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 TiO₂ nanoparticles is prepared by the dispersion method. The nonlinear optical properties of PTh-CN and PTh-CN/TiO₂ nanocomposite are studied using z-scan technique. The polymer solution, polymer film and polymer/TiO₂ nanocomposite film show a strong saturable absorption behaviour. The value of saturation intensity (I_s) is found to be of the order 10¹¹-10¹² W/m², indicating that the materials are useful candidates for photonic applications.

In this communication, we report synthesis and characterization of new D-A conjugated polymers (P1-P3) consisting of electron-donating (D) 3,4-didodecyloxythiophene, electron-accepting (A) 1,3,4- oxadiazole unit and non-conjugation linkers. The conjugated segment in P1-P3 contains only five aromatic rings resulting in short conjugation length, but has an alternate D-A arrangement which significantly enhances the intramolecular charge transfer (ICT) interaction within the segment. As a result, these polymers exhibited lowoptical band gap in the range 2.51–2.76 eV. Fluorescence emission studies revealed that the polymer thin films emit intense blue light with emission maxima in the wavelength rage 430–480 nm. All three polymers undergo both oxidation and reduction processes under electrochemical conditions. Further, these polymers (P1–P3) exhibit low-lying HOMO and LUMO levels as a result of D-A structure of the conjugated segment. Polymer light-emitting devices were fabricated using these polymers as emissive layer with a device configuration of ITO/MoO₃/polymer/LiF/Al. The test device based on P2 emitted blue light with a low threshold voltage of 5 V. Z-scan studies reveal that the polymers exhibit a strong optical limiting behavior. The value of the nonlinear absorption coefficient (β) of polymers is of the order 10⁻¹¹m/W which indicates that these materials may be accomplished for fabricating optical limiters.