Theoretical Investigation on Triplet Excitation Energy Transfer in Fluorene Dimer

Triplet-triplet energy transfer in fluorene dimer with electronic structure calculations. The two is investigated by combining rate theories key parameters for the control of energy transfer, electronic coupling and reorganization energy, are calculated based on the diabatic states constructed by the constrained density functional theory. The fluctuation of the electronic coupling is further revealed by molecular dynamics simulation. Succeedingly, the diagonal and off-diagonal fluctuations of the Hamiltonian are mapped from the correlation functions of those parameters, and the rate is then estimated both from the perturbation theory and wavepacket diffusion method. The results manifest that both the static and dynamic fluctuations enhance the rate significantly, but the rate from the dynamic fluctuation is smaller than that from the static fluctuation.

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.

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.

Environment-assisted excitation energy transfer in LH1-RC-type and LH2-type trimers

In this work,we study environment-assisted excitation energy transfer(EET) through calculating energy transfer efficiency(ETE) in LH1-RC-type and LH2-type trimers,which can be used to mimic energy transfer behaviors in the basic unit cells of LH1-RC and LH2 light-harvesting complexes.Quantum state evolution of the trimers is described by a non-Hermitian quantum master equation.ETE in these trimer systems is investigated by the use of numerical solutions at finite temperatures for the non-Hermitian master equation.We theoretically reveal the temperature-assisted ETE enhancement.It is found that highly efficient EET with nearly unit efficiency may occur in the nearby regime of the critical point of quantum phase transition.

Properties of Picosecond Fluorescence of Super High-Yield Hybrid Rice

Thylakoid membrane preparations of super high-yield hybrid rice (Oryza sativa L.), Liangyoupeijiu (P9) and Shanyou 63 (SH 63) were used for investigating its spectral and time properties by using picosecond time-resolved fluorescence spectrum measuring system. The thylakoid membrane preparations of P9 and SH 63 were excited by an Ar+ laser with a pulse width of 120 ps, repetition rate of 4 MHz and wavelength of 514 nm. The time constants of the excited energy transfer in these two varieties at flowering stage and grain filling stage were calculated from the experimental data. Based on the comparative studies of the time and spectral properties of the excited fluorescence in these ultrafast dynamic experiments the following was found: at both the flowering stage and grain filling stage, the speed of the excitation energy transfer, in photosystem was faster than that in photosystem II in P9 variety; and the speed of the excitation energy transfer at grain filling stage was faster than those at flowering stage for both rice varieties; the experiments also implied that the components and assembly of pigments in SH 63, but not in P9, changed during the process from flowering stage to grain filling stage for in these two rice varieties.

The Hierarchical Stochastic Schrodinger Equations: Theory and Applications

The hierarchical stochastic Schrodinger equations(HSSE)are a kind of numerically exact wavefunction-based approaches suitable for the quantum dynamics simulations in a relatively large system coupled to a bosonic bath.Starting from the influence-functional description of open quantum systems,this review outlines the general theoretical framework of HSSEs and their concrete forms in different situations.The applicability and efficiency of HSSEs are exemplified by the simulations of ultrafast excitation energy transfer processes in large-scale systems.

Ligand-dependent aggregation-enhanced photoacoustic of atomically precise metal nanocluster

Atomically precise metal nanoclusters(MNCs),as a potential type of photoacoustic(PA)contrast agent,are limited in application due to their low PA conversion efficiency(PACE).Here,with hydrophilic Au25SR18(SR=thiolate)as model NCs,we present a result that weakly polar solvent induces aggregation,which effectively enhances PA intensity and PACE.The PA intensity and PACE are highly dependent on the degree of aggregation,while the aggregation-enhanced PA intensity(AEPA)positively correlates to the protected ligands.Such an AEPA phenomenon indicates that aggregation actually accelerates the intramolecular motion of Au NCs,and enlarges the proportion of excited state energy dissipated through vibrational relaxation.This result conflicts with the restriction of intramolecular motion mechanism of aggregation-induced emission.Further experiments show that the increased energy of AEPA originates from the aggregation inhibiting the intermolecular energy transfer from excited Au NCs to their surrounding medium molecules,including solvent molecule and dissolved oxygen,rather than restricting radiative relaxations.This study develops a new strategy for enhancing the PA intensity of Au NCs,and contributes to a deeper understanding of the origin of the PA signal and the excited state energy dissipation processes for MNCs.

Dynamical and allosteric regulation of photoprotection in light harvesting complex Ⅱ

Major light-harvesting complex of photosystemⅡ(LHCⅡ)plays a dual role in light-harvesting and excited energy dissipation to protect photodamage from excess energy.The regulatory switch is induced by increased acidity,temperature or both.However,the molecular origin of the protein dynamics at the atomic level is still unknown.We carried out temperature-jump time-resolved infrared spectroscopy and molecular dynamics simulations to determine the energy quenching dynamics and conformational changes of LHCⅡtrimers.We found that the spontaneous formation of a pair of localα-helices from the 310-helix E/loop and the C-terminal coil of the neighboring monomer,in response to the increased environmental temperature and/or acidity,induces a scissoring motion of transmembrane helices A and B,shifting the conformational equilibrium to a more open state,with an increased angle between the associated carotenoids.The dynamical and allosteric conformation change leads to close contacts between carotenoid lutein 1 and chlorophyll pigment 612,facilitating the fluorescence quenching.Based on these results,we suggest a unified mechanism by which the LHCⅡtrimer controls the dissipation of excess excited energy in response to increased temperature and acidity,as an intrinsic result of intense sun light in plant photosynthesis.