Studies On Spectral Characteristics,Structural Features And Exciton Dynamics Of Some Pigment Aggregates

Based on the techniques of absorption,fluorescence and Raman spectroscopy,the structures and energy transfer of pigment aggregates in thylakoid and carotenoid aggregates in aqueous solution are studied.Combining the Frenkel exciton theory the absorption spectral characteristics and exciton evolution of pigment aggregate systems are analyzed.The internal and external factors influencing the energy absorption and transfer are discussed.The steady excitation and emission spectra of the ethanol solution containing Chl a and Chl b are detected before and after the addition of p-ionone.The coordination structures of Chl and β-ionone are optimized by Gauss 09 program.The calculated efficiency of energy transfer between Chl a and Chl b shows that the coordination of Chlorophyll to(3-ionone increases the π conjugation degree which leads to the redshift of the absorption spectra,enhancement of fluorescence intensity and improvement in energy transfer efficiency between Chl a and Chl b.The excitation spectra and polarization fluorescence spectra of spinach thylakoid at different temperature and magnetic field are investigated and the structural features of pigment aggregates in photosystem are obtained.The results show that the aggregate structures are changed by the acting on the hydrogen bonds under proper temperature and magnetic field which are associate to the efficient energy transfer.Then the structural features of the lutein and β-carotene aggregates in tyrosine solution with different concentrations are obtained by the analysis of absorption,emission and Raman spectra.It shows that the interaction between tyrosine and the ionone ring of carotene increases the conjugation length of the long chain of carotene which enhances the fluorescence intensity and energy transfer between molecules.The molecular structure and molecular mechanism of energy transfer function are studied by the absorption spectra of the carotene aggregates at different temperatures.It indicates that β-carotene forms H-aggregate at lower temperature(15℃)and with the increase of temperature it tends to form J-aggregate.Last using Frenkel exciton model three kinds of aggregates are studied.By the calculation of their absorption spectra and exciton dynamics,the evolution time of exciton in the aggregate with different environmental factors are obtained.The results show that the distance between adjacent pigments in aggregate plays an important role and the synergies of pigment aggregate is one of the important factor for efficient energy transfer in photosynthesis.Based the results the pigment aggregate model characterized with gradient site energy is proposed.The purpose of this paper is to make clear the process of absorption and transfer of light and to understand the long distance transmission of exciton in antenna system.It will provide a theoretical reference for the development of photoelectric conversion material with high efficiency.