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

A new series of four D-A-D configured conjugated oligomers with H-type structure, possessing two thinphene-imidazo [2,1-b][1,3,4]thiadiazole branches and thiophene (TIT), thiophene-1,3,4-oxadiazole-thiophene (TITO), thiazolo [5,4-(1)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 pi-conjugation and to understand the influence of central core on nonlinear absorption coefficient (beta(eff)) 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 (beta(eff)) of 1.62 and 2.71 x 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.