Effects of substituents on enriching optical limiting action of novel imidazo[2,1-b][1,3,4]thiadiazole fused thiophene based small molecules
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 work, three new donor–acceptor–donor (D–A–D) type organic molecules (ThITD1–ThITD3) were designed and synthesized, wherein ITD is an electron acceptor unit and thiophene/ phenyl moieties are electron donor units that produce 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 were discussed based on structural modifications. The third–order nonlinear optical (NLO) properties analyzed by Z–scan technique revealed that the molecules exhibit effective two photon absorption (TPA) with ThITD3 possessing substantially higher effective TPA coefficient (βeff) than that of ThITD1 and ThITD2, which is comparable to βeff values reported. The results unravel that ITD as an acceptor with an appropriate π–linker will be a promising entrant in the field of optoelectronics/photonics. Herein, the thiophene–ITD ring system for NLO applications is explored and reported for the first time.