EPR parameters such as zero-field splittings (zfs) and anisotropic g values of rare-earth metal centered porphyrin monomers, Y(TPP)+ and Y(OEP)+, and double-decker dimers, [Y(TPP)2]-, [Y(OEP)2]-, and [La(TPP)2]-, were measured in the lowest excited triplet (T1) states by a time-resolved electron paramagnetic resonance (TREPR) technique. The zfs parameter D of Y(OEP)+ was smaller than that of ZnOEP, and its gzz was smaller than that of Y(TPP)+. From the analyses of these data and the temperature dependence of the steady state EPR spectra, it was found that the decreases in the D and gzz values of Y(OEP)+ were due to a spin-orbit coupling between the Jahn-Teller split T1 and T2 states. By comparing the D values of the dimers with those of the corresponding monomers, we estimated a charge resonance character, b2, as 0.34, 0.26, and <0.25 for [Y(OEP)2]-, [Y(TPP)2]-, and [La(TPP)2]-, respectively. The b2 value was larger for the OEP dimer than those for the TPP dimers. We evaluated the b2 values using a semiempirical calculation and showed that b2 was larger for the 3(a1ueg) electronic configuration than that for the 3(a2ueg) configuration.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry