Synthesis by Heck Coupling of Soluble, Blue-Light-Emitting Fully Conjugated Poly(<i>p</i>-phenylenevinylene)s with Highly Phenylated Side Groups

Abstract

Two new fully conjugated poly(p-phenylenevinylene)s (PPVs) were prepared by Heck coupling between p-divinylbenzene and two dibromides. The latter were synthesized by a six-step synthetic route using pyrylium salts. The polymers carried on the same phenyl ring two side oligophenyls per each repeat unit with various chemical structures. These polymers were amorphous and showed an excellent solubility being soluble in common organic solvents (THF, chloroform, methylene chloride, 1,2-dichloroethane). No weight loss was observed approximately up to 320−370 °C in N2 or air, and the anaerobic char yield was around 80% at 800 °C. The Tg values ranged from 106 to 122 °C, and they could be controlled by the chemical structure of the side substituents. The polymers behaved as strongly blue-light-emitting materials in THF solution with PL maximum at 453 or 461 nm. These values are among the bluest emission peaks that have been reported for a fully conjugated PPV. The bulky side oligophenyls caused significant steric hindrance which interrupted the conjugation in the PPV backbone. At low temperature, the PL maximum in THF was red-shifted by 2−10 nm in comparison with the respective room temperature spectra. The red shift was greater for the polymer that carried longer side oligophenyls. The bulky side oligophenyls hindered chain interactions, and the polymer displayed little tendency for aggregate formation. The PL quantum yields in THF were 0.24−0.31