Phenothiazine-Thiophene Hydrazide Dyad: An Efficient "On-Off" Chemosensor for Highly Selective and Sensitive Detection of Hg2+ Ions

A Review on Recent Development of Phenothiazine-Based Chromogenic and Fluorogenic Sensors for the Detection of Cations, Anions, and Neutral Analytes

This review provides an in-depth examination of recent progress in the development of chemosensors, with a particular emphasis on colorimetric and fluorescent probes. It systematically explores various sensing mechanisms, including metal-to-ligand charge transfer (MLCT), ligand-to-metal charge transfer (LMCT), photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and fluorescence resonance energy transfer (FRET), and elucidates the mechanism of action for cation and anion chemosensors. Special attention is given to phenothiazine-based fluorescence probes, highlighting their exceptional sensitivity and rapid detection abilities for a broad spectrum of analytes, including cations, anions, and small molecules. Phenothiazine chemosensors have emerged as versatile tools widely employed in a multitude of applications, spanning environmental and biomedical fields. Furthermore, it addresses existing challenges and offers insights into future research directions, aiming to facilitate the continued advancement of phenothiazine-based fluorescent probes.

Highly Sensitive and Selective Recognition of Zn2⁺ and Fe2⁺ Ions Using a Novel Thiophene-Derived Hydrazone Dual Fluorometric Sensor

The selective detection of Zn2⁺ and Fe2⁺ ions is critical in environmental and biological studies. Schiff base chemosensors hold promise, but exploration of thiophene-derived variants remains limited. This work introduces a novel thiophene-derived Schiff base sensor (TBH), synthesized through the condensation reaction of thiophene-2-carboxaldehyde with benzil-bis-hydrazone, for the selective detection of Zn2⁺ and Fe2⁺ ions. TBH exhibits remarkable selectivity, with a significant 185-fold fluorescence enhancement for Zn2⁺ and complete quenching 99% for Fe2⁺, allowing for distinct detection of both ions. Notably, TBH demonstrates high binding affinity towards Zn2⁺ and Fe2⁺, even in the presence of competing cations, forming stable 1:1 complexes. This finding is supported by absorption and emission titration studies and FT-IR analysis as well. This easily synthesized, rapid and cost-effective sensor offers a promising approach for sensitive and differentiated dual detection of Zn2⁺ and Fe2⁺ in environmental and biological systems.

Synthesis and spectral characterization of the phenothiazine-thiosemicarbazide probe for the optical solid-state detection of Hg2+ and Cu2

In this study, a phenothiazine-thiosemicarbazide (PTZDS) probe was synthesized and characterized. The synthesized PTZDS probe exhibited a yellow color, with a native fluorescence emission at λemission = 550 nm and λexcitation = 450 nm. Over other metal ions, the probe exhibited significant selectivity and sensitivity towards Hg2+ and Cu2+. The probe showed fluorescence quenching along with a minor shift in the absorbance spectra from 400 to 450 nm and 430 nm in the presence of Hg2+ and Cu2+, respectively. In addition, the color of the synthesized probe remarkedly faded with the addition of Hg2+ or Cu2+. Fluorescence measurements, infrared spectroscopy (IR), and density functional theory studies were employed to elucidate the binding process in the PTZDS + Cu2+ and PTZDS + Hg2+ sensor systems. Furthermore, photophysical investigations of the synthesized probe with Hg2+ and Cu2+ were performed. Finally, the probe was successfully employed as a solid-state thin layer chromatography (TLC) optical sensor for detecting Hg2+ and Cu2+ ions.

Synthesis of a quinoxaline-hydrazinobenzothiazole based probe-single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples

A novel quinoxaline-hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct "single-point" colorimetric and fluorescent detection of Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10^-7 M, 9.92 × 10^-8 M, 8.21 × 10^-8 M, and 1.14 × 10^-7 M for Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.

Recent development of small-molecule fluorescent probes based on phenothiazine and its derivates

Fluorescence probes, as analytical tools with the ability to perform rapid and sensitive detection of target analytes, have made outstanding contributions to environmental analysis and bioassays. Considering the expanding developments in these areas, fluorophores play a key role in the de-sign of fluorescence probes. Compared to classical fluorophores, phenothiazines with elec-tron-rich characteristics have been widely applied to construct electron donor-acceptor dyes, which exhibit outstanding performance in both fluorimetric and colorimetric analysis. In addition, these probes also exhibit the pronounced ability in both solution and solid-state, achieving portable detection for environmental analysis. In this review, we summarize recent advances in the performance of phenothiazine-based fluorescent probes for detecting various analytes, especially in cations, anions, ROS/RSS, enzyme and other small molecules. The general design rules, response mechanisms and practical applications of the probes are analyzed, followed by a discussion of exiting challenges and future research perspectives. It is hoped that this review will provide a few strategies for the development of phenothiazine-based fluorescent probes.

A Highly Selective Hg2+ Fluorescent Chemosensor Based On Photochromic Diarylethene With Quinoline Unit

A novel diarylethene-based fluorescent chemosensor containing a quinoline unit (1o) had been designed and synthesized. 1o showed good photochromic ability and fluorescence switching properties by alternating UV/vis light irradiation. The chemosensor showed high "Turn-off" fluorescent selectivity for Hg²⁺ by competitive tests of the fluorescence reaction in the presence other ions in acetonitrile solution. The stoichiometry between the compound 1o and Hg²⁺ was 1:1 by Job's plot curve and HRMS analysis. In addition, the LOD for Hg²⁺ was calculated as 60 nM. The fluorescence emission can be back to the "Turn-on" state by adding EDTA. Based on these facts, a molecular logic gate that including four input signals (UV/vis and Hg²⁺/EDTA) and one output signal (fluorescent intensity at 491 nm) was designed.

Novel allyl-hydrazones including 2,4-dinitrophenyl and 1,2,3-triazole moieties as optical sensor for ammonia and chromium ions in water

It is critical to take safety action if carcinogenic heavy metals and ammonia can be detected quickly, cheaply, and selectively in an environmental sample. As a result, compound 4a [4-(1-(2-(2,4-Dinitrophenyl)hydrazineylidene)-3-(naphthalen-2-yl)allyl)-5-methyl-1-phenyl-1 H-1,2,3-triazole] and compound 4b [4-(1-(2-(2,4-Dinitrophenyl)hydrazineylidene)-3-(naphthalen-2-yl)allyl)-1-(4-fluorophenyl)-5-methyl-1 H-1,2,3-triazole] were prepared. The aldol condensation process of 4-acetyl-1,2,3-triazoles 1a,b (Ar = C6H4; 4-FC6H4) with 2-naphthaldehyde yields 1-acetyl-1,2,3-triazoles 1a,b (Ar = C6H4; 4-FC6H4) (5-methyl-1-aryl-1 H-1,2,3-triazol-4-yl) -3-(naphthalen-2-yl)prop-2-en-1-ones 3a,b with a yield of around 95%. The target compounds 4a,b are obtained in around 88% yield by condensation of 3a,b with (2,4-dinitrophenyl)hydrazine in a refluxing acidic medium. Compounds 4a,b exhibited possible colorimetric detection for chromium ion in the range of 0-14 ppm and ammonia in the range of 0-20 ppm. As a result, this research suggests that strong electron-withdraw groups in related probes can improve anion detection ability, while the conjugation effect should also be considered while building structures.

A novel coumarin-benzopyrylium based near-infrared fluorescent probe for Hg2+ and its practical applications

A novel colorimetric and ratiometric NIR fluorescent probe for Hg²⁺ was designed and synthesized based on a coumarin-benzopyrylium platform. The ring-open form of the probe exhibits NIR absorption (670 nm) and emission (720 nm). The probe shows high sensitivity, high selectivity and rapid response (30 s) to Hg²⁺. The detection limit was as low as 6.94 nM. The probe shows high stability in a wide pH range from 2 to 10. Moreover, the probe can be employed for detecting Hg²⁺ in food and biological samples.

A sulfur-containing fluorescent hybrid porous polymer for selective detection and adsorption of Hg2+ ions

A dual-function material, that is, a sulfur-containing fluorescent hybrid porous polymer, has been simply prepared and utilized to simultaneously detect and capture Hg2+ with high efficiency and selectivity.