Two-phase activated colorimetric and ratiometric fluorescent sensor for visual detection of phosgene via AIE coupled TICT processes

Electron-donating and -withdrawing groups discriminate the fluorometric sensing of phosgene

Phosgene, diphosgene, and chlorine are called choking agents due to their acute toxicity to the respiratory system by directly attacking through inhalation and causing acute hypoxia, asphyxia and death. For these reasons, small-molecule fluorescent probes have been developed for their detection to ensure public safety. In this regard, two thiophene-based chemodosimetric fluorescent probes TCAO ((Z)-3-(4-(dimethylamino)phenyl)thiophene-2-carbaldehyde oxime) and HMBT ((Z)-4-(2-((hydroxyimino)methyl)thiophen-3-yl)benzonitrile) were designed, synthesized and characterized using 1H-NMR, 13C NMR, FT-IR spectroscopy and HRMS methods. Probe TCAO exhibited higher selectivity and sensitivity for detecting phosgene than probe HMBT. The electron-donating group (EDG) and electron-withdrawing group (EWG) play a crucial role in detecting phosgene. TCAO, bearing EDG, exhibited a fluorescence 'turn-on' response by the NGP-assisted conversion of aldoxime to the cyano group in the presence of phosgene; whereas HMBT, bearing EWG, did not show any fluorometric response. Therefore, further studies were conducted on TCAO, and the quantum yield changed from Φ = 0.043 to Φ = 0.155 in the presence of phosgene. The limit of detection for TCAO was estimated to be as low as 51 nm. In addition, onsite monitoring for visual detection was performed using the easy-to-handle paper-strip method.

A Ratiometric Benzimidazole-Based Fluorescent Probe for The Recognition of Phosgene in Solution and Gaseous Phases

Considering the high toxicity and widespread application of phosgene, there is an urgent need to develop a simple and sensitive method for detecting phosgene. In this work, we designed and synthesized a novel ratiometric fluorescent probe 1 containing fluorophores of benzimidazole and benzothiazole. Probe 1 showed excellent sensitivity (< 30 s) and selectivity (LOD = 3.82 nM) for phosgene and significant ratiometric fluorescence changes. In addition, 1-loaded polystyrene membrane test strips were used to conveniently and efficiently detect phosgene gas (0.5 ppm) via the naked eye and the RGB APP of the smartphone, indicating that this probe has great potential for phosgene detection in the gaseous phase.

A novel near-infrared fluorescent probe for ultrasensitive and visual detection of mitochondrial viscosity

The development of fluorescent probes capable of detecting abnormal changes in cellular mitochondrial viscosity is of great significance, as these changes have been connected to many diseases. In this study, the conventional tetraphenylethylene (TPE) molecule was modified to fabricate a novel near-infrared fluorescent, TTPB, which was then used to measure the mitochondrial viscosity. Due to the introduction of TPE and pyridine groups, TTPB had an AIE effect and mitochondrial targeting function. Meanwhile, TTPB was extremely sensitive to variations in viscosity for the twisted intramolecular charge transfer (TICT) phenomenon. The logarithm of fluorescence intensity (logI620) of the probe demonstrated an excellent linear connection with the logarithm of viscosity (logη) in the viscosity range of 1.2 ∼ 956.0 cP, indicating the probe could quantitatively detect viscosity. Moreover, TTPB was able to visually track autophagy in addition to detecting the mitochondrial viscosity in the inflammatory cell model. These results showed that the probe was anticipated to be employed for the early diagnosis of related diseases.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

Ratiometric Fluorescent Probe for the Detection of Nanomolar Phosgene in Solution and Gaseous Phase: Advancing Crime Detection Applications

Phosgene, an exceptionally hazardous gas, poses a grave concern for the health and safety of the general public. The present study describes a fluorescent ratiometric probe for phosgene employing 2-(naphthalen-2-yl) benzo[d]oxazol-5-amine (NOA) with an amino group as the recognition site. NOA detects phosgene through the intramolecular charge transfer mechanism. The electron-rich amine group of NOA attacks the electrophilic carbonyl group of phosgene, resulting in a quick response within 20 s. NOA demonstrates a low detection limit of 60 nM while maintaining high selectivity and sensitivity toward phosgene. The final product was isolated and verified by nuclear magnetic resonance spectroscopy. The probe can detect phosgene not just quickly in a solution environment but also in its solid state. The probe's applications in fingerprint imaging and bioimaging are also demonstrated.

A new highly sensitive fluorescent probe for visualization of phosgene in liquid and gas phases

Phosgene is an important and widely used highly toxic chemical that poses a serious potential threat to public health and property if leaked or abused. Therefore, developing an efficient and convenient detection method for phosgene is of great significance. In this work, we synthesized a novel fluorescent probe, BCyP, based on benzohemicyanine for highly selective and sensitive detection of phosgene in both liquid and gas phases. The probe uses amino alcohol as a specific recognition group for phosgene and does not fluoresce due to the strong intramolecular charge transfer effect (ICT). However, in the presence of phosgene, the amino alcohol part in the probe can form oxazolidinone in situ with phosgene, reducing the ICT effect in the probe molecule and lighting fluorescence, thus realizing the selective phosgene detection. The probe exhibits good specificity towards phosgene, with significant fluorescence enhancement (approximately 400-fold), a remarkable Stokes shift (139 nm), a fast response speed (less than 17 s), and a low detection limit (0.12 ppm). Additionally, we prepared a phosgene detection paper strip loaded with the probe on filter paper and combined it with color recognition software on a smartphone to achieve visual detection of phosgene in the gas phase.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Substituent Effect on AIE mechanism of two coumarin derivatives: uncommon TICT fluorescence in aggregation state

Two coumarin derivatives, 7-diethylamino-3-(4-nitrophenyl)coumarin (DNC) and 7-hydroxy-3-(4-nitrophenyl)coumarin (HNC), were synthesized via Knoevenagel condensation of salicylaldehyde derivatives with 4-nitrophenylacetonitrile and then cyclization reaction. Both of them were characterized by single-crystal X-ray diffraction. The molecules of DNC are stacked via π-π interaction, while the hydrogen bond interactions instead of π-π interaction were observed in the crystal packing of HNC. Both of DNC and HNC showed solvatochromic properties and aggregation-induced emission (AIE) activities, but the AIE characteristics of them were entirely different. HNC exhibited an AIE phenomenon as the result of the restriction of twisted intramolecular charge transfer (TICT), while DNC emitted peculiar dual fluorescence which was assigned to the emission based on the inhibition of TICT state formation and the emission from the TICT state respectively.

Activity-based fluorescent probes for sensing and imaging of Reactive Carbonyl species (RCSs)

This review explains various strategies for developing fluorescent probes to detect reactive carbonyl species (RCS). There are sevaral number of mono and diacarbonyls among 30 varieties of reactive carbonyl species (RCSs) so far discovered, which play pivotal roles in pathological processes such as cancer, neurodegenerative diseases, cardiovascular disease, renal failure, and diabetes mellitus. These RCSs play essential roles in maintaining ion channels regulation, cellular signaling pathways, and metabolisms. Among RCSs, Carbon moxide (CO) is also utilized for its cardioprotective, anti-inflammatory, and anti-apoptotic effects. Fluorescence-based non-invasive optical tools have come out as one of the promising methods for analyzing the concentrations and co-localizations of these small metabolites. There has been a tremendous eruption in developing fluorescent probes for selective detection of specific RCSs within cellular and aqueous environments due to its high sensitivity, high spatial and temporal resolution of fluorescence imaging. Fluorescence-based sensing mechanisms such as intramolecular charge transfer (ICT), photoinduced electron transfer (PeT), excited-state intramolecular proton transfer (ESIPT), and fluorescence resonance energy transfer (FRET) are described. In particular, probes for dicarbonyls such as methylglyoxal (MGO), malondialdehyde (MDA), along with monocarbonyls that include formaldehyde (FA), carbon monoxide (CO) and phosgene are discussed. One of the most exciting advances in this review is the summary of fluorescent probes of dicarbonyl compounds.

Construction of a ratiometric phosgene probe by chromophore formation from auxochrome

A new fluorescent probe for ratiometric detection of phosgene is reported. This probe was constructed with classic 1,8-naphthalimide and 2-(2-aminophenyl)benzimidazole by Ullmann coupling reaction. After exposure to phosgene, yellow fluorescence weakened while blue fluorescence enhanced significantly. There was a ratiometric response between 542 nm and 490 nm. The detection limit (LOD) was 6.7 nM and the response time was within 200 s in CHCl₃. Meaningfully, a new chromophore, benzo [4,5]imidazo[1,2-c]quinazolin-6(5H)-one, was formed after 2-(2-aminophenyl)benzimidazole unit reacted with phosgene, and the ratiometric response was achieved by two chromophores in which the mechanism was confirmed by ¹H NMR spectra, HRMS and theoretical calculation. Furthermore, test papers and nanofibers were fabricated with the probe, which could sensitive detection of phosgene within 10 min and 1 min respectively.

Visual detection of viscosity through activatable molecular rotor with aggregation-induced emission

Food safety has become one of the urgent affairs in the global public health studies, and irregular viscosity is closely associated with the food spoilage extent. In this study, one kind of activatable molecular rotor (TPA-PBZ) based on triphenylamine derivates has been synthesized via the Schiff base condensation reaction. This rotor is comprised by donor-accepter conjugated structure, with aggregation induced-emission feature and a large Stokes shift of 160 nm in water. The rotation of aromatic rings in TPA-PBZ is restricted in high-viscosity microenvironment, with the gradually increasing fluorescence emission signal at 568 nm. Significantly, this rotor TPA-PBZ has successfully been applied not only in the determination of thickening effects of food gum, but also in the detection of viscosity enhancement during the liquid food spoilage process. This molecular rotor can be utilized as an intelligent monitor platform for food quality and safety inspection in viscosity-related conditions.