Electronic absorption spectra of copper corroles: unexpected substituent effects in trans-meso-A2B-triarylcorrole complexes

The Soret maxima of copper triarylcorroles are exquisitely sensitive to substitutions on the meso phenyl groups. Similar substituent effects are also known, in more muted form, for Mn and Fe corroles. In contrast, the Soret maxima Ag, CrO and MoO triarylcorroles are essentially invariant with respect to phenyl-group substituents. TDDFT calculations suggest that the unique substituent sensitivity in the copper case results from phenyl-to-Cu(d(x2-y2)) charge transfer character in the main peaks of the Soret region. To probe the phenonmenon in even greater depth, we have examined here the electrochemistry and electronic absorption spectra of a series of copper trans-A(2)B-triarylcorrole complexes, where the para substituents on the aryl groups include CF3, H, CH3, and OCH3. Although both 5,15- and 10-substituents appear to influence the oxidation and reduction potentials of the copper corroles in a simple, additive manner, they affect the Soret maxima very differently. Thus, for a given 10-substituent, 5,15-aryl substituents exert a strong, "normal" substituent effect on the Soret maximum. For given 5,15-substituents, however, the 10-substituent has almost no effect on the Soret maximum. An attempt has been made to relate these somewhat curious observations to a molecular orbital picture based on copper triphenylcorrole.