Synthesis, optical and electroluminescent properties of an alternating copolymer of triphenylamine and fumaronitrile

A new conjugated alternating copolymer of triphenylamine and fumaronitrile, TPA–FN, was synthesized via Heck coupling reaction and characterized by GPC, UV–vis, 1H NMR and elemental analysis. The polymer film showed two absorption peaks at ca. 370 nm and 500 nm, respectively, and a narrow bandgap of 1.72 eV. The photoluminescence spectrum of TPA–FN film displayed a main peak at ca. 724 nm and a shoulder peak at ca. 808 nm, indicating that the polymer could be a near-infrared luminescent polymer. Cyclic voltammetry measurements revealed a lower LUMO energy level of TPA–FN at −3.85 eV. The lower LUMO level could be ascribed to the introduction of the electron-withdrawing fumaronitrile with two cyano groups attached to trans-vinylene, and it favors the electron injection for the application in the polymer light-emitting diodes (PLEDs). A single-layer PLED based on TPA–FN was fabricated and the device showed the turn-on voltage of 6 V and the maximum luminance of 136 cd/m2 at 11.5 V.