Direct Introduction of Cysteine Derivatives into the Chain End of Helical Poly(quinoline-2,3-diylmethylene)s: Densely Packed Monolayers on Au Substrates

Abstract

Highly reactive functional groups at polymer chain ends, integral for creating structurally diverse functional polymers and composites, present challenges in their introduction both pre- and postpolymerization. This study reported a method for directly introducing a sulfhydryl group, known for its specific reactivity, to the chain ends of polymers. Utilizing poly(quinoline-2,3-diylmethylene)s (PQMs) that form π-stacked helical structures via living polymerization initiated by a palladium complex, a novel approach was employed, where a cysteine derivative was added after converting the terminal palladium complex into an acyl palladium complex using carbon monoxide. The sulfhydryl group of cysteine formed a thioester bond, subsequently undergoing an S→N acyl shift to bond the cysteine derivative at the chain end of PQM through an amide bond while preserving the reactivity of the sulfhydryl group. This functionalization facilitated the easy introduction of various substituents at the end of the PQMs, enhancing their functional versatility. We finally focused on monolayer formation by specifically binding SH groups to Au. A cysteine derivative was introduced at the chain end of a π-stacked helical PQM that formed a monolayer film on a Au substrate. Remarkably, atomic force microscopy and scanning tunneling microscopy confirmed the formation of a uniform film containing densely packed π-stacked helical polymers on the Au substrate.