Synthesis by the Gilch Method of Blue-Light-Emitting Poly(<i>p</i>-phenylenevinylene) Derivatives Bearing Highly Phenylated Pendants

Abstract

Two novel poly(p-phenylenevinylene) (PPV) derivatives bearing highly phenylated side groups with different chemical structures were prepared by Gilch dehydrohalogenation polyaddition. The intermediate substituted 1,4-bis(bromomethyl)benzenes (monomers 6 and 11) were synthesized by a convenient synthetic route utilizing pyrylium salts. The polymers were amorphous and showed limited solubility in THF, chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, and 1,2-dichlorobenzene. They displayed relatively high Tg values (158−176 °C) and good thermal stability, being stable up to approximately 270−350 °C in N2 or air and affording anaerobic char yields of 53−56% at 800 °C. The bulky side groups caused a significant steric effect on the PPV backbone and reduced the chromophore length. The solutions of polymers in THF emitted blue light with a maximum around 455 nm. This emission maximum is blue-shifted in comparison with that of other previously synthesized PPVs that emit green to red light. At low temperature, the photoluminescence (PL) spectra of polymers in THF became broader and were extended to longer wavelengths in comparison with the corresponding room-temperature spectra. The PL spectra of thin films of polymers were red-shifted with respect to those of solutions and showed a maximum at 476 nm