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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°C whereas the hyperbranched polymer P2 showed better thermal stability with an onset of decomposition at 375°C. Polymer P2 showed lower band gap energy (1.96 eV) than that of P1 (2.09 eV). 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 2 V. 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 (β) of the polymers is of the order 10 À10 mW À1 which indicates that these materials may be accomplished for fabricating optical limiters.

Two new thiophene‐based donor–acceptor (D–A) conjugated polymers, PDTOFV and PDTOCN, are synthesized and characterized. The polymers are readily soluble in common organic solvents and exhibit good thermal stability with onset decomposition temperature (Td) in the range 310−330°C. Cyclic voltammetry studies revealed that polymers possess low‐lying highest occupied molecular orbital (HOMO) energy levels (−5.94 eV for PDTOFV and −5.86 eV for PDTOCN) and low‐lying lowest unoccupied molecular orbital (LUMO) energy levels (−3.35 eV for PDTOFV and −3.55 eV for PDTOCN). The optical band gap is calculated from onset absorption edge of the polymer film. The polymers exhibit green fluorescence with fluorescence quantum yields (ϕfl) of 38% and 42%, respectively, for PDTOFV and PDTOCN. Polymer light‐emitting diodes (PLEDs) are fabricated using these polymers with a device configuration of ITO/PEDOT:PSS/polymer/Al. The device based on PDTOFV emitted green light with Commission Internationale de I'Eclairage (CIE) coordinate values of (0.25, 0.39). Whereas, the device based on PDTOCN showed white light emission with CIE coordinate values of (0.32, 0.35), which is very close to the values (0.33, 0.33) of standard white light emission. The threshold voltages of the PLEDs are determined by current density‐voltage characteristics and are found to be 7.3 and 3.9 V for PDTOFV and PDTOCN, respectively. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

In this paper, we report the synthesis, characterization and optical properties of a donor-acceptor conjugated polymer, PTh-CN, containing 3,4-didodecyloxythiophene and cyanovinylene units. The polymer possesses a low band gap of 1.75 eV as calculated from the onset absorption edge. From the electrochemical study, the HOMO and LUMO energy levels of the polymer are figured out to be −5.52 eV and −3.52 eV, respectively. Polymer light-emitting diodes are fabricated using PTh-CN as the emissive layer with a device configuration of ITO/PEDOT:PSS/PTh-CN/Al. The device showed stable saturated red electroluminescence with CIE coordinate values (0.65, 0.32) at 12 V, which are very close to the values for standard red demanded by the NTSC. In addition, the device showed good colour stability under different bias voltages and the threshold voltage of the PLED device is found to be as low as 3.1 V. Further, a nanocomposite of the polymer and TiO 2 nanoparticles is prepared by the dispersion method. The nonlinear optical properties of PTh-CN and PTh-CN/TiO 2 nanocomposite are studied using z-scan technique. The polymer solution, polymer film and polymer/TiO 2 nanocomposite film show a strong saturable absorption behaviour. The value of saturation intensity (I s) is found to be of the order 10 11-10 12 W/m 2 , indicating that the materials are useful candidates for photonic applications.