A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water

Triazine-Containing Pyridinium Organic Polymer Based on 4-Amino-1,8-naphthalimide Tröger's Base for Selective Fluorescent Sensing of Organoarsenic Feed Additives in Water

A new triazine containing pyridinium organic polymer (TB-Py-COP) based on 4-amino-1,8-naphthalimide Tröger's base is developed and employed as a fluorescent chemosensor for selective sensing of organoarsenic feed additives in water. TB-Py-COP was readily synthesized by reacting "V-shaped" bis-[N-(4-pyridyl)methyl)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine with cyanuric chloride in DMF at 100 °C for 3 days. TB-Py-COP exhibited a strong fluorescence emission in water and displayed selective, reversible fluorescence sensing responses for the roxarsone feed additive at the nanomolar (19 nM) level of sensitivity. The Stern-Volmer quenching constant (K SV) was determined to be 1.4 × 104 M-1. The selective sensing of roxarsone was further demonstrated in competitive environments, lake water, and buffer solutions.

Perfluoroalkylated benzoic acid-based phase-selective supramolecular self-assembly system for dye removal

In this study, perfluoroalkylated derivatives of benzoic acid S-6 and O-6 were designed and synthesized as supramolecular gelators using a simple one-step method. Both S-6 and O-6 could form gels in various organic solvents. Notably, these compounds have potential applications in environmental remediation, with S-6 demonstrating significant promise for oil spill treatment. After five recycling cycles, the recovery rate of the gelation capacity for diesel oil remained above 90%. Xerogels derived from O-6 at a concentration of 5 wt% in pump oil effectively adsorbed Rhodamine B (RhB). The adsorption process primarily involved chemical adsorption, electrostatic interactions between the O-6 xerogel and the cationic RhB dye, as well as physical adsorption within the xerogel's pores. In summary, benzoic acid derivatives represent a kind of multifunctional, recyclable, and efficient materials.

Multifunctional N-fused fluorescent probes for detection of iron ions and nitro explosives

In this work, two novel probes 4a and 4b were synthesized through Suzuki-Miyaura coupling reaction, whose structures were further confirmed by 1H NMR, 13C NMR, high-resolution mass spectrometry (HRMS) and X-ray single crystal diffraction. The optical properties of the obtained molecules were investigated accordingly. Owing to different bridging fluorophores, there are certain differences in optical performance and detection ability between the two synthesized compounds. Especially, due to the subtle difference in orbitals energy and electron distribution displayed by the DFT calculations, 4a possesses the characteristics of dual-state emission (DSE) molecule, while 4b is an aggregation-induced emission (AIE) molecule. Interestingly, these two molecules can be developed into multifunctional detection probes, successfully applied for the fluorescence recognition of iron ions and common nitroaromatic compounds (NACs). At the same time, the probe molecules can also be applied to the detection of NACs in aqueous environment. What's more, they can also be loaded on test strips and thin-films for fluorescence identification of NACs, thus being expected to be developed into portable detection tools for NACs.

A Chromo-fluorogenic Probe for Selective Detection of Picric Acid Alongside Its Recovery by Aliphatic Amines and Construction of Molecular Logic Gates

Nitroaromatic compounds are illicit explosive chemicals. For environmental security and homeland safety, selective and sensitive identification of these secondary-class explosives has been a reason for the exhaustive research arena of chemists for about a decade. We introduced a sensitive optical sensor with desalted neutral red (NR) dye. After ingressing picric acid (PA) in acetonitrile, the probe becomes non-fluorescent, displaying a colorimetric change from yellow to pink. The quenched phenomena and the changed color were re-established with aliphatic amine, trimethylamine (TEA). The reversibility is produced cyclically, both in fluorimetrically and spectrophotometrically. The detection limit for PA with our probe comes out as 0.639 µM; this value is significantly lower than many chemosensors available in the literature. Also, NR-stained filter paper strips-based test kit analysis has been deployed as a displayable photonic device for in-situ detection of PA. Furthermore, the whole system was conceptualized to produce single input, single output, and double input single output logic gates, which can be applied to digital devices. The chronological input manner as NTP (NR- TEA-PA) pushed us to configure a molecular keypad lock system, the basis of digital locking devices. The repeatable & reversible detection system exhibits "Write read- Erase-read Write-read' type memory devices.

Tröger's Base as a Potential Bridge to Type-I Photosensitizers: Mechanism and Antitumor Applications

In contrast to Type-II photodynamic therapy (PDT), Type-I PDT with less oxygen consumption has shown great potential against tumor hypoxia. However, there are limited strategies available for designing Type-I photosensitizers (PSs). Herein, we present a promising strategy for synthesizing Type-I PSs (TBC-1-TBC-4) using Tröger's base (TB) framework. The TB framework can promote intersystem crossing efficiency and create an electron-rich environment, making it the most likely site for electron transfer to O2 to generate Type-I ROS. As anticipated, TBC-1-TBC-4 demonstrates Type-I ROS generation capability and their impressive visible light-harvesting ability significantly enhances this capability. Among them, TBC-1 demonstrates outstanding biocompatibility and PDT efficiency in vitro under both normoxia and hypoxia. Furthermore, TBC-1 effectively inhibits tumor growth in vivo, with negligible side effects. This is attributed to TBC-1's efficient generation of Type-I ROS and endoplasmic reticulum targeting ability. This study thus offers useful insights into developing Type-I PSs.

An ultrasensitive 2,4,6-trinitrophenol nanofluidic sensor inspired by olfactory sensory neurons in sniffer dogs

Explosives, as high-energy materials, could generate huge destructive explosions along with a massive release of energy. The regulatory or illegal transportation of explosives threatens the peace and stability worldwide. Among the many high-powered explosives, 2,4,6-trinitrophenol (TNP) is not only frequently used in many terrorist attacks, but also seriously jeopardizes environmental safety and human health. Hence, dependable methods for high-sensitivity, rapid and portable detection are desperately needed. Inspired by olfactory sensory neurons (OSNs) in sniffer dogs, we present a nanofluidic sensor for ultrasensitive TNP detection by in situ growing dense UiO-66-NH2 layers on the surface of anodic aluminum oxide (AAO) nanochannels. TNP could be specifically captured by UiO-66-NH2 of the sensor through charge transfer to form Meisenheimer complexes, which cause the ionic current change. The TNP concentrations are quantitatively analyzed by monitoring the changed ionic current. And the detection range is from 10-14 to 10-10 g mL-1 with a limit of detection as low as 6.5 × 10-16 g mL-1, which is far beyond those of the state-of-the-art sensors. This work provides a novel strategy for ultrasensitive detection of TNP as well as other explosives, which opens new and promising routes to various breakthroughs in the fields of homeland security, military applications, security inspections and environmental monitoring.

Sequential effects of two cations on the fluorescence emission of a coordination polymer with Zn4O core in node

Distinct changes in the fluorescence emissions of free ligand 5-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)isophthalic acid (H2NAPHISO) than a 2D-zinc-coordination polymer of it, caused by sequential interactions with different sets of binary cations were observed. The coordination polymer having unsymmetrical Zn4O core of tetranuclear zinc-node could be dispersed in dimethylformamide without its degradation. The coordination polymer had an emission peak at 435 nm (quantum yield = 0.082) which was selectively quenched by adding Fe2+ ions. Based on this quenching, the Fe2+ ions in aqueous solution could be detected with a detection limit 42.57 nM. The metal ions such as Li+, Na+, Cd2+, Hg2+, Al3+ did not interfere in the detection; but each of these ions together with Fe2+ ions showed characteristic shift of the emission spectra. The H2NAPHISO in dimethyl formamide was non-fluorescent, but showed emission at 452 nm upon addition of Cd2+ or Zn2+ ions. This new emission of H2NAPHISO caused by zinc or cadmium ions was not quenched by Fe2+ ions. Various cations had affected the emission of the H2NAPHISO with Zn2+ which was much different from the corresponding changes caused by the same ion on the emission of the coordination polymer. For example, the Mn2+ and Zn2+ ions together in a solution of the ligand showed a broad emission spectrum spreading over 380-450 nm, but ions Sn2+ and Zn2+ together had showed emission at a shorter wavelength (380 nm). These allowed to modulate the emission of the ligand by binary combination of metal ions.

Unveiling Route for the Synthesis of Tröger's Bases Through Azide Rearrangement

This study introduces a novel method for producing Tröger's bases by utilizing the rearrangement chemistry of benzyl azide. This method offers a convenient and adaptable pathway for synthesizing these important molecular structures with potential for further advancements. By reacting benzyl azide derivatives with TfOH under the presence of water, this process generates iminium ion, formaldehyde, and aniline intermediates in situ. Notably, this conversion is reversible under acidic conditions, allowing for the regeneration of the iminium ion and ultimately leading to the formation of the desired Tröger's base product. Additionally, this method could decrease the risk of exposure to an excess amount of formaldehyde.

Tracking the cellular uptake and phototoxicity of Ru(ii)-polypyridyl-1,8-naphthalimide Tröger's base conjugates

Ruthenium(ii) complexes are attracting significant research attention as a promising class of photosensitizers (PSs) in photodynamic therapy (PDT). Having previously reported the synthesis of two novel Ru(ii)-polypyridyl-1,8-naphthalimide Tröger's base compounds 1 and 2 with interesting photophysical properties, where the emission from either the Ru(ii) polypyridyl centres or the naphthalimide moieties could be used to monitor binding to nucleic acids, we sought to use these compounds to investigate further and in more detail their biological profiling, which included unravelling their mechanism of cellular uptake, cellular trafficking and cellular responses to photoexcitation. Here we demonstrate that these compounds undergo rapid time dependent uptake in HeLa cells that involved energy dependent, caveolae and lipid raft-dependent mediated endocytosis, as demonstrated by confocal imaging, and transmission and scanning electron microscopy. Following endocytosis, both compounds were shown to localise to mostly lysosomal and Golgi apparatus compartments with some accumulation in mitochondria but no localisation was found to the nucleus. Upon photoactivation, the compounds increased ROS production and induced ROS-dependent apoptotic cell death. The photo-activated compounds subsequently induced DNA damage and altered tubulin, but not actin structures, which was likely to be an indirect effect of ROS production and induced apoptosis. Furthermore, by changing the concentration of the compounds or the laser used to illuminate the cells, the mechanism of cell death could be changed from apoptosis to necrosis. This is the first detailed biological study of Ru(ii)-polypyridyl Tröger's bases and clearly suggests caveolae-dependent endocytosis is responsible for cell uptake - this may also explain the lack of nuclear uptake for these compounds and similar results observed for other Ru(ii)-polypyridyl complexes. These conjugates are potential candidates for further development as PDT agents and may also be useful in mechanistic studies on cell uptake and trafficking.

An extensive experimental and DFT studies on highly selective detection of nitrobenzene through deferasirox based new fluorescent sensor

A deferasirox based substituted triazole amine sensor TAD has been synthesized for the highly selective detection of nitrobenzene in real samples. Sensor TAD exhibited selective quenching response against nitrobenzene among the other nitroaromatic compounds (NACs). Photoinduced electron transfer (PET) process was devised as plausible sensing mechanisms which was supported via UV-visible and fluorescence spectroscopy, 1H NMR titration experiment, density functional theory (DFT) analysis and Job's plot. Non-covalent interaction (NCI) analysis and Bader's quantum theory of atoms in molecules (QTAIM) analysis were performed to investigate the presence of non-covalent interactions and symmetry perturbation theory (SAPT0) was performed for energy decomposition and quantitative analysis of interaction energies between sensor TAD and NB. Furthermore, sensor TAD was practically applied for the identification of NB in real samples.

Regulating donor-acceptor system toward highly efficient dual-state emission for sensitive response of nitroaromatic explosives

Dual-state emission luminogens (DSEgens) as fluorophores emit efficiently in solution and solid forms have gained increasing concern in the field of chemical sensing. Recent efforts by our group led to the identification of DSEgens as an easy-to-visualize nitroaromatic explosives (NAEs) detection platform. However, none of the previously studied NAEs probes show effective improvement in sensitivity. Here, we designed a series of benzoxazole-based DSEgens through multiple strategies driven by theoretical calculations, revealing their improved detecting performance on NAEs. Compounds 4a-4e exhibit thermal- and photo-stability, large Stokes shift as well as sensitivity solvatochromism (except for 4a and 4b). A subtle balance between rigid conjugation and distorted conformation endows these D-A type fluorophores 4a-4e with DSE properties. Furthermore, 4d and 4e show aggregation-induced emission phenomenon caused by distorted molecular conformation and restricted intramolecular rotation. Interestingly, DSEgen 4e displays anti-interference and sensitivity towards NAEs with a detection limit of 10^-8 M. It can be applied for expedient and distinct visual identification of NAEs not only in solution but also on filter paper and film, supporting this new DSEgen as reliable NAEs chemoprobe.

Investigation of the interaction between the functionalized mesoporous silica nanocarriers and bovine serum albumin via multi-spectroscopy

It is well known that the physicochemical properties of nanocarriers, which are closely related to the surface modification of nanoparticles, have crucial impacts on their biological effects. Herein, the interaction between functionalized degradable dendritic mesoporous silica nanoparticles (DDMSNs) and bovine serum albumin (BSA) was investigated for probing into the nanocarriers' potential toxicity using multi-spectroscopy such as ultraviolet/visible (UV/Vis), synchronous fluorescence, Raman and circular dichroism (CD) spectroscopy. BSA, owing to its structural homology and high sequence similarity with HSA, was employed as the model protein to study the interactions with DDMSNs, amino-modified DDMSNs (DDMSNs-NH₂) and hyaluronic acid (HA) coated nanoparticles (DDMSNs-NH₂-HA). It was found that the static quenching behavior of DDMSNs-NH₂-HA to BSA was accompanied by an endothermic and hydrophobic force-driven thermodynamic process, which was confirmed by fluorescence quenching spectroscopic studies and thermodynamic analysis. Furthermore, the conformational variations of BSA upon interaction with nanocarriers were observed by combination of UV/Vis, synchronous fluorescence, Raman and CD spectroscopy. The microstructure of amino residues in BSA changed due to the existence of nanoparticles, for example, the amino residues and hydrophobic groups exposed to microenvironment and the alpha helix (α-helix) content of BSA decreased. Specially, through thermodynamic analysis, the diverse binding modes and driving forces between nanoparticles and BSA were discovered because of different surface modifications on DDMSNs, DDMSNs-NH₂ and DDMSNs-NH₂-HA. We believe that this work can promote the interpretation of mutual impact between nanoparticles and biomolecules, which will be in favor of predicting the biological toxicity of nano-DDS and engineering functionalized nanocarriers.

Synthesis, characterization, and heparin-binding study of a self-assembled p-cymene-Ru(II) metallocycle based on a 4-amino-1,8-naphthalimide Tröger's base supramolecular scaffold

We report the very first example of a self-assembled p-cymene-Ru(II) metallocycle based on a green emitting 4-amino-1,8-naphthalimide Tröger's base (TBNap) supramolecular scaffold. A new cleft-shaped TBNap-derived di-4-picolyl donor was synthesized and reacted in a 2 : 2 stoichiometry ratio with a dinuclear Ru(II) acceptor (Ru-A) to generate a [2 + 2] self-assembled metallocycle (TBNap-Ru-MC) in good yield. Both TBNap and TBNap-Ru-MC showed positive solvatochromism in different solvents with varying polarities. In addition, the binding propensity of cationic TBNap-Ru-MC toward the heparin polyanion was determined using fluorescence titration studies. The initial fluorescence emission of TBNap-Ru-MC was quenched upon the gradual addition of the heparin polyanion, and the Stern-Volmer quenching constant (K_SV) was calculated to be 3.97 × 10⁵ M^-1.

Recent advances in fluorescence chemosensors for ammonia sensing in the solution and vapor phases

Developing low-cost and reliable sensor systems for the detection of trace amounts of toxic gases is an important area of research. Ammonia (NH₃) is a commonly produced industrial chemical and a harmful colorless pungent gas released from various manufacturing and processing industries. Continuous exposure to NH₃ vapor causes serious menace to human health, microorganisms, and the ecosystem. Exposure to relatively higher concentrations of NH₃ severely affects the respiratory system and leads to kidney failure, nasal erosion ulcers, and gastrointestinal diseases. Excessive accumulation of NH₃ in the biosphere can cause various metabolic disruptions. As a consequence of this, therefore, suitable sensing methods for selective detection and quantification of trace amounts of NH₃ are of utmost need to protect the environment and living systems. Given this, there have been significant research advances in the preceding years on the development of fluorescence chemosensors for efficient sensing and monitoring of the trace concentration of NH₃ both in solution and vapor phases. This review article highlights several fluorescence chemosensors reported until recently for sensing and quantifying NH₃ in the vapor phase or ammonium ions (NH₄⁺) in the solution phase. The wide variety of fluorescence chemosensors discussed in this article are systematically gathered according to their structures, functional properties, and fluorescence sensing properties. Finally, the usefulness and existing challenges of using the fluorescence-based sensing method for NH₃ detection and the future perspective on this research area have also been highlighted.

A Highly Efficient Fluorescent Sensor Based on AIEgen for Detection of Nitrophenolic Explosives

The detection of nitrophenolic explosives is important in counterterrorism and environmental protection, but it is still a challenge to identify the nitroaromatic compounds among those with a similar structure. Herein, a simple tetraphenylethene (TPE) derivative with aggregation-induced emission (AIE) characteristics was synthesized and used as a fluorescent sensor for the detection of nitrophenolic explosives (2, 4, 6-trinitrophenol, TNP and 2, 4-dinitrophenol, DNP) in water solution and in a solid state with a high selectivity. Meanwhile, it was found that only hydroxyl containing nitrophenolic explosives caused obvious fluorescence quenching. The sensing mechanism was investigated by using fluorescence titration and ¹H NMR spectra. This simple AIE-active probe can potentially be applied to the construction of portable detection devices for explosives.

Carbazole-Equipped Metal-Organic Framework for Stability, Photocatalysis, and Fluorescence Detection

The useful yet underutilized backfolded design is invoked here for functionalizing porous solids with the versatile carbazole function. Specifically, we attach carbazole groups as backfolded side arms onto the backbone of a linear dicarboxyl linker molecule. The bulky carbazole side arms point away from the carboxyl links and do not disrupt the Zr-carboxyl framework formation; namely, the resultant MOF solid ZrL1 features the same net as that of the unfunctionalized dicarboxyl linker, also known as the PCN-111 net or UiO-66 net. The ZrL1 structure features only half linker occupancy (about 6 out of the 12 linkers around the Zr₆O₈ cluster being missing) and partially collapses upon activation (acetone exchange and evacuation). Notably, the stability improves after heating in diphenyl oxide at 260 °C (POP-260 treatment; to form ZrL1-260), as indicated by the higher crystallinity and surface area of the activated ZrL1-260 sample. The ZrL1-260 samples achieve 72% yield in photocatalyzing reductive dehalogenation of phenacyl bromide; ZrL1 can detect nitro-aromatic compounds via fluorescence quenching, with selectivity and sensitivity toward 4-nitroaniline, featuring a limit of detection of 96 ppb.

Design, Synthesis, and Anticancer Studies of a p-Cymene-Ru(II)-Curcumin Organometallic Conjugate Based on a Fluorescent 4-Amino-1,8-naphthalimide Tröger's Base Scaffold

A unique V-shaped "chiral" supramolecular scaffold, N-(4-pyridyl)-4-amino-1,8-naphthalimide Tröger's base (TBNap), was synthesized in good yield from a precursor N-(4-pyridyl)-4-amino-1,8-naphthalimide (Nap). TBNap was characterized using different spectroscopic methods and the molecular structure was elucidated by diffraction analysis. A new p-cymene-Ru(II)-curcumin conjugate (TB-Ru-Cur) was designed by reacting TBNap dipyridyl donor and ruthenium-curcuminato acceptor [RuCur = (p-cymene)Ru-(curcuminato)Cl] in the presence of silver triflate. TB-Ru-Cur was isolated in quantitative yield and characterized using Fourier transform infrared (FT-IR), NMR (¹H, ¹³C, and ¹⁹F), and electrospray ionization mass spectrometry (ESI-MS), and the molecular structure has been predicted using a computational study. Both TBNap and TB-Ru-Cur exhibited intramolecular charge transfer (ICT)-based fluorescence emission. Furthermore, the anticancer properties of TBNap, Ru-Cur, and TB-Ru-Cur were assessed in different cancer cell lines. Gratifyingly, the conjugate TB-Ru-Cur displayed fast-cellular internalization and good cytotoxicity against HeLa, HCT-116, and HepG2 cancer cells and the estimated IC₅₀ value was much lower than that of the precursors (TBNap and Ru-Cur) and the well-known chemotherapeutic drug cisplatin.

Hierarchical supramolecular co-assembly formation employing multi-component light-harvesting charge transfer interactions giving rise to long-wavelength emitting luminescent microspheres

Charge transfer (CT) interaction induced formation of a hierarchical supramolecular assembly has attracted attention due to its wide diversity of structural and functional characteristics. In the present work, we report the generation of green luminescent microspheres from the charge transfer interaction induced co-assembly of a bis-naphthyl dipicolinic amide (DPA) derivative with tetracyanobenzene (TCNB) for the first time. The properties of these self-assemblies were studied both in solution and the solid-state using spectroscopic and a variety of microscopy techniques. The X-ray crystal structure analysis showed a mixed stack arrangement of DPA and TCNB. The molecular orbital and energy level calculations confirm the charge transfer complex formation between DPA and TCNB. Furthermore, energy transfer was observed from the green luminescent CT complex to a red-emitting dye, pyronin Y, in the microsphere matrix, leading to the formation of a light-harvesting tri-component self-assembly.

A smartphone-based platform for ratiometric visualization of SARS-CoV-2 via an oligonucleotide probe

COVID-19 necessitates the development of reliable and convenient diagnostic tools. In this work, a facile 3D-printed smartphone platform was constructed that achieved reliable visual detection of SARS-CoV-2 by eliminating the effect of ambient light and fixing the camera position relative to the sample. The oligonucleotide probe is modified with orange-red-emitting TAMRA working as an internal standard and green-emitting FAM serving as a sensitive sensing agent. Under 365-nm UV excitation, the emission wavelengths of TAMRA and FAM are 580 nm and 518 nm, respectively. When the probes interact with the targets, the green fluorescence gradually restores while the orange-red fluorescence remains stable. Thus, a striking color transition from orange-red to green could be observed by the naked eye. The detection limit of SARS-CoV-2 nucleic acid is 0.23 nM, and the entire process of color change could be completed in 25 min. Furthermore, the RGB value analysis of the sample solution was conducted using a smartphone for reliable and reproducible discrimination of SARS-CoV-2. The proposed smartphone platform might establish a general method for visual detection of SARS-CoV-2 nucleic acid as well as other virus-related diseases.

γ-Cyclodextrin-based [2]rotaxane stoppered with gold(I)-ethynyl complexation: phosphorescent sensing for nitroaromatics

A [2]rotaxane is assembled by γ-cyclodextrin (γ-CD) with threaded 1,4-diethynylbiphenyl and bulky Au(I)-phosphine stoppers. The phosphorescence of the [2]rotaxane has been observed in aerated aqueous solution and found to be quenched by nitroaromatics due to γ-CD-based co-binding, providing a sensitive approach towards explosive-sensing.

Water-soluble ionic liquid as a fluorescent probe towards distinct binding and detection of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol in aqueous medium

Owing to the escalating threat of criminal activities and pollution aroused by 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP), development of a proficient sensor for the detection of these explosives is highly demanded. Herein, a water-soluble ionic liquid-tagged fluorescent probe, 1-ethyl-3-(3-formyl-4-hydroxybenzyl)-1H-benzimidazol-3-ium chloride (EB-IL) has been designed and synthesized for the detection of TNT and TNP in 100% aqueous medium. The EB-IL fluorescent probe displayed strong cyan-blue fluorescence at 500 nm which gets quenched upon the addition of TNT/TNP over other concomitant nitro-compounds. The distinct binding response of EB-IL towards TNT could be due to the formation of hydrogen bonding between the acidic proton of benzimidazolium (C2-H) and nitro group of TNT. Meanwhile, the selective binding of TNP with EB-IL could be due to the exchange of counter Cl^- anion of EB-IL with picrate anion. The fluorescence quenching of EB-IL by TNT could be attributed to the resonance energy transfer (RET) and that of TNP is ascribed to the anion-exchange process. The developed sensor is extremely selective and sensitive towards TNT and TNP with high quenching constants of 1.94 × 10⁵ M^-1 and 2.32 × 10⁶ M^-1 and shows a lower detection limit of 159 nM and 282 nM, respectively.

Selective Detection of Picric Acid and Pyrosulfate Ion by Nickel Complexes Offering a Hydrogen-Bonding-Based Cavity

This work describes the synthesis and characterization of three mononuclear nickel complexes supported with amide-based pincer ligands. All three complexes presented an H-bonding-based cavity due to the migration of amidic protons to the appended heterocyclic rings that formed H-bonds with the metal-ligated solvent molecule(s). These complexes functioned as the nanomolar chemosensors for the detection of picric acid and pyrosulfate ion as inferred by the detailed absorption and emission spectral studies while further supported with FTIR, NMR, and mass spectra of the isolated products. We also illustrate a few practical detection methods for the sensing of picric acid in the solution state as the naked-eye colorimetric methods and in the solid state by employing polystyrene films.

Synthesis of water-soluble, ultrabright Cu nanoclusters with core-shell structure via facile reduction approach for determination of 4-nitrophenol

In this work, we reported a facile reduction approach for fabrication of water-soluble and ultrabright Cu nanoclusters with core-shell structure. A certain amount of reducing agent as NaBH₄was introduced into the polyethyleneimine-stabilized Cu nanoclusters (CuNCs@PEI) system, which exhibited 4-fold fluorescence enhancement along with a blue shift of the emission peak. The variations of morphology, valence states and functional groups demonstrated that a Cu shell was formed surround CuNCs (defined as CuNCs-Cu@PEI), attributable to metal complex (PEI-Cu⁺and PEI-Cu²⁺) reduction. The effect of core-shell morphology on luminous and electron relaxation mechanism of CuNCs-Cu@PEI was investigated via temperature-dependent steady and time-resolved fluorescence measurements. The CuNCs-Cu@PEI with a high fluorescence quantum yields of 22.59% were able to homogeneously disperse in aqueous phase, indicating their potential applications in biological labeling, sensing and invivoimaging. Finally, the CuNCs-Cu@PEI was employed as a fluorescence probe to determine 4-nitrophenol, of which the detection limit was much lower than initial CuNCs@PEI.

Synthesis and characterization of a mononuclear zinc(ii) Schiff base complex: on the importance of C-H⋯π interactions

A zinc(ii) complex, [ZnL(H₂O)]·H₂O {H₂L = 2,2′-[(2,2-dimethyl-1,3-propanediyl)bis(nitrilomethylidyne)]bis[6-ethoxyphenol]} has been synthesized and characterized by UV-vis and IR spectroscopy. The structure of the complex has been confirmed by X-ray crystallography and the noncovalent interactions characterized using Hirshfeld surface analysis. In addition to the conventional H-bonds involving the Zn-coordinated and non-coordinated water molecules, interesting C–H⋯π interactions between the H-atoms belonging to aliphatic part of the ligand (2,2-dimethyl-1,3-propanediyl) and the Zn-coordinated aromatic rings are established. These interactions have been studied using DFT calculations (PBE0-D3/def2-TZVP) and characterized using molecular electrostatic potential (MEP) surfaces and the noncovalent interaction (NCI) plot index analyses.

The strength of the C–H⋯π interaction in the solid state of [ZnL(H₂O)]·H₂O has been evaluated using DFT calculations and also analysed using the MEP surface and NCI plot index computational tool.

Fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TBNaps) possessing (orthogonal) 'α-amino acids', esters and di-peptides and their solvent dependent photophysical properties

The synthesis of fifteen luminescent bis-naphthalimide based Tröger's bases (TBNaps) derived from 4-amino-1,8-naphthalimide (4-Amino-Nap) precursors is described; these scaffolds possess α-amino acids, esters or di-peptides conjugated at the imide site and show minor fluorescence in aqueous solution while being highly emissive in organic solvents. The investigation shows that these TBNaps possessing ICT excited state properties are capable of generating either positive or negative solvatochromic effects in response to changes in polarity and/or the hydrogen bonding capabilities of the medium.

Base-Catalyzed, Solvent-Free Synthesis of Rigid V-Shaped Epoxydibenzo[b,f][1,5]diazocines

A novel method for the synthesis of epoxydibenzo[b,f][1,5]diazocines exhibiting a V-shaped molecular architecture is reported. The unique approach is based on unprecedented base-catalyzed, solvent-free autocondensation and cross-condensation of fluorinated o-aminophenones. The structure of the newly synthesized diazocines was confirmed independently by X-ray analysis and chiroptical methods. The rigidity of the diazocine scaffold allowed for the separation of the racemate into single enantiomers that proved to be thermally stable up to 140 °C. Furthermore, the inertness of the diazocine scaffold was demonstrated by performing a series of typical transformations, including transition metal-catalyzed reactions, proceeding without affecting the bis-hemiaminal subunit.

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

An NH2-modified {EuIII2}–organic framework for the efficient chemical fixation of CO2 and highly selective sensing of 2,4,6-trinitrophenol

An amino-functionalized microporous material of {(Me2NH2)4[Eu4(DDAC)3(HCO2)(OH2)2]·8DMF·9H2O}n with hierarchical pore voids displays efficient chemical fixation of CO2 and highly selective sensing of 2,4,6-trinitrophenol.