Electronic properties and electroluminescence of monosubstituted polyacetylenes and their mixtures with disubstituted polyacetylene

Monosubstituted polyacetylenes (PA), that is, poly(phenylacetylene) (PPA) d erivatives 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 sub stituents. Although PL of these PPA derivatives is very weak, we have obser ved electroluminescence (EL), which is considered to be related to the natu re of the self-trapped excitonic states of these polymers. The EL character istics were found to depend on the substituents of polymers. In the mixture of poly(o-trimethylsilylphenylacetylene) (PPA-oSiMe(3)) with the strong lu minescent disubstituted PA, poly(1-phenyl-2-p-n-butylphenylacetylene) (PDPA -nBu), the enhancement of PL of PPA-oSiMe(3) was not observed. However, EL of PPA-oSiMe(3) was enhanced in the mixture with PDPA-nBu, which is explain ed in terms of excitation energy transfer.