2-Hydroxyacetophenone and ethylenediamine condensed Schiff base: Fluorescent sensor for Al3+ and PO43−, biological cell imaging and INHIBIT logic gate

Investigation of Mechanochromic Luminescence of Pyrene-based Aggregation-Induced Emission Luminogens: Correlation between Molecular Packing and Luminescence Behavior

To better understand the correlation between molecular structure and optical properties such as aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) emission, two new pyrene-based derivatives with substitutions at the 4- and 5-positions (1HH) and at the 4-, 5-, 9-, and 10-positions (2HH) were designed and synthesized. Cyano groups were introduced at the periphery of the synthesized compounds (1HCN, 1OCN, 1BCN, 2HCN, 2OCN, and 2BCN) to investigate the influence of these groups on the emission properties of the pyrene derivatives both in solution and in the solid state. The fluorescence emission performance of these compounds in water/acetone mixtures was simultaneously studied, revealing outstanding aggregation-induced emission properties. The typical shift in emission maxima to higher values was attributed to J-aggregate formation in the aggregate state. Careful investigation of the crystal structures demonstrated abundant and intense intermolecular interactions, such as C-H…π and C-H…N hydrogen bonds, contributing to the remarkable mechanochromic luminescence performance of these compounds. The MCL properties of all the compounds were investigated using powder X-ray diffraction, and the remarkable mechanochromic properties were attributed to J-aggregate phenomena in the solid state. These results provide valuable insights into the structure-property relationship of organic MCL materials, guiding the design of efficient organic MCL materials.

Novel fluorescent probe for sequential recognition of Zn2+ and pyrophosphate in aqueous based on aggregation-induced emission

A new fluorescent probe (E)-4-(4-([2,2':6',2''-terpyridin]-4'-yl)styryl)-1-dodecylpyridin-1-ium (TPy-SD), with the aggregation-induced emission (AIE) property in aqueous solution, has been synthesized and characterized. The new probe, TPy-SD exhibited excellent selectivity and sensitivity towards Zn²⁺ with a relatively low detection limit (1.76 × 10^-7 M). The addition of Zn²⁺ is thought to disrupt the AIE property of TPy-SD, thereby leading to a fluorescence blue shift. Interestingly, the complex of probe TPy-SD with Zn²⁺ (Zn (II) TPy-SD), with molar ratio of 1:1, can be used as a simple, sensitive, and rapid means for the detection of pyrophosphates (PPi) in solution (water/DMSO = 99:1). As evidenced by transmission electron microscopy (TEM), dynamic light scattering (DLS) and fluorescence emission spectroscopy, this detection is thought to be due to the strong affinity between PPi and Zn²⁺, which brings out Zn²⁺ from the coordination cavity of chemical sensor TPy-SD, thus realizing the detection and recognition of PPi. Therefore, the new AIE fluorescent probe can be used as a dual probe for the detection of cations and anions.

Real time sensor for Fe3+, Al3+, Cu2+ & PPi through quadruple mechanistic pathways using a novel dipodal quinoline-based molecular probe

A quinoline-based small molecular probe, H₂L was designed, synthesized and characterized by different spectroscopic methods. It was utilized as a multi-responsive probe for the detection of Fe³⁺, Al³⁺, Cu²⁺ and PPi. It showed very selective instant turn-on fluorimetric response towards Fe³⁺and Al³⁺ with a detection limit in nanomolar range. Solutions of H₂L containing Fe³⁺ or Al³⁺ could sequentially sense PPi by a turn-off mechanism. Also, H₂L could determine the presence of Cu²⁺ very selectively among a series of other metal ions by a sharp change in colour. Detection of Cu²⁺ through colorimetry was further investigated by systematic UV-Vis studies and the potential of H₂L to act as a potential colorimetric sensor for Cu²⁺ was suitably established. Filter-paper strip experiments were conducted to demonstrate the practical utility of the proposed sensor. Potential applications of H₂L as a sensor for pH in the acidic range has also been explored.

Selective and recyclable tandem sensing of PO43- and Al3+ by a water-stable terbium-based metal-organic framework

Herein, a luminescent water-stable terbium-based metal-organic framework (MOF) {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and used for the recyclable sensing of PO₄^3- and Al³⁺ in tandem. MOF 1 acts as a fluorescent sensor for PO₄^3- by the luminescence "turn-off" mechanism with high selectivity over other anions, such as F^-, Cl^-, Br^-, I^-, NO₃^-, H₂PO₄^-, HSO₄^-, HCO₃^-, HSO₃^-, SO₄^2-, CO₃^2- and HPO₄^2-. The formed PO₄^3-@1 complex further acts as the Al³⁺ sensor with the luminescence "turn-on" mechanism, also with high selectivity over diverse inorganic cations of Fe²⁺, Mn²⁺, Co²⁺, Ni²⁺, Hg²⁺, Na⁺, K⁺, Li⁺, Ag⁺, Mg²⁺, Ca²⁺, Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺. The detection process for both PO₄^3- and Al³⁺ can be directly observed with naked eyes under the UV light at 365 nm. The detection limits for PO₄^3- and Al³⁺ are 1.1 μM and 6.6 μM, respectively. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.

A Naphthalimide-Based Fluorescence "Off-on-Off" Chemosensor for Relay Detection of Al3+ and ClO. Front Chem 2019;7:549. [PMID: 31428604 PMCID: PMC6687763 DOI: 10.3389/fchem.2019.00549]

A novel Al³⁺ chemosensor NPA was designed and synthesized on basis of the mechanism of ICT and CHEF. Upon addition of Al³⁺, the probe NPA displayed a bright green fluorescence under UV radiation and visual color change from yellow to colorless. Spectrum titrations showed that NPA could be recognized as a fluorescent turn-on probe with 10^-8 M detection level. The probe was successfully applied in real water sample and test paper. More important, NPA-Al³⁺ complex were used as a fluorescent turn-off probe for the detection of ClO^- with the detection as low as 2.34 × 10^-8 M. The performance of NPA to Al³⁺ and NPA-Al³⁺ complex to ClO^- demonstrated that NPA could be served as a sensitive probe and exhibit INHIBIT logic gate behavior with Al³⁺ and ClO^- as inputs.

A dual-function probe based on naphthalene for fluorescent turn-on recognition of Cu2+ and colorimetric detection of Fe3+ in neat H2O

A simple naphthalene derivative, 6-hydroxy-2-naphthohydrazide (NAH), was designed and synthesized through two facile steps reactions with the 6-hydroxy-2-naphthoic acid (NCA) as the starting material. In neat H₂O (10% 0.01 M HEPES buffer, v/v, pH = 7.4), probe NAH showed a highly selective and sensitive response towards Fe³⁺ via perceptible color change and displayed "turn-on" dual-emission fluorescence response for Cu²⁺. The binding stoichiometry ratio of NAH/Cu²⁺ and NAH/Fe³⁺ were all confirmed as 1:1 by the method of fluorescence job's plot and UV-Vis job's plot, respectively. Probe NAH can be used over a wide pH range for the determination of Fe³⁺ (2.0-10.0) and Cu²⁺ (6.0-10.0) without interference from other co-existing metal ions. A possible detection mechanism was the hydrolysis of NAH upon the addition of Fe³⁺ or Cu²⁺, thereby leading to the formation of 6-hydroxy-naphthalene-2-carboxylic acid (NCA) which was further confirmed by the various spectroscopic techniques including FT-IR, ¹H NMR titration and HRMS. Moreover, NAH was successfully applied to the detection of Cu²⁺ and Fe³⁺ in tap water, ultrapure water and BSA.

Condensation Product of 4-Methoxybenzaldehyde and Ethylenediamine: "Off-On" Fluorescent Sensor for Cerium(III)

The condensation product (L) of 4-methoxybenzaldehyde and ethylenediamine has been synthesised and characterised. L showed a 21 times enhancement in fluorescence intensity on interaction with Ce³⁺ in CH₃OH at λ_max = 360 nm when excited with 270 nm photons. Metal ions K⁺, Na⁺, Al³⁺, Co²⁺, Hg²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Mg²⁺ and Ca²⁺ do not interfere. The stoichiometry of binding and the binding constants were determined from spectroscopic data and found to be 1:1 and 10^4.8 M respectively. The detection limit was found to be 10^-5.2 M. The protonation/de-protonation of water molecules coordinated to Ce³⁺ was found to show interesting behaviour on the fluorescence of L:Ce³⁺.