Photoswitch and nonlinear optical switch: Theoretical studies on 1,2-bis-(3-thienyl)-ethene derivatives

The 1,2-bis-(3-thienyl)-ethene derivatives are known to be good photoswitches. A large number of experiments have been carried out on different classes of these molecules to find out the most effective photoswitch. We have selected several highly efficient representative model photoswitch molecules of this class and studied their structures, photophysics, and different molecular properties at the ground and vertically excited states using density functional technique together with its time-dependent analog. These analyses are motivated toward the understanding of the effective molecular criteria, which are to be satisfied by a molecule in order to be good photoswitch. The theoretical investigations indicate that the capped ethene derivatives of this class of molecules are more effective photoswitches than the uncapped ones. Our contention has been verified by carrying out similar calculations on a well-known thermally irreversible photoswitch molecule of this class. Since the transition of the open to the closed form in photoswitching devices is the key factor for the molecules to exhibit such properties, and, moreover, since the molecules are thermally stable, they could be used for designing nonlinear optical (NLO) switches. One such possibility has been explored theoretically using a model molecular system.