Melanins Enhance Radical Scavenging Through Wavelength‐Selective Excited‐State Manifold Diversity

Abstract

ABSTRACT Melanin is a ubiquitous pigment that mitigates photoinduced damage in biological systems through light absorption, heat dissipation, and radical scavenging. While these functions have traditionally been considered independent, recent studies suggest that they may be intrinsically coupled, with radical scavenging activity enhanced with light irradiation. However, the underlying photophysical mechanism remains unclear. Here, we present the first comprehensive wavelength‐dependent comparison of representative eumelanin (cephalopod‐ink‐derived melanin and polydopamine) and allomelanin (fresh and oxidized DHN melanins) spanning UV, visible, and near‐infrared excitation regimes. By combining radical scavenging assays, ultrafast transient absorption spectroscopy, and electron paramagnetic resonance spectroscopy, we demonstrate that light‐enhanced radical scavenging is a universal yet strongly excitation‐energy‐dependent behavior across chemically distinct melanin classes. We further identify the breadth of the excited‐state absorption (ESA) manifold and ESA‐to‐bleach ratio, and not excited‐state lifetime nor photoinduced semiquinone‐like radical accumulation, as the photophysical descriptors most closely associated with scavenging enhancement. These findings establish a unified framework linking excited‐state photophysics, photochemical redox activity, and photoprotection functions of melanins.