Pillararene-Based Supramolecular Polymers for Adsorption and Separation

Supramolecular polymers have attracted increasing attention in recent years due to their perfect combination of supramolecular chemistry and traditional polymer chemistry. The design and synthesis of macrocycles have driven the rapid development of supramolecular chemistry and polymer science. Pillar[n]arenes, a new generation of macrocyclic compounds possessing unique pillar-shaped structures, nano-sized cavities, multi-functionalized groups, and excellent host-guest complexation abilities, are promising candidates to construct supramolecular polymer materials with enhanced properties and functionalities. This review summarizes recent progress in the design and synthesis of pillararene-based supramolecular polymers (PSPs) and illustrates their diverse applications as adsorption and separation materials. All performances are evaluated and analyzed in terms of efficiency, selectivity, and recyclability. Typically, PSPs can be categorized into three typical types according to their topologies, including linear, cross-linked, and hybrid structures. The advances made in the area of functional supramolecular polymeric adsorbents formed by new pillararene derivatives are also described in detail. Finally, the remaining challenges and future perspectives of PSPs for separation-based materials science are discussed. This review will inspire researchers in different fields and stimulate creative designs of supramolecular polymeric materials based on pillararenes and other macrocycles for effective adsorption and separation of a variety of targets.

A pillar[5]arene noncovalent assembly boosts a full-color lanthanide supramolecular light switch

A photo-responsive full-color lanthanide supramolecular switch was constructed from a synthetic 2,6-pyridine dicarboxylic acid (DPA)-modified pillar[5]arene (H) complexing with lanthanide ion (Ln3+ = Tb3+ and Eu3+) and dicationic diarylethene derivative (G1) through a noncovalent supramolecular assembly. Benefiting from the strong complexation between DPA and Ln3+ with a 3 : 1 stoichiometric ratio, the supramolecular complex H/Ln3+ presented an emerging lanthanide emission in the aqueous and organic phase. Subsequently, a network supramolecular polymer was formed by H/Ln3+ further encapsulating dicationic G1via the hydrophobic cavity of pillar[5]arene, which greatly contributed to the increased emission intensity and lifetime, and also resulted in the formation of a lanthanide supramolecular light switch. Moreover, full-color luminescence, especially white light emission, was achieved in aqueous (CIE: 0.31, 0.32) and dichloromethane (CIE: 0.31, 0.33) solutions by the adjustment of different ratios of Tb3+ and Eu3+. Notably, the photo-reversible luminescence properties of the assembly were tuned via alternant UV/vis light irradiation due to the conformation-dependent photochromic energy transfer between the lanthanide and the open/closed-ring of diarylethene. Ultimately, the prepared lanthanide supramolecular switch was successfully applied to anti-counterfeiting through the use of intelligent multicolored writing inks, and presents new opportunities for the design of advanced stimuli-responsive on-demand color tuning with lanthanide luminescent materials.

Silica-based mesoporous ion-imprinted fluorescent sensors for the detection of Pb2+in aqueous environments

In this work, an environment-friendly core-shell material based on CDs@SiO₂as the core and mesoporous ion-imprinted layer as the shell was reported. As a highly sensitive and accurate fluorescent sensor for the detection of Pb²⁺in environmental water, the composition combined ion imprinting technology with quantum dots to selectively quench the fluorescence of CDs by metal coordination in the presence of Pb²⁺, and the visual change of gradually weakening blue color could be observed by the naked eye for visual detection. The mesoporous structure significantly improved the detection recognition rate of CDs@SiO₂@MIIPs.The molecularly imprinted sensor presented a favorable linear relationship over a Pb²⁺concentration range from 10 nmol l^-1to 100 nmol l^-1and a detection limit of 2.16 nmol l^-1for Pb²⁺. The imprinting factor of the CDs@SiO₂@MIIPs was 5.13. The sensor has a fast detection rate, is highly selective in the identification of Pb²⁺, and can be reused up to 10 times. The applicability of the method was evaluated by the determination of Pb²⁺in spiked environmental water samples with satisfactory results.

Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2

A novel gelator (1) based on a bis-pyridine derivative was designed and synthesized, which could form stable gels in methanol, ethanol, acetonitrile, ethyl acetate, DMF/H₂O (4/1, v/v) and DMSO/H₂O (4/1, v/v). The self-assembly process of gelator 1 was studied by field emission scanning electron microscopy (FESEM), UV–vis absorption spectroscopy, fluorescence emission spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction and a water contact angle experiment. Gelator 1 exhibited obvious AIE behavior. On the base of its AIE, the gel of 1 could detect Hg²⁺, which resulted in fluorescence quenching and a gel–sol transition. ¹H NMR titration experiments with Hg²⁺ revealed that the metal coordination interaction induced the fluorescence quenching and the breakdown of the noncovalent interaction in the gel system. This research provides a new molecular mode for designing a functional self-assembly gel system.

Recent Applications of Pillar[n]arene-Based Host-Guest Recognition in Chemosensing and Imaging

Pillar[n]arene is a novel kind of synthetic supramolecular macrocyclic host characterized by its particular pillar-shaped structure consisting of an electron-rich cavity and two finely adjustable rims. Benefiting from its rigid structure, facile synthesis, ease of functionalization, and outstanding host-guest chemistry, pillar[n]arene shows great potential for diverse applications. Significantly, the host-guest recognition of pillar[n]arene provides a novel approach for chemosensing and imaging. Herein, this Review critically and comprehensively reviews the applications of pillar[n]arene-based host-guest recognition in chemosensing and imaging. The sensing and imaging mechanisms as well as the unique roles and advantages of pillar[n]arene-based host-guest recognition are summarized. In addition, preparations of hybrid materials based on pillar[n]arene and inorganic materials are also introduced comprehensively in the light of chemosensing and imaging. Finally, current challenges and perspectives on pillar[n]arene-based host-guest recognition in chemosensing and imaging are outlined.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

Supramolecular Engineering Strategy to Construct BODIPY-Based White Light Emission Materials

Two kinds of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyads BDP-OH containing 4-hydroxystyrene groups and BDP-PY bearing pyridinyl units were prepared. In addition, a naphthalene derivative NAP-PY modified by pyridinyl moieties substituent was made. The above three dyads could be used to construct white-light emission (WLE) material by a supramolecular engineering strategy due to their three primary colors of blue, green and red. The supramolecular correlations between the hydroxyl group of BDP-OH and the pyridinyl groups of NAP-PY and BDP-PY were confirmed by ¹ H NMR titration, 2D NOESY and FTIR. A fluorescence monitor application was carried out based on the realization of WLE. This work might be useful for designing other WLE supramolecular systems and image display.