Luminescent poly(1,4-phenylene vinylene-4,4′-biphenylene vinylene)s containing oligo(ethylene oxide) or hexyloxy side groups

Two soluble poly(1,4-phenylene vinylene-4,4′-biphenylene vinylene)s (P1, P2) were synthesized through the Wittig condensation, in which P1 and P2 contain flexible oligo(ethylene oxide) and hexyloxy side groups, respectively. Furthermore, a blend of P1 with lithium perchlorate (P1–LP) was obtained to investigate the effect of doping. The polymers show good solubility in common organic solvents and are thermally stable (Td>315 °C). The optical properties of the polymers, both in solution and as cast films, were investigated by absorption and photoluminescence (PL) spectra, whereas the electrochemical characteristics were obtained using cyclic voltammetric measurement. The LUMO levels of P1, P2, and P1–LP are −3.18, −3.21 and −3.79 eV and the band-gaps are 1.95, 2.18, and 1.27 eV, respectively. Double-layer light-emitting diodes (ITO/PEDOT/Polymer/Al) were successfully fabricated to investigate their electroluminescent (EL) properties. The PL and EL spectral maxima of P1, P2, and P1–LP locate at 507–509 nm and 511–516 nm, indicating that they are yellowish-green emitting materials. The turn-on electric field was 4.2×105, 5.6×105, and 3.4×105 V/cm and maximum luminance was 175, 268, and 620 cd/m2 for P1, P2, and P1–LP, respectively.