Hydrogel-Controlled Electropolymerization of Polynorepinephrine through Confined Noncovalent Self-Assembly

Polymerization of monomers confined within hydrated polymer networks represents a promising strategy for engineering multifunctional, bioinspired interfaces. However, the role of the hydrogel environment in directing polymer growth and the resulting physicochemical properties remains poorly understood. Here, we demonstrate that chitosan hydrogels act as chemically programmed confined reaction environments that govern the electropolymerization of polynorepinephrine (PNOR). The polymer growth inside the matrix leads to hydrogel restructuring and hierarchical noncovalent self-assembly with only minor changes in the chemical composition of both components. The resulting composite exhibits permanently immobilized catechol/quinone redox centers, enhanced broadband optical absorption, and pronounced fluorescence quenching, demonstrating coupled electrochemical and photophysical functionality. Density functional theory reveals that electrostatic interactions are the main factor driving the composite formation with the supportive role of π-cation and hydrogen bonds. Moreover, oxidation of PNOR from the catechol to quinone state substantially modifies the electronic structure responsible for the observed optical response. The results establish hydrogel-controlled, confinement-driven electropolymerization as a general strategy for programming the electrochemical and optical properties of hydrogel interfaces through controlled molecular organization rather than extensive covalent modification.