Magnetic circular dichroism studies. Part XXVI. Magnetic circular dichroism spectra of porphyrin dianions

Abstract

The m.c.d. spectra of alkyl-substituted porphyrin dianions show a positive A term for the Q_0–0 band and unresolved A-terms in the Q_0–1 band. A major difference with respect to the corresponding dications is the lower intensity of a negative A term for one vibronic component of the Q_0–1 band in the dianions. Magnetic moments of 2·3–3·1 Bohr magnetons were obtained by curve fitting for the Q_0–0 band. Moment analysis for the entire Q band gave smaller values of 0·6–1·5 Bohr magnetons. This discrepancy is interpreted to be a consequence of the weakly allowed character of the transition. The corresponding porphyrin dications were found to have smaller magnetic moments. Identification of the Q_0–0 band in the m.c.d. spectrum of porphin dianion is difficult, because of its low intensity.