Allosteric Chiral Recognition of Eu(III) Complex for Chiral Co(III) Complex Observed by Time‐Resolved Circularly Polarized Luminescence Spectroscopy

Steady‐state and time‐resolved circularly polarized luminescence (CPL) are investigated for aqueous solutions of [Eu(pda) 2 ] − (pda = 1,10‐phenanthroline‐2, 9‐dicarboxylic acid) containing Δ/Λ‐[Co(en) 3 ] 3+ (en = ethylenediamine). CPL signals (| g lum | ≈ 0.2 at maximum) are observed for the solutions at the f–f transition in [Eu(pda) 2 ] − , where the sign depends on the chirality of [Co(en) 3 ] 3+ . The emission intensity decreases with the increase of concentration of [Co(en) 3 ] 3+ ([Co]). Time‐resolved emission measurements show that the temporal profiles are well reproduced by three emission lifetime components τ 1 ≈ 10 μs, τ 2 ≈ 40‐100 μs, and τ 3 ≈ 100‐750 μs, where the lifetimes depend on [Co]. The shorter lifetimes of τ 1 and τ 2 are attributed to associated species of [Eu(pda) 2 ] − and [Co(en) 3 ] 3+ , in which the energy transfer occurs. The time‐resolved CPL reveals that the τ 1 ‐ and τ 2 ‐components exhibit CPL, but the τ 3 ‐component exhibits no CPL signal. Mole‐ratio dependence of Δ/Λ‐[Co(en) 3 ] 3+ for the CPL signal shows that the CPL is exhibited from two associated species, such as [Eu(pda) 2 ] − ·{[Co(en) 3 ] 3+ } 2 , and the homo‐associated species are favored over hetero‐associated species. This indicates that a structural change induced by initial association of Δ/Λ‐[Co(en) 3 ] 3+ promotes further association of Δ/Λ‐[Co(en) 3 ] 3+ . This is a chiral recognition by allosteric effect.