Interaction of ground and excited (S1) states of C60 and C70 with aromatic amines:: Exciplex and charge-transfer emissions

Emissions from both exciplexes and excited charge-transfer (CT) complexes have been observed for the fullerene-aromatic amine systems in nonaromatic solvents and solvent mixtures using steady-state fluorescence measurements. Support for the exciplex and CT emissions has also been obtained from the time-resolved fluorescence measurements. Both emissions are very sensitive to the polarity of the solvents. From the solvatochromic shifts of the emission maxima, dipole moments (mu) of the exciplexes and the excited CT complexes have been estimated. For C-60-N,N-dimethylaniline (DMAN) and C-60-N,N-diethylaniline (DEAN) systems, the mu values for the exciplexes and the excited CT complexes are in the ranges 10-12 and 25-27 D, respectively. Both species are thus very polar in nature. In aromatic solvents the fullerene-aromatic amine systems behave differently, without forming any exciplexes, though the fullerene emissions are quenched by the amines with almost diffusion-controlled rates. CT emissions are also not observed in the aromatic solvents. The pi-electrons of the solvent molecules are supposed to be responsible for the unusual behavior of these solvents on the present systems.