Multichromophoric Perylenediimide–Silicon Phthalocyanine–C60 System as an Artificial Photosynthetic Analogue

Sequential photoinduced energy transfer followed by electron transfer and the formation of charge‐separated states, which are primary events of natural photosynthesis, have been demonstrated in a newly synthesized multichromophoric covalently linked triad, PDI‐SiPc‐C60. The triad comprises a perylenediimide (PDI), which primarily fulfils antenna and electron‐acceptor functionalities, silicon phthalocyanine (SiPc) as an electron donor, and fulleropyrrolidine (C60) as a second electron acceptor. The multi‐step convergent synthetic procedure developed here produced good yields of the triad and control dyads, PDI‐SiPc and SiPc‐C60. The structures and geometries of the newly synthesized donor–acceptor systems have been established from spectral, computational, and electrochemical studies with reference to appropriate control compounds. Ultrafast energy transfer from 1PDI* to SiPc in the case of PDI‐SiPc and PDI‐SiPc‐C60 was witnessed. An energy‐level diagram established from spectral and electrochemical data suggested the formation of two types of charge‐separated states, that is, PDI‐SiPc.+‐C60.− and PDI.−‐SiPc.+‐C60 from the 1SiPc* in the triad, with generation of the latter being energetically more favorable. However, photochemical studies involving femtosecond transient spectroscopy revealed the formation of PDI‐SiPc.+‐C60.− as a major charge‐separated product. This observation may be rationalized in terms of the closer spatial proximity to SiPc of C60 compared to PDI in the triad. The charge‐separated state persisted for a few nanoseconds prior to populating the 3SiPc* state during charge recombination. The persistence of charge separation? A silicon phthalocyanine has been asymmetrically appended with perylenediimide and fulleropyrrolidine moieties through different linking units (see figure). The optical, energy‐transfer (ET), and electron‐transfer (EnT) properties of the resulting triad have been investigated.