Department of Chemistry
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Item Luminescent triazolo-fused pyrido[3,4-b]pyrazines as novel fluorophores(Elsevier, 2024-12) Khungar, Bharti; Sakhuja, RajeevA series of organic fluorophores based on novel [1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine architecture were synthesized by a simple two-step protocol. Synthesized organic fluorophores exhibit blue-to-green fluorescence and their UV absorption and fluorescent emission properties were studied. The photophysical properties of synthesized derivatives were tuned by introducing functionalities of varying electronic nature on the core nucleus. The luminescence maxima of the synthesized compounds are found in the range from 427 nm to 503 nm, and the quantum yields ranging from 0.01 to 0.64 were calculated. Among various synthesized molecules, 3-(4-bromophenyl)-8,9-bis(4-methoxyphenyl)-[1,2,4]triazolo [4′,3':1,2]pyrido [3,4-b]pyrazine showed highest quantum yield (ΦF = 0.64), and was further explored for its solvatochromic, acidochromic, aggregation induced fluorescence studies along with theoretical HOMO-LUMO calculationsItem Synthesis, Absorption, and Fluorescence Studies of Coumaryl-Labelled Amino Acids and Dipeptides Linked Via Triazole Ring(CSIRO, 2015-04-07) Sakhuja, Rajeev; Pant, Debi D.Fluorophores based on 4-triazolyl, 7-hydroxy-4-triazolylmethyl, 4-O-triazolylmethyl, and 7-O-triazolylmethyl coumaryl-tagged amino acids and dipeptides were synthesized by copper-catalyzed [3 + 2] cycloaddition reaction between azido- or alkynyl-functionalized coumarins with alkynyl- or azido-functionalized amino acid and dipeptides in good-to-excellent yields. Steady-state absorption and the fluorescence properties of the synthesized conjugates were studied. The chemical applicability of these amino acid and peptide-based fluorophores was successfully demonstrated by their linear elongation by further tagging them with appropriate C- or N-terminus amino acid.Item Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces(ACS, 2016) Sakhuja, Rajeev; Pant, Debi D.The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.Item One-Pot Synthesis of Carbon Nanodots in an Organic Medium with Aggregation-Induced Emission Enhancement (AIEE): A Rationale for “Enzyme-Free” Detection of Cholesterol(ACS, 2017-07-24) Sakhuja, RajeevAddressing the limitations associated with the detection of cholesterol, we present a one-pot synthesis of a carbon nanodot (CD) in an organic medium (CDorg) from a novel bile acid hydrazone-based organogel. Interestingly, CDorg possesses the aggregation-induced emission enhancement (AIEE) phenomenon, which rationally aids in the “enzyme-free” detection of cholesterol through a fluorescence turn-on mechanism. On dilution of the THF/water mixture of CDorg with its poor solvent (water), a 9.8-fold enhancement in its photoluminescence (PL) emission is witnessed. Such an enhancement in PL emission is credited to the occurrence of molecular restrictions due to the formation of nanoaggregates of CDorg, thereby initiating a radiative pathway for exciton decay. Excitingly on adding cholesterol to CDorg, we observed a similar enhancement in its PL emission without the use of any cholesterol oxidase (ChOx) enzyme. The limit of detection and limit of quantification of cholesterol is found to be as low as 1.09 and 3.64 μM, respectively. Hence, this contribution highlights the enzyme-free fluorescence turn-on detection of cholesterol by a novel CD rationally designed to extend its applicability in an organic medium, where it is still considered a major restraint.Item Detection of Hg2+ ions in aqueous medium using an indole-based fluorescent probe: Experimental and theoretical investigations(Elsiever, 2017-12) Sakhuja, Rajeev; Pant, Debi D.Mercury pollution is a widespread danger to human health and environment. Due to limitations associated with the existing Hg2+ chemosensors, development of new, efficient and selective chemosensors capable of sensing mercury ions in aqueous medium remains a demanding area of research. In this regard, an indole-based fluorescent probe has been synthesized and characterized by detailed spectroscopic analysis. The probe showed a high selectivity and sensitivity towards Hg2+ by giving significant fluorescence quenching over other tested cations in H2O/DMF (7:3, v/v) medium. The association constant (Ka) was 6.4 × 103 M− 1 between sensor and Hg2+. The detection limit of sensor to Hg2+ was found to be 0.143 μM (143 nM). The experimental results have been verified with Density Functional Theory.