Why the Photochemical Reaction of Phenol Becomes Ultrafast at the Air-Water Interface: The Effect of Surface Hydration

Photochemical reactions at the air-water interfacecan show remarkably different rates from those in bulk water. Thepresent study elucidates the reaction mechanism of phenolcharacteristic at the air-water interface by the combination ofmolecular dynamics simulation and quantum chemical calculationsof the excited states. We found that incomplete hydrogen bonding to phenol at the air-water interface affects excited states associatedwith the conical intersection and significantly reduces the reactionbarrier, resulting in the distinctively facilitated rate in comparisonwith the bulk phase. The present study indicates that the reaction dynamics can be substantially different at the interfaces in general,reflecting the difference in the stabilization energy of the electronicstates in markedly different solvation at the interface.