APPLICATION OF CIRCULARLY-POLARIZED LUMINESCENCE SPECTROSCOPY TO THE SOLUTION STRUCTURE OF RACEMIC POLYAMINOCARBOXYLATE LANTHANIDE(III) COMPLEXES

Circularly polarized luminescence from 1:1 complexes of Eu(III) with triethylenetetra-aminehexaacetic acid (TTHA) following excitation with circularly polarized light is reported. This observation is consistent with a solution structure for this complex that is chiral, and stable on the emission time scale of Eu(III) (approximately 1.2 ms). Additional measurements show only a slight dependence on temperature, and an estimate for the activation energy for racemization (23 kcal/mol) may be obtained. Attempts at detecting enantio-selective quenching of Tb(TTHA)3- by optically active Ru(phen)2/3+ are also reported. Although significant quenching was observed, and the time-decay of the Tb(III) emission was not mono-exponential, no enantio-selectivity was found. This latter result may be interpreted in terms of the lack of discriminating short-range diastereomeric interactions between the chiral ion pairs.