Analysis of enantioselective quenching of tris(2,6-pyridinedicarboxylate)terbate(3-) luminescence by resolved tris(1,10-phenanthroline)ruthenium(2+) in methanol and in water

Abstract

Circularly polarized luminescence is observed from racemic solutions of Tb( 2,6-pyridinedicarbo~ylate)~~ when small amounts of resolved Ru( 1 ,lO-phenanthr~line)~*+ are added. This phenomenon has been attributed to enantioselective quenching of the terbium complex by the ruthenium species, resulting in a nonracemic excited-state population. In this work, a simple kinetic scheme for this quenching process is presented, and it is demonstrated that the individual diastereomeric rate constants may be determined directly through numerical fitting of the biexponential decay of the total luminescence intensity. This is shown to give essentially the same results as numerical fitting of the time decay of the luminescence dissymmetry factor when data from both of these measurement techniques are available. It is also demonstrated that the enantioselectivity in the chiral quenching is solvent dependent. In aqueous solutions, for example, addition of A-(-)-Ru(phen)?+ results in an exam of L~-T~( D P A )~~-, Le., the A enantiomer is quenched more efficiently, whereas in methanol the opposite enantiomer is in excess.

Intermolecular chiral recognition processes probed by chiroptical luminescence

“…The influence of solvent on enantiopreferential quenching kinetics has been characterized for Ln(dpa) 3À 3 -Co(R,R-chxn) 3þ 3 systems in several amphiprotic solvents. [5][6][7][8]10 The results from previous studies combined with the results obtained in the present study provide an opportunity to compare the chirality-dependent quenching kinetics of Ln(dpa) The primary focus of the work presented in this article is to determine the sensitivity of quenching rate parameters (and enantioselectivity) to a change in solvent type (amphiprotic vs. aprotic solvent), and to changes in the cation of the Ln(dpa) ). Time-resolved chiroptical luminescence (TR-CL) measurement techniques are used to observe the Eu(dpa) 3À 3 -Co(R,R-chxn) 3þ 3 and Tb(dpa) 3À 3 -Co(R,R-chxn) 3þ 3 quenching processes, and the results of these studies are analyzed using a phenomenological model of the enantiopreferential quenching kinetics.…”

“…3+ are those that can provide acceptor levels for Eu*-to-Co and Tb*-to-Co energy transfer processes (where Eu* and Tb* denote Eu(dpa) 3À 3 and Tb(dpa) 3À 3 complexes in their 5 …”

Use of Polarization Spectroscopy in Studies of Lanthanide Complexes in Solution

“…It has also been demonstrated recently that non-racemic excited states can be generated from racemic ground states through enantioselective excited state quenching [19][20][21][22][23]. These experiments rely on the differential diastereomeric interaction between chiral acceptors and the racemic donor lanthanide complexes.…”

Circularly polarized luminescence and enantiomeric energy transfer discrimination of chiral Tb(III)–Nd(III) EDDS and related complexes

“…Using sharp and strong spectral lines of Tb(III) and Eu(III) ions as CPL probes, characterization of the chiral structures of various Ln(III) complexes in solution was performed from various points of view in the past 30 years. Enantiomeric discrimination of chiral energy transfer has been investigated mainly among racemic-Tb(III) dpa (dpa: dipicolinic acid) complexes and optical active Co(III) or Ru(II) complexes in solution [7][8][9][10][11][12]. Under circularly polarized light excitations, rac-Tb(III)dpa is considered to be optically resolved to pure enantiomers.…”