Reversible thermal and photochemical switching of liquid crystalline phases and luminescence in diphenylbutadiene-based mesogenic dimers

The synthesis and study of the photo- and thermoresponsive behavior of a series of novel asymmetric mesogenic dimers, consisting of a cholesterol moiety linked to a diphenylbutadiene chromophore via flexible alkyl chains are reported. These mesogenic dimers possess the combined glass forming properties of the cholesterol moiety and the photochromic and luminescent properties of the butadiene moiety. Photoinduced cis/trans isomerization of the butadiene chromophore in these materials could be utilized to bring about an isothermal phase transition from the smectic to the cholesteric state. By photochemically controlling the cis/trans isomer ratio, the pitch of the cholesteric could be continuously varied making it possible to tune the color of the film over the entire visible region, and the color images thus generated could be stabilized by converting them to N* glasses. These materials were also polymorphic, exhibiting two crystalline forms possessing distinctly different fluorescence properties. The ability to thermally switch these materials from one crystalline form to the other in a reversible manner also makes them useful for recording fluorescent images.