Picosecond kinetics of p-dimethylaminobenzonitrile

The nanosecond and picosecond resolved dual fluorescences of p-dimethylaminobenzonitrile (DAB), in various solvents and glasses excited by 266 nm 20 ps FWHM laser pulses, have been investigated. Pulse-limited rise times are exhibited by the b*-state emission whose decay in turn feeds directly the risetime of a*-state emission at 440-600 nm in most solvents studied. The a*-state emission was monitored at 520-600 nm in order to eliminate contribution from the b*-state. Within the experimental resolution, the b*-state fluorescence decay times vary approximately linearly with solvent viscosity. The a*-state fluorescence decay times vary with both solvent and temperature, and may reflect either thermally assisted intersystem crossing from the solvated singlet a*-state (presumably of twisted internal charge transfer character) to a corresponding solvated triplet of slightly higher energy, or a thermally activated internal conversion of the ¹TICT to the ground state.