Electronic Properties and Electroluminescence of Monosubstituted Polyacetylenes and Their Mixtures with Disubstituted Polyacetylene

Abstract

Monosubstituted polyacetylenes (PA), that is, poly(phenylacetylene) (PPA) derivatives with various substituents attached at the ortho -position of the phenyl ring, have been studied. The valence band top and the bandgap energy of these polymers were estimated in the range from -5.5 eV to -5.9 eV (vs vacuum level) and from 1.9 eV to 2.3 eV, respectively, depending on the substituents. Although PL of these PPA derivatives is very weak, we have observed electroluminescence (EL), which is considered to be related to the nature of the self-trapped excitonic states of these polymers. The EL characteristics were found to depend on the substituents of polymers. In the mixture of poly( o -trimethylsilylphenylacetylene) (PPA- o SiMe 3 ) with the strong luminescent disubstituted PA, poly(1-phenyl-2- p - n -butylphenylacetylene) (PDPA- n Bu), the enhancement of PL of PPA- o SiMe 3 was not observed. However, EL of PPA- o SiMe 3 was enhanced in the mixture with PDPA- n Bu, which is explained in terms of excitation energy transfer.