Pyrazine-Based Water-Soluble Conjugated Polymer Synthesis Enabled by Synchronized Pyrazine Construction and Polymerization

Abstract

Water-soluble conjugated polymers (WSCPs), distinguished by their unique optoelectronic properties and water solubility, have found versatile applications. Despite the fact that pyrazine and its fused ring serve as pivotal building blocks in high-performance conjugated polymers, the exploration of WSCPs incorporating a pyrazine ring in the backbone has been limited due to synthetic challenges. Herein, we developed a new synthetic strategy with synchronized pyrazine construction and polymerization that can transform vinyl azides into pyrazine cores under metal-free and open-to-air conditions. Employing this approach, we designed and prepared a series of novel pyrazine-based WSCPs with good water solubility and fluorescence properties. Remarkably, the photoluminescence intensity of WSCPs with free carboxyl groups surpassed that of conjugated polymers featuring ester groups. Single crystal X-ray diffraction analysis and DFT calculations indicated that this enhancement could be attributed to the presence of pyrazine rings and carboxyl groups in the polymer backbone, facilitating the formation of intermolecular hydrogen bonds. These interactions could effectively restrict vibrational relaxation and minimize the loss of energy via nonradiative decay pathways, ultimately resulting in higher emission intensity.