Poly(p-phenylene vinylene) derivatives containing triazole or oxadiazole segments: Connector effect in optical, electrochemical, and electroluminescent properties

To study the effect of connector structure between hole- and electron-transporting segments, we synthesized and characterized new electroluminescent polymers P1-P7 consisting of hole-transporting 1,4-bis(hexyloxy)-2,5-distyrylbenzene (DSB: P1 and P2) and electron-transporting 4-(4-(hexyloxy)phenyl)-3,5-diphenyl-4H-1,2,4-triazole (TAZ: P3 and P4) or 2-(2,5-bis(hexyloxy)-4-(5-phenyl-1,3,4-oxadiazol)phenyl)-5-phenyl-1,3, 4-oxadiazole (DIOXD: P5-P7) segments linked by different connectors. The connectors between hole- and electron-transporting segments are (1) 1,4-phenylene in P3 and P5, (2) 1,4-divinylbenzene in P4 and P6, and (3) 4,4′-biphenyl in P7. Three corresponding end-capped model polymers P1-M, P2-M, and P3-M were also synthesized to evaluate the effect of end groups. From optimized semiempirical MNDO calculations, the adjacent benzene rings between DSB and TAZ or DIOXD chromophores in P3, P5, and P7 twist about 81°-89°. The effect of twisted architectures and connectors in optical and electrochemical properties for P1-P7 have been discussed by comparing with copolymers PI and P2, which possess single bond or ether spacer as connectors. From cyclic voltammograms, the torsion in P3, P5, and P7 confines electron delocalization and leads to simultaneously enhanced hole and electron affinity as compared to those of P1 and P2. Furthermore, double-layer light-emitting diodes with a configuration of ITO/PEDOT:PSS/P1-P7/A1 all reveal green-yellow electroluminescence with maximum luminance at 8-320 cd/m² and their performances are greatly influenced by the connector's structure.