Reversible trans–cis photoisomerization of new pyrrolidene heterocyclic imines

A series of novel pyrrolidene imines bearing functionalized aryl or naphthyl moieties was synthesized and their photochromic properties studied by UV spectroscopy. UV irradiation of these heterocyclic Schiff bases at room temperature promotes the trans–cis photoisomerization of the CN double bond with formation of a variable amount of the cis-isomer that, in the absence of light, returns thermally to the original form in few seconds. The thermal cis–trans re-isomerization of these molecular switches is much more slower than for the common benzylidene aniline-type imines, allowing the observation of the photochromic phenomena at room temperature. Strong electron-donor substituents in the para-position of the aniline part of the molecule decreases even more the kinetics of the thermal cis–trans re-isomerization leading to a manifest change in the UV spectrum.