Acid/base responsive pseudo[3]rotaxanes from amine naphthotubes and bis-pyridinium/isoquinolinium guests.

A novel cooperative pseudo[3]rotaxane system was successfully constructed by the inclusion complexation of two identical amine naphthotubes with a bis-pyridinium/isoquinolinium guest. Single crystal structure analysis revealed that weak Csp3-H⋯O hydrogen bonds between the two hosts are responsible for the positive cooperativity during the formation of pseudo[3]rotaxanes. Moreover, intermolecular charge-transfer interactions between the electron-rich host and the electron-poor guests were observed. The pseudo[3]rotaxanes showed pH-controllable association/dissociation processes with naked-eye color changes in solution.

Biomimetic Hydrogen-Bonded G ⋠C ⋠G ⋠C Quadruplex within a Tetraphenylethene-Based Octacationic Spirobicycle in Water.

In biological systems, nucleotide quadruplexes (such as G-quadruplexes) in DNA and RNA that are held together by multiple hydrogen bonds play a crucial functional role. The biomimetic formation of these hydrogen-bonded quadruplexes captured by artificial systems in water poses a significant challenge but can offer valuable insights into these complex functional structures. Herein, we report the formation of biomimetic hydrogen-bonded G ⋅ C ⋅ G ⋅ C quadruplex captured by a tetraphenylethene (TPE) based octacationic spirobicycle (1). The spirobicyclic compound possesses a three-dimensional (3D) crossing dual-cavity structure, which enables the encapsulation of four d(GpC) dinucleotide molecules, thereby realizing 1 : 4 host-guest complexation in water. The X-ray structure reveals that four d(GpC) molecules further form a two-layer G ⋅ C ⋅ G ⋅ C quadruplex with Watson-Crick hydrogen bonds, which are stabilized within the dual hydrophobic cavities of 1 through the cooperative non-covalent interactions of hydrogen bonds, CH⋅⋅⋅π interactions, and hydrophobic effect. Due to the dynamically-rotational propeller chirality of TPE units, 1 with adaptive chirality can further serve as a chiroptical sensor to exhibit opposite Cotton effects with mirror-image CD spectra for the pH-dependent hydrogen-bonded assemblies of d(GpC) including the Watson-Crick G ⋅ C ⋅ G ⋅ C (pH 9.22) and Hoogsteen G ⋅ C+ ⋅ G ⋅ C+ (pH 5.74) quartets through the host-guest chirality transfer in water.

Precise Recognition in Water by an Endo-Functionalized Cavity: Tuning the Complementarity of Binding Sites.

Precise binding towards structurally similar substrates is a common feature of biomolecular recognition. However, achieving such selectivity-especially in distinguishing subtle differences in substrates-with synthetic hosts can be quite challenging. Herein, we report a novel design strategy involving the combination of different rigid skeletons to adjust the distance between recognition sites within the cavity, which allows for the highly selective recognition of hydrogen-bonding complementary substrates, such as 4-chromanone. X-ray single-crystal structures and density functional theory calculations confirmed that the distance of endo-functionalized groups within the rigid cavity is crucial for achieving high binding selectivity through hydrogen bonding. The thermodynamic data and molecular dynamics simulations revealed a significant influence of the hydrophobic cavity on the binding affinity. The new receptor possesses both high selectivity and high affinity, which provide valuable insights for the design of customized receptors.

Hierarchical Two-Level Supramolecular Chirality of an Achiral Anthracene-Based Tetracationic Nanotube in Water.

Herein, we report an achiral anthracene-based tetracationic nanotube (1⋅4Cl- ) that shows two levels of supramolecular chirality: namely, conformationally adaptive host-guest complexation with nucleoside triphosphates (e.g. ATP, GTP, CTP, and UTP) and twisted packing of the chiral host-guest complexes in water. Interestingly, achiral 1⋅4Cl- exhibits chiral recognition for ATP/GTP and CTP/UTP through structural transformation of its intramolecular M- and P-twisted conformation as the first level of supramolecular chirality, which leads to adaptive chirality with opposite CD responses. Furthermore, the formation of chiral M-1⋅4Cl- ⊃ATP can promote an intermolecular P-twisted dimeric packing of anthracene rings as the second level of supramolecular chirality to achieve assembled chirality with strong circularly polarized luminescence arising from the excimer ((+)-CPL, glum ≈10-2 ) in water.

Tetraphenylethene-Based Platinum(II) Bis-Triangular Dicycles with Tunable Emissions.

Tunable luminescent materials have attracted considerable interest for their wide applications in electronic optical devices, biological probes and sensors, tunable displays, and security technologies. Herein, we describe a strategy of coordination-driven self-assembly in order to prepare discrete tetraphenylethene-based platinum(II) bis-triangular dicycles 1 and 2 with aggregation-induced emission properties. The X-ray structure confirms that they possess two triangular cavities in which free rotation of the central TPE unit is restricted. As a kind of fluorescent material, the AIE-active dicycles have good emissions with wide tunability based on their aggregate states by changing different solvents, adjusting the temperature, or combining them with other dyes (e.g., perylene) via a co-assembly process.

Aggregation-Induced Emission and Light-Harvesting Function of Tetraphenylethene-Based Tetracationic Dicyclophane.

Here we report one-pot synthesis of tetraphenylethene-based tetracationic dicyclophane (1) and its self-assembly behaviors with aggregation-induced emission (AIE) and light-harvesting function. Confirmed by X-ray crystal structure and high resolution transmission electron microscopy, this tetracationic dicyclophane can self-assemble into a 3D supramolecular framework to form crystalline nanospheres (2) finally, which exhibits a strong emission (ΦF = 97.7%) via AIE effect in aqueous solution. Interestingly, AIE-active 2 as a single-molecule-based fluorescent supramolecular platform can encapsulate an organic dye (e.g., Nile red) to form light-harvesting nanospheres (3) further with a large red-shift (Δλ = ∼70 nm), highly efficient energy-transfer ability (ΦET = 77.5%), and high antenna effect (14.3).

Cucurbit[10]uril-Based [2]Rotaxane: Preparation and Supramolecular Assembly-Induced Fluorescence Enhancement.

As the cucurbit[n]uril (CB[n]) homologue with the largest cavity size, cucurbit[10]uril (CB[10]) can encapsulate big guests to form interesting host-guest complexes/assemblies. Herein, we report the preparation and fluorescence properties of CB[10]-based [2]rotaxane (CB[10]·1) formed from cucurbit[10]uril and dumbbell-like guest 1. This [2]rotaxane (CB[10]·1) is assembled by C═O···N+ ion-dipole interactions between oxygen atoms of the carbonyl fringed portals of CB[10] and the positively charged pyridinium units of 1 via the slipping method under heating at 95 °C in DMSO. In contrast, other cucurbit[n]uril (CB[n], n = 6-8) homologues cannot form rotaxanes with 1 due to their smaller cavities. The dumbbell-like guest 1 is a poor emitter in DMSO. Interestingly, the formation of CB[10]·1 renders the restriction of intramolecular rotation of TPE, which features a strong fluorescent intensity, long lifetime, and high quantum yield. Furthermore, CB[10]·1 is shown to aggregate plate-like structures with various sizes in different solvents (DMSO, THF, or CHCl3), resulting in a stepwise aggregation-induced emission enhancement effect. This kind of CB[10]-based [2]rotaxane may be used to fabricate luminescent systems with unique emission properties.

Unraveling the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in aqueous host-guest complexation.

In biological systems, nucleosides play crucial roles in various physiological processes. In this study, we designed and synthesized four achiral anthracene-based tetracationic nanotubes (1-4) as artificial hosts and chiroptical sensors for nucleosides in aqueous media. Notably, different nanotubes exhibit varied chirality sensing on circular dichroism (CD)/circularly polarized luminescence (CPL) spectra through the host-guest complexation, which prompted us to explore the factors influencing their chiroptical responses. Through systematic host-guest experiments, the structure-chirality sensing relationship between achiral anthracene-based tetracationic nanotubes and nucleosides in the host-guest complexation was unraveled. Firstly, the CD response originates from the anthracene rings situated at the side-wall position, resulting from the right-handed (P)- or left-handed (M)-twisted conformation of the macrocyclic structure. Secondly, the CPL signal is influenced by the presence of anthracene rings at the linking-wall position, which results from intermolecular chiral twisted stacking between these anthracene rings. Therefore, these nanotubes can serve as chiroptical sensor arrays to enhance the accuracy of nucleotide recognition through principal component analysis (PCA) analysis based on the diversified CD spectra. This study provides insights for the construction of adaptive chirality from achiral nanotubes with dynamic conformational nature and might facilitate further design of chiral functional materials for several applications.

Selective recognition and enrichment of C70 over C60 using an anthracene-based nanotube.

Selective recognition and enrichment of fullerenes (e.g., C60 and C70) remains challenging due to the same diameter and geometrical similarity. Herein, we report a hexagonal anthracene-based nanotube (1) through a one-pot Suzuki-Miyaura cross-coupling reaction. With anthracene-based side walls and pyridine linkers, 1 features a nano-scale tubular cavity measuring 1.2 nm in diameter and 0.9 nm in depth, along with pH-responsive properties. Interestingly, the electron-rich 1 shows high binding affinity (K a ≈ 106 M-1) and selectivity (K s ≈ 140) to C70 over C60 in toluene, resulting from their different contribution of π-π interactions with the host. The protonation of 1 simultaneously alters the electronic properties within the nanotube, resulting in the release of the fullerene guests. Lastly, the selective recognition and pH stimuli-responsive properties of the nanotube have been utilized to enrich C70 from its low-content mixtures of fullerenes in chloroform.

Chiral recognition of neutral guests by chiral naphthotubes with a bis-thiourea endo-functionalized cavity.

Developing chiral receptors with an endo-functionalized cavity for chiral recognition is of great significance in the field of molecular recognition. This study presents two pairs of chiral naphthotubes containing a bis-thiourea endo-functionalized cavity. Each chiral naphthotube has two homochiral centers which were fixed adjacent to the thiourea groups, causing the skeleton and thiourea groups to twist enantiomerically through chiral transfer. These chiral naphthotubes are highly effective at enantiomerically recognizing various neutral chiral molecules with an enantioselectivity up to 17.0. Furthermore, the mechanism of the chiral recognition has been revealed to be originated from differences in multiple non-covalent interactions. Various factors, such as the shape of cavities, substituents of guests, flexibility of host and binding modes are demonstrated to contribute to creating differences in the non-covalent interactions. Additionally, the driving force behind enantioselectivity is mainly attributed to enthalpic differences, and enthalpy -entropy compensation has also been observed to influence enantioselectivity.

Adaptive chirality of achiral tetraphenylethene-based tetracationic cyclophanes with dual responses of fluorescence and circular dichroism in water.

Two tetraphenylethene-based tetracationic cyclophanes 1 and 2 were synthesized via a one-step SN2 reaction without using any template. Based on the fluorescence and rotational conformation of the tetraphenylethene units, these water-soluble cyclophanes exhibited adaptive chirality with dual responses of turn-on fluorescence and induced circular dichroism when combined with nucleotides and DNA in water.

Synthesis and aqueous anion recognition of an imidazolium-based nonacationic cup.

An imidazolium-based nonacationic cup (1·9X; X = PF6- or Cl-) was synthesized via step-by-step SN2 reactions without using any template. The water-soluble 1·9Cl- as a molecular container can encapsulate anionic nucleoside triphosphate and dinucleotide molecules (e.g., ATP and NADH) inside its cavity through hydrogen bonds and electrostatic interactions in aqueous solution.

Tetraphenylethene-based tetracationic dicyclophanes: synthesis, mechanochromic luminescence, and photochemical reactions.

Two tetraphenylethene-based tetracationic dicyclophanes 1 and 2 were synthesized via a one-step SN2 reaction. Based on the central TPE unit and the slight difference of the outer linkers, 1 and 2 exhibited a classic aggregation-induced emission but contrasting mechanochromic luminescence under grinding, vaporing, or hydrostatic pressure in the solid state, and photochemical reactions with various emitting colours induced by photoirradiation in the solution state.