Synthesis and nonlinear optical characterization of new poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}

A new donor–acceptor type poly{2,2′-(3,4-didodecyloxythiophene-2,5-diyl)bis5-(2-thienyl)-1,3,4-oxadiazole]} (P) was synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge-transporting property of the copolymer was investigated by UV–vis, fluorescence emission spectroscopic and cyclic voltammetric studies. The copolymer shows UV absorption maxima at 375 nm and displays bluish-green fluorescence in DMF solution. Its electrochemical band gap was determined to be 2.07 eV. The nonlinear optical (NLO) properties of the copolymer was investigated at 532 nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques with nanosecond laser pulses. The copolymer exhibits strong optical limiting behavior due to effective three-photon absorption (3PA). Values of the effective 3PA coefficient (γ), third-order nonlinear susceptibility (χ⁽³⁾) and figure of merit (F) have been calculated.