The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands

Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as Eu(III), Tb(III) and Sm(III)) or near infrared emitting ions (like Nd(III), Yb(III) and Er(III)), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.

High yielding synthesis of 2,2'-bipyridine macrocycles, versatile intermediates in the synthesis of rotaxanes

We present an operationally simple approach to 2,2'-bipyridine macrocycles. Our method uses simple starting materials to produce these previously hard to access rotaxane precursors in remarkable yields (typically >65%) across a range of scales (0.1-5 mmol). All of the macrocycles reported are efficiently converted (>90%) to rotaxanes under AT-CuAAC conditions. With the requisite macrocycles finally available in sufficient quantities, we further demonstrate their long term utility through the first gram-scale synthesis of an AT-CuAAC [2]rotaxane and extend this powerful methodology to produce novel Sauvage-type molecular shuttles.

Imaging agents

Guest editors Christopher J. Chang, Thorfinnur Gunnlaugsson and Tony D. James introduce the Imaging Agents issue of Chemical Society Reviews

Self-assembly of a redox active water soluble Pd6L8 ‘molecular dice’

Self-assembly of a water soluble redox active Pd(ii) “molecular dice” was achieved employing a tri-cationic donor. The Pd₆ dice is quite stable in water in a wide range of temperatures despite the expected weaker donor ability of the cationic pyridyl donor.

A single-step acid catalyzed reaction for rapid assembly of NH-1,2,3-triazoles

NH-1,2,3-Triazole moieties are a part of the design of various biologically active compounds, pharmaceutical agents and functional materials.

Bodipy-C60 triple hydrogen bonding assemblies as heavy atom-free triplet photosensitizers: preparation and study of the singlet/triplet energy transfer

Supramolecular triplet photosensitizers based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (B-1, B-2 and B-3, which show absorption at 505 nm, 630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C60 was used as the complementary hydrogen bonding module (C-1), in which the C60 part acts as a spin converter for triplet formation. Visible light-harvesting antennae with methylated thymine were prepared as references (B-1-Me, B-2-Me and B-3-Me), which are unable to form strong H-bonds with C-1. Triple H-bonds are formed between each Bodipy antenna (B-1, B-2 and B-3) and the C60 module (C-1). The photophysical properties of the H-bonding assemblies and the reference non-hydrogen bond-forming mixtures were studied using steady state UV/vis absorption spectroscopy, fluorescence emission spectroscopy, electrochemical characterization, and nanosecond transient absorption spectroscopy. Singlet energy transfer from the Bodipy antenna to the C60 module was confirmed by fluorescence quenching studies. The intersystem crossing of the latter produced the triplet excited state. The nanosecond transient absorption spectroscopy showed that the triplet state is either localized on the C60 module (for assembly B-1·C-1), or on the styryl-Bodipy antenna (for assemblies B-2·C-1 and B-3·C-1). Intra-assembly forward-backward (ping-pong) singlet/triplet energy transfer was proposed. In contrast to the H-bonding assemblies, slow triplet energy transfer was observed for the non-hydrogen bonding mixtures. As a proof of concept, these supramolecular assemblies were used as triplet photosensitizers for triplet-triplet annihilation upconversion.

Sensor targets

Guest editors Christopher J. Chang, Thorfinnur Gunnlaugsson and Tony D. James introduce the Sensor Targets issue of Chemical Society Reviews

Anion binding and transport properties of cyclic 2,6-bis(1,2,3-triazol-1-yl)pyridines

A series of cyclic 2,6-bis-(1,2,3-triazolyl)-pyridine anion receptors with thiourea functionalities were synthesized by click reaction of 2,6-diazidopyridine with protected propargylamine followed by condensation of a bisthiocyanate derivative with a series of diamines. Their chloride binding affinities as well as their transport properties in POPC bilayers were examined. These receptors were found to function as anion carriers, which can mediate both Cl(-)/NO3(-) antiport and H(+)/Cl(-) symport, and the transport activity of these hosts were dominated by their lipophilicity.

Luminescent platinum(ii) complexes with self-assembly and anti-cancer properties: hydrogel, pH dependent emission color and sustained-release properties under physiological conditions

Luminescent platinum(ii) complexes show anti-cancer and pH-dependent self-assembly and sustained-release properties under physiological conditions.

Supramolecular interactions are of paramount importance in biology and chemistry, and can be used to develop new vehicles for drug delivery. Recently, there is a surge of interest on self-assembled functional supramolecular structures driven by intermolecular metal–metal interactions in cellular conditions. Herein we report a series of luminescent Pt(ii) complexes [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ [HC^N^N^pyr = 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine)] containing pincer type ligands having pyrazole moieties. These Pt(ii) complexes exert potent cytotoxicity to a panel of cancer cell lines including primary bladder cancer cells and display strong phosphorescence that is highly sensitive to the local environment. The self-assembly of these complexes is significantly affected by pH of the solution medium. Based on TEM, SEM, ESI-MS, absorption and emission spectroscopy, and fluorescence microscopy together with cell based assays, [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes were observed to self-assemble into orange phosphorescent polymeric aggregates driven by intermolecular Pt(ii)–Pt(ii) and ligand–ligand interactions in a low-pH physiological medium. Importantly, the intracellular assembly and dis-assembly of [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ are accompanied by change of emission color from orange to green. These [Pt(C^N^N^pyr)(C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> NR)]⁺ complexes accumulated in the lysosomes of cancer cells, increased the lysosomal membrane permeability and induced cell death. One of these platinum(ii) complexes formed hydrogels which displayed pH-responsive and sustained release properties, leading to low-pH-stimulated and time-dependent cytotoxicity towards cancer cells. These hydrogels can function as vehicles to deliver anti-cancer agent cargo, such as the bioactive natural products studied in this work.

Self-assembly formation of a healable lanthanide luminescent supramolecular metallogel from 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands

The self-assembly and rheological studies of self-healing Eu(iii) luminescent metallogels from a btp (2,6-bis(1,2,3-triazol-4-yl)pyridine) ligand is described.

Functionalizable red emitting calcium sensor bearing a 1,4-triazole chelating moiety

Herein we developed a functionalizable OFF–ON red emitting fluorescent calcium probe based on a new chelating system formed by CuAAC click chemistry (Huisgen cycloaddition).

A tunable ratiometric pH sensor based on phenanthro[9,10-d]imidazole covalently linked with vinylpyridine

We synthesized phenanthro[9,10-d]imidazole in combination with thiophene tethered pyridine as our target molecule PITP. Under different pH conditions either the imidazolyl or the pyridinyl nitrogen is protonated and red shifted by more than 115 nm.

π-Electron rich small molecule sensors for the recognition of nitroaromatics

In this review article we provide an overview of the recent developments made in small molecule-based turn-off fluorescent sensors for nitroaromatic explosives with special focus on organic and H-bonded supramolecular sensors.

Lanthanide luminescent logic gate mimics in soft matter: [H+] and [F−] dual-input device in a polymer gel with potential for selective component release

Non-covalent incorporation of responsive luminescent lanthanide into a polymer gel produces three-output logic circuit with significant naked-eye colour changes.