Synthesis and Characterization of some Benzothiazole Based Conjugated Molecules in view of their Potential Optoelectronic Properties

Abstract

1t-Conjugated small molecules are emerging as significant components in the realm of organic semiconductors owing to their optoelectronic properties. A substantial surge in their incorporation in different electronic gadgets has been witnessed during the last two decades. Five such molecules were synthesized (BTP 1-5) that structurally incorporated benzothiazole and stilbene moieties. Benzothiazole substructure, being an excellent electron acceptor, actively participates in charge transfer processes which consequently makes it a good choice for such applications. The stilbene part also exhibits appreciable charge movement properties due to its extended conjugation. Schematically, the target compounds were synthesized by a series of reactions including cyclization reaction to synthesize benzothiazole ring containing substrate (32) that was followed by benzylic bromination to form bromide (33) and then Arbuzov reaction to acquire phosphonate ester (34), which was the precursor for Homer-Wadsworth-Emmons (HWE) reaction to synthesize the target alkenes (39, 40, 41, 42, 43). Different electron withdrawing groups were incorporated in the structure to analyze their impact. ATR-FTIR analysis advocated for the presence of functionalities present in the proposed structures. The photophysical studies revealed that these compounds absorb light in ultraviolet region (Am ax = 359-371 nm) due to 1t 1t* and in violet region (Amax = 378-392 nm) due to n-1t* transitions. Consequently, these compounds appeared yellow in colour, the colour complementary to violet. Photoluminescence studies showed the emissive properties of these compounds in violet-blue region (Aemi = 417-485 nm). In cyclic voltarnmetric analysis, the synthesized compounds showed low oxidation potential (Aonset = 0.87-0.99 V). Narrow HOMO-LUMO energy gap was observed for the synthesized compounds (Eg = 2.9- 3.1 eV). The photophysical and electrochemical analysis suggested the potential of these compounds to be employed in OLEDs, fluorescent sensors, photoswitches and other semiconducting materials.