Photophysical observations on Cr(III) bis-cyclam dimers

Chromium(III) complexes of the mononucleating cyclam, ([14]aneN4)X2, and binucleating biscyclam, ([14]aneN4)2X4, ligands were prepared and their photophysical properties examined. Acido amine cis-monomer and cis,cis-dimer pairs containing X=chloro, bromo and thiocyanato complexes were examined for photophysical manifestations of metal–metal coupling in these saturated macrocyclic systems. UV–vis absorption and emission show anomalous features in the dimer spectra versus their monomer parents for the bromo and thiocyanato complexes in accord with what would be predicted based on a charge transfer mediated exchange process; however, the excited state properties of these molecules show an opposite behavior and thus an interpretation of the observed behavior based on an exchange mechanism is not possible.