The structural transformations and photo-induced processes in salicylidene alkylimines

The detailed comparative investigations of the mechanism of the fluorescent properties, formation and photochromic reaction in the salicylidene alkylimine (SALK) molecules with various N-Alk substituents and in corresponding more rigid model structures without C–Ph ring (A) twist have been carried out by the experimental and quantum-chemical methods.

The crucial role of the A ring twist and the importance of the N-Alk substituent structure in the light-induced processes including the ESIPT, TICT formation, fluorescence with anomalous Stokes shift (ASS) and the formation of the metastable coloured so-called “post-TICT” structures has been shown. The mechanism of these processes is similar to that of the salicylidene aniline (SA) molecule but there are some important distinctions caused mainly by the lack of the l_N–π_Ph electrons interactions and also by the steric ones. In general the decrease of the photochromic efficiency and the increase of the ASS in comparison to the SA molecule are provoked by the SALK structures’ peculiarities.