Magnetic circular dichroism of charge-transfer and coupled-chromophore systems

Abstract

The megnetic circular dichroism (MCD) of 1,10-phenanthroline and of its chelate complexes, [Cu(phen)₂]⁺, and [M(phen)₃]²⁺, where M is an iron-group or group 2B metal ion, have been recorded over the frequency range 16 000–50 000 cm^–1. The results show that the strong p-and β-band of phenanthroline at 37 000 and 44 000 cm^–1, respectively, are mutually perpendicularly polarized, and that the weaker α-band at 30 000 cm^–1 has vibronic components of mixed polarization. There is no inter-ligand exciton contribution to the Faraday terms governing the MCD in the ligand absorption region of the spectra of the complex ions, the MCD of the complex resembling that of the free ligand in this region. The charge-transfer band of the copper(I) and iron-group metal complexes is associated with an A-term in the MCD spectrum, indicating that the hole generated in the d¹⁰ or strongfield d⁶ ground electron configuration by the charge-transfer excitation lies partly, or largely, respectively, in an orbital doublet in the excited state.