Mapping Nonlinear Solvation at the Air-Organic-Solution Interface Using an Azide Probe.

Quantitative insight into interfacial solvation remains limited, despite broad relevance to chemical transformations at aqueous boundaries. Here, we employ surface-anchored azide monolayers as molecular probes to quantify and tune solvation at the air-organic-solution interface. The interface is modulated using organic/water mixtures, mixed monolayers containing alcohol surfactants, and solute additives, such as inorganic salts, urea, and formic acid. Among these, water mixtures involving dimethyl sulfoxide (DMSO) or ethylene glycol (EG) prove to be most effective for tuning solvation, establishing design principles for controlling interfacial reactions. Moreover, we map the nonlinear behavior arising from preferential partitioning, one of the invoked explanations for the distinct reactivity at the air-water interface.