Converging optical and electrochemical detection strategies for multimodal hydrazine sensing: insights into substituent-driven diverse response.

A pair of pyrene-based chalcogen derivatives have been developed, which demonstrate multimodal ratiometric response towards hydrazine. Although these probes share a common pyrene core and differ primarily in the electronic nature of their terminal side arms, they display distinct photophysical properties. Notably, both probes undergo significant spectral changes upon the addition of hydrazine, but probe 1 exhibits a more pronounced interaction (∼5-fold fluorescence enhancement) than probe 2, attributed to the higher level of aggregation in probe 2, rendering the binding site less accessible to the incoming analyte. Additionally, we have explored electrochemical techniques, including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), for hydrazine detection. Our molecular design strategy relies on ratiometric-responsive specific cyclization triggered by hydrazine, leading to the disruption of the π-conjugated system and the subsequent suppression of intramolecular charge transfer (ICT) processes, along with dis-assembly of the aggregated probe molecules. These probes enable the nakеd-eye detection of hydrazine, with a low detection limit of 7.33 ppb and 7.58 ppb for probe 1 and 2, respectively. Furthermore, we have investigated cost-effective probe-coatеd paper strips for the detection of hydrazine in water.

Label-free multimodal analysis of copper ions at below permissible exposure limit in the aqueous medium.

An anthraimidazoledione based amphiphilic dye molecule was synthesized that shows formation of tuneable charge-transfer state in solution, susceptible to change in pH, polarity and hydrogen bonding ability of the medium. The compound also showed formation of nanoscopic self-assembled structure in water medium. The probe molecule can achieve multimodal detection (colorimetric, fluorimetric and electrochemical) of copper ions as low as 0.3 ppm in the aqueous medium. Addition of copper leads to dose-dependent ratiometric change in solution color from yellow to purple. The mechanistic investigation indicates that the coordination of copper ions was possible via simultaneous engagement of both imidazole nitrogen ends and neighbouring hydroxyl unit. Not only optical property, the changes in microenvironment also influence the selectivity as well as sensitivity of the probe molecule towards Cu2+ ions. Further, the optical probe is used for detection as well as quantification of copper ions in natural water samples without any sample pretreatment. Low-cost, reusable paper strips are developed for rapid, on-location detection of residual Cu2+ in real-life samples.

Fluorescent Nanoassembly of Tetrazole-Based Dyes with Amphoteric Surfactants: Investigation of Cyanide Sensing and Antitubercular Activity.

Tetrazole-based easily synthesizable fluorogenic probes have been developed that can form self-assembled nanostructures in the aqueous medium. Though the compounds could achieve detection of cyanide ions in apolar solvents, such as, THF, significant interference was observed from other basic anions, such as F-, AcO-, H2PO4-, etc. On the other hand, a highly specific response was observed for CN- ions in the aqueous medium. However, the sensitivity was so poor that it could hardly be useful for real-life sample analysis. Interestingly, the co-assembly of such probe molecules with hydroxyethyl-anchored amphoteric surfactants could drastically improve the sensitivity toward CN- ions in water without dampening their excellent selectivity. Also, it was observed that the degree of fluorescence response for CN- ions depends on the nature of the polyaromatic scaffolds (naphthyl vs anthracenyl), the nature of the surfactant assembly (micelle vs vesicle), etc. The mechanistic investigation indicates the hydrogen bonding interaction between the tetrazole -NH group and cyanide ions in the aqueous medium, which can effectively change the electronics of the tetrazole unit, resulting in alteration in the extent of charge transfer interaction. Then, the biocompatible composite materials (dye-surfactant assemblies at different ratios) were tested for antituberculosis activity. Fortunately, in a few cases, the compositions were found to be as effective as the commercially available antituberculosis drug, ethambutol.

Sequence-Specific Relay Recognition of Multiple Anions: An Interplay between Proton Donors and Acceptors.

Ratiometric detection of analyte is highly deserving since the technique is free from background correction. This work reports the design and synthesis of a pyridine-end oligo p-phenylenevinylene (OPV) derivative, 1 and its application in ratiometric dual-mode (both colorimetric and fluorogenic) recognition of dual anions, bisulfate (LOD=12.5 ppb) followed by fluoride (LOD=18.2 ppb) by sequence-specific relay (SPR) technique. The colorless probe turns brown with addition of bisulfate and again becomes colorless with the sequential addition of fluoride ion. In addition to such naked-eye color change, interestingly the ratiometric spectroscopic signals are reversible and evidently, the probe is reusable for several cycles. Besides, in presence of bisulfate, the protonated probe molecules, owing to their larger amphiphilic characteristics, formed self-assembled nanostructures. In addition to colorimetric and fluorescent changes, 1 H NMR titration and systematic DFT study evidently establish the underneath proton transfer mechanisms. Such reusable OPV-based chemosensor particularly with the capability of naked-eye recognition of dual anions using the SPR technique is seminal and possibly the first report in the literature.

Site-specific ammonia adsorption and transduction on a naphthalimide derivative molecule - a complementary analysis involving ab initio calculation and experimental verification.

Naphthalene diimide derivatives (NDIs) have exhibited significant potential for sensing applications owing to their excellent photo-stability, environmental stability, reasonable electronic conductivity, and ability to form nanostructures with diverse morphologies through self-assembly. However, no systematic analysis has been performed to rationalize molecular-level interactions between ammonia (NH3) and functionalized NDI probes, which is essential for systematic performance optimizations of NDI-based NH3 sensors. Therefore, this work proposes a phenylalanine-functionalized NDI derivative (NDI-PHE) as a model host for NH3 adsorption. Subsequent molecular interactions have been comprehensively studied following a complementary approach using ab initio calculation and experimental investigation. Specifically, NH3 adsorption at different atomic positions of NDI-PHE has been investigated using ab initio calculation, where the adsorption energy, charge transfer, and recovery time have been emphasized. The environmental stability of NDI-PHE and the underlying transduction mechanism during NH3 adsorption have been experimentally demonstrated to complement the theoretical analysis. The results exhibit that the presence of phenylalanine groups acts as an anchoring moiety and augments NH3 adsorption via hydrogen bonding and proton transfer interaction. Specifically, a highly stable room temperature adsorption of NH3 near a carboxylic phenylalanine group has been observed with a suitable recovery time at higher temperatures. NH3 adsorption results in electron transfer to the host molecule leading to the formation of stable radical anion species, which significantly modulated the frontal molecular orbitals of NDI-PHE, suggesting superior transduction for both electrochemical and optical detection.

Differential response for multiple ions: a smart probe to construct optically tunable molecular logic systems.

A rhodamine-based optical probe has been designed through a one-pot synthetic protocol involving phenanthroline as a binding motif. The compound showed a bright pink coloration specifically upon the addition of Cu2+ and Hg2+ ions. However, the appearance of bright red fluorescence was observed only in the presence of Hg2+. Considering both, we can detect and discriminate these two ions even at ppb level concentration. Furthermore, these in situ generated metal complexes were utilized for the selective recognition of CN- and I- ions. Pre-coated TLC plates were developed for rapid on-site detection of these toxic ions even in remote places. Finally, on a single molecular probe based on differential opto-chemical interactions with different ions (Cu2+, Hg2+, CN- and I-), we were able to design numerous trivial (OR, NOR) and non-trivial (INHIBIT, IMPLICATION, COMPLEMENT, TRANSFER, NOT-TRANSFER) logic gates. Most fascinatingly, we can switch the logic response from one type to another by simply tuning only the optical output channel.

Anion binding studies with anthraimidazoledione-based positional isomers: A comprehensive analysis of different strategies for improved selectivity.

In the present work, we have reported the design of three different positional isomers of anthraimidazoledione-based charge transfer probes and their anion-binding properties under various conditions. In the acetonitrile medium, the meta isomer showed ratiometric optical response towards basic anions, such as F-, CN-, AcO- and H2PO4-. Based on the differences in the hydrogen bonding ability of these anions, we observed distinguishable output signal, particularly in fluorescence. Though meta and para isomers showed effective interaction with anions, the response was relatively weak for the ortho isomer. We suspected that the presence intramolecular hydrogen bond between pyridine nitrogen and imidazole -NH group might be responsible for such poor performance. Further, we have employed two different strategies to improve the selectivity towards anions. In the first case, selective recognition of anions was achieved using suitable metal ions (Cu2+, Zn2+, Ca2+, and Al3+) as masking agents. On the contrary, we have varied the water content (0, 10, 30 and 50% v/v) in the acetonitrile-water mixture in the second case. The anions with relatively large hydration enthalpy showed no detectable interaction with probe in presence of water. Finally, we used the present system to detect cyanide ion in various natural water samples (tap, pond, and seawater). Also, low-cost reusable paper strips were developed as an alternative method for rapid, on-location detection of CN- ions.

Synthetic Supramolecular Host for D-(-)-Ribose: Ratiometric Fluorescence Response via Multivalent Lectin-Carbohydrate Interactions.

Easily synthesizable, carbazole-based organic nanoaggregates have been designed for selective detection of D-(-)-ribose at physiological pH. The addition of D-ribose results in a ratiometric change in fluorescence color from green to cyan (LOD: ∼12 µM). The mechanistic studies indicate the presence of multipoint noncovalent interactions, such as hydrogen bonding and CH⋅⋅⋅π interactions between D-ribose and acyl hydrazone and terminal pyridyl units of the probe molecule. However, such multipoint interactions dissociate the preformed self-assembled nanoclusters and induce change in optical response. The probe molecule was further exploited in analyzing D-ribose content in biological fluids (diluted human urine and blood serum) and oral supplements. The small standard deviation values (2-3.8 %) with nearly quantitative recovery (93.5-105.5 %) indicate the high accuracy of the presented method. Further, low-cost portable device based coated paper strips were designed for 'on-location' rapid, detection of D-ribose even at remote locations.

A Comprehensive Review on Thiophene Based Chemosensors.

The recognition and sensing of various analytes in aqueous and biological systems by using fluorometric or colorimetric chemosensors possessing high selectivity and sensitivity, low cost has gained enormous attention. Furthermore, thiophene derivatives possess exceptional photophysical properties compared to other heterocycles, and therefore they can be employed in chemosensors for analyte detection. In this review, we have tried to explore the design and detection mechanism of various thiophene-based probes, practical applicability, and their advanced models (design guides), which could be thoughtful for the synthesis of new thiophene-based probes. This review provides an insight into the reported chemosensors (2008-2020) for thiophene scaffold as effective emission and absorption-based chemosensors.