Molecular Design of Novel Conjugated Polymers for Blue-Light-Emitting Devices

Abstract

A quantum-chemical study of conformations and electronic structures of polyheterocyclic derivatives with vinylenediheteroatom substituents at the 3- and 4-positions was performed to search for novel blue-light-emitting conjugated polymers. Conformational potential energy curves of the polymers were constructed as a function of the helical angle (a) through semiempirical Hartree-Fock band calculations at the Austin model 1 level. It is found that poly(3,4-vinylenedioxythiophene) possesses a quite flat curve in the range of α = 51.4° - 120°. Replacing S atoms for O atoms greatly increases repulsion between the neighboring units, and thereby the units become perpendicular to one another. Because of the hydrogen bonding between O and NH, poly(3,4-vinylenedioxypyrrole) is predicted to be anti-coplanar and poly(3,4-vinylenediaminofuran) to be nearly anti-coplanar. According to the modified extended Hückel band calculations, the HOMO-LUMO gaps (HLGs) of the polymers, unless the polymer chains are twisted, are close to or slightly smaller than those of their respective mother polymers. Among the polymers, poly(3,4-vinylenedioxythiophene) is presumed to be the most probable candidate for a blue-light emitter because its HLG is within the range of the electronic requirement for blue-light emitters.