Asymmetric induction in quadruple-stranded europium(iii) helicates and circularly polarized luminescence. Issue 29 (4th July 2022)

• Record Type: Journal Article
• Authors: Wang, Yunlu; Zhou, Yanyan; Yao, Zhiwei; Huang, Wenru; Gao, Ting; Yan, Pengfei; Li, Hongfeng
• Is Part Of: Dalton transactions. Volume 51:Issue 29(2022)
• Page Start: 10973
• Page End: 10982
• Publication Date: 2022-07-04
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/d2dt01379g
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Chiral guanidine as counterions of achiral quadruple-stranded dinuclear europium(iii ) helicates, [Eu2 L 4 ] 2−, breaking the racemization equilibrium of assemblies and inducing the circularly polarized emission from Eu 3+ ions. Abstract : Chiral supramolecular lanthanide-helicates are regarded as promising chiroptical materials due to their combination of ground and excited state chirality and special luminescence properties from Ln 3+, named circularly polarized luminescence (CPL). However, the sophisticated and costly asymmetric syntheses decelerate their research progress. Herein, a chiral induction strategy is employed to break the racemic equilibrium of lanthanide helicate by the formation of a compact ion pair. The synthesized chiral guanidine cation (( R / S )-HG) helps to effectively transfer chirality to anionic quadruple-stranded helicate by electrostatic, H bonds, and multiple C–H⋯F and N–H⋯F interactions. The diastereoselective control was confirmed by X-ray crystallography and CD and CPL spectroscopy, where ( S )-HG prefers to bind a P (ΔΔ) helical enantiomer, in contrast a M helicate for ( R )-HG. Additionally, the inconsistency of CD and CPL spectra in assessing the perturbation of a racemic equilibrium discloses their complementary advantages on monitoring molecular chirality. In the case of diastereomeric enrichment equilibrium, three pairs of helicates show high luminescence quantum yields of 42%–54%, and large | g lum | with the values of 0.137–0.266. This work provides an effective strategy to synthesize excellent CPL materials based on racemic lanthanide helicate.