Photoresponsive Materials

During the past few years we have been interested in studying the role of various non-covalent forces in the self-assembly of molecules and harnessing these forces for the design of novel functional materials such as liquid crystals, gels and luminescent solids. Our major interest has been in the design of materials, which can respond in various ways to light. In this context, we have designed some alkoxy-cyano-substituted diphenylbutadienes possessing liquid crystalline phases and investigated their photoinduced isothermal phase transitions. These materials could also be used as photoresponsive dopants for inducing pitch changes in glass forming chiral nematic liquid crystals (N*-glasses). We have also synthesized and studied the photo- and thermo-responsive behavior of some liquid crystalline molecules possessing cholesterol and diphenylbutadiene moieties. These hybrid systems possess the combined N*-glass forming properties of the cholesterol moiety and the photochromic properties of the butadiene chromophore. Photochemical control of the cis/trans isomer ratio in these materials could be used to tune the pitch of the cholesterics and hence the color of the film over the entire visible range, making them useful for developing full color imaging devices. We have also observed, that some amphiphilic butadienes undergo a hierarchical self-assembly starting from small sized vesicles, to larger vesicles which eventually merge together to form a unique type of photoresponsive gel consisting of globular aggregates with solvents entrapped within them. Another aspect of our work involves studying the correlation of molecular packing of materials in the solid state with their photophysical properties. Based on the understanding of these systems we could design diphenylbutadiene-based materials capable of exhibiting either monomer or J-aggregate fluorescence in the solid state. These materials could be used in fluorescence-based temperature sensors and light induced image recording devices.