Electronic excitation transfer in clustered chromophore systems: Calculation of time-resolved observables for intercluster transfer (original) (raw)
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The Journal of Chemical Physics, 1994
Monte Carlo (MC) simulations and an analytical theory are presented to describe electronic excitation transport (EET) among static chromophores constrained to lie on the surfaces of spherical micelles. Both donor-trap (DT) and donor-donor (DD) EET are examined for two types of systems: probe molecules on the surfaces of isolated (low concentration) micelles, and probes on the surfaces of interacting (concentrated) micelles. The EET dynamics are described by the function, (G"(t)), the probability of finding the excitation on the originally excited chromophore. For the isolated micelle calculations, the excitation dynamics depend on the distribution of probes on a single hard sphere surface. For the interacting micelle calculations, the hard sphere structure is accounted for by using the radial pair distribution function, g(r). Both single micelle and many micelle DT calculations do not involve approximations. Consequently, the DT expressions agree exactly with the MC calculations. For the DD calculations, a first order cumulant approximation is used to obtain analytically tractable solutions to (GS(t)). Pade approximants of the cumulant solution, accurate over a broad range of chromophore number and Fiirster interaction strengths, are used to describe DD EET on isolated micelles. For DD EET in many micelle systems, the first order cumulant approach is shown to be a suitable method for intermicelle structural studies. Both the cumulant and MC calculations are simultaneously compared to time resolved flourescence depolarization measurements performed on octadecylrhodamine B(ODRB)/triton X-lOO/water systems made in previous investigations.
Electronic energy transfer in bichromophoric molecular clusters
Chemical Physics, 1993
Intramolecular electronic energy transfer (intra-EET) was investigated in supercooled isolated bichromophoric molecular clusters, under the conditions of supersonic beam expansion. Two types of clusters were studied, the first is the benzene-biacetyl complex. The second cluster was composed of naphthalene and anthracene for which previous work has shown that intra-EET at short range is the dominant decay channel. Investigation of the spectroscopic properties of these chromophores separately and loosely bound in a van der Waals complex helps to understand the influence of the initial vibronic level and of cluster's interchromophoric orientation on the EET rate. The fluorescence excitation spectrum of naphthalene in the presence of anthracene shows quenching, simultaneously with the appearance of new spectral features and emission characteristic to anthracene only, which are indicative of an intra-EET process. The quenching of different excitation levels in naphthalene follow a static Stem-Volmer-like kinetics, with the same quenching rate constant. This can be understood as occurring only because of cluster formation. The relative emission from excited levels of the donor (naphthalene) moiety of the bichromophoric complex was measured as function of the amount of added anthracene (acceptor moiety). The emission intensity shows a pressure. dependence which varies with the particular vibronic excitation of naphthalene, in agreement with the kinetic model. This is an evidence for the 1: 1 cluster composition and suggests that the intra-EET rate differs for different vibronic states of naphthalene. Similar results are obtained for the benzene-biacetyl system. Evidence is given for the formation of a bichromophoric molecular complex between benzene and biacetyl in the jet. Excitation of several vibronic levels of the benzene chromophore shows quenching of benzene emission with simultaneous appearance of biacetyl fluorescence emission. The quenching follows an apparent Stem-Volmer kinetics as a function of added acceptor pressure, indicative of EET in a binary benzene-biacetyl complex. The quenching efftciency depends on the particular vibronic excitation of the benzene moiety which is explained in terms of resonances in the spectral overlap between the two chromophores.
Physical Review E, 1994
An algorithm is developed in order to solve the stochastic Liouville equation describing energy transfer between a donor-donor pair of reorienting chromophores. The algorithm requires the fluctuating part of the Liouville equation in the form of trajectories. In this particular case the molecular reorientation of the chromophores was simulated by means of a Brownian dynamic simulation technique where each of the two molecules are allowed to undergo a restricted rotational diffusion in a cone potential. Numerical results are presented for the correlation function (y{t}y{0}), representing the probability that the initially excited donor sti11 is excited at a later time t. Results are given for the weak or Forster regime and for a simple case in the strong or slow motion regime. The time resolved fluorescence anisotropy r (t) is also calculated for different molecular reorientational rates and cone potentials.
Energy transfer efficiency in the chromophore network strongly coupled to a vibrational mode
Physical Review E, 2015
Using methods of condensed matter and statistical physics, we examine the transport of excitons through the Fenna-Matthews-Olson (FMO) complex from a receiving antenna to a reaction center. Writing the equations of motion for the exciton creation/annihilation operators, we are able to describe the exciton dynamics, even in the regime when the reorganization energy is of the order of the intra-system couplings. In particular, we obtain the well-known quantum oscillations of the site populations. We determine the exciton transfer efficiency in the presence of a quenching field and protein environment. While the majority of the protein vibronic modes are treated as a heat bath, we address the situation when specific modes are strongly coupled to excitons and examine the effects of these modes on the quantum oscillations and the energy transfer efficiency. We find that, for the vibronic frequencies below 16 meV, the exciton transfer is drastically suppressed. We attribute this effect to the formation of "polaronic states" where the exciton is transferred back and forth between the two pigments with the absorption/emission of the vibronic quanta, instead of proceeding to the reaction center. The same effect suppresses the quantum beating at the vibronic frequency of 25 meV. We also show that the efficiency of the energy transfer can be enhanced when the vibronic mode strongly couples to the third pigment only, instead of coupling to the entire system.
The mechanism of short-range intramolecular electronic energy transfer in bichromophoric molecules
The Journal of Physical Chemistry, 1984
A study of intramolecular energy transfer (intra-ET) in a series of bichromophoric molecules consisting of cyclic a-diketones incorporating an ortho-, meta-, or para-substituted benzene ring is reported. Most spectroscopic properties of these molecules are described by a superposition of those of their constituent chromophores. Unique for the bichromophore molecule is the fact that, depending on the molecular geometry, energy absorbed by the aromatic chromophore is transferred in part to the a-diketone and both chromophores emit their characteristic fluorescence spectra. An extensive study was made of the intramolecular electronic energy transfer process in solution as a function of temperature. The results indicate that the transfer efficiency is strongly structure dependent suggesting that a Dexter type exchange interaction is responsible for singlet-singlet intra-ET between close chromophores in a bichromophoric molecule. The thermal dependence observed in some cases is attributed to conformational factors. A general theoretical analysis of intra-ET in bichromophoric molecules provides expressions for donor fluorescence decay and for its fluorescence quantum yield in terms of the average distance between donor and acceptor moieties and the flexibility of the chains connecting donor and acceptor. Comparison with the present experimental data supports the predictions of this analysis. It is concluded that intra-ET in bichromophoric molecules is indeed governed by short-range exchange interactions.
Intermolecular Electronic Excitation Transfer in a Confined Space: A First-Principles Study
2005
The process of intermolecular electronic excitation transfer (EET) in a monodimensional supramolecular arrangement of molecules in confined space has been modelled and investigated by means of first-principles molecular dynamics simulations. The chosen model system consists of a wire of chlorine molecules hosted in the noncrossing channels of the zeolite bikitaite. The time evolution of the system in its first excited singlet state has been described by the restricted open shell Kohn–Sham formalism. Simulation results have highlighted that excitation, initially localized on a guest molecule, is transferred to an adjacent moiety in the molecular wire on the picosecond scale via a collision-induced Dexter-type short range EET. Analysis of the modifications of the electronic structure of the system brought about by EET has given insight into the microscopic details of the process.
Journal of Photochemistry and Photobiology A: Chemistry, 1996
Results are presented on the intramolecular electronic energy transfer (intra-EET) in bichromophoric molecules of the type benzene-adiketone, in which the interchromophore bridge contains methyl substituents/3 to the c~-dicarbonyl acceptor chromophore. These results show that singlet-singlet intra-EET is independent of substitution and can be explained by a model assuming Dexter-type short-range exchange interaction. For singlet-triplet and triplet-triplet transfer, there are indications that the phosphorescence yield of the acceptor is larger than that for non-substituted bichromophoric molecules. This can be explained by through-bond interaction promoting EET via a long-range superexchange mechanism, by variations in the non-radiative decay of the triplet state of the acceptor or by chemical reaction.
The Journal of Physical Chemistry A, 2001
An improved application is presented of the Monte Carlo method including simultaneous parameter fitting to analyze the experimental time-resolved fluorescence and fluorescence anisotropy decay of two organized molecular systems exhibiting a number of different, nonisotropic energy transfer processes. Using physical models and parameter fitting for these systems, the Monte Carlo simulations yield a final set of parameters, which characterize the energy transfer processes in the investigated systems. The advantages of such a simulation-based analysis for global parametric fitting are discussed. Using this approach energy transfer processes have been analyzed for two porphyrin model systems, i.e., spin-coated films of zinc tetra-(octylphenyl)-porphyrins (ZnTOPP) and the tetramer of zinc mono(4-pyridyl)triphenylporphyrin (ZnM(4-Py)TrPP). For the ZnTOPP film energy transfer rate constants of ∼1 × 10 12 s -1 and ∼80 × 10 9 s -1 have been found, and are assigned to intra-and interstack transfer, respectively. For the tetramers, the transfer rate constants of 38 × 10 9 and 5 × 10 9 s -1 correspond to energy transfer to nearest and next nearest neighbor molecules, respectively. The results are in agreement with a Förster type energy transfer mechanism. 9499 P I | ∼ 3/2 (1sin 2 R sin 2 φ) (cos φ cos R cos sin ηsin φ sin sin η + cos φ sin R cos η) 2 (11) P I ⊥ ∼ 3 / 2 (1sin 2 R sin 2 φ) (-sin R cos sin η + cos R cos η) 2 (12) Energy Transport in Organized Molecular Systems
Criteria for quantum coherent transfer of excitons between chromophores in a polar solvent
2004
We show that the quantum decoherence of Forster resonant energy transfer between two optically active molecules can be described by a spin-boson model. This allows us to give quantitative criteria, in terms of experimentally measurable system parameters, that are necessary for coherent Bloch oscillations of excitons between the chromophores. Experimental tests of our results should be possible with Flourescent Resonant Energy Transfer (FRET) spectroscopy. Although we focus on the case of protein-pigment complexes our results are also relevant to quantum dots and organic molecules in a dielectric medium.