First-Principles Studies on the Efficient Photoluminescent Iridium(III) Complexes with C∧N═N Ligands

Small substituent groups as geometric controllers for tridentate platinum(ii) complexes to effectively suppress non-radiative decay processes

For phosphorescent emitters, the rigidity of the geometry is a crucial indicator, which can directly determine the non-radiative decay rate. In this article, density functional theory (DFT) calculations were performed to investigate the influence of the small substituent groups on the rigidities of tridentate Pt(ii) complexes in detail. The calculated results indicate that the small substituent groups can serve as geometric controllers to suppress the structural distortion on going from the ground state (S0) to the lowest-lying triplet excited state (T1) (Jahn-Teller distortion). For instance, when electron-donating substituent groups, including -NH2, -N(CH3)2 and -OCH3, were employed, the rigidities of the corresponding Pt(ii) complexes can be effectively enhanced because the highest occupied molecular orbital (HOMO)-HOMO-1 energy gaps could be increased. Different from the electron-donating substituent groups, electron-withdrawing substituent groups, i.e., -NO2 and -COCH3, can cause a negligible change in HOMO and HOMO-1 energies during the S0 → T1 transition process, and therefore, for Pt-NO2 and Pt-COCH3, no Jahn-Teller distortion occurs. According to the calculated results, the rigidities of tridentate Pt(ii) complexes could be raised via tuning the energies of the frontier molecular orbital (FMO) with the help of small substituent groups.

Highly efficient electrochemiluminescence labels comprising iridium(iii) complexes

Highly efficient iridium ECL labels exhibiting various emission colors have been developed. Importantly, BSA labeled with the novel iridium labels displays much more intense ECL than the same amount labeled by a traditional ruthenium label in ProCell buffer solution.

A theoretical study on the electronic and photophysical properties of two series of iridium(iii) complexes with different substituted N^N ligand

The density functional theory has been applied to explore the geometrical, electronic and photophysical properties of the recently reported pyrazolyl-pyridine- or triazolyl-pyridine-containing iridium(iii) complexes 1 and 2.

Computational insights into the photophysical and electroluminescence properties of homoleptic fac-Ir(C^N)3 complexes employing different phenyl-derivative-featuring phenylimidazole-based ligands for promising phosphors in OLEDs

The electronic structures and photophysical properties of three homoleptic iridium(iii) complexes IrL₃ with C^N ligands are investigated by means of the density functional theory method.

Highly efficient orange phosphorescent organic light-emitting diodes based on an iridium(iii) complex with diethyldithiocarbamate (S^S) as the ancillary ligand

A novel iridium(iii) complex Ir(dpp)₂(dta) with diethyldithiocarbamate (S^S) as the ancillary ligand was synthesized and characterized. The polymer organic light-emitting device based on Ir(dpp)₂(dta) has been fabricated.

Luminescent Re(I) terpyridine complexes for OLEDs: what does the DFT/TD-DFT probe reveal?

The electronic structure and spectroscopic properties of a series of rhenium(I) terpyridine complexes were investigated using density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods. The influence of different substituent groups on the optical and electronic properties of Re(I) terpyridine complexes has also been explored. The reorganization energy calculations show that the substituted Re(I) terpyridine complexes are better electron transport materials with high quantum efficiency in OLED devices due to their high electron transport mobility and low λ(electron) values, whereas the unsubstituted complex shows relatively balanceable charge transfer abilities with the higher efficiency in organic light emitting devices (OLEDs). An NBO analysis reveals that n→σ* interactions are mainly responsible for the ground state stabilization of all the complexes. QTAIM results show that in all cases, Re-CO bonds are shared type transient interactions as reported in the other metal ligand complexes. The absorption is associated with (1)MLCT/(1)LLCT/(1)ILCT character while the emission transition has (3)MLCT/(3)LLCT/(3)ILCT character as revealed by a natural transition orbital (NTO) analysis. The higher quantum yields reported for the complexes 4-6 are found to be closely related to both its smaller ΔE(S1-T1), higher μ(S1), E(T1) and moderate (3)MLCT character. The calculated results show that Re(I) terpyridine complexes, particularly complexes 4-6, are suitable candidates for OLED materials.

Binding interaction between 2-(naphthalen-1-yl)-1-p-tolyl-1H-phenanthro[9,10-d]imidazole and semiconductor nanomaterials

The binding interaction of bioactive phenanthrimidazole with nanoparticulate WO3, Fe2O3, Fe3O4, CuO, ZrO2 and Al2O3 has been studied by electronic and life time spectral studies. The phenanthrimidazole adsorbs strongly on the surface of nanosemiconductor, the apparent binding constants have been determined from the fluorescence quenching. In the case of nanocrystalline insulator, fluorescence quenching through electron transfer from the excited state of the phenanthrimidazole to alumina is not possible, but it is due to energy transfer process.

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.

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.

Tuning the electronic and phosphorescence properties of blue-emitting iridium(iii) complexes through different cyclometalated ligand substituents: a theoretical investigation

A DFT/TDDFT investigation was performed to estimate the OLED performance of six reported and seven newly designed iridium(iii) complexes.

Enhancing the electronic properties and quantum efficiency of sulfonyl/phosphoryl-substituted blue iridium complexes via different ancillary ligands

The influence of the ancillary ligands for iridium complexes on the electronic structures, absorption and emission spectra, and quantum efficiency was investigated. The results reveal that they not only tune the energy gap but also enhance the quantum efficiency.

Highly efficient electrochemiluminescence from iridium(iii) complexes with 2-phenylquinoline ligand

Bis-(methylated 2-phenylquinoline) iridium(iii) complexes demonstrated the strongest ECL.

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.

Contrasting emission behaviour of phenanthroimidazole with ZnO nanoparticles

A new fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-phenanthro [9,10-d]imidazole has been synthesized and characterized by spectroscopic techniques. Nanoparticulate ZnO enhances the fluorescence of the synthesised fluorophore. The absorption, fluorescence, lifetime, cyclic voltammetry and infrared studies reveal that fluorophore is attached to the surface of ZnO semiconductor. Photo-induced electron transfer (PET) explains the enhancement of fluorescence by nanoparticulate ZnO and the apparent binding constant has been obtained. Adsorption of the fluorophore on ZnO nanoparticle lowers the HOMO and LUMO energy levels of the fluorophore. The strong adsorption of the phenanthrimidazole derivative on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the organic molecule to the zinc ion on the surface of nanocrystal.

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.

Fluorescence quenching of organic molecule by insulator

A new kind of fluorophore 2-(4-fluorophenyl)-1-phenyl-1H-benzo[d]imidazole (FPPBI) has been synthesized and characterized by (1)H NMR, (13)C NMR, mass spectral studies and single crystal XRD. The energy transfer from FPPBI to Al2O3 nanocrystals has been studied by absorption, fluorescence and lifetime spectroscopic methods. The association between nanoparticles and FPPBI is explained from both absorption and fluorescence quenching data. The distance between FPPBI and Al2O3 as well as the critical energy transfer distance has been deduced.

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.