V. Kalaiarasi

Enhancing photoluminescent behavior of 2-(naphthalen-1-yl)-1,4,5-triphenyl-1H-imidazole by ZnO and Bi2O3.

A fluorophore 2-(naphthalen-1-yl)-1,4,5-triphenyl-1H-imidazole [NTI] has been designed, synthesized and characterized by (1)H NMR, (13)C NMR, mass and single crystal XRD. Absorption, emission, lifetime and cyclic voltammetry have been made to deduce the interaction between NTI and ZnO and Bi2O3 nanocrystals. NTI act as a new host for ZnO and Bi2O3 nanocrystals that enhance its luminescence. The apparent binding constant has been obtained. Adsorption of the NTI on ZnO and Bi2O3 nanocrystals lowers the HOMO energy level of the NTI. The strong adsorption of the NTI on the surface of ZnO and Bi2O3 nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. SEM and EDS spectra confirmed the adsorption of NTI on the surface of nanocrystals.

Optical properties of 1-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)naphthalen-2-ol--ESIPT process.

This article presents optical, electrochemical, and thermal properties of novel class of green fluorescent 1-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)naphthalen-2-ol. Detailed photo physical and quantum chemical studies have been performed to elucidate the excited state intramolecular proton transfer (ESIPT) reaction leading a large stokes shifted fluorescence emission from the phototautomer. The results of quantum chemical investigations confirmed the intramolecular charge transfer characteristics of the ESIPT tautomers. The high photoluminescence quantum yield is ascribed to twisted chromophores due to phenyl substituents at 1,2-position of the imidazole ring which restricted intramolecular motion, leading to an optically allowed lowest optical transition without self quenching.

Photophysical and excited-state intramolecular proton transfer of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol: DFT analysis.

Fluorescent phenenthrimidazole derivatives have been synthesized and characterized by (1)H, (13)C NMR and mass spectral analyses. Synthesized compounds have been. The solvent effect on the absorption and fluorescence bands has been analyzed and supplement by computational studies. Phenenthrimidazole containing hydroxy group shows a single prominent absorption and emission in polar solvents and dual emission in non-polar solvents due to excited state intramolecular proton transfer (ESIPT). The ESIPT of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol was cross validated by the analysis of optimized geometry parameters, potential energy surface (PES), mullikens charge distribution on the heavy atoms and molecular orbitals of its tautomers. Nonviability of ground state electron transfer was explained by HOMO-LUMO analysis. The intramolecular hydrogen bonding (IMHB) interaction has been explored by the calculation of electron density ρ(r) and the Laplacian Δ(2)ρ(r) at the bond critical point (BCP) using atoms-in-molecule (AIM) method and by calculation of hyper conjugative interaction between N17 lone pair and σ*(O53⋯H54) using natural bond orbital (NBO) analysis.

Estimation of Excited State Dipolemoments from Solvatochromic Shifts–Effect of pH

Multicomponent, highly efficient, catalytic synthesis of some polysubstituted imidazole under solvent-free condition is reported. Characterization of polysubstituted imidazole have been carried out by X-ray diffraction (XRD) and spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends not only on the polarity of the medium but also on the hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on both the absorption and emission spectral results have been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazole fit satisfactorily to a single exponential kinetics. The prototropic studies of N,N-dimethyl-4-(1,4,5-triphenyl-1H-imidazol-2-yl)naphthalen-1-amine (DTINA) reveal that two monocations [imidazole nitrogen protanated (MC1) and dimethylamino nitrogen protanated (MC2)] and a dication [both imidazole nitrogen and dimethylamino nitrogen protanated (DC)] are formed by protonation in both ground and excited states. These observations are in consistent with quantum chemical calculations.

Dynamics of Solvent Controlled ESIPT of π-Expanded Imidazole Derivatives - pH Effect

A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

Characterization and electronic spectral studies of 2-(naphthalen-1-yl)-4,5-diphenyl-1H-imidazole bound Fe2O3 nanoparticles

Multicomponent, one-pot, highly efficient, indium trifluoride (InF3) catalytic synthesis of 2-(naphthalen-1-yl)-4,5-diphenyl-1H-imidazole under solvent-free condition is reported. Characterization of imidazole has been carried out by spectral techniques. The synthesized phosphated imidazole (PI) and phosphated imidazole bound magnetic nanoparticles (PIBMN) were characterized using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction (XRD). The photophysical characteristics of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles were investigated by steady-state absorption and emission spectroscopy as well as time resolved fluorometry. From these experiments, the position of the spectral maxima (λabs, λexc and λemi), and lifetime (τ) of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticle have been determined.

Enhancing the photoluminescence of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole anchored to superparamagnetic nanoparticles.

Synthesis and characterization of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole has been carried out by spectral studies. The synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles were characterized using fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction (XRD). The photophysical characteristics of the synthesized phosphated imidazole and phosphated imidazole bound magnetic nanoparticles were investigated by steady-state absorption and emission spectra as well as time resolved fluorometry. The intensities of absorption and emission maxima increase in the following order, phosphated imidazole bound Fe2O3>phosphated imidazole>imidazole.

Donor-acceptor binding interaction of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole with semiconductor nanomaterials.

The dynamics of photoinduced electron injection from 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole (NTI) to pristine ZnO, Mn-doped TiO2 and BaTiO3 nanoparticles have been studied by absorption, fluorescence and lifetime spectroscopic methods. Both the absorption and fluorescence results suggest the association between the nanoparticles and NTI. The calculated free energy change (ΔGet) confirms the electron injection from NTI to nano semiconductors. The critical energy transfer distance between NTI and the nanoparticles have been deduced. The emission of NTI is enhanced by pristine ZnO and quenched by Mn-doped TiO2 and BaTiO3 nanoparticles which are likely due to change of LUMO and HOMO levels of NTI on its association with nano semiconductors. The strong adsorption of the NTI on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. Electron injection from photoexcited NTI to the CB(S(∗)→S(+)+eCB(-)) is likely to be the reason for the fluorescence enhancement.

Multiple linear regression solvatochromic analysis of donar-acceptor imidazole derivatives.

Catalytic synthesis of some polysubstituted imidazoles under solvent-free condition is reported and their characterization has been carried out spectral techniques. Electronic spectral studies reveal that their solvatochromic behavior depends both the polarity of the medium and hydrogen bonding properties of the solvents. Specific hydrogen bonding interaction in polar solvents modulated the order of the two close lying lowest singlet states. The solvent effect on absorption and emission spectral results has been analyzed by multiple parametric regression analysis. Solvatochromic effects on the emission spectral position indicate the charge transfer (CT) character of the emitting singlet states both in a polar and a non polar environment. The fluorescence decays for the imidazoles fit satisfactorily to a bi exponential kinetics. These observations are in consistent with quantum chemical calculations.

Photoinduced Intramolecular Electron Transfer and Electronic Coupling Interactions in π- Expanded Imidazole Derivatives

An intramolecular excited charge transfer (CT) analysis of imidazole derivatives has been made. The determined electronic transition dipole moments has been used to estimate the electronic coupling interactions between the excited charge transfer singlet state (1CT) and the ground state (S0) or the locally excited state (1LE). The properties of excited 1CT state imidazole derivatives have been exploited by the significant contribution of the electronic coupling interactions. The excited state intramolecular proton transfer (ESIPT) analysis has also been discussed.