Synthesis and electroluminescence properties of a novel tetraphenylsilane-oxadiazole-diphenyl(para-tolyl)amine polymer

A novel triarylaminooxadiazole-containing tetraphenylsilane light-emitting polymer (PTOA) has been synthesized. Excellent thermal stability was observed due to the presence of a rigid tetraphenylsilane-based polymer backbone (T_g = 218 °C, T_d = 373 °C). In solution, PTOA shows photoluminescence (PL) with an emission maximum at 426 nm, which is attributed to the light-emitting unit of the triarylaminooxadiazole group. In solid film, the emission maximum of PL is observed at 458 nm, a 32 nm red-shift from the PL in solution. The solvatochromic effect and excimer formed in the solid film are responsible for the red-shifting and broadening of the PL emission band. The PL stability and morphology of the PTOA solid film were further investigated by thermal annealing at elevated temperatures. No significant difference in the PL spectra or morphology was observed between a pristine sample and a repeatedly thermally annealed film (at 200 °C). PTOA-based PLED shows EL with a main peak at 458 nm accompanied by a shoulder at around 530 nm. The light emission from electromer or electroplex leads to a broadening of the EL spectra (400-650 nm), which corresponds to the interaction between the oxadiazole and diphenyl(4-tolyl)amine groups in different polymer segments or chains. A sky blue emission (Commission Internationale de L'Eclairage (CIE_x,y) coordinates (0.20,0.23)) was obtained for PTOA-based PLED. The brightness and efficiency of the PLED can be as high as 248 cd/m² and 0.54 cd/A, respectively. The EL of PTOA-based PLED has been further improved by blending the PTOA with poly(n-vinylcarbazole) (PVK) in different concentrations. The effects of concentration on the PL and EL were studied for the PTOA-PVK composite film-based PLEDs.