Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Selective Detection of Fe3+, F-, and Cysteine by a Novel Triazole-Linked Decaamine Derivative of Pillar[5]arene and Its Metal Ion Complex in Water

Appropriately functionalized pillar[n]arenes are elegant supramolecular hosts for ion and molecule sensing. A water-soluble decaamine derivative of pillar[5]arene (APA) bearing triazole and amide moieties is synthesized. The ion and molecular recognition properties of APA are studied by fluorescence, UV-visible, and ¹H nuclear magnetic resonance (NMR) spectroscopy. The APA selectively detects Fe³⁺ among 11 studied ions, which are important in several biological processes. Moreover, the in situ prepared Fe³⁺ complex of APA (FeAPA) exhibits the highest responsiveness toward F^- (∼12-fold) among 11 anions and cysteine (∼120-fold) among the 20 naturally occurring amino acids by a fluorescence turn-on mechanism.

A Luminescent Probe for Ratiometric Optical Detection of HgII and Turn-On Fluorescent Sensing of CuII

Luminescent detection of heavy metals continues to be of growing importance considering their increasing inseparable roles in modern day lifestyle. To this end, we report a simple yet interesting thiourea derivative that results in detection of Cu^II in a turn-on fashion via a chemodosimetric redox reaction leading to oxidative cyclization of the chemosensor molecule. Elaborate studies with regard to the sensing process have been performed along with the proposal of a plausible cyclization mechanism of the molecule. Furthermore, the probe optically detects Hg^II , yet another heavy metal of prime importance, discernable even to the naked eye. The occurrence of a coordination complex has been proved by UV/Visible spectroscopic experiments as well as ESI-mass spectrometry.

Supramolecular neuromuscular blocker inhibition by a pillar[5]arene through aqueous inclusion of rocuronium bromide

A water-soluble pillar[5]arene, decafunctionalized with thioether and carboxylate fragments, was synthesized as a structural analogue of Sugammadex. Its ability to restore the contraction of the diaphragm muscle by encapsulating the muscle relaxant rocuronium bromide was demonstrated. Using UV-vis, NMR and fluorescence spectroscopy, it was shown that the muscle relaxant is associated with the pillar[5]arene with an association constant of 4500 M-1 and a stoichiometry of 1 : 1. The structure of the inclusion complex of the pillar[5]arene with rocuronium bromide was additionally investigated by quantum chemical methods.

A novel boronic acid-based fluorescent sensor for selectively recognizing Fe3+ ion in real time

Boronic acid provides faster fluorescence response to Fe3+ compared to other reported sensors, which is critical for continuous dynamic detection. Herein, we reported a novel boronic acid-based sensor 4 that could recognize Fe3+ ion in real time. After 10 equiv. of Fe3+ ion (1 mM) was added, the fluorescence of sensor 4 was immediately quenched by 96%. While other ions, including Ba2+, Ca2+, Cr2+, Cd2+, Co2+, Cs2+, Cu2+, Fe2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+ or Zn2+, respectively, did not change the fluorescence significantly. Further tests indicated that the high selectively sensing Fe3+ ion benefits from the two boronic acid functionalities in the structure. Moreover, interference experiments showed this sensor has an excellent anti-interference ability. In addition, we performed binding activity test in rabbit plasma and other real samples for practical applications, obtaining similar results. And the thin layer loading sensor 4 was also successfully applied to recognize Fe3+ ion among various ions. Therefore, 4 may serve as a potential sensor for continuous monitoring and detecting Fe3+ ion in real time.

Water-soluble diboronic acid-based fluorescent sensors recognizing d-sorbitol

Water-soluble diboronic acid sensor 15c exhibited higher selectivity for d-sorbitol than monoboronic acid sensor 1 and hydroxy derivative 2. And it could be applied for d-sorbitol sensing and analysis in real samples.

A water-soluble fluorescent chemosensor based on Asp functionalized naphthalimide for successive detection Fe3+ and H2PO4−

The selective recognition of target ions in water is very important and the development of novel water-soluble chemosensor is still an intriguing challenge. Herein, a novel water-soluble fluorescent sensor based on aspartic acid (Asp) functionalized 1,8-naphthalimide derivative (Asp-NI) has been designed and synthesized. The sensor Asp-NI could dissolve in water and successively detect Fe3+ and H2PO4− in water solution with high selectivity and sensitivity. The detection limits are 4.97 × 10−7 mol/L for Fe3+ and 5.27 × 10−6 mol/L for H2PO4−. Other coexistent competitive metal ions (Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, and Mg2+) showed no interference in the Fe3+ detection process. The sensor Asp-NI could act as a Fe3+ and H2PO4− controlled “On–Off–On” fluorescent switch. More interestingly, the Fe3+ induced fluorescence quenching process could be totally reversed by the addition of H2PO4−, this “On–Off–On” switching process could be repeated several times with little fluorescence loss. Notably, the actual usage of sensor Asp-NI was further demonstrated by test kits.

A water-soluble pillar[5]arene-based chemosensor for highly selective and sensitive fluorescence detection of l-methionine

Cationic pillar[5]arene (AWP5) was employed as a water-soluble chemosensor for recognition of amino acids. AWP5 could fluorescently detect l-methionine in water with high selectivity and sensitivity.

A novel iodination-triggered competitive coordination mechanism: indirect detection of Hg2+and I−using a simple copillar[5]arene-based fluorometric sensor

Proposed mechanism for the detection of Hg²⁺and I⁻byDBP5.

A copillar[5]arene-based fluorescence “on–off–on” sensor is applied in sequential recognition of an iron cation and a fluoride anion

A copillar[5]arene-based [c2]daisy-chain dimer is applied in sequential detection of Fe³⁺ and F⁻ through a competitive complexation reaction.

Construction of stimuli-responsive supramolecular gel via bispillar[5]arene-based multiple interactions

A linear supramolecular polymer has been constructed from host–guest recognition. Furthermore, the linear supramolecular polymer could self-assemble to form a supramolecular gel at high concentration, which exhibited external stimuli-responsiveness.

Pillararene-based fluorescent chemosensors: recent advances and perspectives

This feature article summarizes recent research in the pillararene-based fluorescent chemosensor field in terms of ion sensing, small molecule recognition, biomolecule detection, fluorescent supramolecular aggregates, and biomedical imaging.

Configuration-independent AIE-active supramolecular polymers of cyanostilbene through the photo-stable host–guest interaction of pillar[5]arene

We report a cyanostilbene system with retained AIE activity at Z and E isomeric state through host–guest of pillar[5]arene.

A novel functionalized pillar[5]arene-based selective amino acid sensor forl-tryptophan

The sensing mechanism of the sensorBTAP5forl-Trp.

Pillar[5]arene-based fluorescent polymer for selective detection and removal of mercury ions

A novel pillar[5]arene-based fluorescent polymer has been synthesized, and it is used for fluorescence detection and removal of the toxic mercury ions.

Efficient sensing of fluoride ions in water using a novel water soluble self-assembled supramolecular sensor based on pillar[5]arene

By rationally introducing competitive coordination, the supramolecular sensors could reversibly sense Fe³⁺ and F⁻ in water with high selectivity and sensitivity.