Mechanistic Study on Photooxidation of Triarylphosphines by Time-Resolved Infrared Spectroscopy

Abstract

Upon laser flash photolysis on a solution of triarylphosphine Ar₃P in acetonitrile or dichloromethane using a YAG laser at 266 nm, transient absorption was observed by time-resolved infrared spectroscopy. Rate constants were determined for the formation step of the absorption. Dependency of the rate on [Ar₃P] and atmosphere, along with independent observation in laser flash photolysis/UV-Vis spectroscopy of the Ar₃P solutions, suggests that electron transfer occurs from Ar₃P to the singlet photoexcited state of Ar₃P, generating triarylphosphine radical cation Ar₃P^·+, which reacts with a trace amount of H₂O in the solvent to give the final product Ar₃P˭O, which has been observed in steady-state photolysis.

Keywords:

• Laser flash photolysis
• radical cation
• time-resolved infrared spectroscopy
• triarylphosphine

Acknowledgments

One of the authors (S.Y.) greatly appreciates financial support by Tezukayama research grant 2009.