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)(S nPh3)(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 ra dicals show pronounced chemically induced dynamic electron polarization (CI DEP) effects due to the ST0 and ST-1 radical pair mechanisms (RPM). The rel ative 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 therm ally nonequilibrated sigma-bond-to-ligand charge transfer (SBLCT) excited s tates.