Theoretical Investigation On Energy And Electron Transfer In Fullerenes,Benzenedicarboxylic Acid And Other Organic Aggregates

The researches of photophysical and photochemical processes in organic conjugated materials play an important role for improving the efficiency of organic photovoltaic and luminescent devices.On account of the complexity in organic molecular systems,theoretical description for these processes is still faced with many challenges,such as accurately calculating the electron-phonon coupling?transfer integral?driving force etc as well as combining with the rational quantum dynamics method.Based on the first principles calculations and the theory of electron transfer dynamics,we studied the energy and electron transfer processes in four organic systems,which provided some examples for exploring the photophysical processes in organic conjugated materials.The contents include:1.Theoretical simulations of intramolecular intersystem crossing rates for fullerenes.Among the numerous energy and electron transfer processes,the excited triplet states of organic molecules are paid a lot of attention because of their long lifetime and luminescent properties.Firstly,we studied the intersystem crossing and the relevant photophysical properties for 12 cage-type fullerenes(C60?C110).The existing experimental work explored the intersystem crossing properties of fullerenes merely referring to the energy gap between two excited states.However,the theoretical simulations could reveal the correlations between reorganization energies,driving forces,spin-orbit couplings and molecular structures.And the intersystem crossing rates of excited singlet states to excited triplet states could be obtained combining with the semiclassical Marcus formula.It turned out that excepting C60?C70 and C92 molecules,the rates of other systems were almost zero.This manifested that intersystem crossing property was irrelevant with the atomic number in fullerenes.2.The influence of organic molecular aggregated structures to phosphorescent efficiency.In the experimental report,aggregates of terephthalic acid and isophthalic acid induced the phosphorescence.However,the corresponding mechanism is not clear.From our theoretical investigations for the two molecules,it was found that the aggregation-induced phosphorescence phenomenon could not be explained clearly via the direct channel for excited singlet to triplet states.We thus proposed that the charge transfer state may bridge these two states.And this assumption was confirmed by the calculations for the energies and charge transfer couplings.On this basis,we also explained the mechanism of aggregation induced phosphorescence phenomenon for oxidized DPPY crystals.3.Photoinduced electron transfer in phenylene bridged Mo2 dimers.Experimentally,under light excitation,the system yielded two intramolecular charge transfer states:[Mo2]-ph-[Mo2]+ and[Mo2]-ph--[Mo2]+.And the charge recombination rate of former was larger than the one of latter.The charge recombination reaction lay in the Marcus inverted region,and the nuclear tunneling effect should be taken into consideration for the rate simulation.Hence,we employed Fermi's golden rule to calculate rates.The results manifested that the driving forces were the main influence factors for rates.The larger driving force of latter caused smaller rate and this result was consistent with the behavior of the reaction in Marcus inverted region.