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

Efficient and chromaticity stable green and white organic light-emitting devices with organic-inorganic hybrid materials

Efficient inverted bottom emissive organic light emitting diodes (IBOLEDs) with tin dioxide and/or Cd-doped SnO2 nanoparticles as an electron injection layer at the indium tin oxide cathode:electron transport layer interface have been fabricated. The SnO2 NPs promote electron injection efficiently because their conduction band (-3.6 eV) lies between the work function (W f) of ITO (4.8 eV) and the LUMO of the electron-transporting molecule (-3.32 eV), leading to enhanced efficiency at low voltage. The 2.0% SnO2 NPs (25 nm) with Ir(ddsi)2(acac) emissive material (SnO2 NPs/ITO) have an enhanced current efficiency (η c, cd A-1) of 52.3/24.3, power efficiency (η p, lm W-1) of 10.9/3.4, external quantum efficiency (η ex, %) of 16.4/7.5 and luminance (L, cd m-2) of 28 182/1982. A device with a 2.0% Cd-doped SnO2 layer shows higher η c (60.6 cd A-1), η p (15.4 lm W-1), η ex (18.3%) and L (26 858 cd m-2) than SnO2 devices or control devices. White light emission was harvested from a mixture of Cd-SnO2 NPs and homoleptic blue phosphor Ir(tsi)3; the combination of blue emission (λ EL = 428 nm) from Ir(tsi)3 and defect emission from Cd-SnO2 NPs (λ EL = 568 nm) gives an intense white light with CIE of (0.31, 0.30) and CCT of 6961 K. The white light emission [CIE of (0.34, 0.35) and CCT of 5188 K] from colloid hybrid electrolyte BMIMBF4-SnO2 is also discussed.

Antibacterial activities and DNA-cleavage properties of novel fluorescent imidazo-phenanthroline derivatives

Design and biological activities of fluorescent imidazo-phenanthroline derivatives; (E)-5-((4-((4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenoxy)methyl)benzylidene)amino)- isophthalicacid, 2 and 2-(4-(((5-chloroquinolin-8-yl)oxy)methyl)phenyl)-1H-imidazo[4,5f] [1,10]phenanthroline, 3, have been reported. Their characterizations were performed by spectroscopic techniques. Their promising photophysical behaviours were observed in absorbance and fluorescence studies. The antibacterial activities of the compounds were determined against seven different microorganisms; Bacillus subtilis ATCC 6633(G + ), Pseudomonas aeruginosa ATCC 29853(G-), Escherichia coli ATCC 35,218 (G-), Enterococcus faecalis ATCC 292,112 (G + ), Salmonella typhimurium ST-10 (G-), Streptococcus mutans NCTC 10,449 (G + ), and Staphylococcus aureus ATCC 25923(G + ). MIC values of 3 was determined as 156,25 μM on all tested bacteria. A preliminary study of the structure-activity relationship (SAR) also revealed that the antimicrobial activity depended on the substituents on the phenyl ring. The electron withdrawing Cl-substitued compound 3 most favour for antimicrobial activity even at lowest concentration compared to other compounds. DNA-cleavage activities of the compounds were also investigated. The interactions of the compounds with supercoiled pBR322 plasmid DNA were obtained by agarose gel electrophoresis. All imidazo-phenanthroline derivatives were found to be highly effective on DNA, even at the lowest concentrations because of their planar nature which provides ease of bind to the helix structure of DNA.

Synthesis and optical studies of Y-shaped imidazole derivatives

A novel series Y-shaped π-expanded imidazole based chromophores was designed and synthesized. The series contains thirteen 2-aryl-4,5-bis[2-(aryl)vinyl)]-1H-imidazoles (6a-6m), which were characterized by spectroscopic analysis. The structures of compounds 6d and 6j were also confirmed by X-ray crystallographic analysis. The optical studies were investigated using absorption and emission measurements in dichloromethane. The fluorescence quantum yields were observed varying in 0.22-0.59 range, but the compounds with nitro substituent did not show the fluorescence. The absorption and emission study of the series helped us to understand the effect of substituents on the optical properties of compounds as well.

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%).

A hybrid inorganic–organic light-emitting diode using Ti-doped ZrO2 as an electron-injection layer

We have fabricated stable efficient iridium(iii)-bis-5-(1-(naphthalene-1-yl)-1H-phenanthro[9,10-d]imidazole-2-yl) benzene-1,2,3-triol (acetylacetonate) [Ir(NPIBT)₂ (acac)] doped inverted bottom-emissive green organic light-emitting diodes using Ti-doped ZrO₂ nanomaterials as the electron injection layer. The current density (J) and luminance (L) of the fabricated devices with Ti-doped ZrO₂ deposited between an indium tin oxide cathode and an Ir(NPIBT)₂ (acac) emissive layer increased significantly at a low driving voltage (V) compared with control devices without Ti-doped ZrO₂. The Ti-doped ZrO₂ layer can facilitate the electron injection effectively and enhances the current efficiency (η_c) of 2.84 cd A⁻¹ and power efficiency (η_p) of 1.32 lm W⁻¹

Ti-doped ZrO₂ facilitates electron injection effectively, leading to enhanced current efficiency of 2.84 cd A⁻¹ and power efficiency of 1.32 lm W⁻¹

A dodecanethiol-functionalized Ag nanoparticle-modified ITO anode for efficient performance of organic light-emitting devices

Increment of current efficiency with DT-Ag NPs coated devices was strongly related to energy transfer between radiated light generated from CBP:Ir(mpidmb)₂(acac) emissive layer and LSPR excited by DT-Ag NPs layer.

Highly phosphorescent green emitting iridium(iii) complexes for application in OLEDs

Phenanthrimidazole based iridium(iii) complexes show good performance in terms of brightness and power and current efficiencies.

1-(3,5-Di-meth-oxy-phen-yl)-4,5-dimethyl-2-phenyl-1H-imidazole

In the title mol-ecule, C19H20N2O2, the imidazole ring makes dihedral angles of 57.29 (5) and 31.54 (5)° with the attached di-meth-oxy-phenyl residue and the phenyl ring, respectively. The dihedral angle between the di-meth-oxy-phenyl and phenyl rings is 61.15 (5)°. In the crystal, pairs of C-H⋯N hydrogen bonds connect the mol-ecules into inversion dimers.

Interaction of fluorescent sensor with superparamagnetic iron oxide nanoparticles

To sense superparamagnetic iron oxides (Fe2O3 and Fe3O4) nanocrystals a sensitive bioactive phenanthroimidazole based fluorescent molecule, 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d] imidazole has been designed and synthesized. Electronic spectral studies show that phenanthroimidazole is bound to the surface of iron oxide semiconductors. Fluorescent enhancement has been explained on the basis of photo-induced electron transfer (PET) mechanism and apparent binding constants have been deduced. Binding of phenanthroimidazole with iron oxide nanoparticles lowers the HOMO and LUMO energy levels of phenanthroimidazole molecule. Chemical affinity between the nitrogen atom of the phenanthroimidazole and Fe(2+) and Fe(3+) ions on the surface of the nano-oxide may result in strong binding of the phenanthroimidazole derivative with the nanoparticles. The electron injection from the photoexcited phenanthroimidazole to the iron oxides conduction band explains the enhanced fluorescence.

Solvent effects on the absorption and fluorescence spectra of rhaponticin: experimental and theoretical studies

Rhaponticin (RH) possesses a variety of pharmacological activities including potent antitumor, antitumor-promoting, antithrombotic, antioxidant and vasorelaxant effects. The fundamental photophysics of RH is not well understood. In this work, solvent effect on the photoluminescence behavior of RH was studied by fluorescence and absorption spectra. The bathchromic shift was observed in absorption and fluorescence spectra with the increase of solvents polarity, which implied that transition involved was π→π. A quantitative estimation of the contribution from different solvatochromic parameters, like normalized transition energy value (E(T)(N)), was made using the linear stokes shift (Δν) relationship based on the Lippert-Suppan equation. The ground state and excited state dipole moments were calculated by quantum-mechanical second-order perturbation method as a function of the dielectric constant (ε) and refractive index (n). The result was found to be 2.23 and 3.67D in ground state and excited state respectively. The density functional theory (DFT) was used to obtain the most stable structure, electronic excitation energy, dipole moments and charge distribution. The analysis revealed that the RH exhibited strong photoinduced intramolecular charge transfer (ICT), and the intermolecular hydrogen bonding ability of the solvent was the most important parameter to characterize the photophysics behavior of RH. The hydrogen bonding effect occurred at the localized electron-acceptor oxygen at the glycoside bond. The experimental and theoretical results would help us better understand the photophysical properties of RH.

Characterization, physiochemical and computational studies of the newly synthesized novel imidazole derivative

The photophysical properties of imidazole derivative were studied in several solvents. The observed fluorescence quantum yield 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 solvent effect on the absorption and fluorescence bands was analyzed by a multi-component linear regression in which several solvent parameters were analyzed simultaneously. DFT calculations were carried out in order to find out the NBO analysis, HOMO-LUMO energies, MEP studies and hyperpolarisability behaviour. This chromophore possess more appropriate ratio of off-diagonal versus diagonal β tensorial component (r=β(xyy)/β(xxx)=0.12) which reflects the in plane non-linearity anisotropy. Since they have largest μβ(0) value, the reported imidazole can be used as potential NLO material. Within this context, reasonable conclusions concerning the steric hindrance in the chromospheres, push-pull character, hyperpolarisability of the imidazole and their application as NLO materials will be drawn.

Effective fluorescent chemosensors for the detection of Zn²+ metal ion

Benzimidazole derivatives synthesized from three components assembling condensation reaction behaves as a selective fluorescent sensor for Zn(2+) metal ion. These benzimidazole derivatives were 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 increase in the fluorescence enhancement can be explained on the basis of photo induced electron transfer (PET) mechanism. The blockage of the photoinduced electron transfer process from benzimidazole ring to aryl fluorophore induced by Zn(2+) co-ordination induced emission enhancement.

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).

Photophysical studies of fused phenanthrimidazole derivatives as versatile π-conjugated systems for potential NLO applications

Two new heterocyclic imidazole derivatives consists of π-conjugated system attached to a phenanthrimidazole moiety have been synthesized in moderate yield by the condensation of 1,10-phenanthroline-5,6-dione with substituted aromatic aldehydes and 4-methoxyaniline in the presence of ammonium acetate in ethanol medium. The photophysical properties of these imidazole derivatives were studied in several solvents. These derivatives were evaluated concerning their solvatochromic properties and molecular optical nonlinearities. Their electric dipole moment (μ) and hyperpolarizability (β) have been calculated theoretically and the results indicate that the extension of the π-framework of the ligands has an effect on the NLO properties of these imidazole derivatives. The non-zero tensor components of these imidazole derivatives reveal that they possess potent non-linear optical (NLO) behavior. The energies of the HOMO and LUMO levels and the molecular electrostatic potential (MEP) energy surface studies have exploited the existence of intramolecular charge transfer (ICT) within the molecule.

New iridium complexes with cyclometalated 2-arylimidazole ligands as highly efficient saturated green emitters

Phosphorescence studies of a series of heteroleptic cyclometalated iridium(III) complexes have been carried out. From the photoluminescent properties, it was found that these complexes possess dominantly (3)MLCT and (3)π-π* excited states. The solvent shifts are interpreted in terms of Reichardt-Dimroth solvent E(T) parameters and Marcus theory. 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 reveal that k(r) increases with increasing λ(em) and linear correlation between ln(k(nr)) and energy gap. The effect of E(g) and ΔQ(e) on k(nr) is discussed in detail.

Photoinduced electron-transfer from imidazole derivative to nano-semiconductors

Bioactive imidazole derivative absorbs in the UV region at 305 nm. The interaction of imidazole derivative with nanoparticulate WO3, Fe2O3, Fe3O4, CuO, ZrO2 and Al2O3 has been studied by UV-visible absorption, FT-IR and fluorescence spectroscopies. The imidazole derivative adsorbs strongly on the surfaces of nanosemiconductor, the apparent binding constants for the association between nanomaterials and imidazole derivative have been determined from the fluorescence quenching. In the case of nanocrystalline insulator, fluorescence quenching through electron transfer from the excited state of the imidazole derivative to alumina is not possible. However, a possible mechanism for the quenching of fluorescence by the insulator is energy transfer, that is, energy transferred from the organic molecule to the alumina lattice. Based on Forster's non-radiation energy transfer theory, the distance between the imidazole derivative and nanoparticles (r0∼2.00 nm) as well as the critical energy transfer distance (R0∼1.70 nm) has been calculated. The interaction between the imidazole derivative and nanosurfaces occurs through static quenching mechanism. The free energy change (ΔGet) for electron transfer process has been calculated by applying Rehm-Weller equation.

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).

Optical properties of organic nonlinear optical crystal--a combined experimental and theoretical study

The optical properties of the synthesized imidazole derivative, 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole, has been studied both experimentally and theoretically. Fluorescence enhancement have 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. Quantum chemical calculations of heat of formation, optimized geometry, NLO, HOMO-LUMO, MEP and NBO analysis of 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole (mpdsi) have been carried out by using density functional theory (DFT/B3LYP) method with 6-31G(d,p) as basis set. This chromophore possess more appropriate ratio of off-diagonal versus diagonal β tensorial component (r=β(xyy)/β(xxx)=-0.002) which reflects the inplane non-linearity anisotropy. Since they have largest μβ(0) value, the reported imidazole can be used as potential NLO material. The solvent effect on the absorption and fluorescence has been analyzed simultaneously.

Luminescent study on the binding interaction of bioactive imidazole with bovine serum albumin-A static quenching mechanism

Novel bioactive imidazole derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. The interaction between the imidazole derivative and bovine serum albumin (BSA) was investigated by fluorescence and UV-vis absorption spectroscopy. The fluorescence quenching of BSA by the imidazole derivatives may be due to the formation of imidazole-BSA complex. The fluorescence quenching mechanism of BSA by imidazole was analyzed and the binding constant has been calculated. The binding distance between imidazole and BSA was obtained based on Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant between imidazole and BSA was also examined.

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.

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.

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.