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.