Ayyanar Siva

Aminobenzohydrazide based colorimetric and ‘turn-on’ fluorescence chemosensor for selective recognition of fluoride

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F(-) ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. (1)H NMR studies confirm that the F(-) ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.

Synthesis and photophysical properties of triphenylamine-based multiply conjugated star-like molecules

Novel triphenylamine-based star-like molecules 11 were synthesized and characterized using FT-IR, 1H, 13C, and DEPT-135 NMR spectroscopy, and MALDI-TOF mass spectrometry. The absorption and emission spectra of star-like molecules were studied in different solvents. The effect of solvent polarity and aggregation studies on the absorption and emission spectra has also been studied. The new star-like molecules are found to exhibit broad absorption and emission band along with intramolecular charge transfer character. The fluorescence spectra of triphenylamine derivatives shift from blue to green wavelength on increasing the extended conjugation of the molecule. The experimental results indicate that there is cooperative enhancement originating from the inter-branch coupling and an increase in the light-harvesting ability upon increasing the conjugated molecule size.

Ultrasonic assisted dimeric cinchona based chiral phase transfer catalysts for highly enanatioselective synthesis of epoxidation of α,β-unsaturated ketones

New types of bis-quaternary ammonium bromide as chiral multisite phase transfer catalysts derived from cinchona alkaloids have been developed and evaluated for the enantioselective epoxidation of chalcones in the presence of lower concentrations of various oxidants, bases and ultrasonic irradiation conditions. Under optimized conditions, excellent chemical yields of up to 98% along with the highest enantioselectivities of about 98% were obtained by using the reported catalysts.

Piezoflurochromism and Aggregation Induced Emission Properties of 9, 10-bis (trisalkoxystyryl) Anthracene Derivatives

We report the synthesis of trisalkoxy substituted 9, 10-bis styrylanthracene derivatives (C8-ant and C12-ant) by Heck coupling with very good yield and their photophysical properties. Both C8-ant and C12-ant exhibit aggregation induced emission (AIE), mechnoflurochromism and thermochromism. Trisubstituted 9, 10-distyrylanthracene molecules having all the luminescent properties in a single molecule are first of its kind.

Highly enantioselective asymmetric Henry reaction catalyzed by novel chiral phase transfer catalysts derived from cinchona alkaloids

A new type of di-site chiral phase transfer catalyst has been designed and synthesized from cinchona alkaloids as a chiral precursor. The prepared catalysts are applied in the asymmetric Henry reaction to a wide range of aldehydes using mild concentrations of a base and solvent and under room-temperature conditions. Under the optimized reaction conditions, the highest chemical yields up to 99% along with an excellent enantiomeric excess (ee) up to 99% were obtained using the prepared cinchona alkaloid based chiral phase transfer catalysts.

A tunable ratiometric pH sensor based on phenanthro[9,10-d]imidazole covalently linked with vinylpyridine

A rational design of the novel phenanthro[9,10-d]imidazole based pH sensing fluorophore PITP was developed, in which phenanthroimidazole acts as a donor and pyridine acts as an acceptor. Various spectral studies confirm that the protonation occurs at two different nitrogen centres, each of which produces an observable color change depending on the pH of the buffer solution. DFT calculations also support the experimental results. We show that PITP can be used as a ratiometric and colorimetric pH sensor in the acidic region.

Highly enantioselective Michael addition reactions with new trimeric chiral phase transfer catalysts

New types of mesitylene based tri-site containing asymmetric quaternary ammonium salts 9a and 9b have been prepared and used as efficient chiral phase transfer catalysts for enantioselective Michael addition reactions between the chalcones and diethylmalonate under mild reaction conditions such as lower concentration of base, catalyst and ultrasonic conditions with very good chemical yields (up to 98%) and ees (up to 99%).

Synthesis, characterization and aggregation induced emission properties of anthracene based conjugated molecules

Aggregation induced emission-active branched and linear 9,10-distyrylanthracene derivatives with different length alkoxy chains have been designed, synthesized and the effect of chain length on the solid-state fluorescence properties systematically investigated. All the three anthracene derivatives possess typical aggregation induced emission (AIE) properties, i.e., they exhibit faint emission in their solutions, but intense emission in their aggregate states, as a result of the dominant nonradiative decay of free intramolecular torsion in the solution and also the restricted torsional motion from supramolecular interaction in the solid states. The results show that these materials exhibit not only AIE properties, but also observed were position and chain length dependent fluorescence properties. The shorter alkoxy chains were more red shifted than the longer ones and also different aggregation behaviours for branched and linear molecules were observed. This work demonstrates once again the accessibility of tuning the solid-state optical properties of organic fluorophores by combining the simple alternation of molecular chemical structures and the physical change of aggregate morphology under external stimuli.

A new series of bipyridine based chiral organocatalysts for enantioselective Henry reaction

A series of binaphthol based chiral organocatalysts were synthesized and applied as metal-free organocatalysts in the enantioselective Henry reaction. These organocatalysts enabled the Henry reaction with a lower concentration of catalysts at room temperature affording the desired S- or undesired R-enantiomers. The formation of R- and S-enantiomers of β-nitroalcohol products strongly depends on the temperature/substrate inversion of configuration for the effective catalytic enantioselective Henry reaction in high yields (up to 97%) with excellent enantioselectivities (up to 99% ee).

Palladium Nanoparticles Supported on Nitrogen-rich Containing Melamine-based Microporous Covalent Triazine Polymers as Efficient Heterogeneous Catalyst for C−Se Coupling Reactions

In the present work, microporous nitrogen containing covalent triazine polymers (CTPs) TATAM was synthesized from condensation of 4,4′4′′‐(1,3,5‐triazine‐2,4,6‐triyl) tribenzaldehyde (TATA) and melamine under solvothermal conditions to obtain nitrogen‐ rich triazine containing polymeric supported materials (TATAM). Further, palladium nanoparticles (Pd NPs) were supported on TATAM polymeric networks (Pd@TATAM). The synthesized Pd@TATAM CTPs material was thoroughly characterized by FT‐IR, UV‐DRS, solid state 13C‐CPMAS, XPS, powder X‐ray diffraction, TGA, SEM, TEM. In addition, the characterized Pd@TATAM CTPs were applied to check the catalytic application. The Pd@TATAM was shown to be an efficient and reusable heterogeneous solid catalyst for the formation of C−Se bond through coupling of aryl halide and elemental selenium, dimethyl sulfoxide as a solvent at 100 °C for about 6 h. Besides the absence of metal leaching for catalytic system, it is also observed that the catalyst can be reused for three consecutive cycles with a minimal decrease in its activity.