Phase-Resolved Dual Control of Phenol Photodissociation at the Air-Water Interface From Structure-Resolved Statistics

Phenolic photodissociation at the air-water interface proceeds orders of magnitude faster than in bulk water, yet the structural origins of this acceleration remain insufficiently understood. Here, we present a descriptor-level analysis supporting a dual-control picture, in which phase-dependent photodissociation reflects both πσ*-related dark-state accessibility and the local solvent's capacity to accommodate transferred electron density. We construct a structure-resolved, statistics-driven framework that bypasses snapshot-level multireference conical-intersection searches by identifying solvent-side dark-state acceptor orbitals {σ_p*}, constructing their energy distribution ε(σ_p*), and linking it to local microenvironment descriptors that quantify coordination saturation and directional constraint. Truncated cluster models prove unreliable because boundary microstates dominate acceptor selection and mask the intrinsic interface-bulk contrast. Periodic slab models remove this bias: the interfacial ε(σ_p*) distribution is shifted lower by approximately 0.7 eV and substantially broadened relative to bulk, predominantly through within-motif energy-window shifts rather than differences in hydrogen-bond topology. Low-coordination, weakly constrained microenvironments correlate systematically with lower ε(σ_p*), and small-system SA-CASSCF diagnostics support the same trend direction. Together, these descriptor-level signatures indicate that the air-water interface favors both dark-state access and transferred-electron stabilization, providing transferable inputs for multiphase photochemical modeling and strategies for tuning interfacial reactivity through control of defect-rich microstate supply.