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

Laser flash photolysis at 266 nm 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 100 ns after the laser flash was judged to result from the triarylphosphine radical cation, Ar3P•+, 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, kobs, is expressed by kobs = kO2[O2] + kAr[Ar3P] + ks. The first term in this expression represents the radical coupling of Ar3P•+ with O2, whereas the second term likely results from an ionic reaction of Ar3P•+ with the parent phosphine. This finding suggests that Ar3P•+ undergoes either a radical coupling with oxygen or an ionic reaction with Ar3P to decay. Copyright © 2016 John Wiley & Sons, Ltd.