Formation of Boronate Ester Polymers with Efficient Intrastrand Charge‐Transfer Transitions by Three‐Component Reactions

The three‐component reaction of aryl boronic acids with 1,2,4,5‐tetrahydroxybenzene and 1,2‐bis(4‐pyridyl)ethylene or 4,4′‐bipyridine leads to the formation of dark‐purple boronate ester polymers. Crystallographic analyses show that the polymer strands have a zig–zag geometry, and the bis(dioxaborole) units are connected by dipyridyl linkers through dative B–N interactions. Upon dissolution of the polymers in hot chloroform, most of the B–N connections are broken, which indicates that polymer formation is a reversible process. A computational study provides evidence that the strong color of the polymers is due to efficient intrastrand charge‐transfer excitations from the tetraoxobenzene to the dipyridyl linker.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)