Photophysical properties of C₆₀(C₆H₅)₅Cl: a laser flash photolysis and pulse radiolysis study

Abstract

Photophysical and photochemical properties of the singlet and triplet excited states of monochloropentaphenylfullerene [C₆₀(C₆H₅)₅Cl, MCPPF] have been characterized in two different solvents, benzene and benzonitrile, using two complementary transient absorption techniques, namely picosecond laser flash photolysis and nanosecond electron pulse radiolysis. Singlet-singlet and triplet-triplet absorption spectra have been recorded. The quantum yield of triplet formation (φ _T = 0.45 ± 0.05) and the intrinsic lifetime of the triplet (τ = 100 ± 10 µ s) have been determined. Apart from the intrinsic decay of the triplet to the singlet ground state, another two processes, namely T-T annihilation and quenching by the ground state, make important contribution towards the overal triplet decay rate. Weak charge transfer (CT) complexes are formed between MCPPF and the electron-rich amines diphenylamine (DPA) and triphenylamine (TPA) in benzonitrile solution. On laser excitation, the CT complex undergoes charge separation, but the radical ions undergo very fast geminate recombination to form the triplet state of MCPPF.