Light emitting poly(para-phenylenevinylene-alt-3-tert butyl-meta-phenylenevinylenes)

Poly(para-phenylenevinylene-alt-3-tert-butyl-meta-phenylenevinylene) was synthesized by Wittig condensation with varying ratio of cis and trans olefin bonds. The luminescent properties of the unisomerized and trans-isomerized polymers (1 and 2, respectively) were compared. Nearly identical emission spectra were observed for both polymers in dilute solutions, but the emission intensity of 1 is lower. This is attributed to the cis vinylic moieties in 1, which favor nonradiative excited state decay processes by limiting formation of a planar excited state. Double layer LEDs with the configuration ITO/PPV/(1 or 2)/Ca–Al were fabricated. Substantially better efficiencies and luminances were observed for devices made with polymer 2 as the emissive layer, by comparison to 1. The results show that the elimination of cis olefin defects in these polymers is important for the optimization of LEDs.