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

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.