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 1.2ms). 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. © 1994

Linearly polarized luminescence spectra of Eu(2,6-pyridine-dicarboxylate) \u3c sup\u3e 3- \u3c/sup\u3e \u3c inf\u3e 3 in hydroxylic solution

Emission spectra and linearly polarized emission spectra are reported for Eu(2,6-pyridine-dicarboxylateDPA)3-3 in a hydroxylic glass (water/ethylene glycol, 1:2 by volume) at 157 K. The splitting pattern of the 7FJ←5D0(J=1, 2, 4) emission bands (in order of decreasing energy A2, E; E, E and E, A2, E, E) and their polarization anisotropies upon 465.8 nm irradiation are consistent with the complex having approximate D3 symmetry. The two 7F1←5D0 bands have predominantly (≳80%) magnetic dipole character. The polarization data upon excitation in the 290 nm absorption show that this band involves π→π* ligand transitions, polarized perpendicular to the C2 axis of the DPA ligand. The angle between the C3 axis of the complex and the normal vector to the plane of the pyridine ring is found to be 41°±5°. © 1993

Effect of applied hydrostatic pressure on the enantioselective quenching of the luminescence from rac-tris(2,6-pyridinedicarboxylate)terbium(III) by resolved tris(1,10-phenanthroline)ruthenium(II) in water and methanol

The effect of applied hydrostatic pressure on the enantioselective excited-state quenching of rac-tris(2,6-pyridinedicarboxylate)terbium(III) [Tb(DPA)33-] by optically active tris(1,10-phenanthroline)ruthenium(II) [Ru(phen)32+] is presented. The time dependence of the excited-state luminescence is analyzed in terms of a biexponential decay at pressures from 1 bar to 3 kbar corresponding to the diastereomeric (Δ-Δ and Δ-Δ) quenching reactions. In water solution it is found that the diastereomeric quenching rates and enantioselectivity increase with pressure, while in methanol solution the quenching rates and enantioselectivity decrease. The results are interpreted in terms of a detailed model for the quenching involving solvation effects within the diastereomeric encounter complexes

Comparison of the enantioselective quenching of the luminescence of Dy(III) and Tb(III) tris complexes of 2,6-pyridinedicarboxylate by resolved Ru(1,10-phenanthroline) \u3c inf\u3e 3 \u3c sup\u3e 2+ \u3c/sup\u3e

Comparison is made between the enantioselective excited-state quenching of optically active tris-terdentate D3 complexes of Tb(III) and Dy(III) with 2,6-pyridinedicarboxylate by resolved Ru(1,10-phenanthroline)32+. It is found that the enantioselective quenching of the two species display almost identical dependence on temperature and solvent composition. The quenching is discussed within the contexts of a simple model involving encounter pair formation, reorientation, and energy transfer. From the results given, it is concluded that the enantioselectivity in the quenching does not depend significantly upon the nature of the chiral electronic states of the donor lanthanide ions but rather has its origin in stereochemical structural aspects of the encounter pair formed between the oppositely charged chiral complexes. © 1993 American Chemical Society