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Studies on Monomers and Dimers of Y(III) and La(III) Porphyrin Complexes by Time-Resolved Electron Paramagnetic Resonance

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journal contribution
posted on 29.02.1996, 00:00 by Kazuyuki Ishii, Yasunori Ohba, Masamoto Iwaizumi, Seigo Yamauchi
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.