Integration of the 1,2,3-triazole "click" motif as a potent signalling element in metal ion responsive fluorescent probes

Reaction, Recognition, Relay: Anhydride Hydrolysis Reported by Conformationally Responsive Fluorinated Foldamers in Micelles

Natural membrane receptors are proteins that can report on changes in the concentration of external chemical messengers. Messenger binding to a receptor produces conformational changes that are relayed through the membrane into the cell; this information allows cells to adapt to changes in their environment. Artificial membrane receptors (R)-1 and (S)-1 are helical α-aminoisobutyric acid (Aib) foldamers that replicate key parts of this information relay. Solution-phase 19F NMR spectroscopy of zinc(II)-capped receptor 1, either in organic solvent or in membrane-mimetic micelles, showed messenger binding produced an enrichment of either left- or right-handed screw-sense; the chirality of the bound messenger was relayed to the other receptor terminus. Furthermore, in situ production of a chemical messenger in the external aqueous environment could be detected in real-time by a racemic mixture of receptor 1 in micelles. The hydrolysis of insoluble anhydrides produced carboxylate in the aqueous phase, which bound to the receptors and gave a distinct 19F NMR output from inside the hydrophobic region of the micelles.

Triazole-Extended Anthracenes as Optical Force Probes

Optical force probes (OFPs) are force-responsive molecules that report on mechanically induced transformations by the alteration of their optical properties. Yet, their modular design and incorporation into polymer architectures at desired positions is challenging. Here we report triazole-extended anthracene OFPs that combine two modular ‘click’ reactions in their synthesis potentially allowing their incorporation at desirable positions in complex polymer materials. Importantly, these retain the excellent optical properties of their parent 9-π-extended anthracene OFP counterparts.

Rigid axially symmetrical C60-BODIPY triplet photosensitizers: effect of bridge length on singlet oxygen generation

Two rigid axially symmetrical C₆₀-BODIPY systems with different bridge lengths have been synthesized and the dyad with short bridge generates a higher quantum yield of singlet oxygen.

Chemical Waltz of Organic Molecules "On Water": Saline-Assisted Sustainable Regioselective Synthesis of Fluorogenic Heterobioconjugates via Click Reaction

A new sustainable green protocol for obtaining highly fluorogenic heterobioconjugates by a well-known copper-mediated azide-alkyne cycloaddition click reaction of nonfluorescent 3-azidocoumarins/benzyl azides (2a-f) and terminal alkynes (1a-e) using aqueous NaCl as a cheap and nontoxic salting-out agent under ultrasonication at ambient temperature is described. The presence of aqueous NaCl significantly influences the reaction by disturbing the water kosmotropes and augments the hydrophobic interaction of water-insoluble reactants, thus making the reaction feasible in water at neutral pH. The "beauty" of the presented ecofriendly approach is further boosted up by recycling the aqueous filtrate of the reaction mixture without further addition of NaCl, CuSO₄·5H₂O, and Na ascorbate up to seven cycles, resulting in effectively low copper loading (100 ppm) with excellent turn-over number (4850) and turn-over frequency (88.18 min^-1). A gram-scale synthesis was also successfully achieved with 92% yield, further elaborating the scope of this methodology.

A Ratiometric Fluorescent Probe for K+ in Water Based on a Phenylaza-18-Crown-6 Lariat Ether

This work presents two molecular fluorescent probes 1 and 2 for the selective determination of physiologically relevant K⁺ levels in water based on a highly K⁺ /Na⁺ selective building block, the o-(2-methoxyethoxy)phenylaza-18-crown-6 lariat ether unit. Fluorescent probe 1 showed a high K⁺ -induced fluorescence enhancement (FE) by a factor of 7.7 of the anthracenic emission and a dissociation constant (K_d ) value of 38 mm in water. Further, for 2+K⁺ , we observed a dual emission behavior at 405 and 505 nm. K⁺ increases the fluorescence intensity of 2 at 405 nm by a factor of approximately 4.6 and K⁺ decreases the fluorescence intensity at 505 nm by a factor of about 4.8. Fluorescent probe 2+K⁺ exhibited a K_d value of approximately 8 mm in Na⁺ -free solutions and in combined K⁺ /Na⁺ solution a similar K_d value of about 9 mm was found, reflecting the high K⁺ /Na⁺ selectivity of 2 in water. Therefore, 2 is a promising fluorescent tool to measure ratiometrically and selectively physiologically relevant K⁺ levels.

A BODIPY-Tagged Phosphono Peptide as Activity-Based Probe for Human Leukocyte Elastase

Human leukocyte elastase plays a crucial role in a variety of inflammatory disorders and represents an important subject of biomedical studies. The chemotype of peptidic phosphonates was employed for the design of a new activity-based probe for human leukocyte elastase. Its structure combines the phosphonate warhead with an adequate peptide portion and a BODIPY fluorophore with a clickable ethinylphenyl moiety at meso position. The probe 6 was assembled by copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition. It was characterized as an active site-directed elastase inhibitor exhibiting a second-order rate constant of inactivation of 88400 M^-1s^-1. The suitability of 6 as a fluorescent probe for human leukocyte elastase was demonstrated by in-gel fluorescence analysis. Labeling experiments and inhibition data toward a panel of related proteases underlined the selectivity of the probe for the targeted leukocyte elastase.

Synthesis and photophysical properties of extended π conjugated naphthalimides

A series of π conjugated naphthalimide derivatives having an imide group as an acceptor conjugated with a methoxy arylethynyl or a methoxyphenyl triazole as a donor were prepared by Sonogashira coupling or "click" chemistry. Their photophysical properties were investigated by steady state and time resolved fluorescence spectroscopy and modelled by TD-DFT calculations. Compound Naphth-AlkyneOMe has a high fluorescence quantum yield and displays efficient photoinduced charge transfer in solution as well as in the powder state. Compound Naphth-TriazoleOMe exhibits a very high Stokes shift and its fluorescence quantum yield is low, which can be rationalized by theoretical calculations.

Synthetically simple, click-generated quinoline-based Fe3+ sensors

Simple quinoline-based fluorescent probes for Fe³⁺ have been efficiently synthesized through 'click' reaction. Both probes gave intense fluorescence compared to 8-hydroquinoline in various organic solvents due to the inhibition of the excited state intramolecular photon transfer process, while showing dramatically quenched and red-shifted fluorescence in an aqueous solution, which can be attributed to the hydrogen bond-induced intermolecular excited state proton transfer process. In the presence of Fe³⁺ or in an acidic condition (pH less than 4.0), both probes showed similar quenching of the emission and over 100 nm red-shifts of their emission maxima. The binding mode between the probes and Fe³⁺ has been found to be 1:1 based on Job's plot. A highly sensitive and selective response in their absorption and emission towards Fe³⁺ over many other metal ions, including Cr³⁺ and Cu²⁺, was observed and may be the result of the ground state metal to ligand charge transfer effect from Fe³⁺ to quinoline ligands.

Donor-acceptor-acceptor (D-A-A) type 1,8-naphthalimides as non-fullerene small molecule acceptors for bulk heterojunction solar cells

Donor-acceptor-acceptor (D-A-A) type 1,8-naphthalimide based small molecules SM1 and SM2 functionalized with tetracyanobutadiene (TCBD) and dicyanoquino-dimethane (DCNQ) modules, showing strong absorption in the visible and near-infrared (NIR) region are reported. TCBD and DCNQ linked SM1 and SM2 exhibit multi-redox waves. The electrochemical and optical HOMO-LUMO gaps show similar trends. These SMs exhibit a broad absorption profile which is complementary to the D-A copolymer P donor and also possess an appropriate lowest unoccupied molecular orbital (LUMO) to serve as an acceptor with P with a LUMO level of -3.33 eV. The organic solar cells based on P:SM1 and P:SM2 exhibit a PCE of 4.94% and 6.11%, respectively. The higher value of the PCE for the SM2 based organic solar cells has been attributed to the broader absorption profile, more balanced charge transport and lower photon energy loss. The values of Voc of the organic solar cells for the SM1 acceptor (1.06 V and 1.02 V without and with solvent additive) are the highest values reported for devices based on non-fullerene acceptors to the best of our knowledge. The energy loss (Eloss) of 0.56 eV and 0.48 eV for SM1 and SM2 based devices, respectively is one of the smallest reported for BHJ organic solar cells.

Functional organic click-materials: application in phosphorescent organic light emitting diodes

1,2,3-Triazole has been applied as a novel linker in donor–acceptor materials to control intramolecular charge transfer phenomena.

Light-driven reversible surface functionalization with anthracenes: visible light writing and mild UV erasing

We introduce a methodology to reversibly pattern planar surfaces via the light-induced dimerization of anthracenes, particularly involving a 9-triazolylanthracene motif.

Structure-Property Relationships in Click-Derived Donor-Triazole-Acceptor Materials

To shed light on intramolecular charge-transfer phenomena in 1,2,3-triazole-linked materials, a series of 1,2,3-triazole-linked push-pull chromophores were prepared and studied experimentally and computationally. Investigated modifications include variation of donor and/or acceptor strength and linker moiety as well as regioisomers. Photophysical characterization of intramolecular charge-transfer features revealed ambipolar behavior of the triazole linker, depending on the substitution position. Furthermore, non-centrosymmetric materials were subjected to second-harmonic generation measurements, which revealed the high nonlinear optical activity of this class of materials.

Click-chemistry approaches to π-conjugated polymers for organic electronics applications

Given the wide utility of click-chemistry reactions for the preparation of simple moieties within large architecturally complex materials, this minireview article aims at surveying papers exploring their scope in the area of π-conjugated polymers for application in organic electronics to enable advanced functional properties.

Synthesis and Evaluation of 1,8-Disubstituted-Cyclam/Naphthalimide Conjugates as Probes for Metal Ions

Fluorescent molecular probes for metal ions have a raft of potential applications in chemistry and biomedicine. We report the synthesis and photophysical characterisation of 1,8‐disubstituted‐cyclam/naphthalimide conjugates and their zinc complexes. An efficient synthesis of 1,8‐bis‐(2‐azidoethyl)cyclam has been developed and used to prepare 1,8‐disubstituted triazolyl‐cyclam systems, in which the pendant group is connected to triazole C4. UV/Vis and fluorescence emission spectra, zinc binding experiments, fluorescence quantum yield and lifetime measurements and pH titrations of the resultant bis‐naphthalimide ligand elucidate a complex pattern of photophysical behaviour. Important differences arise from the inclusion of two fluorophores in the one probe and from the variation of triazole substitution pattern (dye at C4 vs. N1). Introducing a second fluorophore greatly extends fluorescence lifetimes, whereas the altered substitution pattern at the cyclam amines exerts a major influence on fluorescence output and metal binding. Crystal structures of two key zinc complexes evidence variations in triazole coordination that mirror the solution‐phase behaviour of these systems.

Thermoresponsive Polymer and Fluorescent Dye Hybrids for Tunable Multicolor Emission

Fully reversible emission color change is achieved by blending a thermoresponsive polymer with dye hybrids. The emission color can be tuned by changing the mixing ratio of each polymer-dye hybrid.

Multicomponent cascade reaction: dual role of copper in the synthesis of 1,2,3-triazole tethered benzimidazo[1,2-a]quinoline and their photophysical studies

One-pot synthesis of 1,2,3-triazole tethered benzimidazo[1,2-a]quinolines through a multi-component reaction is demonstrated. Overall one C–C bond and three C–N bonds are formed in a single step.

Deep-red emissive BODIPY-chlorin arrays excitable with green and red wavelengths

We report here the synthesis and characterization of BODIPY-chlorin arrays containing a chlorin subunit, with tunable deep-red (641-685 nm) emission, and one or two BODIPY moieties, absorbing at 504 nm. Two types of arrays were examined: one where BODIPY moieties are attached through a phenylacetylene linker at the 13- or 3,13-positions of chlorin, and a second type where BODIPY is attached at the 10-position of chlorin through an amide linker. Each of the examined arrays exhibits an efficient (≥0.80) energy transfer from BODIPY to the chlorin moiety in both toluene and DMF and exhibits intense fluorescence of chlorin upon excitation of BODIPY at ∼500 nm. Therefore, the effective Stokes shift in such arrays is in the range of 140-180 nm. Dyads with BODIPY attached at the 10-position of chlorin exhibit a bright fluorescence in a range of solvents with different polarities (i.e., toluene, MeOH, DMF, and DMSO). In contrast to this, some of the arrays in which BODIPY is attached at the 3- or at both 3,13-positons of chlorin exhibit significant reduction of fluorescence in polar solvents. Overall, dyads where BODIPY is attached at the 10-position of chlorin exhibit ∼5-fold brighter fluorescence than corresponding chlorin monomers, upon excitation at 500 nm.

Site-specific conjugation of 8-ethynyl-BODIPY to a protein by [2 + 3] cycloaddition

We report a straightforward synthesis of 8-ethynyl-BODIPY derivatives and their potential as fluorescent labeling compounds using an alkyne–azide click chemistry approach.

Substitution pattern reverses the fluorescence response of coumarin glycoligands upon coordination with silver (I)

Development of sugar-based fluorescence (FL) chemo-probes is of much interest since sugars are biocompatible, water-soluble and structurally rigid natural starting materials. We report here that fluorescent glycoligands with two triazolyl coumarin moieties installed onto the different positions of an identical glucosyl nucleus exert completely reversed optical response to a metal ion. C3,4-, C2,3- and C4,6-di-substituted coumarin glucosides synthesized by a click reaction similarly showed a selective FL variation in the presence of silver (I) among a range of metal cations in an aqueous solution. However, the variation was determined to be converse: the FL of the C3,4-ligand was quenched whereas that of the C2,3/C4,6-ligand tangibly enhanced. FL and NMR titrations suggested that this divergence was due to the distinct complexation modes of the conformationally constrained ligands with the ion. The optimal motifs of the ligand-ion complexation were predicted by a computational simulation. Finally, the C2,3-ligand was determined to be of low cytotoxicity and applicable in the FL imaging of silver ions internalized by live cells.

BINOL-linked 1,2,3-triazoles: an unexpected fluorescent sensor with anion–π interaction for iodide ions

BINOL-derived triazoles could be used in organocatalytic silylation and unexpectedly as fluorescent sensors for the recognition of I⁻.

Absorption and fluorescence signatures of 1,2,3-triazole based regioisomers: challenging compounds for TD-DFT

Photophysical signatures of 1,2,3-triazole regioisomers: a surprisingly challenging problem for TD-DFT.

A highly K(+)-selective phenylaza-[18]crown-6-lariat-ether-based fluoroionophore and its application in the sensing of K+ ions with an optical sensor film and in cells

Herein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K(+) ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18]crown-6 ether analogues. Probe 1 shows a high K(+)/Na(+) selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mM K(+) ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8% per 1 mM K(+) within the range 1-10 mM K(+). The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K(+) ions on both the extracellular and intracellular levels.