Novel poly(3,4-dialkoxythiophene)s carrying 1,3,4-oxadiazolyl-biphenyl moieties: Synthesis and nonlinear optical studies

Two new donor-acceptor types of polymer, poly{2-(biphenyl-4-yl)-5-[3,4-dialkoxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole}s, were synthesized starting from 2,2'-sulfanediyldiacetic acid and diethyl ethanedioate through multi-step reactions. The polymerization was carried out via the polyhydrazide precursor route. The optical and charge-transporting properties of the polymers were investigated using UV-visible and fluorescence emission spectroscopic and cyclic voltammetric studies. The polymers showed bluish-green fluorescence in solutions. The electrochemical band gaps of the polymers were determined to be 2.16 and 2.22 eV. The nonlinear optical properties of the polymers were investigated at 532 nm using the single-beam Z-scan technique with nanosecond laser pulses. The polymers showed strong optical limiting behaviour due to effective three-photon absorption. The values of the three-photon absorption coefficients for the polymers were found to be 9 × 10^-24 and 17 × 10^-24 m³ W^-2, which are comparable to those of good optical limiting materials.