Mesoporous Black Arsenic: Wet-Chemical Synthesis and Its Photo-Enhanced Activity in the C–H Arylation of Heteroarenes under Red Light Illumination

Black arsenic (b-As) is theoretically known for its anisotropic electronic and optical properties, yet its experimental realization remains limited. Here, we report the first bottom-up wet-chemical approach for the synthesis of mesoporous b-As (mb-As), a structurally ordered As-As networked semiconducting material. The as-synthesized mb-As exhibits a direct bandgap of 1.75 eV and a conduction band minimum of -1.40 V vs normal hydrogen electrode, providing a stronger reduction potential than most conventional semiconductors and enabling efficient visible-light-driven single-electron transfer (SET) under 625 nm illumination. These properties were leveraged in photoredox C-H arylation of heteroarenes, where mb-As catalyzed 13 transformations with yields up to 88%, successfully accommodating substrates bearing electron-donating and withdrawing groups as well as aromatic heterocycles. Mechanistic investigations revealed a radical-driven SET pathway involving both photogenerated electrons and holes of mb-As. Importantly, to address concerns regarding the potential toxicity of mb-As, biocompatibility assays performed on two different cell lines demonstrated that >90% cell viability up to 1 mg/L and ca. 70% cell viability at 50 mg/L, distinguishing mb-As from highly toxic arsenic analogues such as As(III) chloride and underscoring its suitability for sustainable catalysis and other possible applications.