The triplet state of styrenes

Abstract

The energy levels of the S₁,S₂ and T₁ states of a range of cyclic and acyclic phenylalkenes have been determined and the structure–excited state energy level relationship examined. The S₂(Franck–Condon maximum)–T₁(absorption onset) energy gap is a constant for all the systems studied (189.5 ± 4 kJ mol^–1). except the severely twisted cis-t-butylstyrene, and thus allows the determination of the triplet energy of simple phenylalkenes merely by obtaining the S₀–S_n spectra. An extensive search for phosphorescence (on direct irradiation and triplet sensitisation) even at 10 K in a nitrogen matrix was unsuccessful and this may be interpreted in terms of a non-radiative relaxation requiring little molecular distortion.