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[Ti[N(Ph)SiMe2]3-tacn]X complexes (X = Cl, 1; I, 2; PF6, 3; BPh4, 4) were studied by NMR and electron absorption and emission methods, which showed that these compounds exist in bromobenzene and dichloromethane solutions as ion pairs. The significant modifications observed in the proton resonances of tacn in C6D5Br, which follow the sequence BPh(4-) > or = PF(6-) > or = I- approximately Cl-, are a qualitative indication of the strength of the interactions that depend on the anion. The reaction of 2 with LiNMe2 led to [Ti(NPh)[NPh(SiMe2)]2-tacn], 5, that forms upon attack of Me2N- at one SiMe2 group. The formation of 5 is discussed on the basis of the interactions identified in solution.

The intramolecular activated nonradiative decay of the first excited singlet of the Rhodamine 3B cation is studied in a large number of polar solvents covering a wide range of viscosities. The photophysics are interpreted in terms of an isomerization process occurring at the diethyl amino group with adiabatic barrier crossing. The experimental data show that friction effects determine the reaction rates, which are modeled in the framework of Kramers and Grote−Hynes theories. The reactant well wavenumber (ω0/2πc) is estimated as 30 cm-1 and coincides with the wavenumber of the barrier top (ωb/2πc) for the less viscous solvents. The former value is invariant with the solvent and is a good approximation to the reactive molecular mode involved in the nonradiative deactivation. The increase in dipole moment at the barrier top relative to the bottom of the reactant well is inferred from intrinsic barrier heights whose stabilization energies vary according to Onsager's theory of dielectrics.

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