On the meaning of parameters of the two state model in the case of photochemical reactions under restricted geometry conditions

The classical Pseudophase Model (a two state model) describes well the reactivity in the presence of receptors. This model assumes that the exchange between free and bound reactants is at equilibrium in spite of the reaction, a condition that usually cannot be maintained if the reactants are excited. However, the equation of the Pseudophase Model holds, at least formally, in this case. The formalism developed to clarify this question indicates that the parameters acquire a somewhat different meaning in the case of photochemical reactions. The experiments carried out in the presence of DNA and β-cyclodextrin support the formalism developed.