Enantioselective assembly of multi-layer 3D chirality

Abstract

The first enantioselective assembly of sandwich-shaped organo molecules has been achieved by conducting dual asymmetric Suzuki-Miyaura couplings and nine other reactions. This work also presents the first fully C-C anchored multi-layer 3D chirality with optically pure enantiomers. As confirmed by X-ray diffraction analysis that this chiral framework is featured by a unique C₂ -symmetry in which a nearly parallel fashion consisting of three layers: top, middle and bottom aromatic rings. Unlike the documented planar or axial chirality, the present chirality shows its top and bottom layers restrict each other from free rotation, i.e., this multi-layer 3D chirality would not exist if either top or bottom layer is removed. Nearly all multi-layered compounds showed strong luminescence of different colors under UV irradiation, and several randomly selected samples displayed aggregation-induced emission (AIE) properties. This work is believed to have broad impacts on chemical, medicinal and material sciences including optoelectronic materials in future.

Keywords: C2-symmetry; aggregation-induced emission (AIE); architecture chirality; multi-layer 3D chirality; multi-layered organic framework (M-LOF); organo sandwich chirality.

Figure 1.

(a) Multi-layer 3D chiral sandwich-shaped molecules. (b) Design of fully C-C bond-anchored chiral multi-layer 3D frameworks. (c) RSA of fully C-C bond-anchored multi-layer 3D targets.

Figure 2.

(a) Synthesis of 4,7-bis(8-bromonaphthalen-1-yl)benzo[c][1,2,5]thiadiazole. (b) Synthesis of chiral 1-arylethylamine or alkylethylamine-attached boronic acids. (c) Synthesis of chiral 1-arylethylamine-derived boronic acids.

Figure 3.

(a) Synthetic results of chiral multi-layer 3D amides. (b) Alternative approaches to chiral multi-layer 3D amides. (c) Synthetic results of chiral multi-layer 3D amides by using branched boronic acids. (d) Synthesis of 4,9-bis(8-phenylnaphthalen-1-yl)naphtho[2,3-c][1,2,5]thiadiazole. Chemical structures in Schemes/Figures are only for concise pictorial presentation; X-ray pictures should be followed by real stereochemical purposes. ^aCombined yields of two diastereoisomers; ^bdetermined by proton NMR.

Figure 4.

(a) and (b) Results of free diamines and N-carbonyl-protected multi-layer 3D chiral compounds. (c) Converting diastereomeric isomers into enantiomers under mild conditions.

Figure 5.

(a) Macrochirality phenomenon of 10e: image under natural light with black background (A1); image under UV light (365 nm) (B1); image under natural light after rotavapor evaporation (C1). Fluorescence images of 16 under different physical conditions (A2, appearance under natural lights; B2, UV irradiation in natural background; C2, UV irradiation in dark background). Spiro textile-type of macro-chirality of 18e formed inside NMR tube (A3 and B3); luminescence of samples under UV light (365 nm): A4-A8 without UV irradiation, B4-B8 with UV irradiation. (b) Photoluminescence (PL) spectra of 10a, 13a, 16, 17, 18e, 18f, 20b, 21b and 21f as solid test samples; excitation wavelength (λ_ex): 532 nm.

Figure 6.

(a) Luminescence of CDCl₃ solutions of samples 17, 18e and 18f in NMR tubes, [c] (mg/ml): A, left = 6.7 and right = 2.2; B, left (18e) and right (18f) = 8. (b) PL spectra of 17 in THF/water mixtures with different water fractions (f_w); c = 1 μM; excitation wavelength (λ_ex): 532 nm. (c) AIE displays of multi-layer 3D molecules: 10a; 18f and 16 in THF/water systems; [c] (M).