Quantum-chemical techniques are applied to model the mechanisms of photoinduced charge transfer from aπ-electron donating group(2,3-dimethoxynaphthalene,D)to aπ-electron-acceptor moiety(2,3-dicyanonaphthalene,A)separated by a bridge of increasing size(n-norbornadiene,n=1~3,B).The main parameters controlling the transfer rate have been calculated: the internal and external reorganization energy terms,the electronic coupling between the initial and final states,and the variation of the Gibbs energy.The charge transfer is shown to proceed in these compounds through two competing mechanisms,super exchage versus bridge-mediated pathways.The excited states of a donor-bridge-acceptor(DBA)model system have been investigated using time-dependent density-functional theory(TD-DFT)in gas phase and in solution.The calculated results are consistent with the experimental observation[1,2].The spectroscopic properties of isolated donor,acceptor,and bridge and the bridge-donor compound have been investigated at the TD-B3LYP/6-31+G* level.The study showed that TD-DFT method gives a good description in the excited state energy calculation,and the calculated results are in acceptable agreement with experimental data[3].