Intramolecular photoinduced electron-transfer processes in buta-1,3-diynyl-benzene-linked porphyrin-fullerene dyad

Intramolecular electron-transfer process of porphyrin-fullerene dyad linked by phenyl buta-1,3-diynyl-phenyl unit (ZnP-sp-C₆₀) was studied by laser flash photolysis. Picosecond fluorescence lifetime and transient absorption measurements revealed that photoinduced charge-separation takes place via the excited singlet state (¹ZnP*) with the rate constant of (1-2) × 10¹⁰ s^-1. For the charge recombination, about a half of the radical-ion pair decayed quickly with 2.9 × 10 ⁹ s^-1 as evaluated from picosecond transient absorption measurements, whereas the remaining half was long-lived with slow decay (1.6 × 10⁶ s^-1) as estimated from nanosecond transient absorption measurements. The lifetime of the radical-ion pair of ZnP-sp-C ₆₀ was longer than those of directly connected dyads with a buta-1,3-diynyl bridge and buta-1,3-diynyl-phenyl bridge by the insertion of an extra phenyl group in addition to the pyrrodino ring.