A fluorescent probe based on phenothiazine for detection of ClO− with naked-eye color change properties

A triple-chromophore based NIR fluorescent chemodosimeter with configurable opto-chemical logic gate functions for multi-analyte recognition of N2H4, CN-, and ClO- in real samples

Developing structurally simple, near-infrared (NIR)-emitting organic fluorescent probes capable of simultaneously detecting multiple analytes remains challenging. Herein, we reported a dual donor-π-acceptor (D'-D-π-A) type NIR-chemodosimeter, TPB with a large stokes shift (ca. 250 nm) based on a novel triphenylamine-phenothiazine-benzothiazole multichromophoric system. With its dual reactive sites i.e. an electrophilic β-vinylic carbon and an oxidizable sulfur atom, TPB demonstrated multi-analyte responsiveness towards N2H4, CN-, and ClO- through distinct fluorescence read-outs. Photophysical analysis revealed ratiometric sensing for N2H4 and CN- with emission colors shifting from faint red to turquoise and light blue, respectively. In contrast, ClO- triggered fluorescence quenching, resulting in complete disappearance of emission color. TPB displayed high sensitivity with minimal interference and exhibited low limit of detection (LOD) values of 0.065 μM, 0.117 μM, and 0.63 μM and rapid response times of 5 min, 2 min, and 12 min, for N2H4, CN- and ClO-, respectively. Comprehensive 1H/13C NMR, HRMS analyses, and TD-DFT studies were conducted to support the proposed mechanistic pathways. The optical responses acquired by sequential analyte interactions ensued us to devise multifunctional molecular logic circuits (YES, NOT, PASS 0, NOR) on a unimolecular platform. To enhance practicality, TPB was incorporated into test strips, allowing solid-phase real-time detection of these analytes. Furthermore, TPB successfully detected N2H4 in various soil-samples, demonstrating its effectiveness in environmental monitoring.

A phenothiazine-based ratiometric fluorescent probe for detecting hypochlorite (ClO-) and its application in foods and water samples

As a significant reactive oxygen species (ROS), ClO- plays versatile roles in daily life and many biological events. However, its abnormal levels are responsible for serious harm to human health. Therefore, it is of crucial interest to develop effective methods for detecting ClO- in foods and living organisms. In this work, a novel fluorescent probe ethyl 2-(3-formyl-2-methoxy-10H-phenothiazin-10-yl)acetate (PEA) for detecting ClO- was presented. It shows the merits of rapid ratiometric response (within 10 s), high selectivity and very large Stokes shift (190 nm). The detection limit of PEA for ClO- was determined to be 0.47 μM. We not only successfully prepared paper test strips for efficient qualitative naked eye ClO- detection, but also demonstrated its potential for the valid detection of ClO- in natural water samples, beverages and foods. Furthermore, the probe PEA was also applied to the fluorescence imaging of ClO- in onion epidermal cells.

A turn-on AIE dual-channel fluorescent probe for sensing Cr3+/ClO- and application in cell imaging

A Cr3+/ClO--enhanced fluorescent probe, DNS (5-(dimethylamino)-N'-(2-hydroxy-4,6-dimethoxybenzylidene)-naphthalene-1-sulfonyl hydrazide), with aggregation-induced emission (AIE) properties was synthesized using dansylhydrazide and 4,6-dimethoxysalicylaldehyde as starting materials. The probe rapidly and selectively detects Cr3+ and ClO- in a solvent system of H2O/DMSO (2:8). Upon binding with Cr3+/ClO-, the probe exhibits a significant fluorescence enhancement, with minimal interference from other ions. The detection limits (LOD) were determined to be 5.36 × 10-7 mol/L for Cr3+ and 3.65 × 10-7 mol/L for ClO-. The binding mechanisms of DNS with Cr3+/ClO- were investigated through Job's plot, 1H NMR titration, and mass spectrometry. Furthermore, the probe's low cytotoxicity and biocompatibility suggest its potential for detecting exogenous Cr3+/ClO- and endogenous ClO- in living cells. DNS shows promise for real-time detection and bioimaging applications.

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.

Design, synthesis and application of dual-channel fluorescent probes for ratiometric detection of HClO and H2S based on phenothiazine coumarins

The ubiquity of diverse material entities in environmental matrices renders the deployment of unifunctional fluorescent indicators inadequate. Consequently, this study introduces a ratiometric dual-emission fluorescent sensor (Probe CP), synthesized by conjugating phenothiazine coumarin to hydroxycoumarin through a piperazine linker for concurrent detection of HClO and H2S. Upon interaction with HClO, the phenothiazine unit's sulfur atom undergoes oxidation to sulfoxide, facilitating a shift from red to green fluorescence in a ratiometric manner. Concurrently, at the opposite terminus of Probe CP, 2,4-dinitroanisole serves as the reactive moiety for H2S recognition; it restores the blue emission characteristic of 7-hydroxycoumarin while maintaining the red fluorescence emanating from phenothiazine coumarin as an internal standard for ratio-based assessment. Exhibiting elevated specificity and sensitivity coupled with minimal detection thresholds (0.0506 μM for HClO and 1.7292 μM for H2S) alongside rapid equilibration periods (3 min for HClO and half an hour for H2S), this sensor was efficaciously employed in cellular environments and within zebrafish models as well as imaging applications pertaining to alcohol-induced hepatic injury in murine subjects.

Design, synthesis, and biological application of A-D-A-type boranil fluorescent dyes

For the first time, three acceptor-donor-acceptor (A-D-A)-type boranil fluorescent dyes, CSU-BF-R (R = H, CH3, and OCH3), featuring phenothiazine as the donor, were designed and synthesized. CSU-BF-R exhibited remarkable photophysical characteristics, including large Stokes shifts (>150 nm), high fluorescence quantum yields (up to 40%), long-wavelength emissions, and strong red solid-state fluorescence. Moreover, these CSU-BF-R fluorescent dyes were demonstrated to function as highly selective and sensitive ratiometric fluorescent probes for detecting hypochlorous acid (HClO). The preliminary biological applications of CSU-BF-OCH3 for sensing intracellular HClO in living cells and zebrafish were demonstrated. Therefore, CSU-BF-R possess the potential to further explore the physiological and pathological functions associated with HClO and provide valuable insights into the design of high-performance A-D-A-type fluorescent dyes.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.