Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

Shape-Persistent Triptycene-Derived Pillar[6]arenes: Synthesis, Host-Guest Complexation, and Enantioselective Recognitions of Chiral Ammonium Salts

Construction of macrocyclic hosts with a novel structure and excellent property has emerged as an intriguing undertaking for the past few years. Here, we reported the synthesis of shape-persistent triptycene-derived pillar[6]arene (TP[6]). The single crystal structure analysis revealed that the macrocyclic molecule adopts a hexagonal structure, featuring a helical and electron-rich cavity capable of encapsulating electron-deficient guests. In order to obtain chiral TP[6] from an enantiomerically pure triptycene building block, an efficient resolution of chiral triptycene was successfully developed through introducing chiral auxiliaries into triptycene skeletons. The ¹H NMR and isothermal titration calorimetry investigations demonstrated that chiral TP[6] exhibited enantioselectivity toward four pairs of chiral guests containing a trimethylamino group, implying a significant promising application in area of enantioselective recognition.

Advances in Chirality Sensing with Macrocyclic Molecules

The construction of chemical sensors that can distinguish molecular chirality has attracted increasing attention in recent years due to the significance of chiral organic molecules and the importance of detecting their absolute configuration and chiroptical purity. The supramolecular chirality sensing strategy has shown promising potential due to its advantages of high throughput, sensitivity, and fast chirality detection. This review focuses on chirality sensors based on macrocyclic compounds. Macrocyclic chirality sensors usually have inherent complexing ability towards certain chiral guests, which combined with the signal output components, could offer many unique advantages/properties compared to traditional chiral sensors. Chirality sensing based on macrocyclic sensors has shown rapid progress in recent years. This review summarizes recent advances in chirality sensing based on both achiral and chiral macrocyclic compounds, especially newly emerged macrocyclic molecules.

Solvent-Driven Chirality Switching of a Pillar[4]arene[1]quinone Having a Chiral Amine-Substituted Quinone Subunit

Several new chiral pillar[4]arene[1]quinone derivatives were synthesized by reacting pillar[4]arene[1]quinone (EtP4Q1), containing four 1,4-diethoxybenzene units and one benzoquinone unit, with various chiral amines via Michael addition. Due to the direct introduction of chiral substituents on the rim of pillar[n]arene and the close location of the chiral center to the rim of EtP4Q1, the newly prepared compounds showed unique chiroptical properties without complicated chiral resolution processes, and unprecedented high anisotropy factor of up to −0.018 at the charge transfer absorption band was observed. Intriguingly, the benzene sidearm attached pillar[4]arene[1]quinone derivative 1a showed solvent- and complexation-driven chirality inversion. This work provides a promising potential for absolute asymmetric synthesis of pillararene-based derivatives.

Effective enantiomeric identification of aromatic amines by tyrosine-modified pillar[5]arenes as chiral NMR solvating agents

Two novel tyrosine-modified pillar[5]arenes have been synthesized and applied as chiral NMR solvating agents to establish an efficient ¹H NMR method for enantioselective recognition and configuration assignment towards α-aromatic ethylamines.

A Chiral Metal-Organic 1D-Coordination Polymer Upon Complexation of Phenylene-Bridged Bipyrrole and Palladium (II) Ion

Metal-organic 1D-coordination polymers, having unique electronic and optical properties, are expected to be a novel advanced functional material capable of fabricating smart plastics, films, and fibers. In this study, we have synthesized a novel metal-organic 1D-coordination polymer composed of a phenylene-bridged bipyrrole bearing N-alkylimino groups (BPI) and palladium(II) ion. The BPI and Pd(II) form square planar bis(bidentate) complex to form a metal coordinated π-conjugation polymer (Poly-BPI/Pd). It is stable in solutions at room temperature, and allowed measurement of its average molecular weight in SEC (M w = 106,000 and M n = 18,000, M w/M n = 5.88). It also provided a reversible multi redox profile in cyclic voltammetry, most likely originating from strong π-electronic interactions between the BPI components via Pd ion. A variety of substituent groups can be attached to the imino-nitrogens of BPI. A coordination polymer composed of a BPI derivative bearing chiral alkyl chains and Pd(II) showed strong circular dichroism (CD) in the solution due to the unidirectional chiral conformation of the BPI components in the polymer backbone.

Oxacalix[4]arene-bridged pillar[5]arene dimers: syntheses, planar chirality and construction of chiral rotaxanes

Conformationally fixed oxacalix[4]arene-bridged pillar[5]arene dimers comprising a pair of enantiomers and a meso isomer were designed and synthesized. Furthermore, chiral [2]rotaxanes and [3]rotaxanes were constructed. Two pairs of enantiomers for [2]rotaxanes, one pair of enantiomers and a meso isomer for [3]rotaxanes were found, respectively.

Redox-Triggered Chirality Switching and Guest-Capture/Release with a Pillar[6]arene-Based Molecular Universal Joint

A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene-based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self-inclusion and self-exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redox-triggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.