화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.107, No.44, 9269-9283, 2003
Photoinduced multistep energy and electron transfer in an oligoaniline-oligo(p-phenylene vinylene)-fullerene triad
A donor-donor-acceptor triad, OAn-OPV-C-60, With a redox gradient has been synthesized by covalently linking an oligoaniline (OAn), an oligo(p-phenylene vinylene) (OPV), and a fullerene (C-60) in a nonconjugated linear array. Photoluminescence and femtosecond pump-probe spectroscopy studies reveal that photoexcitation of any of the three chromophores of this triad in a polar solvent results in formation of the OAn(-)OPV(+)-C-60(-) charge-separated state, after an efficient ultrafast (< 190 fs) singlet-energy transfer to the fullerene single-texcited state. The initial OAn-OPV+-C-60(-) state can rearrange to the low-energy OAnl-OPV-C-60(-) charge-separated state via an intramolecular redox reaction. Because the competing charge recombination of the OAn-OPV+-C60- state to the ground state is fast and increases with increasing polarity of the solvent, the quantum yield for this charge shift is the highest (similar to0.4) in weakly polar solvents such as chlorobenzene. Once formed, the OAn(+)-OPV-C-60(-) state has a long lifetime (> 1 ns) due to weak electronic coupling between the distant redox sites in the excited state. The stabilization gained is more than I order of magnitude in time. The experimental results are found to be in qualitative agreement with Marcus theory. In thin films, the OAn(+)-OPV-C-60(-) state is formed at a higher rate and in higher quantum yield than in solution.