Comparative study on photoinduced electron transfer from N,N-dimethylaniline (DMA) and 4,4′-methylenebis(N,N-dimethylaniline) (BDMA) to C₆₀ and C₇₀ in toluene

Photoinduced electron transfer reactions from aromatic amines to C₆₀ and C₇₀ were studied by steady-state fluorescence, picosecond time-resolved fluorescence, and picosecond transient absorption. The observed fluorescence quenching efficiency of amines and the change in fluorescence lifetime of fullerenes suggest the formation of a charge transfer complex between fullerenes and amines. The transient absorption spectra show that the fullerene anion and amine cation are immediately produced upon photoexcitation as an ion pair and undergo fast charge recombination to ground state. The time-resolved fluorescence spectra revealed that various amines typically show single-exponential fluorescence decay, but in the case of 4,4′-methylenebis(N,N-dimethylaniline) (BDMA) the decay was distinctly biexponential. This was interpreted as due to the bidentate complexation capability of the latter molecule, which leads to concentration-dependent mixture of monodentate and bidentate complexes, each with its own decay time.