Application In Organic Light-emitting Devices Research Articles

Synthesis of acridone-naphthylamine derivative and its thermally-activated delayed fluorescence studies for application in OLEDs

Acridone (acceptor) and naphthylamine (donor) based Donor-Acceptor-Donor (D-A-D) compound (1) was synthesised, characterised and its thermally-activated delayed fluorescence (TADF) properties were studied in detail. Compound 1 is fluorescent and emits in the green region (550 nm). The energy gap between the ground and the lowest excited singlet (S1) state is estimated to be 2.55 eV. The energy gap between the CT singlet and triplet states (∆EST) was found to be ~0.3 eV. Small ∆ES1-T1 is one of the important criteria for TADF to take place in a molecule and thus detailed photophysics has been studied. Transient lifetime measurements showed an increase in the fluorescence lifetime (τ) on purging with N2, as compared with that in air-saturated solution, indicating the involvement of the triplet state in emission. Emission at 550 nm was also observed with a delay of 100 µs which corresponded to the delayed fluorescence in 1. The lifetime of TADF was found to be 176 µs. Applications of TADF materials in organic light-emitting devices (OLEDs) has gotten attention as TADF materials utilise the triplet excitons which helps in increasing internal quantum efficiency of device. Air-saturated based on 1 were fabricated and their intensity was found to be nearly as high as 17,000 Cd/m2 at 25 mA/cm2 which was comparable to many of the known TADF emitters. Acridone-amine derivatives was synthesized and its photophysical properties were carried out to establish TADF. It was also used in fabrication of OLEDs.

Polycyclic aromatic hydrocarbon-bridged coumarin derivatives for organic light-emitting devices

Three biscoumarin dyes bridged by polycyclic aromatic bridges (anthracen, pyrene and dibenzo[g,p]chrysene) were prepared as the emissive materials for the application of organic light-emitting devices. The relationship between their structures, photophysical properties, electrochemical properties and performances of organic light-emitting devices are described. The multilayered doped devices with a configuration of ITO/NPB (20 nm)/TBADN: biscoumarin compound (x wt%, 30 nm)/TPBi (30 nm)/Liq (2 nm)/Al (100 nm) have been successfully fabricated by vacuum-deposition method. All the devices showed green emission with high electroluminescent efficiencies. Especially, the device based on the compound containing pyrene as a bridge group at 7% doping concentration showed the best performance with a maximum brightness of 10552 cd/m2, maximum luminous efficiency of 5.39 cd/A and maximum external quantum efficiency (EQE) of 2.35%.

Design and synthesis of host materials based on spirofluorene and s-triazine moieties and the applications in organic light-emitting devices

Organic light-emitting devices (OLEDs) attract intensive attentions from both fundamental and applied researchers due to their unique properties of flexibility, light-weight, color-tunability, high electroluminescent efficiency, and ease of device fabrication. The design of the emitting layer (EML) of OLEDs plays a dominant role in ruling the electroluminescent performances. Typically, the EML is composed of a host and an organic emitter. As the emerging emitters for OLEDs, thermally activated delayed fluorescence (TADF) materials are capable of utilizing 100% of the electrically generated excitons. However, the device performances are also limited by charge injection from the electrodes, charge balance in the EML, and the outcoupling schemes. In this contribution, we designed four host materials for the TADF emitter, which were synthesized based on spirofluorene and s-triazine moieties. The physical and chemical properties were characterized via thermogravimetric analysis, differential scanning calorimetry, UV-vis absorption, fluorescence, phosphorescence, cyclic voltammetry measurements. It is found that the four host materials exhibited excellent thermal stability and the peaks of the UV-vis absorption located between 280 and 355 nm, which led to freedom of self-absorption. From the low temperature phosphorescent spectra (77 K), we can determine that the peak wavelengths are 505, 519, 522, 525 nm respectively for DTSF-2-DP-TRZ, SF-2-DTDP-TRZ, SF-4-DTDP-TRZ, and SF-4-TDP-TRZ, which make them ideal as a host for green TADF emitters. To evaluate their performances in the electroluminescence, these host materials were blended with the green TADF emitter, i.e., 2,4,5,6-tetrakis(carbazole-9-yl)-1,3-dicyanobenzene (4CzIPN) with nearly 100% photoluminescence quantum yield, as the emitting layers processed by spin-coating. The used glass substrate was covered with pre-patterned indium tin oxide (ITO). After routine cleaning procedures, the ITO glass substrate was treated with UV-ozone for 20 min. And then the conducting polymer poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) was spin-coated onto the substrate, following with thermal anneal in the glove box. Later, the EML was spin-coated onto PEDOT:PSS from chlorobenzene solution. To improve the charge balance and thus high radiative recombination, we deposited the additional hole blocking layer, electron transporting layer, and electron injection layer onto the EML via vacuum process. By comparing the electroluminescent performances of the devices with the four hosts, we figure out the structure-property relationship. It is well known that the host materials played roles in ruling the exciton utilization. The electroluminescent spectra of the devices are similar with a slight deviation of the peak wavelengths, i.e., 516, 516, 502, and 506 nm respectively for the case using DTSF-2-DP-TRZ, SF-4-TDP-TRZ, SF-2-DTDP-TRZ, and SF-4-DTDP-TRZ as the hosts, which could be ascribed to the different polarity of the host-guest environment and the slightly incomplete of host-guest energy transfer. In our investigation, we found that the host DTSF-2-DP-TRZ exhibited high glass transition temperature, well-match energy levels, and bipolar charge injection. Therefore, the device with DTSF-2-DP-TRZ rendered a maximum brightness of 6600 cd/m2, a maximum current efficiency of 51.3 cd/A, and a maximum external quantum efficiency of 16.6%, which are superior to those of the devices with the other hosts. This work provides a guidance for exploring host materials for efficient OLEDs with TADF as the emitter. Further works on material and device optimization would lead to better electroluminescent performances to meet the requirements of mass production.

Four-membered red iridium(iii) complexes with Ir-S-P-S structures: rapid room-temperature synthesis and application in OLEDs.

In this work, with sulfur-containing ancillary ligands of triethylamine salts of bis(4-methoxyphenyl)-phosphinodithioic acid (omess) and bis(3,5-di-tert-butyl-4-methoxyphenyl)phosphinodithioic acid (tbuss), two four-membered red iridium(iii) complexes (tfmpqz)2Ir(omess) and (tfmpqz)2Ir(tbuss) with Ir-S-P-S structures were synthesized rapidly at room temperature within 5 min, in which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as the main ligand. The calculated Gibbs free energy changes of the complex formation reactions prove that they are exothermic and thermodynamically beneficial processes. Both Ir(iii) complexes show almost the same PL emissions at 624 and 623 nm with high phosphorescence quantum yields of 0.60 and 0.72, respectively. Using the two complexes as emitters, both organic light-emitting devices (OLEDs) with the structure of ITO/HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/TAPC ((bis(4-(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/(tfmpqz)2Ir(omess) or (tfmpqz)2Ir(tbuss):26DCzppy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12 wt%, 10 nm)/TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/LiF (1 nm)/Al (100 nm) achieve good performances. Particularly, due to the introduction of tert-butyl groups into the (tfmpqz)2Ir(tbuss) complex, its device exhibits better device properties with a maximum luminance of 26 184 cd m-2, maximum current efficiency of 30.24 cd A-1, maximum power efficiency of 22.61 lm W-1 and maximum external quantum efficiency of 21.50% with CIE coordinates at (0.65, 0.34).

Nickel nanoparticles-super yellow (PDY-132) nanoblends for organic light emitting devices

We report the synthesis of nickel nanoparticles (NPs) by wet chemical route and its blend with emissive PDY-132(super yellow) matrix for application in Organic Light-Emitting Devices (OLEDs). Wet Chemical Synthesis allows the successful synthesis of CTAB (Cetyl Trimethyl Ammonium Bromide) capped nickel (Ni) nanoparticles having a size of 5–7 nm. The synthesized colloidal having nanoparticles can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. From the experimental results, it is observed that turn on voltage decreases to 3.54V from 9V and current increases to 14mA from 4mA after adding Ni NPs into the emissive layer. The narrowing and sharpening of electroluminescence were observed.

Preparation and characterization of ruthenium based organic composites for optoelectronic device application

Ruthenium based solid state organic LED was fabricated by the dispersion of aluminum oxide nanocomposite using solution cast technique. Different analytical techniques such as XRD, FTIR, DSC, SEM, Photoluminescence, Electroluminescence and I–V characteristics were carried out on the prepared samples. XRD showed polycrystalline nature of the prepared films. DSC revealed that the microporous organic membrane was thermally stable up to 363 °C. SEM showed the degree of roughness of OLED. Photoluminescence studies were carried out on the prepared samples in the wavelength ranging from 300 to 900 nm. It is evident from the results that the intensity of the peak was increased with the dispersion of Al2O3 nanopaticles in the Ru complex. The I–V characteristics of Al2O3 doped OLED of (bpy)2 Ru[bpy(Al)2O3](BF4)2 have showed higher efficiency which is suitable for display device application. Thus it was found out that the ruthenium based composites could be promising candidates for organic light emitting device applications.

One-Step Synthesis of Spirobi[fluorene] and Spiro[fluorene-9,9′-xanthene] Derivatives and Their Applications in Organic Light-Emitting Devices: Performance Enhancement and Related Optical Phenomena

One-Step Synthesis of Spirobi[fluorene] and Spiro[fluorene-9,9′-xanthene] Derivatives and Their Applications in Organic Light-Emitting Devices: Performance Enhancement and Related Optical Phenomena

Systematic color tuning of a family of firefly oxyluciferin analogues suitable for OLED applications

The firefly oxyluciferin analogues have great potential application in organic light-emitting devices because of their high fluorescent efficiency. The emission color of these analogues can be tuned by chemical functionalization. To reveal the molecular structures, optoelectronic properties, and structure–property relationships of these analogues, an in-depth theoretical investigation was elaborated via quantum chemical calculation. The calculated ionization potentials, electron affinities, and reorganization energies show that introduction of dimethylamino and double bond can significantly affect the carrier injection and transport characteristics. We also calculated the singlet-to-triplet exciton-formation cross-section ratio (σS/σT), the exciton formation fractions (χs), the absorption and emission spectra. The calculated σS/σT values range from 1.00 to 10.17, and the corresponding χs are ca. 0.25–0.77. The calculated emission spectra range from 403.93 to 631.09 nm. It can be deduced that these studied firefly oxyluciferin analogues can serve as efficient blue, green, orange and red light-emitting electroluminescent materials.

Monocyclometalated Gold(III) Complexes Bearing π-Accepting Cyanide Ligands: Syntheses, Structural, Photophysical, and Electrochemical Investigations.

The synthesis, structural, photophysical, and electrochemical investigations of a series of gold(III) monocyclometalated complexes bearing ancillary ligands with π-accepting properties is reported. Complexes of the type [(C(∧)N)Au(C≡N)2] [C(∧)N = 2-phenylpyridine (ppy) (1), 2-(p-tolyl)pyridine (tpy) (2), 2-(2-thienyl)-pyridine (thpy) (3), 2-(5-methyl-2-thienyl)pyridine (5m-thpy) (4), 1-phenylisoquinoline (piq) (5)], and [(N(∧)N)Au(C≡N)2] [N(∧)N = 3,5-bis(phenyl)-2-(2'-pyridyl)pyrrole (pyrpy) (6)] were prepared, and the influence of both the cyanide as an ancillary ligand as well as the different electronic properties of the cyclometalating ligands (1-5) and the chelating bidentate (6) on the triplet emission properties were studied. The physicochemical properties were evaluated by a variety of physical methods, and the structure of selected complexes was further confirmed by X-ray diffraction studies. Complexes 1-5 display long-lived emission in solution, neat solid, spin coated PMMA films, and at 77 K in 2-MeTHF. The emission energies were strongly dictated by the cyclometalating ligands independent of the cyanide ligand, which is in quite a contrast to the previously reported dicyano complexes of iridium(III) and the isoelectronic platinum(II) complexes. The nonemissive behavior of complex 6 in any medium further highlights the importance that the good σ-donating properties of the cyclometalating ligand alone is not decisive in rendering the gold complexes emissive, but also the appropriate placement of the energy level of the ligand orbitals is also important. Detailed photophysical studies in conjunction with density functional theory and time-dependent density functional theory calculations support the origin of the emission to be a metal perturbed intra ligand (3)IL (π-π*) delocalized over the cyclometalating ligand. The stability of the complexes combined with good emission quantum yields and tunability of the emission energies makes these complexes suitable alternatives to the relatively less stable monocyclometalated gold(III) diaryl or dialkyne complexes for organic light emitting device applications.

Narrow bandgap covalent–organic frameworks with strong optical response in the visible and infrared

We propose a new series of covalent–organic frameworks. These materials have narrow band gaps, leading to strong near infrared optical response. Density functional theory calculations are used to explore their properties. These novel infrared active materials may have potential applications in organic light-emitting devices, chemical and biological sensing, hybrid solar cells, or electroluminescence.

Novel 1,8-naphthalimide derivatives for standard-red organic light-emitting device applications

A 1,8-naphthalimide derivative has been demonstrated to be a high performance standard-red EL material.

Theoretical Investigation on Firefly Oxyluciferin Analogs Bearing an Amino Group Used as Organic Light-Emitting Diodes Materials

Firefly oxyluciferin has great potential application in organic light-emitting devices, because of the high efficiency and wide range of multicolor light from green to red. To gain an insight into the structure-property relationships, a set of firefly oxyluciferin analogs bearing an amino group with benzopyran, biphenyl, bipyridine, phenanthrene, phenanthroline, fluorine and coronene instead of benzothiazole ring were designed. In this study, a systematic investigation into them was carried out using the density functional theory and time-dependent density functional theory methods. The calculated values show that bipyridylaminooxyluciferin (BPAOL) and orthophenanthrolylaminooxyluciferin (PMAOL) with nitrogen atom have smaller the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies, larger ionization potential (IP) and electron affinity (EA) values than biphenylaminooxyluciferin (BIAOL) and phenanthrylaminooxyluciferin (PHAOL) with carbon atom. Compound aminooxyluciferin (AOL), BIAOL, BPAOL, PHAOL, PMAOL, fluorenylaminooxyluciferin (FLAOL) and coronenylaminooxyluciferin (COAOL) can be used as electron-injection/transporting materials. AOL, PHAOL, FLAOL and COAOL can be used as blue light-emitting materials. These results indicate that the firefly Chinese Journal of Organic Chemistry ARTICLE Chin. J. Org. Chem. 2015, 35, 432~438 © 2015 Chinese Chemical Society & SIOC, CAS http://sioc-journal.cn/ 433 oxyluciferin analogs bearing an amino group have many interesting properties and are good candidates for optoelectronic application.

Low-cost zinc complexes for white organic light-emitting devices

A series of blue fluorescent Zn (II) tetradentate Schiff base complexes has been designed and synthesized for applications in organic light-emitting diodes. The five complexes were investigated as dopant materials or as single emitters of multilayered p-i OLEDs. White OLEDs were achieved using these compounds as dopants of 4,4′,4″-tris(N-carbazolyl)triphenylamine and best devices exhibited a high quality white-light emission with remarkable CIE (Commission Internationale de l'Eclairage) coordinates (0.33, 0.34). When used as single emitters, sky-blue and blue electroluminescent devices were prepared, except with one complex that gave yellow OLEDs. Optical properties of these complexes were examined by UV–visible absorption and luminescence spectroscopy. Their electrochemical properties are also reported. These results open the route to the development of cost-effective complexes for white organic light-emitting devices applications.

Enlarging the π system of phosphorescent (C^C*) cyclometalated platinum(II) NHC complexes.

Cyclometalated (C^C*) platinum(II) N-heterocyclic carbene (NHC) complexes are emerging as a new class of phosphorescent emitters for the application in organic light-emitting devices (OLEDs). We present the synthesis of six new complexes of this class to investigate the influence of extended π systems. Therefore, six different NHC ligands with a varying number of additional phenyl substituents were used in combination with the monoanionic acetylacetonate (acac) ligand to obtain complexes of the general formula [(NHC)Pt(II)(acac)]. The complexes were fully characterized by standard techniques and advanced spectroscopic methods ((195)Pt NMR). For all complexes the solid-state structure determination revealed a square-planar coordination of the platinum atom. Absorption and emission spectra were measured in thin amorphous poly(methyl methacrylate) films at room temperature. Four compounds emit in the blue-green region of the visible spectrum with quantum yields of up to 81%.

Synthesis of Bicarbazole-based Ambipolar Hosts and Application in Organic Light-emitting Devices

Synthesis of Bicarbazole-based Ambipolar Hosts and Application in Organic Light-emitting Devices

Synthesis and Properties of Novel Hole-Transporting Materials Containing Triphenylamine and Bipyridine Units

Novel hole-transporting materials (M1, M2) containing triphenylamine and dipyridine units have been synthesized and characterized. Two compounds have excellent solubility in common solvents. The optical, electrochemical and thermal properties of the materials were studied in detail. The results show that two compounds have green emission in dichloromethane, high thermal stability and proper HOMO levels. The properties of compounds M1 and M2 indicate that two compounds are candidates for the application in Organic light-emitting devices as hole-transporting materials.

LUMINESCENCE ENHANCEMENT OF OLED PERFORMANCE BY DOPING COLLOIDAL MAGNETIC FE<sub>3</sub>O<sub>4</sub> NANOPARTICLES

We report synthesis of magnetic Fe3O4 nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Poly∞uorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5{10nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence e-ciency increases by doping with MNPs into emissive layer. Difierent dopant concentrations varied from 0,4% to 2% were monitored. It was observed that the electroluminescence increases up to 1%w/v doping ratio. The luminance of OLEDs increased from 15.000cd/m 2 to 24.000cd/m 2 in comparison pristine device with 1% MNP doped device.

Pyrene‐Based Y‐shaped Solid‐State Blue Emitters: Synthesis, Characterization, and Photoluminescence

A series of pyrene-based Y-shaped blue emitters, namely, 7-tert-butyl-1,3-diarylpyrenes 4 were synthesized by the Suzuki cross-coupling reaction of 7-tert-butyl-1,3-dibromopyrene with a variety of p-substituted phenylboronic acids in good to excellent yields. These compounds were fully characterized by X-ray crystallography, UV/Vis absorption and fluorescence spectroscopy, DFT calculations, thermogravimetric analysis, and differential scanning calorimetry. Single-crystal X-ray analysis revealed that the Y-shaped arylpyrenes exhibited a low degree of π stacking owing to the steric effect of the bulky tert-butyl group in the pyrene ring at the 7-position, and thus, the intermolecular π-π interactions were effectively suppressed in the solid state. Despite the significantly twisted nonplanar structures, these molecules still displayed efficient intramolecular charge-transfer emissions with clear solvatochromic shifts on increasing solvent polarity. An intriguing fact is that all of these molecules show highly blue emissions with excellent quantum yields in the solid state. Additionally, the two compounds containing the strongest electron-accepting groups, CN (4 d) and CHO (4 f), possess high thermal stability, which, together with their excellent solid-state fluorescence efficiency, makes them promising potential blue emitters in organic light-emitting device applications.

Versatile Fluorinated Derivatives of Triphenylamine as Hole-Transporters and Blue-Violet Emitters in Organic Light-Emitting Devices

A series of triphenylamine derivatives end-capped with various fluorinated phenyl (TPAF) have been designed and synthesized for the application in organic light-emitting devices (OLEDs). By changing the substitution pattern of electron-withdrawing groups, such as F and CF3, the ability of hole-transport, energy levels, and thermal stability of these, TPAF are tuned, which are supported by density functional study of their geometry and electronic structure. TPAF can be used as either hole-transporters or blue-violet emitters in OLEDs. Among TPAF, the device with TPA-(2)-F as hole-transport material achieved the maximum current efficiency of 4.7 cd A–1, which was much higher than that of the typical N,N′-di(1-naphthalenyl)-N,N′-diphenyl-4,4′-diamine-based device. This good performance of the TPA-(2)-F-based device was attributed to the more balanceable injected carriers in the device by tuning hole injection and transport. More importantly, nondoped blue OLEDs utilizing TPAF as the emitters exhibited blue-violet emissions peaking between 408 and 428 nm with Commission Internationale de L’Eclairage coordinates in a range of (0.16–0.18, 0.06–0.12), which were also expected to be a new material class with an enhanced current efficiency/color purity compromise for future blue light-emitting devices.

Synthesis and properties of new luminescent hole transporting materials containing triphenylamine and carbazole units

Two new blue luminescent hole transporting materials (HTM) containing triphenylamine, carbazole units and olefinic linkers (TM1 and TM2) were synthesized via Wittig reaction and characterized by 1H NMR, FT-IR, and HRMS. The compounds show good solubility in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran and dimethyl formamide. Their optical, electrochemical and crystalline properties were investigated by using UV–Vis, photoluminescence (PL) spectra, cyclic voltammetry (CV) and differential scanning calorimetry (DSC), respectively. Quantum-chemical calculation was performed to obtain their optimized structures and the electron distribution of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The UV–Vis absorption and PL spectra of the two compounds in solid state were found to be similar to that when they were in dilute THF, which suggests that these compounds remain as an amorphous state in solid films. CV measurements show that the two compounds embody suitable HOMO levels (in a range of −5.28 to −5.23eV) for hole injection, which is consistent with the calculation consequence. Two compounds possess high glass-transition temperature (Tg) at 96.61 and 90.74°C for TM1 and TM2, respectively, suggesting the two compounds could form stable amorphous glassy states. The experimental results show that the synthesized compounds have great potential for application in organic light-emitting devices (OLEDs).