Emission detected circular dichroism from long-lived excited states: application to chiral Eu(III) systems

The measurement of the difference in intensity of luminescence following excitation with left and right circularly polarized light for racemic terdentate Eu(III) complexes with 2,6-pyridine dicarboxylic acids perturbed by the addition of (+)-dimethyltartrate and for tris chiral complexes of Eu(III) with (R,R)-N,N'-bis(1-phenylethyl)-2,6-pyridine-dicarboxamide are presented. The experimental technique used for these measurements is identical in design to fluorescence detected circular dichroism spectroscopy, but is referred to in this manuscript as emission detected circular dichroism (EDCD) because of the long lifetime of the Eu(III) excited state requiring specialized instrumentation. These measurements required relatively slow modulation of the incident circular polarization, which was accomplished with a liquid crystal polarizer. The results are compared with conventional CD measurements, and additional characteristics and potential applications of EDCD are presented.