Synthesis and Photoinduced Intramolecular Processes of Light-Harvesting Silicon Phthalocyanine-Naphthalenediimide-Fullerene Connected Systems

Photoinduced intramolecular processes of a newly synthesized pentad composed of silicon phthalocyanine (SiPc) that is connected with two units of naphthalenediimide (NDI) and fullerene C-60 to form SiPc-(NDI)(2)-(C-60)(2) have been studied and the results are compared with the reference compounds, namely, the SiPc-(NDI)(2) triad and NDI-C-60 dyad. Upon photoexcitation, the main quenching pathway in polar solvents involved electron transfer via the singlet excited states of SiPc-(NDI)(2)-(C-60)(2) and SiPc-(NDI)(2), but not NDI-C-60 for which the energy transfer is dominant. The occurrence of electron-transfer processes of SiPc-(NDI)(2)-(C-60)(2) and SiPc-(NDI)(2) were studied by time-resolved emission and transient absorption techniques and confirmed by redox measurements and molecular orbital calculations with ab initio B3LY/3-21G(*) methods. Fast and efficient charge-separation processes via the singlet excited states of NDI and SiPc were monitored, followed by charge recombination to populate the C-60 and We triplet states. The lifetimes of charge-separated states were estimated as 1000 and 250 ps for SiPc-(NDI)(2)-(C-60)(2) and SiPc-(NDI)(2), respectively.