Site-Specific Molecular Engineering Redirects Radical Pathways for Selective Photocatalytic Coupling of Methane to C2+ Hydrocarbons.

Toward carbon neutrality, multi-carbon synthesis from photo-driven oxidative coupling of CH4 (POCM) remains a formidable challenge due to the activity-selectivity trade-off, originating from sluggish surface reaction kinetics and uncontrolled reactive radical reactions. Herein, alkyl thiols (C9SH) were site‑specifically grafted onto Au sites supported on planar TiO2, forming the archetypal C9S-Auδ+/Au/TiO2 system featuring covalent gold-thiolate interplay. Combined experimental and theoretical analyses revealed that covalent Au-thiolate interaction could modulate the interfacial electronic structure and upshift the d‑band center of Au sites, thereby strengthening *CH3 adsorption and lowering the C─C coupling barrier, thus suppressing the ·O2 --driven overoxidation. Moreover, the reconstructed C9S-Auδ+ sites acted as rapid electron extraction channels, drawing electrons from adjacent Au nanoparticles and preserving long-lived photogenerated holes for C─H activation. Meanwhile, the alkyl chains served as "molecular fences", effectively promoting local CH4 enrichment and stabilizing *CH3 intermediates. The optimized C9S-Auδ+/Au/TiO2 photocatalyst exhibited an excellent yield of 22.92 mmol gcat -1 h-1 for C2+ products with 93.9% selectivity, ranking it among the state-of-the-art noble-metal-loaded photocatalysts for POCM. This work establishes site-specific molecular engineering as an effective strategy to regulate interfacial charge redistribution and redirect radical coupling pathways, enabling CH4 conversion to multi-carbon products with enhanced activity and selectivity simultaneously.