Solvation of photolytically generated p-aminophenylthiyl radicals studied by sub-picosecond transient absorption.

By pump-and-probe spectroscopy, the photolysis of bis-(p-aminophenyl) disulfide in diethyl ether has been followed with sub-picosecond time resolution. The visible absorption band of generated p-aminophenylthiyl radicals rises in two stages: an unresolved fast initial rise is followed by a second, exponential rise with a time constant of 5.9 ps. During the second process, the peak absorption of the band shifts from its initial position at 557.9 to 572.0 nm. A rate-equation model quantitatively accounts for the observations. The first stage is assigned to the formation of the radical pair in a common solvent cage, and the second stage to the separation and solvation of the radicals