Synthesis, photophysics, and electroluminescence of new quinoxaline-containing poly(p-phenylenevinylene)s

Four new soluble poly(p-phenylenevinylene) (PPV) derivatives containing one or two quinoxaline moieties per repeat unit, either in the main chain or as pendants to the main chain, were synthesized, characterized, and explored as emissive and electron transport materials in polymer light-emitting diodes (LEDs). Polymers containing one quinoxaline moiety per repeat unit (QXPV1 and QXPV3) showed low melting transitions (< 100 degrees'C), whereas those with two quinoxaline moieties per repeat unit (QXPV2 and QXPV4) had relatively high glass transition temperatures (> 140 degreesC). The polymers emit blue to green light (404-536 nm) in dilute solution and blue-green to yellow light (470-563 nm) in the solid state. The photoluminescence emission was well-described by single-exponential decay with lifetimes ranging from 200 ps to 2.2 ns in both dilute solution and thin film, indicating lack of intermolecular emissive species in the solid state. PPV derivatives with quinoxaline moieties in the main chain (QXPV1 and QXPV2) showed facile reversible electrochemical reductions with electron affinities of 2.63-2.75 eV. As emissive materials in LEDs, greenish-yellow electrolumineseence with a brightness of up to 450 cd/m(2) was obtained from single-layer diodes of QXPV1 with aluminum cathode in air.