Natesan Srinivasan

Synthesis and Photophysics of Some Novel Imidazole Derivatives Used as Sensitive Fluorescent Chemisensors

Some novel imidazole derivatives were developed for highly sensitive chemisensors for transition metal ions. Since these compounds are sensitive to different external stimulations such as UV irradiation, heat, increasing pressure and changing the environmental pH causing colour change and so they can be used as a ′multi-way′ optically switchable material. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg2+, Pb2+ and Cu2+ and this was suggested to result from the suppression of radiationless transitions from the n-π* state in the chemisensors. The existence of C-H….O intramolecular hydrogen bonding in dmphnpi is confirmed by the Natural Bond Orbital analysis (NBO). The Mulliken, NBO charge analysis and the HOMO-LUMO energies were also calculated. The electric dipole moment (μ) and the first-hyperpolarisability (β) value of the investigated molecules have been studied both experimentally and theoretically which reveal that the synthesized molecules have microscopic non-linear optical (NLO) behaviour with non-zero values. Ground and excited state DFT calculation were carried out in order to find out dipole moment and energy.

Synthesis, Structure, Luminescent and Intramolecular Proton Transfer in Some Imidazole Derivatives

A group of novel 2-aryl imidazole derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dmip and dmtip) have been studied using emission spectroscopy and it was detected that the two distinct ground state rotamers of I and II are responsible for the normal and the tautomer emission respectively. In hydrocarbon solvent, the tautomer emission predominates over the normal emission for both dmip and dmtip. This reveal that rotamer II is responsible for the tautomer emission and it is stabler than rotamer I which causes the normal emission. In alcoholic solvent like ethanol, a dramatic enhancement of normal emission is observed which was due to increased solvation, the more polar rotamer I become stabler than rotamer II. In dioxane—water mixtures it is observed that the addition of water inhibits the ESIPT process due to the formation of the intermolecular hydrogen bonding involving water. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state.

An Intramolecular Charge Transfer Fluorescent Probe: Synthesis, Structure and Selective Fluorescent Sensing of Cu+2

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, aromatic aldehyde and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practically and economically attractive and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazoles (dpip and dptip) have been studied using emission spectroscopy and it was detected that the two distinct ground state rotamers are responsible for the normal and the tautomer emissions. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives were performed and discussed. DFT analysis about HOMO, HOMO-1, LUMO and LUMO + 1 were carried out and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state.

Physicochemical studies of molecular hyperpolarizability of imidazole derivatives.

A series of substituted imidazoles have been synthesized in very good yield under solvent free condition by grinding 1,2-diketone, arylaldehyde, arylamine and ammonium acetate in the presence of molecular iodine as the catalyst. The short reaction time, good yield and easy workup make this protocol practically and economically attractive and the imidazoles are characterized by NMR spectra, X-ray, mass and CHN analysis. The push-pull character of series of imidazoles have been analyzed by the quotient of the occupations of the bonding (π) and anti-bonding (π*) orbitals of the central linking -N=C-C=C- unit. Excellent correlation of the push-pull parameter with the corresponding bond lengths d(CN) and d(CC) strongly recommend both the occupation quotients (π*/π) and the corresponding bond lengths are reasonable sensors for quantifying the push-pull character and for the molecular hyperpolarizability ß(0) of these compounds. To support the experimental results, theoretical calculations (heat of formation, NLO, NBO and vibrational analysis) were also made. Within this context, reasonable conclusions concerning the steric hindrance in the chromospheres, push-pull character, hyperpolarizability of the imidazoles and their application as NLO materials will be drawn.

A physiochemical study of azo dyes: DFT based ESIPT process.

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.

Surface modifications of CuO nanoparticles using Ethylene diamine tetra acetic acid as a capping agent by sol–gel routine

The uncapped and capped CuO nanoparticles were synthesized by sol-gel process. Ethylene diamine tetra acetic acid (EDTA) used as a capping agent to control the size and morphology of the CuO nanoparticles. Control the nanostructure and optical properties of CuO nanoparticles are deliberate by using capping agent. The obtained samples were characterized by means of UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS). UV-Visible technique used to measure the band gap of the synthesized samples. The XRD spectra of the synthesized samples confirmed the CuO nanoparticles with monoclinic structure. The occurrences of capping agent have been analyzed by Fourier transform-infrared spectroscopy (FT-IR). The FT-IR study revealed that the transmittance peaks at 501cm(-1) and 592cm(-1) were CuO stretching mode, and 677cm(-1) was CuO monoclinic phase of the uncapped CuO nanoparticles. Further, SEM study find out the morphology of the synthesized samples, where the surface morphology changes occurred with an addition of capping agent. Moreover, the capping mechanism has been discussed based on the chemical reaction between the CuO nanoparticles and the functional groups of the capping agent.

Synthesis and characterization of cluster of grapes like pure and Zinc-doped CuO nanoparticles by sol–gel method

Pure CuO and Zn-doped CuO nanoparticles were synthesized from sol-gel process by reacting copper acetate monohydrate with a urea in distilled water at 80°C. The synthesized Samples were different concentrations but same annealing temperature at 400°C. The obtained samples were characterized by means of UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM) and Energy dispersive X-ray spectroscopy (EDS). UV-visible technique used to measure the band gap of the synthesized samples. The XRD spectra of the synthesized samples confirmed the CuO nanoparticles with monoclinic structure. All the functional groups of the pure and doped synthesized samples were investigated by FT-IR analysis. The morphological and elemental estimation of the pure and Zn-doped synthesized samples were examined by FE-SEM with EDS.

Synthesis, spectral studies and solvatochromism of some novel benzimidazole derivatives--ESIPT process.

Some novel benzimidazole derivatives were synthesized and characterized by (1)H, (13)C NMR mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. The solvent effect on the absorption and fluorescence bands has been analyzed. The energetic analysis of the potential energy surface (PES), HOMO and LUMO levels [DFT/B3LYP/6-31G(d,p)] evidenced the existence of excited state intramolecular proton transfer (ESIPT) in hydroxy benzimidazole derivative.

Physicochemical studies of some novel Y-shaped imidazole derivatives--a sensitive chemisensor.

Some novel Y-shaped imidazole derivatives were developed for highly sensitive chemisensors for transition metal ions. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg(2+), Pb(2+) and Cu(2+) and it is due to the suppression of radiationless transitions from the n-π* state in the chemisensors. The HOMO-LUMO energies, electric dipole moment (μ) and the first-hyperpolarizability (β) values of the investigated molecule have been studied theoretically which reveal that the synthesized molecules have microscopic non-linear optical (NLO) behaviour with non-zero values.

Evidence for Strong Mixing Between the LC and MLCT Excited States in Some Heteroleptic Iridium (III) Complexes

The synthesis, structure and photophysical properties of series of new luminescent cyclometalated Iridium (III) complexes are reported. The cyclometalated ligand used here is 2-aryl imidazole and the auxiliary ligand is acetyl acetone (acac). The crystal structure of the complex (dmdpi)2Ir(acac) (5) show that the Iridium(III) ion resides in a distorted octahedral environment. All complexes exhibit bright photoluminescence (PL) at room temperature and (fpdmdmpi)2Ir(acac) 4 has a high solution PL quantum efficiency of 0.56. The role played by electron releasing and electron withdrawing substituents of the 2-arylimidazole ligands towards the stability of HOMO and how the substituent influences the luminescent behaviour are discussed. Furthermore those substituents have effect on the contribution to mixing between 3(π-π*) and 3(MLCT) for the lowest excited states.