Browsing by Author "Avanish Kumar Singh"

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A coumarin derived turn ‘off–on-off’ probe for selective sequential monitoring of Al3+ and Cu2+ ions with bio-imaging application
(Elsevier B.V., 2024) Sarita Gond; Avanish Kumar Singh; Pranjalee Yadav; Pradeep Kumar; S. Srikrishna; Vinod P. Singh
Herein, a coumarin-based chemosensor (E)-N'-(1-(2-oxo-2H-chromen-3-yl)ethylidene) thiophene-2-carbohydrazide (ACT) has been synthesized and thoroughly characterized by using various spectroscopic techniques. The molecular structure of the probe has been confirmed by single crystal X-ray diffraction technique. Hirshfeld surface analysis has also been carried out to investigate weaker interactions in the probe molecule. ACT shows a highly selective enhanced fluorometric response towards Al3+ in ethanol among different competing cations. Upon interaction with Al3+, a new complex ACT-Al3+ is formed which displays a strong yellow fluorescence due to chelation enhanced fluorescence process (CHEF). Furthermore, in situ ACT-Al3+ complex is exploited for sequential recognition of Cu2+ with fluorescence turn-off via paramagnetic quenching mechanism among different competing cations. This study presents an exceptionally low detection limits of ACT for Al3+ and Cu2+ ions (2.33 × 10−11 and 1.96 × 10−11 M, respectively). Furthermore, the binding constants of ACT for Al3+ and Cu2+ were found to be 7.97 × 104 and 9.79 × 104 M−1, respectively. The binding mechanism has been verified by 1H NMR titration and DFT calculations. Sensing behaviour of ACT towards Al3+ and Cu2+ have also been exploited in the development of paper strip kit and intracellular application in 3rd instar larvae of Drosophila. © 2024 Elsevier B.V.
A coumarin-derived multi-faceted optical material with molecular logic gate for bioimaging
(Royal Society of Chemistry, 2025) Amit Kumar Singh; Pranjalee Yadav; Aayoosh Singh; Avanish Kumar Singh; Shashi Kant Sharma; Vijay Kumar Sonkar; Vinod Prasad Singh
The development of stimuli-responsive, multi-faceted chromic materials has gained the interest of the material science community recently, owing to their vast range of applications in several areas simultaneously, such as viscosity, temperature, and pressure detectors. In this context, a coumarin-derived organic luminophore, HCFH, has been designed and extensively investigated for its characteristics, such as aggregation-induced emission (AIE), viscochromism, piezochromism, thermochromism, and distinguishable fluorometric detection of Zn2+ and Cu2+ ions in water. The emission intensity of HCFH amplifies 111-fold with the addition of water in tetrahydrofuran (THF), validating its aggregation-induced emission (AIE) nature. Multi-colored piezochromism is observed in the ‘crystalline’, ‘pristine’, and ‘ground’ forms of HCFH as non-emissive, weakly cyan-emissive, and bright green-emissive, respectively. Further, powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses indicate a crystalline-to-amorphous phase transition during grinding. HCFH exhibits remarkable photophysical properties, including viscosity, polarity, and temperature-dependent emissions. The probe selectively detects Zn2+ and Cu2+ ions with limits of detection (LOD) of 1.14 and 1.54 nM, respectively, employing chelation-enhanced fluorescence (CHEF) and inhibition of photo-induced electron transfer (PET) for Zn2+ and paramagnetic fluorescence quenching for Cu2+. The Job's plots indicate 1 : 2 and 1 : 1 (M : L) binding stoichiometries for Zn2+ and Cu2+, respectively, which are confirmed by their single-crystal structures. Molecular logic gates and paper strip kits are also developed utilizing their sensing capabilities. HCFH has been found highly effective in bio-imaging of Zn2+ and Cu2+ in HeLa cells. Microscopic examination of the cells indicates that the probe is localized in both the cytosol and mitochondria of the cells. © 2025 The Royal Society of Chemistry.
A highly selective coumarin-based chemosensor for dual sensing of Cu2+ and Zn2+ ions with logic gate integration and live cell imaging
(Royal Society of Chemistry, 2024) Avanish Kumar Singh; Amit Kumar Singh; Shashi Kant Sharma; Vijay Kumar Sonkar; Vinod P. Singh
In this paper, a coumarin-based Schiff base chemosensor has been synthesized and developed to detect Cu2+ and Zn2+ ions in nanomolar concentrations. The probe selectively distinguishes Cu2+ and Zn2+ from among several metal ions in DMF : H2O (7 : 3, v/v, pH 7.4) HEPES buffer. The structure of the probe and its sensing behavior were investigated by FT-IR, UV-vis, fluorescence, HRMS, and NMR analyses, along with X-ray crystallography and computational studies. CIH detects Zn2+ and Cu2+ using different strategies: CHEF-induced fluorescence enhancement and paramagnetic fluorescence quenching, respectively. Job's plots show a 1 : 1 binding interaction between CIH and Cu2+ or Zn2+ ions. The binding constant values for Cu2+ (1.237 × 105 M−1) and Zn2+ (1.24 × 104 M−1) suggest a better ability for Cu2+ to interact with CIH than Zn2+. An extremely high sensitivity of the probe was highlighted by its very low detection limits (LOD) of 5.36 nM for Cu2+ and 3.49 nM for Zn2+. The regeneration of the probe with the addition of EDTA in its complexes allows the formation of molecular logic gates. CIH has been successfully employed in mitotracking and intracellular detection of Zn2+ and Cu2+ in SiHa cells. © 2024 The Royal Society of Chemistry.
A novel 3-acetyl coumarin based AIE luminophore for colorimetric recognition of Cu2+ and F− ions
(Elsevier B.V., 2023) Sarita Gond; Pranjalee Yadav; Avanish Kumar Singh; Vinod P. Singh
A 3-acetyl coumarin appended probe 3-((Z)-1-((E)-((2-hydroxynaphthalen-1-yl) methylene) hydrazono)ethyl)-2H-chromen-2-one (CNH) has been successfully synthesized and characterized by different spectroscopic tools via IR, 1H & 13C NMR and HRMS. The probe displays solvent dependent colorimetric detection of Cu2+ and F− ions in THF and DMF media, respectively. CNH interacts with Cu2+ in 1:1 stoichiometry with limit of detection 1.4 × 10−6 M. The color change of probe with addition of Cu2+ ions is due to ligand to metal charge transfer (LMCT) as suggested by UV–Vis spectra and DFT studies. Furthermore, CNH interacts with F− in 1:1 stoichiometry with detection limit 1.32 × 10−6 M by proton transfer mechanism from O-H to F−, which enhances the electron density on CNH molecule as suggested by UV–Vis, NMR titration and DFT studies. In addition to intriguing colorimetric sensing applications, CNH displays remarkable aggregation induced emission (AIE) property in DMF/water binary mixture. The probe is almost non-fluorescent in solution but becomes strongly emissive in aggregate/solid state. The formation of aggregates at higher water content is confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS) studies in mixed water media. DLS measurements suggest the increase in average particle size from 100 nm to 299 nm upon increasing water fractions from (fw = 10%) to (fw = 90%). AFM studies also provide additional information about the aggregates at higher water fraction. In the range of 100–500 nm, the topography of surface shows that the aggregates are spherical in shape (fw = 90%). © 2022 Elsevier B.V.
A Stimuli Responsive Multifunctional Smart Luminophore with Aggregation-Induced Enhanced Emission
(John Wiley and Sons Inc, 2025) Aayoosh Singh; Amit Kumar Singh; Pranjalee Yadav; Avanish Kumar Singh; Pradeep Kumar; Saripella Srikrishna; Vinod Prasad Singh
The development of multifunctional luminophores with tunable and stimuli-responsive optical properties is critical for the advancement of sensing, bioimaging, and optoelectronic technologies. Herein, a novel coumarin-based smart luminogen, (E)-N'-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)ethylidene)thiophene-2-carbohydrazide (ETH) is developed that exhibits pronounced multistimuli responsive behavior including aggregation-induced enhanced emission (AIEE), solvatochromism, viscochromism, reversible mechanochromism, and acidochromism. ETH shows solid-state fluorescence modulation on applying mechanical stress and exposing in acid/base vapor, with reversible redshifted emission. The ETH coated paper enables its practical applications in pressure-sensitive devices and portable acid vapor detection kits. In a mixed CH3CN–H2O system, ETH functions as a solvent-controlled dual-mode fluorescent probe, showing a turn-on response to Zn2+ and a turn-off response to Cu2+ with high sensitivity. Job's plot revealed 2:1 ligand-to-metal stoichiometry for Zn2+ and 1:1 for Cu2+. The fluorescent aggregates of ETH enable selective detection of Cu2+ through a disaggregation-induced fluorescence quenching mechanism. A portable cotton-swab-based test kit is developed for practical and on-site detection of Cu2+. ETH demonstrates excellent biocompatibility, as predicted by in vivo fluorescence imaging in Drosophila larval gut tissues. The combination of reversible optical switching, high fluorescence quantum yield and structural adaptability establish ETH as a novel multifunctional material for sensing, live-cell imaging, and smart optoelectronic devices. © 2025 Wiley-VCH GmbH.
Carbazole-quinoline based ultrasensitive fluorometric sensor for detection of Hg2+ in aqueous medium: Crystal structure, DFT and real sample application
(Elsevier B.V., 2025) Avanish Kumar Singh; Aayoosh Singh; Pranjalee Yadav; Amit Kumar Singh; Vinod Prasad Singh
A novel carbazole-quinoline tagged fluorophore, (E)-9-ethyl-3-((2-(quinolin-2-yl)hydrazineylidene)methyl)-9H-carbazole (QHC), has been synthesized with an excellent yield using the simple one-pot synthesis and its molecular structure is determined by single crystal X-ray diffraction, FT-IR, NMR and mass spectroscopic techniques. QHC has been developed as an ultrasensitive fluorometric sensor for detection of Hg2+ in the presence of competing metal ions in aqueous medium. It exhibited remarkable sensitivity and selectivity towards Hg2+ with limit of detection (LOD) of 2.59 × 10−8 M and a remarkable Stern-Volmer constant (Ksv) of 1.17 × 105 M−1. The Job's plot displayed 1:1 stoichiometry between QHC and Hg2+, with a binding constant (Ka) of 1.01 × 105 M−1. The binding mechanism has been demonstrated by FT-IR, mass spectrometry, 1H NMR titration and density functional theory (DFT) analysis. Upon interaction with Hg2+, the photo-induced electron transfer (PET) from quinoline-carbazole framework to Hg2+ is activated, thereby, completely quenching the fluorescence. The practical applicability of QHC was demonstrated through the development of test kits. Additionally, QHC was successfully employed to detect Hg2+ ions in real water samples, including lake water and Ganga river water, showing its significance in environmental monitoring. © 2025 Elsevier B.V.