Impact of donor–acceptor alternation on optical power limiting behavior of H–Shaped thiophene–imidazo[2,1-b] [1,3,4]thiadiazole flanked conjugated oligomers

Abstract

A new series of four D–A–D configured conjugated oligomers with H–type structure, possessing two thiophene–imidazo [2,1-b][1,3,4]thiadiazole branches and thiophene (TIT), thiophene–1,3,4-oxadiazole–thiophene (TITO), thiazolo [5,4-d]thiazole (TITz), phenyl–thiazolo [5,4-d]thiazole–phenyl (TIPTz) units as central core moieties were efficiently synthesized. These core moieties were specifically selected to increase the planarity, rigidity, stability, extend the π–conjugation and to understand the influence of central core on nonlinear absorption coefficient (βeff) and optical limiting behavior of the synthesized oligomers. The structure-property relationships of these oligomers were established by the optical absorption (UV–Vis), electrochemical (CV) and theoretical (DFT) studies. The “effective two–photon absorption” of oligomers was confirmed by single–beam Z–scan analysis. The exceptional increase in nonlinear response was achieved with the oligomers TITO and TIPTz with nonlinear absorption coefficient (βeff) of 1.62 and 2.71 × 10−10 m W−1, and limiting thresholds of 6.02 and 3.14 J cm−2, respectively, which suggest that these oligomers could be potent materials for practical applications in laser photonics.