Effect of Molecular Structure of Substituents on Green Electroluminescence in Disubstituted Acetylene Polymers

Abstract

Intense green photoluminescence (PL) in the wavelength range of 520 to 540 nm was observed in many poly(diphenylacetylene) (PDPA) derivatives. The band gap energy and the highest occupied molecular orbital (HOMO) energy of these polymers were estimated to range from 2.6 to 2.7 eV and -5.6 to -5.9 eV depending on the substituent. Green electroluminescence (EL) was observed from EL devices fabricated utilizing these polymers. Among these PDPA derivatives, poly(1-phenyl-2- m -(trimethylsilyl)phenylacetylene) (PDPA- m SiMe 3 ) with the smallest band gap energy exhibited the weakest PL and EL of longest wavelength. Polymers with bulkier and/or longer substituents exhibited stronger PL and EL. The results are interpreted in terms of a steric hindrance effect and the interchain interaction depending on the molecular structure of the substituents. In addition, upon electrochemical doping, these light emissive polyacetylene derivatives exhibited evolution of new single midgap absorption suggesting formation of solitons.