FT-EPR study of methyl radicals photogenerated from [Ru(Me)(SnPh3)(CO)2(iPr-DAB)] and [Pt(Me)4(iPr-DAB)]: an example of a strong excitation wavelength dependent CIDEP effect

The photoinduced methyl radical formation from the title complexes [Ru(R)(SnPh3)(CO)2(iPr-DAB)] (R = CH3, CD3; iPr-DAB = N,N‘-diisopropyl-1,4-diaza-1,3-butadiene) and [Pt(Me)4(iPr-DAB)] was the subject of a detailed time-resolved Fourier transform EPR (FT-EPR) study. The FT-EPR spectra of the radicals show pronounced chemically induced dynamic electron polarization (CIDEP) effects due to the ST0 and ST-1 radical pair mechanisms (RPM). The relative contributions of the two CIDEP mechanisms depend on solvent polarity and viscosity. In the case of the [Ru(R)(SnPh3)(CO)2(iPr-DAB)] complexes, the polarization pattern is also strongly excitation wavelength dependent. This effect is attributed to extremely fast reactions from different thermally nonequilibrated σ-bond-to-ligand charge transfer (SBLCT) excited states.