Femtosecond depolarization dynamics of tris(8-hydroxyquinoline) aluminum films

For vapor-deposited tris(8-hydroxyquinoline) aluminum thin films, steady-state and subpicosecond transient optical anisotropy are investigated. It is found that the transient absorption anisotropy decays within tens of picoseconds. With a simple model calculation, the excited state population and anisotropy decay dynamics are disentangled, and the latter signal, the depolarization of the excited state, is explained by the energy transfer between the non-orthogonally-coordinated quinolate ligands. It is also shown that there are two pathways for this fast interligand energy transfer.     

Theoretical study on the effects of nitrogen and methyl substitution on tris-(8-hydroxyquinoline) aluminum: an efficient exciton blocking layer for organic photovoltaic cells

We studied the effect of nitrogen and methyl substitution on tris-(8-hydroxyquinoline) aluminum (Alq(3)) with density functional theory, which has been adopted as an exciton blocking layer (EBL) in organic photovoltaic cells (OPVCs). The substitution of electron withdrawing nitrogen on the phenoxide moiety of Alq(3) lowers the highest molecular orbital (HOMO) level, thus photogenerated excitons can be effectively blocked in OPVC. Additional substitution of methyl on the pyridine moiety makes that Alq(3) has a smaller electron reorganization energy, which results in higher electron mobility with keeping HOMO level almost intact. Therefore, nitrogen and methyl simultaneous substitution shows high performance both in exciton blocking and electron mobility. This is the origins of the short circuit current enhancement in OPVC with 4-hydroxy-8-methyl-1,5-naphthyridine aluminum chelate (Alq(3) with the substitution of both nitrogen and methyl group) EBL.     

Stability constants of iron(III)-8-hydroxyquinoline complexes

Spectrophotometric determination of the formation constants of iron(III)-8-hydroxyquinoline complexes in 0.1 M sodium perchlorate solution at 25° gave the values K₁=[FeOx²⁺]/([Fe³⁺][Ox^-])=4.9·10¹³, K₂=[FeOx₂⁺]/([FeOx²⁺][Ox^-])=4.2·10¹² and K₃=[FeOx₃]/([FeOx₂⁺][Ox^-])=3.9·10¹⁰. FeOx₂OH and FeOx(OH)₂ are obtainable as solid phases. FeOx₃ (K_sp=3·10^-44, intrinsic solubility 1.6·10^-7 M) dissolves in basic solutions to form FeOx₂(OH)₂ -In a solution saturated with FeOx³, ([FeOx₂(OH)₂^-][Ox^-])/[OH^-]²=7.7·10^-5.     

Studies on extraction of In(III) with 8-hydroxyquinoline

The equilibrium molalities of In³⁺ in extraction reaction: In³⁺(aq)+3HOx(org) = In(Ox)₃(org) + 3H⁺(aq) were measured at ionic strengths from 0.13 to 2.54 mol·kg^?1 in the aqueous phase containing Na₂SO₄ as the supporting electrolyte and at constant initial molality of extractant, HOx, in the organic phase at temperatures from 278.15 to 308.15 K, where HOx and Ox mean 8-hydroxy-quinoline and its anion, respectively. The standard extraction constants K at various temperatures were obtained by two methods proposed in our previous paper.     

Ligand exchange dynamics in aluminum tris-(quinoline-8-olate): a solution state NMR study

The exchange kinetics between the three symmetry-inequivalent ligands in the meridianal isomer of aluminum tris-(quinoline-8-olate) (Alq(3)), a widely used electron-transporting and light-emitting material in the field of organic light emitting diodes, have been studied using two-dimensional exchange NMR spectroscopy in solution. The three inequivalent ligands were found to exchange on a time scale of about 5 s(-)( 1) at room temperature. A simple first-order mechanism based on consecutive 180 degrees flips of the ligands is sufficient to quantitatively explain the experimental data. Activation enthalpies between 83 and 106 kJ mol(-)( 1) were found for the flips of the three inequivalent ligands. The activation entropies are positive, suggesting a highly disordered transition state. These findings elucidate the internally mobile nature of the Alq(3) complex, and may have important implications for the morphology of vapor deposited thin films of Alq(3) as well as for crystallization-assisted device failures.     

Chemistry between magnesium and multiple molecules in tris(8-hydroxyquinoline) aluminum films

Metal organic contacts are at the basis of devices such as organic light emitting diodes (OLEDs). Here, we report a theoretical investigation of the chemical interaction between a Mg atom and an organic film made of tris(8-hydroxyquinoline)aluminum (Alq3) molecules. The latter is modeled either by an isolated molecule or by a bulk crystal. Using first-principles molecular dynamics for structural optimization, we find that an isolated Alq3 molecule and a Mg atom form an ion-pair. However, when the metal atom interacts with molecules in a bulk crystalline environment, we find that an organometallic complex is energetically preferred over the ion-pair. The complex formation is an effect of the environment which makes possible the interaction of the metal atom with several adjacent molecules. Here, our calculated O(1s) and N(1s) core level shifts agree well with recent experimental data on Alq3 films exposed to Mg. Our results resolve the apparent contradiction between experiment and predictions made in previous calculations in which a single Alq3 molecule was used to model a thin film.     

High basicity of phosphorus-proton affinity of tris-(tetramethylguanidinyl)phosphine and tris-(hexamethyltriaminophosphazenyl)phosphine by DFT calculations

It is shown by approximate but reliable DFT calculations that the title compounds represent very strong superbases in gas phase and MeCN. In particular, tris-(hexamethyltriaminophosphazenyl)phosphine has a proton affinity, PA, of 295.5 kcal mol(-1) and records a pKa(MeCN) of 50 +/- 1 units.     

ICP-AES detection of ultratrace aluminum(III) and chromium(III) ions with a microcolumn preconcentration system using dynamically immobilized 8-hydroxyquinoline on TiO2 nanoparticles.

Titanium dioxide nanoparticle dynamically loaded with 8-hydroxyquinoline (nanometer TiO2-Oxine) was used as a solid-phase extractant for the preconcentration of trace amounts of aluminum(III) and chromium(III) prior to their determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimal conditions for preparing nanometer TiO2-Oxine were obtained. Also, the separation/preconcentration conditions of analytes, including the effects of the pH, the sample flow rate and the volume, the elution solution and the interfering ions on the recovery of the analytes were investigated. At pH 6.0, the adsorption capacity of nanometer TiO2-Oxine was found to be 5.23 mg g(-1) and 9.58 mg g(-1) for Al(III) and Cr(III), respectively. An enrichment factor of 50 was achieved by this method, and the detection limits (3sigma) for Al(III) and Cr(III) were 1.96 and 0.32 microg L(-1) respectively. The proposed method was applied for the determination of trace Al(III) and Cr(III) in biological samples and lake water with satisfactory results.     

High-performance liquid chromatography of 8-hydroxyquinoline chelates of aluminium and cobalt(III)

Summary The 8-hydroxyquinoline chelates of Co(III) and Al(III) may be separated by high-performance liquid chromatography using a silica column and 5% methanol in chloroform as mobile phase. Using detection at 254 nm, the method provided detection limits of 0.9 ng of Co(III) and 17 ng of Al(III) in a 10 mm³ injection.     

DFT studies and vibrational spectra of isoquinoline and 8-hydroxyquinoline

The geometry, frequency and intensity of the vibrational bands of isoquinoline (IQ) and 8-hydroxyquinoline (8-HQ) were obtained by the density functional theory (DFT) calculations with the B3LYP functional and 6-31 G* basis set. The vibrational spectral data obtained from the solid phase mid and far FT-IR and FT-Raman spectra of IQ and 8-HQ are assigned based on the results of the normal coordinate calculations. The observed and the calculated spectra are found to be in good agreement.     

CP/MAS 13C NMR characterization of the isomeric states and intermolecular packing in tris(8-hydroxyquinoline) aluminum(III) (Alq3)

The isomeric states and intermolecular packing of tris(8-hydroxyquinoline) aluminum(III) (Alq(3)) in the alpha-, gamma-, and delta-crystalline forms and in the amorphous state, which are important for understanding the light-emitting and electron-transport properties, have been analyzed by CP/MAS (13)C NMR. This simple NMR experiment shows that the isomeric state of alpha- and amorphous Alq(3) is meridional, whereas that of gamma- and delta-Alq(3) is facial. In the amorphous Alq(3), the inclusion of facial isomers has been under debate. Our experiments show that meridional isomers are dominant in the amorphous Alq(3), although the existence of facial isomers cannot be completely denied. The local structure of amorphous Alq(3) is similar to that of alpha-Alq(3) and is significantly different from those of gamma- and delta-Alq(3). Among these Alq(3) samples, the effect of intermolecular interaction is not found only for gamma-Alq(3). This finding can explain the good solvent solubility of gamma-Alq(3), compared with the other crystalline forms. It is also shown that the structures are locally disordered not only for amorphous Alq(3) but also for alpha-Alq(3), although clear X-ray diffraction peaks are observed for alpha-Alq(3). In contrast, the local structures of gamma- and delta-Alq(3) are well defined. A clear relation is found between the spectral patterns of CP/MAS (13)C NMR and the fluorescence wavelengths; the samples, which consist of facial isomers, show blue-shifted fluorescence compared with those of meridionals.     

Characterization of the triplet state of tris(8-hydroxyquinoline)aluminium(III) in benzene solution

The lowest triplet state of tris(8-hydroxyquinoline)aluminium(III) (Alq3) has been prepared by pulse radiolysis/energy transfer from appropriate donors in benzene solutions and has an absorption maximum around 510 nm with a lifetime of about 50 mus. It is quenched by molecular oxygen, leading to singlet oxygen formation. From flash photolysis and singlet oxygen formation measurements, a quantum yield of triplet formation of 0.24 was determined for direct photolysis of the complex. A value of 2.10 +/- 0.10 eV was determined for the energy of the lowest triplet state by energy transfer studies and was confirmed by phosphorescence measurements on Alq3, either in the heavy atom solvent ethyl iodide or photosensitized by benzophenone in benzene. Dexter (exchange) energy transfer was observed from triplet Alq3 to platinum(II) octaethylporphyrin.     

甲基丙烯酸-8-羟基喹啉-镧配合物的合成及与DNA的作用

合成了配合物La(C4H6O2)2(hq)(C4H6O2=甲基丙烯酸,hq=8-羟基喹啉),通过元素分析、摩尔电导、红外光谱、紫外光谱和热重分析手段对产物进行表征。此外,采用紫外吸收光谱、荧光光谱,研究了配合物与鲱鱼精DNA之间的相互作用。结果显示配合物与鲱鱼精DNA作用的结合常数K=7.59×103L·mol-1,配合物与DNA的作用摩尔比为1∶1,作用模式为嵌插作用。     

A DFT study of reactions of Ru(III) anticancer drug KP1019 with 8-oxoguanine and 8-oxoadenine

Structural Chemistry - The cytotoxic activities of KP1019 and other Ru(III) drugs are believed to be associated with their binding with DNA. Here, we report the density functional theory (DFT)...     

High-efficiency tris(8-hydroxyquinoline)aluminum (Alq3) complexes for organic white-light-emitting diodes and solid-state lighting

Combinations of electron-withdrawing and -donating substituents on the 8-hydroxyquinoline ligand of the tris(8-hydroxyquinoline)aluminum (Alq(3)) complexes allow for control of the HOMO and LUMO energies and the HOMO-LUMO gap responsible for emission from the complexes. Here, we present a systematic study on tuning the emission and electroluminescence (EL) from Alq(3) complexes from the green to blue region. In this study, we explored the combination of electron-donating substituents on C4 and C6. Compounds 1-6 displayed the emission tuning between 478 and 526 nm, and fluorescence quantum yield between 0.15 and 0.57. The compounds 2-6 were used as emitters and hosts in organic light-emitting diodes (OLEDs). The highest OLED external quantum efficiency (EQE) observed was 4.6%, which is among the highest observed for Alq(3) complexes. Also, the compounds 3-5 were used as hosts for red phosphorescent dopants to obtain white light-emitting diodes (WOLED). The WOLEDs displayed high efficiency (EQE up to 19%) and high white color purity (color rendering index (CRI≈85).     

The structure of the blue luminescent delta-phase of tris(8-hydroxyquinoline)aluminium(III) (Alq3)

The existence of the facial isomer in the delta-phase of Alq3 is proven by X-ray structural analysis, revealing that both the different molecular structure and the weaker overlap of the pi-orbitals of hydroxyquinoline ligands belonging to neighboring Alq3 molecules as compared to other phases (alpha, beta) are likely to be the origin of the significantly different optical properties of delta-Alq3.