Microscopic chiral pockets in a tris(chelated) iridium(iii) complex as sites for dynamic enantioselective quenchingElectronic supplementary information (ESI) available: CD spectra of the enantiomers of [Ir(bzq)2(phen)]+; adsorption behaviour of Ir(iii) by clay minerals; quantum yield of Ir(iii) in various solvents; emission spectra of Ir(iii) in clay suspensions; stereochemical effects of emission from Ir(iii) adsorbed by SAP; enhancement of the luminescent quantum yield of [Ir(bzq)2(phen)]+ ads

• Main Authors: Takimoto, Kazuyoshi, Tamura, Kenji, Watanabe, Yutaka, Yamagishi, Akihiko, Sato, Hisako
• Format: Journal Article
• Language: English
• Published: 26.03.2018
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c7nj04688j

An attempt to develop a chiral luminescent probe with enantioselectivity is described. A tris(chelated) iridium( iii ) complex with bulky ligands, [Ir(bzq) 2 (phen)] + (bzqH = benzo[ h ]quinoline; phen = 1,10-phenanthroline), was synthesized and optically resolved into Δ- and Λ-enantiomers. The complex (denoted as Ir( iii )) was emissive in non-polar organic solvents, while in aprotic and protic polar solvents it was less emissive. When Ir( iii ) was adsorbed by the colloidal particles of synthetic saponite (denoted as SAP), it recovered its emitting capability even in a solvent containing water. Emission from Ir( iii ) adsorbed by SAP was quenched by adding [Ru(acac) 3 ] (acac = acetylacetonato, denoted as Ru( iii )). The Stern-Volmer constant ( K SV ) exhibited remarkable stereoselectivity; K SV = 15 900 ± 900 M −1 for Δ-Ir( iii )/Δ-[Ru(acac) 3 ] (or Λ-Ir(I iii )/Λ-[Ru(acac) 3 ]) and 7000 ± 500 M −1 for Δ-Ir( iii )/Λ-[Ru(acac) 3 ] (or Λ-Ir( iii )/Δ-[Ru(acac) 3 ]). The dependence of the emission lifetime on the concentration of Ru( iii ) indicated that quenching proceeded dynamically. On the basis of the molecular model, it was postulated that a microscopic pocket surrounded by the bulky ligands at the top of adsorbed Ir( iii ) acted as a site discriminating the chirality of an approaching molecule. A microscopic pocket surrounded by bulky ligands in Ir( iii ) acted as a site discriminating the chirality of an approaching molecule.