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

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Abstract

Fast moving: A new pentad (see figure) composed of silicon phthalocyanine (SiPc), as electron donor, that is connected with two units of naphthalenediimide (NDI) and fullerene C60, as electron acceptors, undergoes fast and efficient charge-separation processes via the NDI and SiPc singlet excited states.

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Photoinduced intramolecular processes of a newly synthesized pentad composed of silicon phthalocyanine (SiPc) that is connected with two units of naphthalenediimide (NDI) and fullerene C60 to form SiPc-(NDI)2-(C60)2 have been studied and the results are compared with the reference compounds, namely, the SiPc-(NDI)2 triad and NDI-C60 dyad. Upon photoexcitation, the main quenching pathway in polar solvents involved electron transfer via the singlet excited states of SiPc-(NDI)2-(C60)2 and SiPc-(NDI)2, but not NDI-C60 for which the energy transfer is dominant. The occurrence of electron-transfer processes of SiPc-(NDI)2-(C60)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 B3 LYP/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 C60 and SiPc triplet states. The lifetimes of charge-separated states were estimated as 1000 and 250 ps for SiPc-(NDI)2-(C60)2 and SiPc-(NDI)2, respectively.

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