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

ABSTRACT 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.