Synthesis, Two-Photon Absorption, and Optical Power Limiting of New Linear and Hyperbranched Conjugated Polyynes Based on Bithiazole and Triphenylamine

Two new linear and hyperbranched conjugated polymers P1 and P2 have been synthesized by Sonogashira coupling reaction, in which the main chain consists of bithiazole moieties as electron acceptors and triphenylamino groups as donors. The conjugated polymers were characterized by TGA, UV-vis absorption, fluorescence emission, electrochemical cyclic voltammetry, and two-photon absorption measurements. They exhibited excellent solubility in organic solvents and high thermal stability (5% of weight loss at 299 degrees C). The two-photon absorption cross sections (sigma) measured by the open aperture Z-scan technique using 140 femtosecond (fs) pulse were determined to be 1014 and 552 GM per repeating unit for P1 and P2, respectively. This result shows that the sigma of linear conjugated P1 is higher than that of hyperbranched P2, indicating that the linear polymer offers better intramolecular charge transfer ability. In THF, P1 and P2 exhibit intense frequency up-converted fluorescence under the excitation of 140 fs pulses at 800 nm with the peaks located at 580 and 548 nm, respectively. Meanwhile, the optical limiting behaviors for the polymers were studied by using a focused 800 nm laser beam of 140 fs duration. It was found that these polymers also exhibit good optical-limiting properties and make them potential candidates for optical limiters in the photonic fields. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:1830-1839, 2011