Expanding the chemical space of flavins with pentacyclic architecture

Inspired by the prominent redox and optical properties of natural flavins, synthetic flavins have found broad applications in organic, photochemical, and biochemical research. Tailoring these properties of flavins, however, remains a challenge. In this work, we present three pentacyclic flavins (C-PF, O-PF, and S-PF) that leverage a strategic molecular design to modify the flavin's electronic structure. Notably, the oxygen- and sulfur-linked pentacyclic flavins (O-PF and S-PF) exhibit deep-red and NIR emission, respectively, driven by enhanced π-conjugation, substituent effects, and charge separation upon excitation. These heteroatom-incorporated pentacyclic flavins exhibit unusual quasi-reversible oxidation, expanding both optical and redox limits of synthetic flavins. Comprehensive spectroscopic, structural, and computational analyses reveal how heteroatom incorporation within this five-ring-fused system unlocks redox and optical properties of flavin-derived chromophores.