Comprehensive investigation on the reactivity of triarylphosphine radical cations by laser flash photolysis time-resolved UV-Vis spectroscopy

Laser flash photolysis at 266nm was carried out on the acetonitrile solution of triarylphosphines, Ar3P, using a Nd YAG laser under oxygen, air, and argon atmospheres by varying the Ar3P concentration. The spectral change was monitored by time-resolved UV-Vis spectroscopy. A transient absorption that appeared on the TRUV spectrum within 100ns after the laser flash was judged to result from the triarylphosphine radical cation, Ar3P center dot+, based on a comparison with previously reported spectra. The absorption decayed on a time scale of microseconds according to the first-order kinetics, in which the first-order rate constant, k(obs), is expressed by k(obs)=k(O2)[O-2]+k(Ar)[Ar3P]+k(s). The first term in this expression represents the radical coupling of Ar3P center dot+ with O-2, whereas the second term likely results from an ionic reaction of Ar3P center dot+ with the parent phosphine. This finding suggests that Ar3P center dot+ undergoes either a radical coupling with oxygen or an ionic reaction with Ar3P to decay. Copyright (c) 2016 John Wiley & Sons, Ltd.