Determination of the triplet lifetimes of 1,3-cyclopentanediyl biradicals derived from the photodenitrogenation of azoalkanes with time-resolved photoacoustic calorimetry

Abstract

The triplet lifetime of the parent 1,3-cyclopentanediyl (2a) and the 4-methylene and the 1-phenyl derivatives 2b and 2c were determined by time-resolved photoacoustic calorimetry (PAC). For the biradical 2b, PAC was the only suitable method to date for determining its hitherto inaccessible triplet lifetime. A comparison with results for biradicals 2a,c obtained in earlier studies shows that PAC is a reliable method for measuring triplet lifetimes of biradicals. The effect on the triplet lifetimes of allyl and benzyl conjugation at one radical center in 2b,c proved to be insignificant