The role of internal twisting in the photophysics of stilbazolium dyes

Abstract

The synthesis of selectively bridged stilbazolium dyes related to DASPMI is described. The comparison of steady-state and time-resolved fluorescence studies as a function of temperature allows one to develop a kinetic model on the basis of which the high photostability and absence of photoisomerization for these dyes can be understood. There are two possible photochemical deactivation channels: non-radiative decay through single-bond twisting which does not lead to a distinguishable photoisomer and through double bond twisting leading to trans–cis photoisomerization. The latter process is more than one order of magnitude slower than single-bond twisting for these compounds and is only observed in the compound where both single bonds are bridged. Lifetime maxima observed at low temperature indicate a further early structural relaxation not connected with bond twisting but with bond length changes.