Donor-sensitizer-acceptor triad system for photoenergy migration, photoenergy transfer, and electron transfer in a bilayer membrane

A novel photoinduced electron-transfer system was constructed by using a photoenergy-harvesting bilayer membrane composed of two amphiphiles: one having an antenna group tan N-ethylcarbazolyl (ECz) group) and the other having a photoenergy-accepting group (anthryl group) and an electron-accepting group (viologen group). Photoenergy migration among ECz groups occurs in the membrane, and the photoenergy is transferred efficiently to the anthryl group. The excited ECz group reduces the viologen group through the excitation of the anthryl group with a quantum yield of 0.67 in the presence of 3 mol LTC acceptor. The photoinduced electron-transfer process was simulated successfully to determine the number of the excitation migration steps between ECz groups and the electron-transfer rate from the excited ECz group to the viologen group. Interestingly, the transient absorption spectroscopy revealed that the photooxidized chromophore decays faster than the reduced viologen, which has a lifetime longer than a millisecond, suggesting the electron donation to the oxidized chromophore by amide groups in the amphiphile molecules. This membrane is regarded as a donor-sensitizer-acceptor triad system, in which the sensitizer is coupled with two-dimensional array of photoharvesting chromophores, resulted in a more efficient electron transport system than a donor-acceptor diad system.