Ionization and H abstraction in laser photolysis of TMPD. A time-resolved pulsed EPR study

Photoreactions of N,N,N',N'-tetramethyl-para-phenylenediam (TMPD) in alcohols were investigated. Radicals and radical ions created by the laser excitation at 308 nm were detected by means of time-resolved pulsed electron paramagnetic resonance (EPR). The results are consistent with the involvement of the excited triplet state which ionizes or abstracts H atom from the solvent. This short-lived state was identified through the sign of multiplet spin polarization in radical pairs. A triplet mechanism polarization in relatively polar alcohols (such as 2-propanol and cyclohexanol) was observed. In less polar alcohols (octanol, decanol) the H abstraction seems to be the major reaction route. Contrary to Mural et al. we did not find any evidence for singlet-correlated radical ion pairs with J > 0.