Fluorescent Detection of Trace Water in Methanol Based on an Al(III) Chemical Sensor

A highly sensitively "off-on-off" fluorescence probe for detection of aluminum ion and water as well as application in Chinese Baijiu

Developing highly sensitive fluorescent probe for Al3+ and H2O detection is highly desirable, due to aluminum toxicity poses a significant threat to public health. On the other hand, the determination of water content holds immense significance in a wide range of fields such as food processing, pharmaceutical manufacturing. In this paper, a novel acylhydrazone-based fluorescent probe P was successfully synthesized and characterized for the sequential detection of Al3+ and water in alcohols. The probe P exhibited a remarkable "turn-on" response towards Al3+ by emitting yellow fluorescence at 567 nm, with high selectivity and large Stokes shift (147 nm). Meanwhile, the in situ formed P-Al3+ complex demonstrated significant solvatofluorochromic characteristic, which could be utilized as a second probe for detecting water via fluorescence quenching with low detection limit in alcohols (0.008%, methanol; 0.013%, ethanol; 0.013%, isopropanol; 0.037%, n-butanol; vol.%) and acetonitrile (0.072%, vol.%). Moreover, the P-Al3+ complex was able to detect the alcoholic strength of Chinese Baijiu without the interference of other alcohols, providing an excellent recovery rate (100.0-107.0%). Different Chinese Baijius, with various alcoholic strength, could be distinguished by simple test strips. Furthermore, the P-Al3+ complex could also analyze the water content in organic solvents .

An ESIPT-ICT steered naphthylthioic-based ionic probe with dual emissive channels exhibiting CHEF and CHEQ effects

A naphthylthioic-based emissive probe (M) bearing a hydroxyl and amine group was designed and synthesized via a one-step Schiff base reaction process. The probe was characterized spectroscopically using ¹H NMR, UV-Vis and fluorescence spectrophotometers. The probe turned out to be spectroscopically and colorimetrically selective and sensitive to multiple cations and anions. Interestingly, the probe displayed characteristics of excited-state intramolecular proton transfer (ESIPT)-driven dual emissive channels; experiencing fluorescence enhancement upon the molar additions of Al³⁺ as well as the anions used, events presumably ascribed to chelation fluorescence enhancement (CHEF), hydrogen bonding and deprotonation effects. Moreover, the fluorometric titration with Hg²⁺ resulted in ratiometric spectral behaviors of M, with the disappearance of the peak at 450 nm, concomitant with the appearance of a new peak at 520 nm, distinguished by a clear isosbestic point, the same behaviors exhibited by Sn²⁺ and Ag⁺ analytes towards M. The introduction of all other cations used, resulted in fluorescence quenching, attributable to chelation enhanced fluorescence quenching (CHEQ), thereby inhibiting the ESIPT process. The experiments were all carried out in the aqueous environment medium of DMSO–H₂O (9 : 1) at ambient temperature. Theoretical density functional theory calculations were carried out to gain insight into the interaction of M with cations and anions, and their influence on the HOMO–LUMO energy gaps.

A naphthylthioic-based emissive probe (M) bearing a hydroxyl and amine group was designed and synthesized via a one-step Schiff base reaction process.

A highly selective "turn-on" water-soluble fluorescent sensor for gallium ion detection

In this work, a novel sensor, (E)-N′-(3-(tert-butyl)-2-hydroxybenzylidene)thiophene-2-carbohydrazide (1), based on salicylaldehyde and thiophene hydrazide moieties was designed and synthesized. The single-crystal structure of 1 was achieved and studied for understanding its functional properties. The interaction and recognition abilities of 1 with different metal ions were investigated. Sensor 1 showed excellent “turn-on” fluorescence with highly selective and specific recognition ability in the presence of gallium ions (Ga³⁺) in an aqueous solution. The sensing behavior of 1 with Ga³⁺ was also studied by photophysical experiments, ESI-MS analysis, and ¹H NMR titration. The limit of detection (LOD) and limit of quantification (LOQ) of 1 for the detection of Ga³⁺ in an aqueous solution were calculated as 58 nM, and 192 nM, respectively. DFT calculations were carried out to optimize the configuration of 1 and 1–Ga³⁺ complexes and rationalize the photophysical experimental data. Highly selective test strips based on sensor 1 were developed for Ga³⁺ detection. Sensor 1 was also used to detect Ga³⁺ in actual water samples, and a considerable recovery rate was obtained.

In this work, a highly selective water-soluble “turn-on” fluorescent sensor for gallium ion recognition was reported.

"Turn-On" Fluorescent Biosensors for High Selective and Sensitive Detection of Al3+ Ion

A series of new compounds (1-4) based on pyrrole hydrazone Schiff bases were designed and synthesized. The interactions of these new compounds with metal ions and their fluorescent recognition were investigated. All compounds showed "turn-on" fluorescence in the presence of Al3+ in aqueous solution. Their sensing behaviors with Al3+ were studied using photophysical experiments, ESI-MS spectrometry analysis, 1H NMR titration, and DFT calculation. The detection limits of 1-4 for the analysis of Al3+ were found to reach a 10-8 M level in aqueous solution, which are far lower than the WHO guidelines for drinking water (7.41 mM for Al3+). A high selectivity test paper has been fabricated for Al3+ detection based on sensor 3. Theoretical calculations (DFT) have been carried out to elucidate the configuration of 1-4 and their Al complexes and rationalize experimental absorption data.

Covalent organic frameworks as a sensing platform for water in organic solvent over a broad concentration range

A highly crystalline covalent organic frameworks (COFs) formed by condensation reaction between 1, 3, 5-tris (4-aminophenyl) benzene and 4, 4'-biphenyldicarboxaldehyde is utilized as a sensing platform for water in organic solvent over a broad concentration range. The resulting COFs exhibits brilliant fluorescence in various organic solvents such as methanol, DMF, acetonitrile and ethanol, moreover its fluorescence intensity has a significant and rapid response to the content of water in organic solvent over a broad concentration range. The broadest sensing range is achieved over 7%-70% (v/v) for water in DMF, and the lowest limit of detection is 0.042% (v/v) for water in methanol among the investigated organic solvents. The superior properties of the sensing platform expand the application ranges of COFs and endow the resulting COFs with a great prospect in practical applications for highly efficient detecting water in organic solvent.

Excited State Intramolecular Proton Transfer Plus Aggregation-Induced Emission-Based Diketopyrrolopyrrole Luminogen: Photophysical Properties and Simultaneously Discriminative Detection of Trace Water in Three Organic Solvents

Developing solid state near-IR (NIR) emitters and simultaneously discriminative detection of trace water in organic solvents has long been a significant challenge. In this work, a novel diketopyrrolopyrrole-based luminogen (DPP1) with excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) characteristics has been designed and synthesized. Its amorphous and crystal solids show red and NIR-emissive fluorescence at 625 and 675 nm, respectively. When DPP1 reacts with fluoride anion, the resulting system (DPP1·F) can discriminatively detect the water content in aprotic solvents with colorimetric and fluorescent dual modes. Distinct fluorescent responses of "turn-on", "ratiometric turn-off", and "ratiometric turn-on" and low limits of detection of 0.0064, 0.042, and 0. The water-induced sensitive and fast change in THF was applied to the determination of water in foodstuffs in practical solid state indicator paper strips.

Colorimetric and fluorometric dual sensing of trace water in methanol based on a Schiff Base-Al3+ ensemble probe

A new julolidine based Schiff base receptor (L) was synthesized and characterized. L forms a 1:1 complex with Al³⁺ in methanol, resulting in an immediate color change from chartreuse to orange and a remarkable enhancement in its emission intensity along with a bathochromic shift from 540 nm to 570 nm. Addition of trace amounts of water significantly quenches the fluorescence emission, where a decomplexation of Al³⁺ from the L-Al³⁺ complex takes place. The significant quenching effect indicated that the L-Al³⁺ ensemble system can be used to detect trace water in commercial methanol. From the fluorescence titration, the detection limit for sensing water in methanol was estimated to be 0.0047%. We have also made an easy-to-prepare test strip of L-Al³⁺ to detect water in methanol through naked-eye observation, which is possible to realize in situ monitoring.