Synthesis and photoinduced electron transfer in platinum(ii) bis(N-(4-ethynylphenyl)carbazole)bipyridine fullerene complexes

Abstract

Platinum(II) bis(N-(4-ethynylphenyl)carbazole)bipyridine fullerene complexes, (Cbz)₂–Pt(bpy)–C₆₀ and (^tBuCbz)₂–Pt(bpy)–C₆₀, were synthesized. Their photophysical properties were studied by electronic absorption and emission spectroscopy and the origin of the transitions was supported by computational studies. The electrochemical properties were also studied and the free energies for charge-separation and charge-recombination processes were evaluated. The photoinduced electron transfer reactions in the triads were investigated by femtosecond and nanosecond transient absorption spectroscopy. In dichloromethane, both triads undergo ultrafast charge separation from the ³MLCT/LLCT excited state within 300 fs to yield their respective triplet charge-separated (CS) states, namely (Cbz)₂˙⁺–Pt(bpy)–C₆₀˙⁻ and (^tBuCbz)₂˙⁺–Pt(bpy)–C₆₀˙⁻, and the CS states would undergo charge recombination to give the ³C₆₀* state, which subsequently decays to the ground state in 22–28 μs.