Effect of alkyl and aromatic substituents on blue electroluminescence in polyacetylene derivatives

Substituent dependences of electroluminescence (EL) and photoluminescence (PL) in disubstituted polyacetylene derivatives such as poly(1-methyl-2-phenylacetylene) (PMePA), poly(1-ethyl-2-phenylacetylene) (PEtPA), poly(1-n-hexyl-2-phenylacetylene) (PHxPA) and poly(1-methyl-2-naphthylacetylene) (PMeNA) have been studied. Blue light emission was observed from EL devices utilizing PEtPA and PHxPA; and blue-green light emission was observed from those utilizing PMePA and PMeNA. EL intensity, relative EL efficiency and PL intensity increase by one or two orders of magnitude on increasing the alkyl chain length. EL intensity, EL efficiency and PL intensity of PMeNA are higher than those of PMePA. The results are discussed in terms of substituent-dependent interchain interaction and electronic energy states.