Vinyl copolymers containing pendant 1,3,4-oxadiazole chromophores: Preparation and electrochemical and electroluminescent properties

Three vinyl copolymers (P1-P3) containing pendant aromatic 1,3,4-oxadiazole derivatives were prepared from their precursor poly(styrene-ran-4-vinylbenzyl chloride) (weight-average molecular weight = 11,400, polydispersity index = 1.18), which had been synthesized by controlled radical polymerization (reversible addition-fragmentation chain transfer). The copolymers were readily soluble in common organic solvents and were basically amorphous materials with 5% weight loss temperatures higher than 360 degrees C. The photoluminescence spectroscopy results revealed that the architectures of P2 and P3 suppressed aggregate formation in the solid state. The LUMO levels of P2 (-3.10 eV) and P3 (-3.09 eV), estimated from cyclic voltammetry data, were much higher than that of P1 (-3.81 eV). The HOMO levels were in the order of P3 (-5.37 eV) > P2 (-5.77 eV) > P1 (-5.96 eV). However, both the HOMO and LUMO levels of P1-P3 were much lower than that of poly[2-methoxy-5-(2'-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) because of the electron-withdrawing characteristics of the pendant aromatic 1,3,4-oxadiazole groups. The luminance (5860 cd/m(2)) and current efficiency (1.45 cd/A) of an electroluminescence device [indium tin oxide/poly(3,4-ethylene dioxythiophene)/MEH-PPV/Al] were improved significantly to 16,261 cd/m(2) and 4.79 cd/A, respectively, through blending with P2 (50/50). This study suggests that copolymers P1-P3 are versatile materials for electron-transport/injection applications. (C) 2007 Wiley Periodicals, Inc.