<i>ortho</i>-Terphenylene Viologens with Through-Space Conjugation for Enhanced Photocatalytic Oxidative Coupling and Hydrogen Evolution

Abstract

A series of novel <i>ortho-</i>terphenylene viologen derivatives (<i>o-</i>TPV²⁺) with through-space conjugation (TSC) via the combination of <i>ortho-</i>terphenylene skeletons with viologen structure is reported. Their optoelectronic properties can be adjusted by <i>N</i>-arylation or <i>N</i>-alkylation reactions. Compared with other viologen derivatives, <i>o-</i>TPV²⁺ not only exhibits strong photoluminescence but also retards the charge recombination process and stabilizes the diradical state without forming a quinoid structure due to the special TSC effect. Based on their special redox characteristics, <i>o-</i>TPV²⁺ was applied to the photocatalytic oxidative coupling of benzylamine with 96% yield. In addition, <i>p</i>TA-<i>o-</i>TPV²⁺ (tethered with <i>p</i>-toluic acid)-modified g-C₃N₄ was used for visible-light-driven hydrogen production for the first time, exceeding 15 times the rate over unmodified g-C₃N₄.