8-hydroxyquinoline Aluminum Research Articles

Low-temperature solvent-free synthesis route of blue and green luminescent phases of tris(8-hydroxyquinoline)aluminum (AlQ3)

Recent research studies have shifted towards simple, efficient, and more eco-friendly synthesis methods. The current study focuses on using a free-solvent reaction to synthesize trichelate 8-hydroxyquinoline (8HQ) octahedral Al(III) coordination complex (AlQ3), which still represents the most widely used electroluminescent material in organic light-emitting devices (OLEDs). We have developed a new safe and easy route for synthesizing AlQ3 via a pure solid-state reaction between 8HQ and AlCl3 with sodium carbonate as an inorganic base. The formation of the free-solvent prepared AlQ3 was confirmed using FT-IR, UV–Vis spectroscopy, SEM/EDS analysis, powder, and single crystal. Our investigation overturns the belief that fac-AlQ3 is only formed at high temperature; the developed synthesis method enabled the production of blue-fluorescent AlQ3 at room temperature. Furthermore, this study presents a low-temperature synthesis pathway for obtaining pure AlQ3 phases for the first time. We controlled the washing step of the isolated AlQ3 to produce large amounts of blue and green luminescent AlQ3. The optical properties of the samples were determined using photoluminescence (PL) spectroscopy.

Nanoscale interface engineering for enhanced performance in light-emitting-diode devices: ITO/Ag-SRCOOH

In light-emitting diode (LED) devices, the hole-injection layer (HIL) reduces the hole injection barrier (HIB) between the anode and organic layers to obtain favorable conditions for hole transport, which considerably affects device efficiency and performance. However, the fabrication of ultrathin silver (Ag) films for electron and hole transport layers remains challenging. We demonstrated the design of a nanoscale HIL interface with chemisorption-bonded carboxylic acid-terminated alkanethiol self-assembled layers on ultrathin Ag. The device structure consisted of indium tin oxide (ITO)/Ag-mercaptan acid (Ag-SRCOOH)/N, Nj-Di (1-naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/ETL(LiF/Al. Notably, a chemical bond peak was not detected between ITO and ultrathin Ag. However, X-ray photoelectron spectroscopy (XPS) measurements confirmed Ag binding to the thiol group of 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) on the Ag island surface, which is evident from -S-Ag- and -RS-Ag- association peaks. Ultraviolet photoelectron spectroscopy analysis results revealed a reduction in the HIB of device from 0.68 to 0.19 eV. Consequently, the luminance and current density, and current density of the AgNP–MPA device increased by 63-fold, 5.8-fold, and 1.1-fold, respectively. Similarly, the AgNP-MUA device exhibited enhanced performance with a 61-fold increase in luminance, 43-fold increase in current density, and a 1.4-fold increase in current efficiency, respectively. The results of this study not only opened novel avenues for future applications, including operation requiring flexibility and transparency of LEDs, but also proposed the optimization of nanoscale interfaces to enhance LED performance.

Fabrication of Carbon Quantum Dots/Alq3 Layer for NO2 Gas Sensor

The gas sensors were prepared using carbon quantum dots (CQDs) using an electrochemical method after mixing the CQDs with Tris (8-hydroxyquinoline) aluminum (III) (Alq3) polymer. A spin coating technique was used to deposit CQDs/Alq3 composite film on glass substrates with a ratio of 1:1. The CQDs/Alq3 gas sensor showed a sensitivity of about 24٪ at a temperature of 300 ℃, and this was calculated after measuring the change in the resistance of the samples with a response time of 2 and 8sec recovery time. The sensor showed a good response for nitrogen dioxide (NO2) gas. However, the sensitivity, response time, and recovery time for the CQDs gas sensor when exposed to NO2 gas at 300 °C were 78%, 4s, and 129s, respectively. The results showed that the best sensor CQDs/Alq3 led to a reduction in the recovery time, which shows the importance of the Alq3 polymer in improving the properties of the gas sensor.

Effect of growth temperatures on the structural and optical properties of bulk tris-(8-hydroxyquinoline) aluminium (III)

Effect of growth temperatures on the structural and optical properties of bulk tris-(8-hydroxyquinoline) aluminium (III)

Aqueous solution processed transition-metal-doped ZnO as electron injection layers for efficient inverted organic light emitting diodes

Zinc oxide (ZnO) has attracted lots of attention to be used as interfacial materials in organic optoelectronic devices owing to its attractive properties. In this work, a series of transition-metal-doped ZnO thin films were prepared by using a facile aqueous solution process, thereafter these films were employed as electron injection layers (EILs) combined with the tris-(8-hydroxyquinoline) aluminum (Alq3) emitting layer to construct the inverted organic light-emitting diodes (IOLEDs). The transition-metal-doped ZnO EIL-based IOLEDs demonstrate markedly improved device performance compared to the reference neat ZnO EIL-based IOLED. However, different transition-metal ions have much different doping effect on the device performance. CoCl2 doped ZnO EIL based IOLED device possesss an optimal current efficiency of 5.52 cd A−1, which is increased about 40% compared to the device with the neat ZnO as EIL. The enhancement might be attributed to the increased electron mobility and favorable interfacial energy level alignment of the transition-metal doped ZnO EIL for more efficient electron injection. Our findings may provide a promising strategy to improve the electron injection properties of ZnO film in the OLED devices.

Tris(8-hydroxyquinoline)aluminium in a polymer matrix as an active layer for green OLED applications

Tris(8-hydroxyquinoline)aluminium in a polymer matrix as an active layer for green OLED applications

Performance enhancement of blue organic light-emitting devices by inserting BPhen: Alq3 as an n-doping electron transport layer

An n-doping electron transport layer (ETL) that consists of 4-7-diphenyl-1, 10-phenanlhroline (BPhen) and tris(8-hydroxyquinoline) aluminum (Alq3) was applied to enhance the performance of blue organic light-emitting diodes (OLEDs). The resulting n-doping OLED afforded a maximum luminance efficiency of 8.24 cd/A, which was higher than the devices using either BPhen or Alq3 as ETL by 56.9 % and 91.2 %, respectively. In addition, this device was found to possess a higher maximum power efficiency of 5.17 Lm/W compared to the blue OLEDs without such n-doping ETL concentrations. By performing the hole- and electron- ‘only’ devices and the density functional theory (DFT) calculations, we show that the enhancement of the device performance can be attributed to increased electron injection/transport at ETL interfaces and hence improved carrier balance in emission layer (EML).

Spontaneous orientation polarization of flavonoids

Spontaneous orientation polarization (SOP) is macroscopic electric polarization that is attributed to a constant orientational degree of dipole moments of polar molecules on average. The phenomenon has been found in small molecules like H2O at low temperatures and π-conjugated molecules employed in organic light-emitting diodes. In this study, we demonstrate that a thin film of baicalein, a flavonoid compound found in natural products, exhibits SOP and resultant giant surface potential (GSP) exceeding 5500 mV at a film thickness of 100 nm. Vacuum-deposition of baicalein under high vacuum results in smooth and amorphous films, which enables the generation of GSP with a slope of 57 mV/nm in air, a value comparable to the representative of an organic semiconductor showing GSP, tris(8-hydroxyquinoline)aluminum(III) (Alq3). We also found the superior photostability of a baicalein film compared to an Alq3 film. These findings highlight the potential of baicalein in new applications to organic electronics.

Photoluminescence, Optical, and Electrical Properties of Bis(8-Hydroxyquinoline) Zinc and Tris-(8-Hydroxyquinoline) Aluminum Organometallics and Their Films

Photoluminescence, Optical, and Electrical Properties of Bis(8-Hydroxyquinoline) Zinc and Tris-(8-Hydroxyquinoline) Aluminum Organometallics and Their Films

Preparation of Hybrid Films Based in Aluminum 8-Hydroxyquinoline as Organic Semiconductor for Photoconductor Applications.

In the present work, we have investigated an organic semiconductor based on tris(8-hydroxyquinoline) aluminum (AlQ3) doped with tetracyanoquinodimethane (TCNQ), which can be used as an organic photoconductor. DFT calculations were carried out to optimize the structure of semiconductor species and to obtain related constants in order to compare experimental and theoretical results. Subsequently, AlQ3-TCNQ films with polypyrrole (Ppy) matrix were fabricated, and they were morphologically and mechanically characterized by Scanning Electron Microscopy, X-ray diffraction and Atomic Force Microscopy techniques. The maximum stress for the film is 8.66 MPa, and the Knoop hardness is 0.0311. The optical behavior of the film was also analyzed, and the optical properties were found to exhibit two indirect transitions at 2.58 and 3.06 eV. Additionally, photoluminescence measurements were carried out and the film showed an intense visible emission in the visible region. Finally, a photoconductor was fabricated and electrically characterized. Applying a cubic spline approximation to fit cubic polynomials to the J-V curves, the ohmic to SCLC transition voltage VON and the trap-filled-limit voltage VTFL for the device were obtained. Then, the free carrier density and trap density for the device were approximated to n0=4.4586×10191m3 and Nt=3.1333×10311m3, respectively.

Theoretical analysis of OLED performances of some aromatic nitrogen-containing ligands.

It is well-known that tris(8-hydroxyquinoline) aluminum (Alq3) complex and N,N'diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine compound (TPD) are widely used as electron transfer material (ETL) and hole transfer material (HTL) in organic light emitting diode (OLED) structure, respectively. Considering the reference materials, in the present work, the OLED performances of some cyclic aromatic structures such as 4,4'azopyridine [AZPY], 4,4'-bipyridine [BIPY], 1,2-bis[4'-(4-methylphenyl)2,2':6'2″-terpyridin6-yl]ethyne (BISTERPY), 5,5'-diamino-2,2'-bipyridine (DABP), dipyrido[3,2-a:2',3'c]phenazine (DPP), 4,7-phenanthroline (PHEN) including nitrogen atom have been theoretically analyzed. It is important to note that B3LYP/6-31G(d) and B3LYP/TZP levels of the theory were taken into account for the calculations about monomeric and dimeric structures, respectively. Additionally, the calculations of the mentioned monomeric form were performed at B3LYP-D3/6-31G, CAM-B3LYP/6-31G and ωB97X-D/6-31G(d) levels. For a detailed theoretical analysis, the reorganization energies (λe and λh), adiabatic and vertical ionization potentials and electron affinities, the effective transfer integrals (Ve and Vh), and the charge transfer rates (We and Wh) of all compounds were computed by means of computational chemistry tools. In the light of calculated parameters, it is determined that these mentioned aromatic cyclic structures will be used in which layers of OLED structure. The results obtained in this study will be helpful in the design and applications of new molecules as OLED materials in the future.

Impact of Y2O3 Nanosheets on the Microstructural Characteristics of Alq3 Prepared via the Co-precipitation Route for Enhancement of Photodiode Performance.

In the present study, tris-(8-hydroxyquinoline) aluminum (Alq3) and tris-(8-hydroxyquinoline) aluminum/yttrium oxide Alq3/Y2O3 were synthesized by a facile chemical route. The crystal structure, surface morphological nature, and particle size were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) micrographs. Ag/Alq3/p-Si/Al and Ag/Alq3:Y2O3/p-Si/Al diodes were fabricated by the thermal evaporation technique and the electrical characteristics were evaluated from the I-V plots in dark and under illumination intensity. Thermionic emission theory, Cheung-Cheung, and Nord model have been applied to define the main electronic parameters like series resistance (Rs), barrier height (ϕb), and ideality factor (n). The hybrid Ag/Alq3:Y2O3/p-Si/Al diode revealed a nonideal behavior with high shunt resistance Rsh and good photocurrent sensitivity. The C/G-V analysis indicated that both C and G are strongly affected by the presence of trapped charge carriers at the interface states. The obtained results indicated that Rs was decreased whereas the carrier concentration (Na) was increased by loading Y2O3 nanosheets.

The antifouling tris-(8-hydroxyquinoline) aluminum: Titanium dioxide coatings under visible light

Functional antifouling coatings are becoming a direction of developing for marine antifouling coatings. Herein, tris-(8-hydroxyquinoline) aluminum modified with titanium dioxide (AlQ3:TiO2) coatings with photocatalytic antibacterial and fluorescent algae inhibition under visible irradiation were prepared. The AlQ3:TiO2 coatings show high antibacterial activity against E. coli with inhibition efficiencies as high as 97.51 %. Meanwhile, the reactive oxygen species (ROS) and the weak fluorescence produced under visible irradiation have an efficient inhibitory effect on the growth and settlement of algae. Based on the detailed antifouling experiments and electrochemical characterization of the material, a possible antifouling mechanism for AlQ3:TiO2 coatings is proposed.

CRISPR/Cas12a-Mediated Aptasensor Based on Tris-(8-hydroxyquinoline)aluminum Microcrystals with Crystallization-Induced Enhanced Electrochemiluminescence for Acetamiprid Analysis.

Improving the electrochemiluminescence (ECL) efficiency of luminophores has always been the goal of the ECL field. Herein, a novel crystallization-induced enhanced ECL (CIE ECL) strategy was exploited to significantly enhance the ECL efficiency of metal complex tris-(8-hydroxyquinoline)aluminum (Alq3). Alq3 monomers self-assembled and directionally grew to form Alq3 microcrystals (Alq3 MCs) in the presence of sodium dodecyl sulfate. The highly ordered crystal structure of Alq3 MCs not only constrained the intramolecular rotation of Alq3 monomers to decrease nonradiative transition but also accelerated the electron transfer between Alq3 MCs and coreactant tripropylamine to increase radiative transition, thus leading to a CIE ECL effect. Alq3 MCs exhibited brilliant anode ECL emission, which was 210-fold stronger than that of Alq3 monomers. The exceptional CIE ECL performance of Alq3 MCs coupled the efficient trans-cleavage activity of CRISPR/Cas12a assisted by rolling circle amplification and catalytic hairpin assembly to fabricate a CRISPR/Cas12a-mediated aptasensor for acetamiprid (ACE) detection. The limit of detection was as low as 0.79 fM. This work not only innovatively exploited a CIE ECL strategy to enhance the ECL efficiency of metal complexes but also integrated CRISPR/Cas12a with a dual amplification strategy for the ultrasensitive monitoring of pesticides such as ACE.

Study on the exciton dynamic processes of exciplex host–guest system by transient magnetic field effects

Utilizing exciplex as the host and fluorescence emitter with dopant materials has been proved successfully to fabricate highly-efficient organic light-emitting diodes. Exciton evolution and energy transfer in this exciplex host–guest system are complex. Gaining insight into the electroluminescence (EL) mechanisms in exciplex-based devices is key for further optimizing device configuration. Here, we have investigated exciton dynamics in devices with exciplex as host and 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) as red fluorescence emitter. Two exciplexes, 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPY) doped 2,4,6-tris[3-(triphenylphosphine)phenyl]-1,3,5-triazine (POT2T), and 4,4′,4″-tris[3-methylphenyl(phenyl)amino]-triphenylamine (m-MTDATA) doped tris(8-hydroxyquinoline)aluminum(III) (Alq3), with different band energy are utilized as host materials. Combining the measurements of transient EL, transient photoluminescence and magnetic field effect (MFE), it is concluded that Dexter energy transfer, together with Förster resonance energy transfer, are confirmed in the pure fluorescence doped system. Meanwhile, it is found that DCJTB works with the hot excitons mechanism but not a traditional red fluorescence emitter as recognized previously. This work presents that the transient MFE is powerful for detecting excitonic dynamic processes in excipelx based host–guest EL systems.

Triple-Peak Photoluminescence of DNA-Hybrid Alq3 Crystals Emitting a Depressed Single Peak upon Bio-Recognition.

The green organic semiconductor, tris-(8-hydroxyquinoline)aluminum (Alq3), was hybridized with DNA growing in the shape of hexagonal prismatic crystals. In this study, we applied hydrodynamic flow to the fabrication of Alq3 crystals doped with DNA molecules. The hydrodynamic flow in the Taylor-Couette reactor induced nanoscale pores in the Alq3 crystals, especially at the side part of the particles. The particles exhibited distinctly different photoluminescence emissions divided into three parts compared to common Alq3-DNA hybrid crystals. We named this particle a "three-photonic-unit". After treatment with complementary target DNA, the three-photonic-unit Alq3 particles doped with DNAs were found to emit depressed luminescence from side parts of the particles. This novel phenomenon would expand the technological value of these hybrid crystals with divided photoluminescence emissions toward a wider range of bio-photonic applications.

Luminescence of tris (8-hydroxyquinoline) aluminium thin films under synchrotron radiation excitation

The work is dedicated to the investigation of the luminescent properties of Tris (8-hydroxyquinoline) aluminium (Alq3) thin layers using the conventional spectral methods (cathodoluminescence and photoluminescence), as well as the advanced time-resolved luminescent spectroscopy under excitation by the synchrotron radiation in the fundamental absorption edge of this material. The Alq3 films with a thickness of 100–300 nm were deposited by the PVD (Physical Vapor Deposition) method on silicon substrates. The structural properties of Alq3 layers were studied using scanning electronic microscopy and X ray diffraction. The structure of the luminescence spectra of the Alq3 layer in the green-yellow range at 10 K and 300 K confirms the complex structure of the emission centers of this material, associated with the internal fast radiation transitions in the Al3+ molecule surrounded by three 8-hydroxynoline ligands. It has been determined the energy of creation of excitons associated with Alq3 green emission centers, which has been equal to 6.78 eV and 6.86 eV at 10 K and 300 K, respectively.

Characterization of Ag and Dy incorporated Alq3 nanocomposite sheets for potential radiation dosimetry applications

Tris-(8-hydroxyquinoline) aluminum (Alq3) is a highly light emitting metal complex with applications in several electronics devices including photodiodes, organic light emitting diodes (OLEDs), and display technologies. Despite these unique optical properties and applications, no study investigated its response to neutron and beta radiation, particularly in its nanocomposite form. In this work, we synthesized Alq3 nanocomposite sheets based on polymethyl methacrylate (PMMA) polymer for potential radiation dosimetry applications. The sheets were synthesized using PMMA as a proper binder and surfactant agent controlling the Alq3 nanostructure formation. These resultant sheets revealed uniform nanoparticles in the sheets having Alq3 powder similarly Alq3/Dy sheets showed uniform nanoparticles with shiny surrounding and dark spots at the center. While Alq3/Ag indicated a periodic hexagonal colloidal array instead of nanoparticles which may be attributed to the partial interaction between the Alq3/Ag powder with PMMA polymer. The structural and optical properties of the sheets were further investigated using different techniques. Furthermore, these sheets were subjected to different doses of neutron and beta radiation ranging from 100 to 1000 mGy. The irradiated sheets indicated an approximately excellent linear dose response-based Raman, FTIR and PL signals dose variations, implying induced defects, cross-linking and chain scission. Additionally, beta irradiation induced shifts in the PL emission position indicating strong damage besides signal changes. The signal variations derived from the irradiated nanocomposite sheets in addition to PL emission stability and reproducibility suggest the potential applications of these sheets in radiation dosimetry and other future optoelectronic devices.

Structural and Morphological Properties of as-Deposited and Heat -Treated Composite (CuPc/Alq3) Thin Films

In this work, an organic semiconductor of copper (II) phthalocyanine (CuPc) and Tris(8-hydroxyquinoline) aluminum (III) (Alq3) were entirely dissolved in chloroform with various mixing ratios (1:0,0.75:0.25,0.5:0.5,0.25:0.75,0:1) (w/w) to make thin films. They were deposited on a pre-cleaned glass using a spin-coating process and heat-treated at 473 K in vacuum. X-ray diffraction and a scanning electron microscope were used to investigate the films. XRD analysis reveals that CuPc/Alq3 composites have a polymorphic structure, with the exception of Alq3's amorphous structure, the crystallinity increases after annealing, but decreases when the concentration of Alq3 is increased. The quantity of (CuPc) rod-like structure and (Alq3) grain-like islands structure depends on the percentage of the combination. The compositional parameters of as-deposited and annealed thin films were explained using EDX data, which revealed that the sample was close to the nominal composition.

The effect of terminal group of hole injection self-assembled monolayers on the performance of optoelectronic devices on ITO anodes

We demonstrate the effect on the performance of conventional (Indium tin oxide (ITO)/N,Nj-Di (1- naphthyl)-N,Nj-diphenyl-(1,1-biphenyl)-4,4-diamine (NPB)/Tris-(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al) optoelectronic devices when the ITO surface is modified with various types of self-assembled monolayer (SAM)s such as 3-(trimethoxysilyl)propylamine (NH2SAM), Trimethoxy (propyl)silane CH3SAM, and Trimethoxy (3,3,3-trifluoropropyl)silane (F3SAM). The head functional group and chain configuration are trimethoxysilylpropyl (-(CH3O)3Si(CH2)2) and the tail groups distinguished SAMs (-NH2, -CH3, and -CF3). The contact angles of NH2SAM, CH3SAM, and F3SAM deposited on ITO and ITO were 70.7°, 81.42°, 68.23°, and 30.85°, respectively. The SAM-modified ITO's surface morphology Rpv and Rq parameters were reduced from 31.02 nm to 2.0 nm and 1.18 nm–0.26 nm. The work functions values of ITO, ITO/NH2SAM, ITO/CH3SAM and ITO/F3SAM measured by UPS were 4.99eV, 4.39, 5.09 and 5.69eV, respectively. The maximum luminance of the SAM-modified device increased to 166-fold, and the current density 105-fold, compared to the unmodified device when the operating voltage is set to 11 V. Current and power efficiency increased by 1.9 and 2-fold, respectively. The hole injection conditions are enhanced and the hole injection barrier height between ITO/NPB is reduced.