Vikas S. Patil

Synthesis of new ESIPT-fluorescein: photophysics of pH sensitivity and fluorescence.

ESIPT-inspired benzimidazolyl substituted fluorescein dyes were synthesized. PH-sensitivity was determined by the photophysical property measured at a physiological possible pH range. Fluorescence quantum efficiency values were calculated independently at two different emissions. A rational relationship is defined between fluorescence quantum efficiency and calculated HOMO energy.

Indion 190 resin: efficient, environmentally friendly, and reusable catalyst for synthesis of benzimidazoles, benzoxazoles, and benzothiazoles

Abstract An efficient and mild protocol has been developed for the preparation of benzimidazoles, benzoxazoles, and benzothiazoles from reactions of aldehydes with o-substituted aminoaromatics in the presence of catalytic amount of Indion 190 resin. Short reaction time, ambient conditions, simple work-up procedure, high yield, easy availability, reusability, and use of an eco-friendly catalyst are some of the striking features of the present protocol.

Synthesis, Photo-physical and DFT Studies of ESIPT Inspired Novel 2-(2′,4′-Dihydroxyphenyl) Benzimidazole, Benzoxazole and Benzothiazole

AbstractNovel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and 1,2-phenelenediamine, 2-aminophenol, and 2-aminothiophenol respectively. The synthesized 2-(2′,4′-dihydroxyphenyl) benzimidazole, benzoxazole and benzothiazole are fluorescent and the emission characteristic are very sensitive to the micro-environment. They show a single absorption and dual emission with large Stokes shift originating from excited state intramolecular proton transfer. The absorption-emission characteristics of all these compounds are studied as a function of pH. The change in the electronic transition, energy levels, and orbital diagrams of synthesized compounds were investigated by the molecular orbital calculation and were correlated with the experimental spectral emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) [B3LYP/6-31G(d)]. FigureNovel ESIPT inspired benzimidazole, benzoxazole and benzothiazole were synthesized from 2,4-dihydroxy benzoic acid and o- amino aromatics. Single absorption and dual emission are the interesting properties of the synthesized compounds.

Efficient Synthesis of 3-Substituted 1,2,4-Triazolo[4,3-a]pyridine by [Bis(Trifluroacetoxy)iodo]benzene-Catalyzed Oxidative Intramolecular Cyclization of Heterocyclic Hydrazones

Abstract A series of 1,2,4-triazolopyridines have been prepared by oxidative intramolecular cyclization of heterocyclic hydrazones with [bis(trifluroacetoxy)iodo]benzene. General applicability of this simple transformation was confirmed by synthesis of 1,2,4-triazolo[4,3-a]pyridine. The advantages of this protocol are the nontoxicity of catalyst and shorter reaction time to obtain good preparative yield.

Phosphomolybdic Acid: An Efficient and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols)

Abstract An efficient and environmentally friendly method has been developed for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) by condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone in the presence of phosphomolybdic acid as a recyclable catalyst in ethanol at ambient temperature in excellent yields. GRAPHICAL ABSTRACT

2-Methyl-4-oxo-N-(4-oxo-2-phenyl substituted-1,3-thiazolidin-3-yl)-3,4-dihydroquinazoline-5-carboxamides--a new range of fluorescent whiteners: synthesis and photophysical characterization.

Fluorescent quinazolinones were synthesized form ethyl 2-methyl-4-oxo-3,4-dihydroquinazoline −5-carboxylate intermediate. The photophysical properties of the compounds were evaluated in DMF solvent. The experimental absorption and emission of the compounds were compared with the vertical excitation and emission obtained Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) computation. Application of the fluorescent compounds as a fluorescent brightening agent was tested on polyester fiber. Changes in the electronic transition, energy levels, and orbital diagrams of quinazolin-4(3H)-one analogues were investigated using the DFT computations and were correlated with the experimental spectral data. The experimental absorption and emission wavelengths are in good agreement with those predicted using the DFT and TD-DFT.

Intrinsic catalytic activity of an acidic ionic liquid as a solvent for quinazoline synthesis

A greener approach for the synthesis of quinazoline intermediates using an ionic liquid was developed where the ionic liquid is used as an intrinsic reaction catalyst and a solvent. Merits of this reaction are self-catalysis, easy workup process, less reaction time, and environmental friendliness.

Intrinsic catalytic activity of Brønsted acid ionic liquids for the synthesis of triphenylmethane and phthalein under microwave irradiation

A microwave-irradiated, ionic liquid-catalyzed, solvent-free method for the synthesis of triphenylmethane and a phthalein derivative has been developed from different aldehydes or anhydrides and substituted phenols or N,N-diaryl amines, respectively. Short reaction time, ambient reaction conditions, recyclability of catalyst, simple work up and high yields are some of the striking features of the present protocol. The immobilized catalyst could be easily recovered by simple filtration and recycled for up to four cycles without significant decrease in the catalytic activity.

Synthesis, optical properties, dyeing study of dihydropyrimidones (DHPMs) skeleton: Green and regioselectivity of novel Biginelli scaffold from Lawsone

Ionic liquids have increased popularly in last couple of decades as solvent for its greener approach. Here a novel three-component, one-pot condensation yielding 4-phenyl-3,4-dihydrobenzo[g]quinazoline-2,5,10(1H)-trione is reported in halogen free ionic liquid (HFIL). Components of reaction are aldehyde, urea, and β-keto esters in presence of HFIL N-methyl-2-pyrrolidonium hydrogen sulfate [HNMP]+[HSO4]−. Comparative reactions were performed under conventional heating and sonication in HFIL. Solvent utility of HFIL makes purification and separation process artless task offering an advantage of five times recyclability without degrading its activity. The use of HFIL is advantageous over conventional solvent due to very short reaction time and halogen-free volatile solvent utility and recyclability. Latterly these compounds applied as disperse dye on polyester and nylon fiber were found to give moderate color and fastness properties.

Synthesis of novel fluorescent 1,3,5-trisubstituted triazine derivatives and photophysical property evaluation of fluorophores and their BSA conjugates

Abstract Cyanuric chloride was allowed to react with N,N-diethylaniline to obtain 4-(4,6-dichloro-1,3,5-triazin-2-yl)-N,N-diethylaniline, which was converted into six novel 1,3,5-trisubstituted triazine derivatives on reaction with different amino acids. These compounds had UV absorption in the range 352–379 nm, accompanied by intense single emission in the range 420–497 nm with fairly good quantum yield (0.106–0.383). The new compounds were characterized by FT-IR, 1H NMR, 13C NMR, mass spectral, and elemental analyses. These fluorophores were conjugated with protein bovine serum albumin through carbodiimide chemistry between the negatively charged carboxylate groups (-COO-) of the fluorophore and the surface terminated positively charged amino groups (-NH3+) of the protein. The interaction between functionalized amino acids with protein molecules was investigated using fluorescence spectroscopy showing fluorescence enhancement or quenching of the fluorophore after conjugation.