Picosecond kinetics of p-dimethylaminobenzonitrile

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Abstract
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 solventviscosity. 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.