Supramolecular assemblies of Zn(II) complexes with D-π-A ligand for sensing specific organic molecules

It is attractive but challenging to develop effective fluorescent sensors for detecting specific organic compound. In this study, we designed and synthesized three Zn(II) complexes [Zn(3N3PY)2](NO3)2·3.5CH3OH (1), [Zn(3N3PY)(BIN)]·1.5DMF (2) and...

An unprecedented pyridine-based dinuclear mixed-valent ReI/VII oxo-bridged complex: a solvatochromic and AIE-active probe for nanomolar detection of picric acid and trinitrotoluene

This paper describes the synthesis of an unprecedented oxo-bridged rheniumI/VII (Re) complex by treating Re2(CO)10 with a pyridyl-linked anthracene-based twisted π-conjugated ligand. The molecular structures of both the ligand and the complex are determined by analyzing IR, NMR, and HR-MS spectra and unequivocally determined using single-crystal X-ray diffraction studies. Unlike previous observations, the complexation occurs uniquely to yield an unprecedented oxo-bridged ReI/VII complex. Such a complex is uncommon, and in most cases, Re(vii) appears as the ReO4- counter ion. The aggregation-induced emission (AIE) feature could have been achieved from this conformationally twisted ligand, but the emission of the ligand was quenched in the aggregated state. The complex exhibited solvatofluorochromic properties with a faint emission. The emission intensity significantly (∼6 times) increased in DMF after the addition of a water fraction of 90%, resulting in a bright orange emission. The AIE is mainly caused by restricted intramolecular rotation (RIR) and is supported by the polarity and viscosity effects. The nanoaggregate formation is captured by SEM, and DLS studies were used to determine the average particle size. After the complexation, the ligand becomes more rigid, and the RIR effect becomes prominent facilitating the AIE effect. The electron-rich aggregate's intense orange emission was used for the selective and sensitive detection of picric acid (PA) and 2,4,6-trinitrotoluene (TNT) at nanomolar levels amongst other nitroaromatics through emission quenching. The detailed mechanistic studies reveal the active role of dynamic quenching and complementary photo-induced electron transfer between the probe and TNT or PA. The easy electron transfer process from the electron-rich to the electron-poor system is confirmed by calculating the lowest unoccupied molecular orbital energy of the associated levels. The application is further extended for on-site PA and TNT detection by permeating the probe on a paper and detected at 10-3 M concentration with the naked eye. The PA/TNT detection efficiency is also confirmed by mixing PA or TNT with soil.

Selective anions mediated fluorescence "turn-on", aggregation induced emission (AIE) and lysozyme targeting properties of pyrene-naphthalene sulphonyl conjugate

We have designed and synthesized a novel pyrene-naphthalene sulphonyl conjugate, 1-((1Z)-(4-((Z)-4-(pyrene-1-yl)methyleneamino)phenylsulfonyl)phenylimino)methyl)naphthalene-2-ol (PSN) through a facile two-step reactions. It was characterized by various spectral techniques. Fluorescence spectral studies showed that compound PSN featured fluorescence enhancement upon increasing the water content in THF. This can be attributed to the phenomena of aggregated induced emission (AIE), which is confirmed by SEM and AFM studies, due to the restriction of CHN isomerization of PSN. The anion sensing of PSN was examined with various anions. Among these anions, H₂PO₄^- and F^- ions were selectively sensing with a low detection limit of 3.52 × 10^-7 M and 7.23 × 10^-7 M, respectively, and an obvious color change from yellow to orange was observed by the naked eye. The mechanism of sensing involved the formation of hydrogen bonding interaction between O-H group of PSN and H₂PO₄^-/ F^- ions. The binding of PSN with LYZ was also examined by docking studies, which shows that H-bonding and hydrophobic interactions play crucial roles for the interaction of LYZ toward PSN.

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.

Recent progress in chemosensors based on pyrazole derivatives

Colorimetric and fluorescent probes based on small organic molecules have become important tools in modern biology because they provide dynamic information concerning the localization and quantity of the molecules and ions of interest without the need for genetic engineering of the sample. In the past five years, these probes for ions and molecules have attracted great attention because of their biological, environmental and industrial significance combined with the simplicity and high sensitivity of absorption and fluorescence techniques. Moreover, pyrazole derivatives display a number of remarkable photophysical properties and wide synthetic versatility superior to those of other broadly used scaffolds. This review provides an overview of the recent (2016-2020) findings on chemosensors containing pyrazole derivatives (pyrazoles, pyrazolines and fused pyrazoles). The discussion focuses on the design and physicochemical properties of chemosensors in order to realize their full potential for practical applications in environmental and biological monitoring (sensing of metal ions, anions, explosives, and biomolecules). We also present our conclusions and outlook for the future.

A stilbazolium dye-based chromogenic and red-fluorescent probe for recognition of 2,4,6-trinitrophenol in water

Probe DMAS-DP in water shows highly selective decrease in absorbance (475 nm) and fluorescence intensity (615 nm) with 2,4,6-trinitrophenol and colour change from red to yellow (visible light) and red fluorescent to black (365 nm light).

Two AIEE-active α-cyanostilbene derivatives containing BF2 unit for detecting explosive picric acid in aqueous medium

Two novel α-cyanostilbene derivatives bearing triphenylamine and BF₂ groups are synthesized (named TPE-B and TPE-BN). The fluorescent emissions of compounds TPE-B and TPE-BN are hypochromatically shifted and bathochromically shifted, respectively, with increasing polarity of the solvents, suggesting that the two compounds have characteristic polarity-dependent solvatochromic effects. Furthermore, they show obvious aggregation-induced emission enhancement (AIEE) phenomenon in THF/water mixture solutions. Meanwhile, compounds TPE-B and TPE-BN emit orange and yellow fluorescence in their solid states, respectively. Most significantly, in aqueous medium, compounds TPE-B and TPE-BN can selectively and sensitively detect picric acid (PA) among a number of nitroaromatic compounds, and their limits of detection (LOD) are calculated as 1.26 × 10⁻⁶ M and 1.51 × 10⁻⁶ M, respectively. The recognition mechanism for PA can be attributed to the photo-induced electron transfer (PET) process and this is supported by density functional theory (DFT) calculation. This research provides two novel compounds for the rational design of AIEE-active materials for sensing systems.

Two α-cyanostilbene derivatives bearing triphenylamine and BF₂ groups exhibit AIEE properties and can detect explosive picric acid in aqueous medium.

Two 2D multiresponsive luminescence coordination polymers for selective sensing of Fe3+, CrVI anions and TNP in aqueous medium

Zn(ii)/Cd(ii)-based 2D coordination polymers have been synthesized as luminescence sensors for the selective and reversible sensing of Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and TNP in water.