Synthesis and study of optical properties of linear and hyperbranched conjugated polymers containing thiophene and triphenylamine units

We report the synthesis of solution processable donor-acceptor type conjugated monomer (M1) and polymers (P1 and P2) consisting of electron-accepting 1,3,4-oxadiazole unit and electron-donating 3,4-didecyloxythiophene, and triphenylamine units through Wittig polycondensation reaction. The linear polymer P1 is thermally stable up to 325 degrees C whereas the hyperbranched polymer P2 showed better thermal stability with an onset of decomposition at 375 degrees C. Polymer P2 showed lower band gap energy (1.96eV) than that of P1 (2.09eV). Polymers P1 and P2 emit yellow and orange light, respectively, under the irradiation of UV light. Electrochemical studies revealed that the polymers possess high-lying highest occupied molecular orbital and low-lying lowest unoccupied molecular orbital energy levels. Polymer light-emitting diodes are fabricated with the device configuration of ITO/PEDOT:PSS/polymer (P1 or P2)/Al. The device based on P2 showed a very low threshold voltage of 2V. The third-order nonlinear optical properties of the polymers are studied using Z-scan technique. Both polymers showed a strong optical limiting behavior. The value of nonlinear absorption coefficient () of the polymers is of the order 10(-10)mW(-1) which indicates that these materials may be accomplished for fabricating optical limiters.