Magnetic Circular Dichroism Studies. 62.1Sign Variation in the Magnetic Circular Dichroism Spectra of Some Perimeter Symmetric Free-Base Porphyrins

Abstract
The MCD bands associated with the four lowest energy electronic transitions of perimeter symmetric porphyrin free-bases have commonly exhibited the “normal” sign pattern of -+-+ in the order of increasing energy. The first known exceptions to this rule, found in a series of tetrakis(o,o′-dihalophenyl)porphyrins, are presented in this communication. The sign inversions in the Q bands as well as the normal sign pattern in the Soret bands (overall pattern: +—+) can be understood on the basis of Michl's perimeter model.

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