Photoacid-solvent clusters

The interpretation of the experimental data for the kinetics of photoacid-solvent clusters is complicated by the substantial fragmentation of the clusters after the excited-state reaction. The heat of reaction is often sufficient to allow the evaporation of one or several solvent molecules [14,16]. This difficulty does not arise when the H atom transfer or proton transfer occurs intramolecularly along a solvent wire attached to a bifunctional chromophore. 

The molecular mechanism of photoacidity of phenol has been investigated theoretically by Sobolewski and coworkers [100-102]. The ab initio calculations on phenol-ammonia cluster predicted that the increased acidity of excited phenol is not due to a property of the optically excited jot state, but rather arises from the nonadiabatic interaction of the jiji state with an optically dark state of jta character. The jot potential energy function is crossed by the jta function, and the jro energy is strongly stabilized when the proton moves from the chromophore to the solvent (ammonia) as illustrated in Figure 2.6 [100]. Hence, they consider that jia state plays a key role in the ESPT reaction of phenol-ammonia cluster. 

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