Femtosecond Photodissociation Dynamics of Bis(julolidine) Disulfide in Polar and Apolar Solvents

Abstract

Following femtosecond photodissociation of bis(julolidine) disulfide, the nascent geminate julolidylthiyl radicals are observed with pump/supercontinuum probe spectroscopy. The radicals are formed in a direct process within 130 fs and in a slower process over 1 ps. Two forms of the radical are distinguished by the appearance kinetics and by their spectra in polar solvents. Semiempirical calculations predict a radical doublet state D1, optically dark and with a dipole moment of 2.3 D, close to the bright and more polar ground state D0. The slower dissociation channel is taken to include internal conversion and relaxation within a reactive manifold of excited parent states and possibly between the accessible radical states. Subpicosecond geminate recombination is observed in viscous solvents. A dimer of the radicals is formed on longer time scales; it reacts with free radicals in a second-order reaction.