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

Promotional effect of silver nanoparticle embedded Ga-Zr-codoped TiO2 as an alternative anode for efficient blue, green and red PHOLEDs

Efficient blue, green and red phosphorescent OLEDs have been harvested from silver nanoparticles embedded at a glass:Ga-Zr-codoped TiO2 interface. The embedded silver nanoparticles at the interface removed the non productive hole current and enhanced the efficiencies. The blue emitting device (456 nm) with emissive layer Ir(fni)3 exhibits a maximum luminance (L) of 40 512 cd m-2 (ITO - 37 623 cd m-2), current efficiency (η c) of 41.3 cd A-1 (ITO - 40.5 cd A-1) and power efficiency (η p) of 43.1 lm w-1 (ITO - 39.8 lm w-1) and external quantum efficiency (η ex) of 19.4% (ITO - 6.9%). A newly fabricated green device based on emissive layer Ir(tfpdni)2(pic) shows intensified emission at 514 nm, luminance of 46 435 cd m-2 (ITO - 40 986 cd m-2), current efficiency of 49.7 cd A-1 (ITO - 47.3 cd A-1), power efficiency of 48.6 lm w-1 (ITO - 41.4 lm w-1) and external quantum efficiency of 17.5% (ITO - 14.9%). The red device (618 nm) with emissive layer Ir(bbt)2(acac) shows luminance of 8936 cd m-2 (ITO - 8043 cd m-2), current efficiency of 6.9 cd A-1 (ITO - 4.6 cd A-1), power efficiency of 5.7 lm w-1 (ITO - 4.9 lm w-1) and external quantum efficiency of 9.3% (ITO - 6.9%).

Influence of molecular structure on the photoluminescence of 2-methyl benzimidazolium picrate: a new fluorescent material

This work reports the structural and photo luminescent characterization of the 2-methyl benzimidazolium picrate salt for the first time. This new material exhibits the π-π stacking of aromatic rings involving the benzimidazolium cation and picrate anion, which is additionally supported with a rare n→π interaction as well as with the extended networks of intermolecular hydrogen bonds in the solid state. The FT-IR and UV characterizations further support the solid state structural features of the salt. However, the spectroscopic results reveal that the stacking of ion pairs, which is observed in the solid state, is not maintained in solution. The DSC result indicates that the material is stable under ambient temperature conditions. Interestingly, upon photo excitation at 325 nm in the solid state, the material shows an unusual red emission around 615 nm, which is probably attributed to the supramolecular stacked nature of the ion pairs, along with a usual picrate centered green emission at 530 nm. However, the fluorescence measurement in solution, wherein the stacking of ion pairs are not maintained, shows only a single peak at lower wavelength. These observations highlight the influencing role of the supramolecular stacking interactions on the photoluminescence of the material, due to which, a chemical sensing action may be envisaged.

Synthesis and studies of electrochemical properties of lophine derivatives

A versatile series of lophine derivatives (1–13) were synthesized and characterized, Fourier transform infrared spectroscopy (FTIR), Liquid Chromatography-Mass Spectrometry (LC-MS), and ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy.

Physico-chemical studies of new luminescent chemosensor for Cu2+

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-phenylpropanoic acid (HBDPPA) has been studied in a series of different solvents. As revealed by absorbance, and emission results, the molecule undergoes fast excited-state intramolecular proton transfer (ESIPT) to yield emission of the corresponding tautomeric species. A large energy barrier for interconversion of the keto-enol rotamers in the ground and excited state have been predicted on the basis of DFT calculations and also supported by HOMO-LUMO energies, PES calculation, NLO and NBO analysis. Hyperpolarizability and octupolar and dipolar components ratio confirmed that HBDPPA can be used as optoelectronic materials. The ground state equilibrium and ESIPT process of HBDPPA are essentially unaffected by the nature of the solvent. Measurements of absorption solvatochromism have been interpreted with Marcus and Reichardt-Dimroth solvent functions to estimate the transition dipoles. Good correlation exists between absorption as well as fluorescence wavenumbers obtained by the multi-component linear regression employing the Taft and Catalan solvent parameters with the experimental values. The prepared Schiff base HBDPPA can be used as a new fluorescent sensor to detect the quantity of Cu(2+) ion in any sample solution depending on the relative intensity change.

DFT based ESIPT process of luminescent chemosensor: Taft and Catalan solvatochromism

Amino acid containing o-hydroxy Schiff base derivative was synthesized and an excited state intramolecular proton transfer (ESIPT) process in o-hydroxy Schiff base (HBMBA) has been studied using solution spectral studies. It was detected that the two distinct ground state isomers I and II are responsible for the emission. By comparing the emission wavelength in hydrocarbon solvent, it was predicted that the trans enol form predominates over the cis enol form. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base 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 fluorescence of HBMBA quenched with the gradual addition of Cu(2+). Therefore the prepared Schiff base HBMBA can be used as a new fluorescent sensor to detect the quantity of Cu(2+) ions in any sample solution depending on the relative intensity change. Measurements of absorption solvatochromism have been interpreted with Marcus and Reichardt-Dimroth solvent functions to estimate the transition dipoles. Good correlation exists between absorption as well as fluorescence wavenumbers obtained by the multi-component linear regression employing the Taft and Catalan solvent parameters with the experimental values.

Potential fluorescent chemosensor based on L-tryptophan derivative: DFT based ESIPT process

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-(1H-indol-3-yl) propanoic acid (HBDIPPA) has been studied in a series of different solvents. An excited state intramolecular proton transfer (ESIPT) process in hydroxy Schiff base has been studied using emission spectroscopy. DFT calculations on energy, HOMO-LUMO energies, MEP, dipole moment, charge distribution of the Schiff base derivative have been performed and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state is shown by PES calculation. Positive values of laplacian ▿(2)ρ((rc)) (2.81) and electron density ρ((rc)) (0.22) are indicative of hydrogen bonds interactions. Absorption as well as fluorescence wavenumbers are correlated with Marcus and Reichardt-Dimroth solvent functions and also with Taft and Catalan solvent parameters. Schiff base HBDIPPA can be used as a new fluorescent sensor.

Synthesis and physico-chemical studies of cyclometalated heteroleptic iridium(III) complexes

Phosphorescent studies of 2-arylimidazole heteroleptic cyclometalated iridium(III) complexes with picolinic acid as the ancillary ligand were made. The observed experimental data reveals that these complexes possess dominantly (3)MLCT and (3)π-π* excited states and the solvent shift of these complexes are interpreted by Reichardt-Dimroth and Marcus solvent functions. The results are consistent with prior assignments on the absorption band to a metal-to-ligand charge transfer excited state associated with chelating ligand. Emission kinetic studies exploited that the radiative transition (k(r)), increases with increasing λ(emi).

Fluorescence spectral studies of some imidazole derivatives

The photophysical properties of imidazole derivatives namely 2-(2,4-difluorophenyl)-4,5-dimethyl-1-p-tolyl-1H-imidazole and N,N-dimethyl-4-(4,5-dimethyl-2-phenyl-1H-imidazol-1-yl)benzenamine, synthesized from an unusual four components assembling, were studied in several solvents. Polarization also plays major role in the increase of excited-state dipole moment (μ(e)). From the spectral results, it was found that there is equilibrium between neutral species and monocationic (MC) species in polar aprotic and polar protic solvents. The basicity of the solvent, C(β) or C(SB) has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with increasing electron-donating ability of the solvent. Therefore, resonance structures 1b and 2b has the positive charge located at the nitrogen atom stabilized in basic solvents.

Synthesis, spectral studies and solvatochromic analysis of novel imidazole derivatives

Bioactive imidazole derivatives were synthesized and characterized by spectral techniques. The photophysical properties of imidazole derivatives were studied in several solvents. The observed spectral shift is attributed to a loss of planarity in the excited state provided by the non-co-planarity of the aryl rings attached to C(2) and N(1) atoms of the imidazole ring. The observed solvatochromic shifts were analyzed in detail by Kamlet-Taft and Catalan parameters. The interaction between bioactive imidazole derivative and bovine serum albumin (BSA) was also investigated.

Light-emitting materials from cyclometalated heteroleptic iridium(III) complexes--A physicochemical study

Phosphorescent studies of 2-arylimidazole heteroleptic cyclometalated iridium(III) complexes with picolinic acid as the ancillary ligand were made. The observed experimental data reveal that these complexes possess dominantly (3)MLCT and (3)π-π* excited states and the solvent shift of these complexes is interpreted by Reichardt-Dimroth and Marcus solvent functions. The results are consistent with prior assignments on the absorption band to a metal-to-ligand charge transfer excited state associated with chelating ligand. Emission kinetic studies exploited that the radiative transition (k(r)) increases with increasing λ(em).

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

Research activities in the field of imidazole-derived push-pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure-property relationships, and the prospective application of such D-π-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain.

Physicochemical studies of bioactive heterocycles of some novel imidazole derivatives as sensitive NLO materials

Some novel imidazole derivatives were developed as 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+), Cu(2+), Zn(2+), Co(2+) and Fe(2+) and this was suggested to result from the suppression of radiationless transitions from the n-π* state in the chemisensors. By DFT calculation HOMO-LUMO energies were calculated, the electric dipole moment (μ) and the hyperpolarizability (β) of the investigated molecules have been studied experimentally and also theoretically. These synthesized molecules were found to have microscopic non-linear optical (NLO) behaviour with non-zero tensor components.

Binding interaction of bioactive imidazole with bovine serum albumin--a mechanistic investigation

A novel Y-shaped imidazole derivative 4-((E)-2-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)vinyl)phenol has been synthesized and characterised by IR, UV-vis, mass and NMR spectral techniques. The mutual interaction of this imidazole derivative (DPTIV) with bovine serum albumin (BSA) was investigated using photoluminescent studies. The fluorescence quenching mechanism of BSA by DPTIV was analyzed and the binding constant has been calculated. The binding distance between DPTIV and BSA was obtained based on the theory of Forester's non-radiation energy transfer. The effect of some common ions on the binding constant between DPTIV and BSA was also examined.

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.

Fluorescence resonance energy transfer from a bio-active imidazole derivative 2-(1-phenyl-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol to a bioactive indoloquinolizine system

Novel donor imidazole derivative, 2-(1-phenyl-1H-imidazo [4,5-f][1,10]phenanthrolin-2-yl)-phenol (PIPP) was screened as highly sensitive chemisensor for transition metal ions and it can be used as a "multi-way" optically switchable material. Solvatochromic effects on the fluorescence behaviour of PIPP were studied in different solvents. The fluorescence of PIPP was highly sensitive to both the polarity as well as protic nature of the solvent. Fluorescence (Forster) resonance energy transfer (FRET) process from PIPP to a potent bioactive indoloquinolizine molecule was studied and it is argued that long-range dipole-dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r(0)) have been determined.