Venugopal Thanikachalam

A physiochemical study of excited state intramolecular proton transfer process: Luminescent chemosensor by spectroscopic investigation supported by ab initio calculations

A group of novel Schiff base derivatives were synthesized and characterized by NMR spectra, X-ray, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy Schiff base (SB4) has been studied using emission spectroscopy and it was detected that the two distinct ground state isomers of I and II are responsible for the emission. The comparison of the emission wavelength in hydrocarbon solvent strongly supports that trans enol form predominates over the cis enol form for Schiff base (SB4). With increasing base concentration of the solutions of hydroxy substituted Schiff bases (SB4 and SB5), two isobestic points are found which confirm the equilibrium among the trans enol form, anion and the cis enol form. The fluorescence of (SB4) quenched markedly with the gradual addition of Cu(2+) but the fluorescence properties of (SB5) was influenced by other metal ions. Therefore Schiff base (SB5) can be used as a new fluorescence sensor to detect the quantity of Cu(2+) ion in any sample solution depending on the relative intensity change. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base 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.

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.

Fluorescence investigation of the interaction of 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole with bovine serum albumin

The interaction between 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole (FPPI) and bovine serum albumin (BSA) was investigated by fluorescence spectral studies. The observed experimental result shows that the imidazole derivative has strong ability to quench the fluorescence of BSA by forming complex which is stabilized by electrostatic interactions. The effective quenching constants (K(sv)) were 2.78 × 10(4), 2.52 × 10(4), and 2.32 × 10(4) at 301, 310, and 318 K respectively. The Stern-Volmer quenching constant (K(sv)), binding site number (n), apparent binding constant (K(A)) and corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were calculated. The distance between the donor (BSA) and acceptor (FPPI) was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence technique. The effect of metal ions such as Cu(2+), Zn(2+), Ca(2+), Mg(2+), Ni(2+), Co(2+), and Fe(2+) on the binding constants between the FPPI and BSA were also studied.

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 chemosensor imidazole derivatives: DFT based ESIPT process.

A series of substituted imidazoles have been synthesized in very good yield under a solvent free condition using molecular iodine as the catalyst. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives have been performed and discussed. DFT analysis about HOMO, HOMO-1, LUMO and LUMO+1 has been carried out and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state that is shown by PES calculation. The molecular electrostatic potential surface (MEP) has also been employed to show the higher electron density at N(3) nitrogen. Fluorescence enhancement has been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n-π* state in the chemosensors.

Mechanistic investigation on binding interaction of bioactive imidazole with protein bovine serum albumin--a biophysical study.

The interaction between bioactive imidazole derivative (PPP) and bovine serum albumin (BSA) was investigated using fluorescence and UV-vis spectral studies. The experimental results showed that the fluorescence quenching of BSA by imidazole derivative was the result of the formation of BSA-PPP complex and the effective quenching constants (K(SV)) were 2.66×10(4), 2.56×10(4), and 2.10×10(4) at 301, 310 and 318 K, respectively. Static quenching and non-radiative energy transfer were confirmed to the result in the fluorescence quenching. The binding site number n, apparent binding constant K(A) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were measured at different temperatures. The process of binding of PPP molecule on BSA was a spontaneous molecular interaction procedure in which entropy increased and Gibbs free energy decreased.

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.

FT-Raman, FT-IR spectra and total energy distribution of 3-pentyl-2,6-diphenylpiperidin-4-one: DFT method

FT-Raman and FT-IR spectra were recorded for 3-pentyl-2,6-diphenylpiperidin-4-one (PDPO) sample in solid state. The equilibrium geometries, harmonic vibrational frequencies, infrared and the Raman scattering intensities were computed using DFT/6-31G(d,p) level. Results obtained at this level of theory were used for a detailed interpretation of the infrared and Raman spectra, based on the total energy distribution (TED) of the normal modes. Molecular parameters such as bond lengths, bond angles and dihedral angles were calculated and compared with X-ray diffraction data. This comparison was good agreement. The intra-molecular charge transfer was calculated by means of natural bond orbital analysis (NBO). Hyperconjugative interaction energy was more during the π-π* transition. Energy gap of the molecule was found using HOMO and LUMO calculation, hence the less band gap, which seems to be more stable. Atomic charges of the carbon, nitrogen and oxygen were calculated using same level of calculation.

Spectrofluorometric studies on the binding interaction of bioactive imidazole with bovine serum albumin: A DFT based ESIPT process

Bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. In hydrocarbon solvent, the tautomer emission predominates over the normal emission and in alcoholic solvent like ethanol; a dramatic enhancement of normal emission is observed which was due to increased solvation. DFT calculation on energy, charge distribution of the rotamers in the ground and excited states of the imidazole derivative 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 in the ground state. The interaction between bioactive imidazole derivative and bovine serum albumin (BSA) was investigated.