Synthesis and characterization of thiophene-based donor-acceptor type polyimide and polyazomethines for optical limiting applications

In this communication we describe the design and synthesis of four new conjugated polymers (P1-P4) based on 3,4-ditetradecyloxythiophene. The required diamine monomer was prepared by a unique catalyst-free reduction process using hydrazine hydrate. The structures of the intermediates and polymers were established by FTIR, H-1 NMR spectroscopy. Molecular weights of polymers were determined by gel permeation chromatographic (GPC) method. Their electrochemical properties were investigated by cyclic voltammetry and linear optical properties were determined by UV-Visible absorption and fluorescence emission spectroscopic techniques. Further, their nonlinear optical properties were evaluated by Z-scan technique using Nd:YAG laser. These polymers showed strong optical limiting behavior with two-photon absorption (2PA) coefficients of the order of 10(-10) m/W, which are comparable to that of good optical limiting materials reported in the literature. Also, it has been observed that the optical nonlinearity enhanced with the increase in donor-acceptor strength of the polymer backbone.