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

Abstract

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 (?<inf>eff</inf>) than ThITD1 and ThITD2, which is comparable to the reported ?<inf>eff</inf> values. The results unravel that ITD as an acceptor with an appropriate ?-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. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.