New optical limiting polymeric materials with different π-electron conjugation bridge structures: Synthesis and characterization

In this communication we describe the design and synthesis of five new conjugated polymers (P1–P5) with various π-electron conjugation bridges. Their structures were established by FTIR, 1H NMR spectroscopy, elemental analysis. The molecular weights of the polymers were estimated by gel permeation chromatographic technique. Further, their electrochemical, linear and nonlinear optical properties were investigated. The electrochemical band gaps of P1–P5 were found to be 1.72–2.35 eV. Their third-order nonlinear optical activities were studied by open aperture Z-scan technique, using a Q-switched, frequency doubled Nd:YAG laser producing 7 nano second laser pulses at 532 nm. Z-scan results reveal that the polymers exhibit self-defocusing nonlinearity and their operating mechanism involves reverse saturable absorption. The polymers showed strong optical limiting behavior due to effective two-photon absorption (2PA) with 2PA coefficients of the order of 10−11 m/W, which is comparable to that of good optical limiting materials in the literature.