[60]Fullerene-based molecular triads with expanded absorptions in the visible region: Synthesis and photovoltaic properties

Photoactive fulleropyrrolidine-perylenetetracarboxylic diimide-porphyrin triad (FPP) and its zinc analogue (ZnFPP) with expanded absorptions in the visible spectral region were synthesized. Steady absorption spectra and cyclic voltammetry (CV) measurement showed rather weak electronic interactions among the component chromophores in the ground state within the triads. Preliminary fluorescence measurements indicated the occurrence of a photoinduced electron-transfer process within the triads. These processes can be elicited either in the excited state of the perylenetetracarboxylic diimide chromophore or in the excited state of the porphyrin chromophore. The existence of photoinduced charge-separated states within triads in solution was confirmed by steady-state photolysis in the presence of methyl viologen (MV2+) as a sacrificed electron acceptor and 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificed electron donor. The photovoltaic devices have been fabricated on the basis of the triads and have shown clear photovoltaic behavior under illumination of white light. Though the power conversion efficiencies under simulated solar illumination of 68 mW(.)cm(-2) were found to be moderate (0.028% for FPP and 0.035% for ZnFPP), it is an encouraging result for application of such molecular donor-acceptor ensembles to photovoltaics.