Synthesis, photo- and electroluminescence properties of asymmetrical alternating copoly(p-phenylenevinylene) derivatives

A series of asymmetrical alternating copoly(p-phenylenevinylene) derivatives (PPVs), poly(2-methoxy-5-alkoxy)-1,4-(phenylene vinylene)-alt-1,4-(phenylene vinylene), have been successfully synthesized via the Wittig polycondensation reaction as potential electroluminescent (EL) materials. These copolymers contain two components, one is phenylene vinylene with asymmetrical flexible side chain to improve the solubility of the copolymer in common solvents and to suppress its crystallization; the other is a rigid phenylene vinylene moiety to improve the luminescent quantum efficiency and the thermal stability. The photoluminescent (PL) properties and thermal behavior of these copolymers have been investigated in detail. The results showed that the PL intensity increased but the thermal stability decreased with increasing side chain length. A double-layer device of ITO/PEDOT–PSS/Polymer 3/Ba/Al showed a greenish yellow emission peaking at 548 nm with a turn-on voltage as low as 6.2 V. A maximum brightness of 534 cd/m2 was obtained at a driving voltage of 10 V.