Observation of the two triplet state conformations of alkyl phenylglyoxylates

Abstract

Step-scan time-resolved FT-IR spectra of alkyl phenylglyoxylates in hexane with a 4 cm⁻¹ spectral resolution reveal splitting of the transient absorption signal near 1650 cm⁻¹ into two closely located peaks with different lifetimes on the nanosecond time scale. This signal had been previously assigned to the triplet state of the starting material that gives rise to the α-hydroxyphenylketene. In the current article, evidence is presented to assign these two peaks to different triplet state conformers only one of which undergoes fast Norrish Type II photoelimination. This assignment was made on the basis of chemical reactivity, steric effects, and kinetic data.