ABSTRACT
A biphenyl based coumarin fluorescent molecule, N,N'-bis(7-diethylamino-2-oxo-2 H-chromen-3-yl)methylene)biphenyl-2-2'-dicarbohydrazide (molecule 1) has been synthesized and characterised. Photophysical studies of 1 exhibit solvent polarity dependent absorption and emission maxima. Citrate capped gold nanoparticles (AuNPs) have been mixed with molecule 1 for the preparation of AuNPs/1 conjugate. The association constant of the AuNPs/1 conjugate has been calculated to 4.54 × 104 M- 1. The AuNPs/1 conjugate has been found to detect Hg2+ ion selectively by fluorescence enhancement. While addition of molecule 1 into the solution of AuNPs, fluorescence intensity of 1 quenched. On addition of several monovalent, divalent and trivalent metal ion into the solution of AuNPs/1 conjugate separately, there was no change in fluorescence intensity of 1 has been observed. However, upon addition of Hg2+ ion into the solution of AuNPs/1 conjugate, the fluorescence intensity enhancement occurred, indicating released of 1 from the surface of AuNPs and probably aggregation of AuNPs took place in presence of Hg2+ ion. The AuNPs/1 conjugate has been found to have a detection limit of 2.3 × 10- 9 M for Hg2+ ion in aqueous solvent. Meanwhile, the AuNPs/1 conjugate have also been successfully applied for the determination of Hg2+ in real water samples.
ABSTRACT
A coumarin based fluorescent molecule, 3-amino-2-cynano-3-(7-diethylamino-2-oxo-2H-chromen-3-yl)-acrylic acid ethyl ester (1) has been synthesized and characterised. Photophysical studies of 1 exhibit polarity dependent shift of its emission maxima which have been explained on the basis the existence of polar excited state of the molecule. Combination of compound 1 and citrate capped AuNPs (AuNPs/1 conjugate) has been used as a sensing tool for heavy metals. AuNPs/1 conjugate has been found to detect Pb2+ selectively by naked-eye color change as well as fluorescence enhancement. On addition of molecule 1 to gold nanoparticles solution, the color of the solution becomes reddish followed by quenching in fluorescence intensity. With gradual addition of Pb2+, the solution of AuNPs/1 conjugate becomes violet accompanied by a fluorescence enhancement. Excited state lifetime measurement revealed that compound 1 exhibits very fast decay pattern in aqueous medium whereas in AuNPs medium the lifetime of 1 increases. Upon addition of Pb2+ ions to that AuNPs/1 solution the lifetime of 1 decreases again. Based on the experimental observations the mechanism of sensing of lead has been proposed thoroughly. Initially compound 1 gets absorbed on the surface of the spherical gold nanoparticles. When Pb2+ is added, probably gold nanoparticles aggregates to form bigger particles by releasing compound 1 from its surface to show fluorescence enhancement.
ABSTRACT
To get an idea about the most probable microporous supramolecular environment in the gel state, gelator molecule 1 has been crystallized from its gelling solvent (dimethylformamide). Crystal structure analysis of 1 shows a strong π···π stacking interaction between the electron-deficient pentafluorophenyl ring and electron-rich naphthyl ring. The gelling solvent situated in the "molecular pocket" stitches the gelators through weak H-bonding interactions to facilitate the formation of an organogel. Scanning electron microscopy analysis exhibits a ribbonlike fibrous morphology that resembles the supramolecular arrangement of 1 in its crystalline state, as evidenced by powder X-ray diffraction. In the presence of external stimuli (tetrabutylammonium fluoride), the organogel of 1 disassembles into sol. This sol-gel transformation phenomenon has been explained on the basis of X-ray single-crystal analysis. Single crystals obtained from the sol state show that naphthylic -OH of 1 gets deprotonated, resulting in C-C bond rotation that plays a major role in the sol-gel transformation. Gelator 1 exhibits weak green fluorescence in the gel state, whereas it shows highly intense yellow fluorescence in the sol state. Furthermore, a reversible sol-gel transformation associated with changes in the spectroscopic properties has been observed in the presence of acids and fluoride ions, respectively.
ABSTRACT
Two amido-schiff bases (3-Hydroxy-naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide and Naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide) have been synthesized having a common structural unit and only differs by a -OH group in the naphthalene ring. Both of them can detect Cu2+ ion selectively in semi-aqueous medium in distinctly different output modes (one detects Cu2+ by naked-eye color change where as the other detects Cu2+ by fluorescence enhancement). The difference in the binding of Cu 2+ with the compounds is the reason for this observation. The detection limit is found to be micromolar region for compound which contains -OH group whereas the compound without -OH group detects copper in nano-molar region. DFT calculations have been performed in order to demonstrate the structure of the compounds and their copper complexes. Practical utility has been explored by successful paper strip response of both the compounds. The biological applications have been evaluated in RAW 264.7.
