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°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.