Unraveling mechanistic map of riboflavin as a photocatalyst in metal-free ATRP: Defining structure-control relationships for sustainable polymerization

Abstract

Designing polymerization procedures that are both efficient and environmentally benign remains a significant challenge. Metal-free ATRP driven by bio-derived photocatalysts presents a promising approach, although its success depends on a well-defined mechanistic understanding. Here, we present a detailed mechanistic map for riboflavin (vitamin B2) and brominated riboflavin derivatives as organic photocatalysts in metal-free ATRP. By combining spectroscopic and electrochemical analyses with polymerization kinetics, we established structure–property relationships that clarify when and why control is achieved or lost. The results define practical operating windows for wavelength, medium, and photocatalyst/initiator loadings; identify failure modes associated with competing redox and hydrogen-atom pathways; and show how tail bromination enhances the photocatalytic activity of the isoalloxazine chromophore while introducing initiation sites. These insights offer valuable guidelines for chromophore tuning and microenvironment engineering to advance efficient, sustainable, and externally switchable metal-free ATRP based on accessible, low-cost flavin scaffolds.