Precise counter anion modulation of the self-assembly behavior-endowed ultrasensitive and specific dual-mode visualization of nitrate.

Pt(II) polypyridine complex-based probe exhibits promising performance in anion detection by the change of the absorption and emission properties based on supramolecular self-assembly. However, whether one can develop a modulation strategy of the counter anion to boost the detection sensitivity and anti-interference capability of the Pt(II) complex-based probe remains a big challenge. Here, an effective modulation strategy was proposed by precisely regulating the interaction energy through adjusting the type of the counter anions, and a series of probes have been synthesized by counter anion (X = Cl, ClO, PF) exchange in [Pt(tpy)Cl]·X (tpy=2,2':6',2''-terpyridine), and thus the colorimetric-luminescence dual-mode detection toward nitrate was achieved.

Electronic Effect Driven Specific and Sensitive Recognition toward GHB.

Precise detection of a trace substance that intrinsically possesses weak chemical activity and less-distinctive spatial structure is of great significance, but full of challenges, as it could not be effectively recognized via either an active covalent reaction process or multiple noncovalent interactions toward its simple structure. Here, the electronic-effect-driven recognition strategy was proposed to visually sense an illicit drug, γ-hydroxybutyric acid (GHB), which was treated as an analyte model due to its inherent simple structure. In particular, a sensing system composed of two probes substituted by the nitro (-NO) and the hydrogen (-H), was constructed with the characteristic yellow coloring and blue fluorescence, as well as high sensitivity (0.

Amination and Protonation Facilitated Novel Isoxazole Derivative for Highly Efficient Electron and Hole Separation.

It is of great importance to understand the intrinsic relationship between phototautomerization and photoelectric properties for the exploration of novel organic materials. Here, in order to chemically control the protonation process, the aminated isoxazole derivative (2,2'-(isoxazolo[5,4-]isoxazole-3,6-diyl)dibenzenaminium, DP-DA-DPIxz) with -N═ as the proton acceptor was designed to achieve the twisted intramolecular charge transfer (TICT) state which was triggered by an excited-state intramolecular proton transfer (ESIPT) process. This kind of protonation enhanced the intramolecular hydrogen bonding, conjugative effect, and steric hindrance effects, ensuring a barrierless spontaneous TICT process.

Controlled Synthesis of Preferential Facet-Exposed Fe-MOFs for Ultrasensitive Detection of Peroxides.

Exposing different facets on metal-organic frameworks (MOFs) is highly desirable to enhance the performance for various applications, however, exploiting a concise and effective approach to achieve facet-controlled synthesis of MOFs remains challenging. Here, by modulating the ratio of metal precursors to ligands, the facet-engineered iron-based MOFs (Fe-MOFs) exhibits enhanced catalytic activity for Fenton reaction are explored, and the mechanism of facet-dependent performance is revealed in detail. Fully exposed (101) and (100) facets on spindle-shaped Fe-MOFs enable rapid oxidation of colorless o-phenylenediamine (OPD) to colored products, thereby establishing a dual-mode platform for the detection of hydrogen peroxide (HO) and triacetone triperoxide (TATP).

Solvation effect enabled visualized discrimination of multiple metal ions.

Highly efficient detection of environmental residual potentially toxic species is of concern worldwide as their presence in an excessive amount would greatly endanger the health of human beings as well as environmental sustainability. The solvation effect is a critical factor to be considered for understanding chemical reaction progress as well as the photophysical behaviors of substances and thus is promising for visualized detection of metal ions. Herein, by applying 5-amino-1,10-phenanthroline (APT) as the optical probe, a sensing strategy was proposed based on the solvation effect modulated complexation of APT towards different metal ions to achieve the visualized discrimination of four critical ions (Cu(II), Zn(II), Cd(II), and Al(III)).

Electrophilicity Modulation for Sub-ppm Visualization and Discrimination of EDA.

Precise and timely recognition of hazardous chemical substances is of great significance for safeguarding human health, ecological environment, public security, etc., especially crucial for adopting appropriate disposition measures. Up to now, there remains a practical challenge to sensitively detect and differentiate organic amines with similar chemical structures with intuitive analysis outcomes.

Design of Highly Efficient Electronic Energy Transfer in Functionalized Quantum Dots Driven Specifically by Ethylenediamine.

The exploration of emerging functionalized quantum dots (QDs) through modulating the effective interaction between the sensing element and target analyte is of great significance for high-performance trace sensing. Here, the chromone-based ligand grafted QDs (QDs-Chromone) were initiated to realize the electronic energy transfer (EET) driven specifically by ethylenediamine (EDA) in the absence of spectral overlap. The fluorescent and colorimetric dual-mode responses (from red to blue and from colorless to yellow, respectively) resulting from the expanded conjugated ligands reinforced the analytical selectivity, endowing an ultrasensitive and specific response to submicromolar-liquid of EDA.

Coherent Modulation of the Aggregation Behavior and Intramolecular Charge Transfer in Small Molecule Probes for Sensitive and Long-term Nerve Agent Monitoring.

Aggregation-induced emission (AIE) shows promising performance in chemical sensing relying on the change of the emission behavior of the probe molecule monomers to the aggregated product. However, whether the response contrast could be further boosted by utilizing the emission property of the aggregated probe and the aggregated product remains a big challenge. Here, an exciting AIE probe regulation strategy was proposed by coherently modulating the aggregation behavior and the intramolecular charge transfer (ICT) property of the probes and thus an aggregated-to-aggregated colorimetric-fluorescent dual-mode detection was achieved.

A Self-Accelerating Naphthalimide-Based Probe Coupled with Upconversion Nanoparticles for Ultra-Accurate Tri-Mode Visualization of Hydrogen Peroxide.

The design and development of ultra-accurate probe is of great significance to chemical sensing in complex practical scenarios. Here, a self-accelerating naphthalimide-based probe with fast response and high sensitivity toward hydrogen peroxide (HO) is designed. By coupling with the specially selected upconversion nanoparticles (UCNPs), an ultra-accurate colorimetric-fluorescent-upconversion luminescence (UCL) tri-mode platform is constructed.

Precise Electron-Withdrawing Strength Modulation of ESIPT Probes for Ultrasensitive and Specific Fluorescence Sensing.

The precise regulation of the electron-withdrawing/electron-donating strength in a probe is of great significance for the design of reaction-based fluorescent probes with specific functionalities. Here, a family of excited-state intramolecular proton transfer (ESIPT)-based probes with fluorescence turn-on sensing properties toward KMnO was designed by precisely modulating the electron-withdrawing strength of the substituents located at the -position of the recognition group. It is found that -F, -CHO, and -H as the electron-withdrawing groups bound at the probe can specifically recognize KMnO, which ensures a blue emission displayed by the reaction products.

Amorphous Copper-Based Nanoparticles with Clusterization-Triggered Phosphorescence for Ultrasensing 2,4,6-Trinitrotoluene.

Amorphous metal-based nanostructures have attracted great attention recently due to their facilitative electron transfer and abundant reactive sites, whereas it remains enigmatic as to whether amorphous copper-based nanoparticles (CuNPs) can be achieved. Here, for synthesizing amorphous CuNPs, glutathione is adopted as a ligand to inhibit the nucleation and crystallization process via its electrostatic repulsion. By subtly tailoring the solvent polarity, not only can amorphous glutathione-functionalized CuNPs (GSH-CuNPs) with phosphorescent performance be achieved after transferring the non-conjugation of GSH ligand to through-space conjugation, namely clusterization-triggered emission, but also the phosphorescence-off of GSH-CuNPs toward 2,4,6-trinitrotoluene (TNT) can be realized by the photoinduced electron-transfer process through the hydrogen bond channel, which is established between carboxyl and amino groups of GSH-CuNPs with the nitryl group of TNT.

A Deep Understanding on the Effective Generation of Twisted Intramolecular Charge Transfer by Protonation in Thiazolo[5,4-]thiazole Derivatives.

The exploration of the intrinsic relationship between the phototautomerization and photoelectric properties is of great significance for the application of the emerging novel organic materials, such as the (bi)heterocyclic thiazolo[5,4-]thiazole derivatives (TzTz). Here, by introducing the chemical-controlling protonation, a barrierless spontaneous rotation movement of the designed TzTz derivative (2,5-diyl-amino-thiazolo[5,4-]thiazole, DA-TzTz) was ensured through the facilitation of the excited-state intramolecular proton transfer (ESIPT) triggered twisted intramolecular charge transfer (TICT) process by the enhancement of the intramolecular hydrogen bonds, steric hindrance effect, and conjugative effect. It is further verified that the hetero S atoms could mostly effect the proton accepting ability of -N═ through comparing with the influences to the intramolecular H-bond between the protonated/nonprotonated amino groups and the -N═ atoms brought by the replacement of them with N or O atoms.

A TD-DFT study of a class of D-π-A fluorescent probes for detection of typical oxidants.

A deep understanding of the fluorescence response mechanisms is the foundation for design-oriented strategies for D-π-A probes for trace hazardous chemicals. Here, from the perspective of electronegativity regulation of the π-bridge recognition site, an electron-donation modulation strategy involving various comprehensive evaluations of the optical and chemical properties is proposed through a series of theoretical analyses. Due to the preferential combined interaction between the π-bridge recognition site and MnO, high electrophilic reactivity and feasible chemical reaction energy barrier, a high-performance filter paper chip and hydrogel chip for the detection of aqueous and air-suspended environmental KMnO was achieved.

A General Twisted Intramolecular Charge Transfer Triggering Strategy by Protonation for Zero-Background Fluorescent Turn-On Sensing.

The exploration of organic fluorescent sensing materials and mechanisms is of great significance, especially for the deep understanding of twisted intramolecular charge transfer (TICT). Here, the electron-donating ability of a chemically protonated amino group and the corresponding excitation primarily ensure the occurrence of excited-state intramolecular proton transfer. Due to the hybridization of the amino group from sp to sp, the steric hindrance effect and conjugative effect together boost the rotation efficiency of the TICT process and the complete elimination of the background fluorescent signal.

Polyethyleneimine-capped copper nanoclusters for detection and discrimination of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol.

The detection and discrimination of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) from analogues are of great importance to global security and are full of challenges in the field of trace sensing. Here, benefitting from the strong electrophilicity of TNT, a sensing strategy is established by synthesizing polyethyleneimine capped copper nanoclusters (PEI-Cu NCs) with abundant -NH groups. By carefully controlling the size and structure of PEI-Cu NCs, Förster resonance energy transfer (FRET) from PEI-Cu NCs to the Meisenheimer complex occurs resulting from their spectral overlap when detecting TNT, while, due to the energy level match of TNP with PEI-Cu NCs, as well as the strong affinity between its -OH and -NH in PEI-Cu NCs, photo-induced electron transfer (PET) is feasibly expected.

Complete Inhibition of the Rotation in a Barrierless TICT Probe for Fluorescence-On Qualitative Analysis.

Inhibition of twisting intramolecular charge transfer (TICT) is one of the most attractive methods for fluorescence-on analysis, whereas it remains enigmatic whether the fluorescence in a TICT-based probe could be thoroughly lightened. Here, for maximizing the fluorescence-on signal of the TICT-based probe, we develop a model by employing chemical reaction to directly cleave the linkage between the rotational electron donor and acceptor with a predisposed fluorescent signal close to zero. To validate this assumption, a nonfluorescent probe with barrierless rotation is successfully achieved by grafting acryloyl with -C═C- recognition sites onto coumarin, and 7-hydroxycoumarin with bright blue fluorescence could be released within 3 s upon probing KMnO with an amount as low as 0.

Highly Retentive, Anti-Interference, and Covert Individual Marking Taggant with Exceptional Skin Penetration.

The development of high-performance individual marking taggants is of great significance. However, the interaction between taggant and skin is not fully understood, and a standard for marking taggants has yet to be realized. To achieve a highly retentive, anti-interference, and covert individual marking fluorescent taggant, Mn -doped NaYF :Yb/Er upconversion nanoparticles (UCNPs), are surface-functionalized with polyethyleneimine (PEI) to remarkably enhance the interaction between the amino groups and skin, and thus to facilitate the surface adhesion and chemical penetration of the taggant.

Ultrasensitive and rapid colorimetric detection of urotropin boosted by effective electrostatic probing and non-covalent sampling.

Leakage and contamination of hazardous chemical substances have been widely recognized as the critical issue in ensuring human health, maintaining environmental sustainability, and safeguarding public security. Urotropin as a crucial raw material in industrial holds a potential threat to aquatic/atmospheric environment with refractory degradation problem, hence, there remains a severe challenge to effectively and on-site monitor urotropin. Here, a general design with all-in-one strategy was presented, in which a highly integrated "pocket sensing chip" combining a sampling unit and a detecting unit together endows a rapid and ultrasensitive colorimetric detection without dead-zone towards urotropin.

D-π-A Dual-Mode Probe Design for the Detection of nM-Level Typical Oxidants.

Although a set of functional molecules with the D-π-A structure has been explored as optical probes for the detection of target analytes, it remains a great challenge to elaborately design a single probe for distinguishing different analytes by their intrinsic oxidation or reduction capabilities and thus to generate distinct optical responses. Here, a unique TCF-based probe (DMA-CN) containing two unsaturated double bonds in the π-conjugation bridge and TCF with different reaction activities that could be cut off by KMnO and NaClO in varying degrees was developed, causing remarkably distinguishable responses for both fluorescence and colorimetric channels to discriminate KMnO and NaClO from each other. The fluorescence and colorimetric limits of detection (LODs) of the proposed DMA-CN toward KMnO were calculated as 60 and 91 nM, respectively, while those for NaClO were 13.

Competitive Delocalized Charge Transfer Boosted by Solvent Induction Strategy for Survivable Colorimetric Detection of ng-Level Urea.

Achieving sensitive and robust colorimetry is of great significance for on-site chemical detection, but has always been a dilemma or at the expense of practicality. Here, from the perspective of solvent, which is commonly the indispensable medium for chemical sensing, the solvent induction strategy concerning the hydrophobic shielding and hydrophilic bonding solvent cage was proposed considering the configuration branching ratio in the reagent and the prevention of the autoxidation channel. Due to the competitive delocalized charge transfer in the probe and the effective viscous drag in the reagent, remarkable sensing signal concentrating and moisture retention capability were achieved.

Electronic Tuning in Reaction-Based Fluorescent Sensing for Instantaneous and Ultrasensitive Visualization of Ethylenediamine.

Manipulation of a multi-physical quantity to steer a molecular photophysical property is of great significance in improving sensing performance. Here, an investigation on how a physical quantity rooted in the molecular structure induces an optical behavior change to facilitate ultrasensitive detection of ethylenediamine (EDA) is performed by varying a set of thiols. The model molecule consisting of a thiol with dual-carboxyl exhibits the strongest fluorescence, which is ascribed to the electron-donating ability and prompted larger orbital overlap and oscillator strength.

Ultrasensitive, Specific, and Rapid Fluorescence Turn-On Nitrite Sensor Enabled by Precisely Modulated Fluorophore Binding.

The precise regulation of fluorophore binding sites in an organic probe is of great significance toward the design of fluorescent sensing materials with specific functions. In this study, a probe with specific fluorescence properties and nitrite detection ability is designed by precisely modulating benzothiazole binding sites. Only the fluorophore bond at the -position of the aniline moiety can specifically recognize nitrite, which ensures that the reaction products displays a robust green emission.

One-Step Instantaneous Detection of Multiple Military and Improvised Explosives Facilitated by Colorimetric Reagent Design.

Although colorimetric detection based on reagents has been widely used in the fields of practical trace analysis, its versatility for detecting multitargets remains the most challenging problem. As a proof of concept, a general colorimetric reagent based on potassium isopropanol (CHKO) and dimethyl sulfoxide for one-step instantaneous detection and discrimination of typical military and improvised explosives was designed. Vivid colors from none to purple red, blue green, yellow green, and green were shown, respectively, when detecting 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), elemental sulfur (S), and potassium permanganate (KMnO).

Qualitative Detection Toward Military and Improvised Explosive Vapors by a Facile TiO Nanosheet-Based Chemiresistive Sensor Array.

A facile TiO nanosheets-based chemiresistive gas sensor array was prepared to identify 11 kinds of military and improvised explosive vapors at room temperature. The morphology of TiO nanosheets was well-controlled by adjusting the concentration of HF applied during the preparation. Owing to the morphology difference, the TiO nanosheet-based sensors show different response values toward 11 kinds of explosives, which is the basis of the successful discriminative identification.

A Colorimetric Artificial Olfactory System for Airborne Improvised Explosive Identification.

The detection of ultralow or nonvolatile target analytes remains a significant challenge for artificial olfactory systems even after decades of development, which severely limits their widespread application. To overcome this challenge, an artificial olfactory system based on a colorimetric hydrogel array is constructed for the first time as a universal representative. As an effective extension of conventional artificial olfactory systems that integrates the merits of its predecessors, the proposed system accurately mimics olfactory mucosa and specific odorant binding proteins using hydrogels endowed with specific colorimetric reagents for the detection of hypochlorite, chlorate, perchlorate, urea, and nitrate.