Effects of substituents on the enrichment of the optical limiting action of novel imidazo[2,1-][1,3,4]thiadiazole fused thiophene-based small molecules

The imidazo[2,1- b ][1,3,4]thiadiazole (ITD) ring is a fused, planar aromatic heterocyclic system consisting of four heteroatoms with a bridgehead nitrogen atom. In this study, three new donor-acceptor-donor (D-A-D)-type organic molecules ( ThITD1-ThITD3 ) were designed and synthesized, wherein ITD was an electron acceptor unit and the thiophene/phenyl moieties were electron donor units that produced a D-A-D configuration. The thiophene-ITD core structure comprises three different groups viz. , thiophene-2-acetonitrile ( ThITD1 ), phenylacetonitrile ( ThITD2 ) and rhodanine-3-acetic acid ( ThITD3 ), and the effect of substituents on the optical and electrochemical properties have been discussed based on structural modifications. The third-order nonlinear optical (NLO) properties analyzed by the Z-scan technique reveal that the molecules exhibit effective two photon absorption (TPA) with ThITD3 possessing substantially higher effective TPA coefficient ( β eff ) than ThITD1 and ThITD2 , which is comparable to the reported β eff values. The results unravel that ITD as an acceptor with an appropriate π-linker will be a promising candidate for application in the field of optoelectronics/photonics. Herein, the thiophene-ITD ring system was explored for NLO applications and reported for the first time. Schematic of the optical limiting action of a novel imidazo[2,1- b ][1,3,4]thiadiazole based small molecule ( ThITD3 ), which blocks high irradiance and transmits low-intensity (less harmful) light.