On the applicability of the two state (pseudophase) model to photochemical reactions under restricted geometry conditions

In this paper a new formulation based on a two state model (pseudophase model) is presented. This formulation explains the results obtained in the quenching of *[Ru(bpy)3]2+ by S2O82− in α-cyclodextrin solutions. The quenching of the excited state of the ruthenium complex by another quencher, [Co(NH3)5pz]3+ (pz = pyrazine), is also studied in order to check the consistency of the equations. The model presented is also valid to be applied to any photochemical process that takes place in restricted geometry conditions. In fact, it explains unexpected results found in previous studies such as the linear Stern–Volmer plots observed when curved plots are predicted, the monoexponential decays obtained when there are two populations of the excited species or the possibility of using the pseudophase model to describe photochemical processes when there is not an equilibrium distribution between the free and bound excited states.

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► Interpretation of photochemical reaction results in restricted geometry conditions.
► Populations of free and bound states out of equilibrium.
► Stern–Volmer equation modified.