Synthesis, Photophysical and Theoretical Studies of Molecular Architecture Based on Excited State Intramolecular Proton Transfer

Abstract

Over the past few years, excited state intramolecular proton transfer (ESIPT) has gained significant interest in the optoelectronics field due to its unique photophysical properties. These properties make ESIPT fluorophores potential candidates for various applications, including fluorescence probes, luminescent materials, molecular logic gates and OLEDs. The combination of ESIPT with intramolecuar charge transfer phenomenon offers advantages as they exhibit large Stokes shift which make them suitable for chemical and biological sensing, imaging and other applications. The research investigations presented in this thesis shed light on the impact of dual - ESIPT process on hydroxyl aryl benzimidazole and benzothiazole based Schiff bases. Also, effect of electron donating and conjugation on one of the ESIPT site was studied through experimental and theoretical methods. It was found that the presence of electron donating unit induce both excited state intramolecular charge transfer (ESICT) and proton transfer mechanism. In some cases, electron donating unit may even dominate over the ESIPT phenomenon. The torsional flexibility around C=N caused the aggregation induced emission in some of the probes. Hydroxyl aryl benzimidazole and benzothiazole Schiff bases exhibited ESIPT, ICT and AIE phenomenon while 8-hydroxyquinoline based Schiff bases demonstrated ICT phenomenon along with ESIPT. In conclusion, the synthesized probes showed interplay of different phenomenons ie. ESIPT, AIE, ESICT and have great potential in bio-imaging, sensing and in the development of optoelectronic devices.