Hydrogen-bonded metal-organic frameworks with multilevel chirality and strong circular dichroism response for circular polarization luminescence

Abstract

In this work, a pair of chiral coordination compounds with formula as Cd[D-OH-bim]2(NO3)2 (1-D) and Cd[L-OH-bim]2(NO3)2 (1-L) (L-OH-bim = (L)-2-(1-Hydroxyethyl)benzimidazole; D-OH-bim = (D)- 2-(1-Hydroxyethyl)benzimidazole) are synthesized for circular polarization luminescence (CPL). Single crystal X-ray diffraction (SCXRD) results show that the 1-D and 1-L contain chiral Cd[OH-bim]2(NO3)2 units composed of Cd center and chiral OH-bim ligand (D- or L-OH-bim) as well as NO3–. The self-assembly of these chiral units by hydrogen bonding interaction generates a 3D hydrogen-bonded framework containing multiple chirality, such as chiral ligand, helical chain, chiral spatial arrangement and chiral framework (chiral space group and chiral topology). The bulk phase with multilevel chirality shows enhanced circular dichroism response and obvious CPL than that of the organic ligands as well as Cd[OH-bim]2(NO3)2 unit.