative transfer of electronic-excitation energy to a saturable acceptor

The study puts toward a theoretical model describing the fluorescence parameters for concentrated solid solutions consisting of complex molecules of two types (donor-acceptor) with nonradiative transfer of electronic-excitation energy with intense pulse excitation. Consideration is given to the dynamics of quenching of the luminescence of the donor molecules due to transfer of electronic-excitation energy to the acceptor molecules. Numerical results are presented in the form of approximation formulas. To whom correspondence should be addressed. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 652–656, September–October, 1999.     

Efficiency of intramolecular electronic energy transfer in coumarin bichromophoric molecules

Intramolecular energy transfer in bichromorhoric molecules consisting of two coumarins linked by a variable number of methylene groups (n = 3, 4, 8, 12), was studied with special attention to the effects of n, temperature, viscosity and solvent nature on the efficiency of transfer. The validity of model compounds for the donor and acceptor moieties was carefully examined. Fluorescence polarization experiments revealed that a non-randomicity of mutual orientation of donor and acceptor can only be small, if any. Dual fluorescence from donor and acceptor was observed in propylene glycol whatever the value of n and at any temperature ranging from -60 to 60°C. Fluorescence from the donor was not detectable in dimethylformamide owing to the very low quantum yield of the donor in this solvent. Transfer efficiencies were determined by three steady-state methods and were found to be more dependent on n in dimethylformamide than in propylene glycol. Incomplete energy transfer is clearly shown in the case of dimethylformamide as a solvent. The effects of temperature are weak in the -60, + 60°C range. The results are discussed in light of theories of energy transfer.     

Synthesis of sterically hindered antipyrines for intramolecular charge transfer facilitated sensing

A new series of sterically hindered antipyrine derivatives have been synthesized by Schiff base condensation for potential fluorescence sensing applications. Their optical, thermal, and electrochemical properties were fully characterized. Broad absorption spectra were observed as a result of the strong intramolecular charge transfer between antipyrine and sterically hindered conjugated moiety. Reversible one electron oxidation couple was observed for most compounds, with carbazole, phenothiazine, and bithiophene functionalized derivatives exhibiting extra reversible one one‐electron oxidation process at higher positive potentials. Cabazole functionalized antipyrine derivative APCZ presents good fluorescence sensing for Co²⁺ and Cu²⁺, with 3.41‐fold enhancement in fluorescence intensity and 2‐fold enhancement in fluorescence quantum yield observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Intramolecular energy transfer in naphthalene-containing polyesters: Experiment and simulation for model compounds derived from five aliphatic dicarboxylic acids and 2-hydroxynaphthalene

Steady-state fluorescence depolarization measurements and molecular dynamics simulations have been used to study the efficiency of nonradiative intramolecular singlet energy transfer between 2-naphthoxy groups, denoted N, in model compounds for polyesters derived from 2,6-dihydroxy-naphthalene and aliphatic dicarboxylic acids. The five bichromophoric compounds studied are the diesters abbreviated as N-OOC-(CH₂)_n-COO-N;n = 2–6, which are condensation products obtained from 2-naphthol and aliphatic dicarboxylic acids. The anisotropy of the fluorescence of these compounds dispersed in a solid matrix of glassy poly(methyl methacrylate) indicates that there is nonradiative singlet energy transfer between naphthoxy groups. The efficiency of this transfer depends onn. A theoretical treatment using molecular dynamics simulations for the conformations of the five model compounds has been performed in order to evaluate the parameters related to the efficiency of the transfer. The experimental and theoretical variation of such parameters withn is consistent with the estimated Förster radius of 9–10 Å for this system.     

光合作用原初过程能量和电荷超快传递过程原理浅析

文章侧重于从物理的角度,介绍光合作用原初过程中能量和电荷超快传递过程的相关物理化学原理,如费米黄金规则,Frster及Dexter传能机制,Marcus电荷转移理论及激子理论.辨析相关原理的适用范围、共性及差异,并力图在上述相关原理的基础上阐述光合膜蛋结构与功能的关系,勾画出该研究方向的基本脉络.     

On the determination of the intramolecular potential energy surface of polyatomic molecules: Hydrogen sulfide and formaldehyde as an illustration

We present here an approach for determining the Hamiltonian of polyatomic molecules that allows one to successfully solve the problem of potential energy surface (PES) determination via construction and diagonalization of a Hamiltonian matrix of large dimension. In the suggested approach, the Hamiltonian is very simple and can be used both for any “normal” polyatomic molecule and for any isotopic species of a molecule. Molecules with two to four equivalent X-Y bonds are considered, and for illustration of the efficiency of the suggested approach, numerical calculations are made for the three-atomic (hydrogen sulfide) and four-atomic (formaldehyde) molecules.     

Fluorescence resonance energy transfer: FRET studies of ligand binding to cell surface receptors

We describe a simple optical system employing fluorescence resonance energy transfer (FRET) to identify potential binding domains on the macrophage scavenger receptor for the ligand maleylated bovine serum albumin (mal-BSA). Using a plasma membrane vesicle system, we placed donor probes on the ligand and acceptor probes in the membrane to determine the distance of bound ligand from the cell surface. Two donors and three acceptors were employed. Transfer between ligand covalently modified with multiple dansyl molecules and hexadecanoylaminoeosin in the membrane yielded a distance of 46.5 ± 7.5 å; transfer from the same type of donors to octadecylrhodamine B in the membrane gave a distance of 58.5 ± 3.0 å. No transfer was observed between ligand mono-labeled with fluorescein and l,l′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanineperchlorate in the membrane. This suggests that the orientation of mal-BSA bound to the receptor places the fluorescein probe too far from the lipid surface to experience energy transfer. The distance information identifies a potential location for the binding site, which can be compared to structural information about the receptor and used to extract a binding sequence.