Structure and Properties of the Triplet State of StyreneDerivatives Studied by Laser‐Flash‐Photolysis

The triplet state of a series of compounds, each containing the styrene moiety, has been studied by nanosecond laser flash photolysis. The lifetimes, the TT absorption spectra and the rate constants for deactivation by several quenchers have been determined. It is shown from these results that, in the triplet state of styrene derivatives in their lowest energy conformation, the double bond is twisted by 90° for flexible molecules (perpendicular triplet) or by an angle as large as allowed by the molecular framework of rigid molecules (twisted triplet). There is no equilibrium between planar and perpendicular (or twisted) triplets, in contrast with the case of stilbene. The influence of substituants on the lifetime of the perpendicular triplet and the mechanism of quenching of this species by oxygen have been investigated.