OLED Applications Research Articles

Effect of cyano substituent on the functional properties of blue emitting Imidazo[1,2-a]pyridine derivatives

High fluorescence efficiency and balanced charge transportation in organic emitters are desirable characteristics for application in OLEDs. Generally, donor-acceptor compounds showing pronounced intramolecular charge transfer exhibit low fluorescence quantum yield. Here, we report D-A fluorophores containing CN-substituted 2-phenylimidazo[1,2-a]pyridine acceptor unit which exhibit good fluorescence characteristics. The positions of donors (triphenylamine/carbazole) and cyano substituents are respectively interchanged to get a series of isomers. All the fluorophores exhibit high fluorescence quantum yield (Фf≥ 0.70) and excellent thermal stability (Td10≥ 390 °C). A dye comprising triphenylamine unit at para-position of C2 phenyl ring exhibited red-shifted emission maxima with larger Stokes shift in the series. Moreover, all the isomers displayed excited-state solvatochromism attributable to the photo-induced intramolecular charge transfer between donors and cyano-imidazo[1,2-a]pyridine acceptor. Addition of the cyano group on imidazopyridine restrained the formation of aggregates in the solid-state and stabilized the lowest unoccupied molecular orbital. Among the all, doped devices constructed with 3 wt% of triphenylamine containing dye revealed excellent performance in the series with a maximum EQE of 6.9%, 2759 cd/m2 luminance, and CIE coordinates (0.16, 0.08) which is very close to the NTSC blue standard.

Synthesis and photosensitization study of red luminescent europium (III) complexes with heterocyclic ligands for application in OLEDs

Six complexes of europium (III) with 1-ethyl-6-fluoro-1,4-dihydroxy-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid (L) as main ligand and 1,10-phenanthroline, bathophenanthroline, neocuprine, 2,2′-bipyridyl, 5,6-dimethyl-1,10-phenanthroline as ancillary ligands were synthesized by grinding technique. Through study of thermogravimetric data, it can be concluded that these complexes exhibit excellent thermal stability which favour their use in organic light emitting diode fabrication. Crystalline nature of complexes was studied by powder XRD and SEM. 1H NMR, 13C NMR, FT-IR spectra displayed the coordination site in complexes and confirmed that ligand is present in the zwitterionic form. On monitoring the emission at 370 nm UV excitation, intense red color was observed at 615 nm due to 5D0 → 7F2 electronic transition. Urbach energy, CIE coordinates, Judd-Ofelt parameters, quantum yield, CCT and lasing parameters were calculated. Refractive index and energy band gap values depicted their uses in semiconductor devices. Further investigation of antimicrobial and antioxidant assays certified the impressive antimicrobial and antioxidant activities of these complexes.

Enhancing quantum efficiency in Pt-based emitters using a pendant closo-monocarborane cluster to enforce charge neutrality

The use of organometallic triplet emitters in OLED applications may be complicated when the luminescent complex bears a formal charge. By designing ligands containing pendant closo-monocarborane clusters [CB11H11]−, it is possible to neutralize the otherwise cationic cores of cyclometalated Pt(II) complexes bearing bis-carbenes, resulting in significantly enhanced photophysical properties. Herein, we report four Pt(II) complexes decorated with a monoanionic closo-monocarborane by coupling the cluster to the classic cyclometallating moiety, phenylpyridine (ppy). All four complexes were fully characterized by NMR, HR-MS, UV–Vis, and cyclic voltammetry. Complexes 1b, 1c and 2a were characterized by single-crystal X-ray diffraction. Moreover, all four complexes show interesting photophysical behaviors, with complex 1a exhibiting a photoluminescent quantum yield of 97% in a 2 wt% PMMA film. This high efficiency prompted the incorporation of 1a and 1c into an OLED device using solution processing, resulting in green emission with CIE coordinates of (0.28, 0.55) for 1a and yellow emission with CIE coordinates of (0.44, 0.50) for 1c. The measured maximum external quantum efficiency (EQEmax) was 18.51% for 1a, an EQEmax that is among the highest for solution-processed OLED devices containing Pt(II) complexes with simple cyclometalated ppy ligands.

Synthesis and macrocyclization-induced emission enhancement of benzothiadiazole-based macrocycle

We presented an effective and universal strategy for the improvement of luminophore’s solid-state emission, i.e., macrocyclization-induced emission enhancement (MIEE), by linking luminophores through C(sp3) bridges to give a macrocycle. Benzothiadiazole-based macrocycle (BT-LC) has been synthesized by a one-step condensation of the monomer 4,7-bis(2,4-dimethoxyphenyl)−2,1,3-benzothiadiazole (BT-M) with paraformaldehyde, catalyzed by Lewis acid. In comparison with the monomer, macrocycle BT-LC produces much more intense fluorescence in the solid state (ΦPL = 99%) and exhibits better device performance in the application of OLEDs. Single-crystal analysis and theoretical simulations reveal that the monomer can return to the ground state through a minimum energy crossing point (MECPS1/S0), resulting in the decrease of fluorescence efficiency. For the macrocycle, its inherent structural rigidity prohibits this non-radiative relaxation process and promotes the radiative relaxation, therefore emitting intense fluorescence. More significantly, MIEE strategy has good universality that several macrocycles with different luminophores also display emission improvement.

Sulfonate‐Functionalized AIEgens: Strategic Approaches Beyond Water Solubility for Sensing and Imaging Applications

AbstractThe development of water‐soluble aggregation‐induced emission (AIE)‐active “light‐up” probes for sensing and imaging purposes has drawn immense research attention in the recent past. One strategy has been to introduce −SO3− groups in AIEgens (AIE‐sulfonates) to increase their hydrophilic properties, and the ionic nature of the corresponding compounds also paves the way for electrostatic interaction with various analytes, in particular, with several biospecies having positively charged surfaces. A significant number of AIE‐sulfonates, many among them having a tetraphenylethylene (TPE) moiety, have been designed and synthesized for the selective detection of a variety of analytes, such as metal ions, small molecules, enzymes, proteins, and bacteria. The strategies for selective detection include, for example, spontaneous complex formation with cations, electrostatic interaction with target‐specific units in the biospecies, and strong hydrophobic interactions. In addition, these AIEgens are used in cell imaging and OLED applications. This Review attempts to provide a summary and discuss recent developments in sulfonate‐functionalized AIE‐active “light‐up” probes in sensing and imaging applications with a focus on the role of the sulfonate functionality in the design and sensing processes.

A multifunctional luminescent material based on quinoxaline and triphenylamine groups: polymorphism, mechanochromic luminescence, and applications in high-efficiency fluorescent OLEDs

TQT exhibits multifunctional luminescence characteristics, such as polymorphism and mechanochromic, with potential application in OLEDs. An extremely high photoluminescence quantum yield of 96.5% is achieved in CBP: TQT-G doped film.

Complete stress release in monolayer ALD-Al2O3 films based on mechanical equilibrium homeostasis to realize a bending radius of 1 mm.

Low-temperature-deposited, transparent, high-barrier-performance atomic layer deposition (ALD) Al2O3 films are widely utilized to protect organic optoelectronic devices. However, because the internal compression residual stresses result in poor mechanical properties, these films are unable to realize independent encapsulation. In this work, we propose a pre-bending and substrate thermal expansion process to fabricate low-residual-stress ALD-Al2O3 films by multistep adjustment of mechanical equilibrium homeostasis, compare and analyze the key properties of the films to determine the optimal processing conditions, and adjust the surface area differences between the film and the substrate to acquire a flat-bottom encapsulation substrate. Therefore, fewer cracks form in ALD-Al2O3 deposited at 40 °C, and no significant increase in the water-vapor-transmission rate (WVTR) occurred after multiple bending processes at a 3 mm radius. Furthermore, both the bending radius for the first crack generation and crack saturation density were optimal, resulting in excellent mechanical stability, and a bending radius of 1 mm was achieved. Finally, we confirm the feasibility of the monolayer ALD-Al2O3 prepared by our process for applications in OLEDs. The encapsulated OLED maintained 94% of its initial efficiency after 10 days of bending in a harsh environment at 30 °C and 90% relative humidity.

AIEE-active V-shaped fused-biscoumarins: synthesis, photophysical and electroluminescence properties

Three AIEE-active V-shaped fused-biscoumarin derivatives were prepared and their potential for application in OLED was explored.

Recent advances of NIR-TADF (λmaxPL/EL > 700 nm) emitters and their applications in OLEDs

This review presents a new vista on the recent advances in molecular design, photophysical and electroluminescence performances of NIR emitters and their OLEDs.

Rational design of multi-functional thermally activated delayed fluorescence emitters for both sensor and OLED applications

Non-conjugated linking as a molecular design strategy to construct multifunctional structures to achieve the TADF feature and sensor properties in a single system.

Aza-triptycene-based homoleptic tris-cyclometalated iridium(III) complexes as highly efficient phosphors in green OLEDs

Three homoleptic tris-cyclometalated iridium (III) complexes (Ir1–Ir3) based on a rigid aza-triptycene unit have been synthesized via a novel one-pot method. The coordination arrangement of Ir2 was revealed by single X-ray structural analysis and the molecule showed a facial configuration. These complexes exhibited excellent thermal stability with Td of 454–520 °C. These complexes exhibit strong green phosphorescence emission with high quantum yields of over 70% due to the introduction of aza-triptycene skeleton with rigid steric hindrance reduced intermolecular interactions. Accordingly, the electroluminescence device based on Ir1, Ir2 and Ir3 exhibit high-brightness of 42194, 48807 and 46332 cd m−2, maximum luminous efficiency of 21.0, 24.7 and 28.5 cd A−1 and high EQE of 6.3, 6.8 and 8.9% at a high doping concentration of 30 wt%. Meanwhile, the non-doped green devices based on Ir1, Ir2 and Ir3 give high-brightness of 20571, 15407 and 10707 cd m−2 and luminous efficiency of 8.5, 9.5 and 5.4 cd A−1, respectively. These results suggest that these materials have potential application in OLEDs.

Peri-N-amine-perylenes, with and without phenyl bridge: Photophysical studies and their OLED applications

Donor-bridge-acceptor framework has been studied widely for their detailed photophysical properties with the aim of efficient long range charge transfer. Carbazole attached with electron acceptors has been used for charge transfer properties, thermally activated delayed fluorescence, exciton dynamics etc. In this study, we synthesized donor–acceptor dyads of seconday amine (carbazole and diphenyl amine) attached to perylene through nitrogen, with phenyl (P-Ph-N-CBZ and P-Ph-N-BP) and without phenyl (P-N-CBZ and P-N-BP). Further their detailed photophysical and electroluminescent properties are discussed. P-N-BP is known and is used as standard in this work. DFT studies show nearly orthogonal geometry of P-N-CBZ with the dihedral angle of ∼ 71° between the planes of perylene and carbazole. For P-Ph-N-BP and P-Ph-N-CBZ, the perylene and amines are adopting almost co-planar geometries. Emission spectra of P-Ph-N-CBZ and P-N-CBZ in dichloromethane are structural with clear vibronic features while for P-Ph-N-BP and P-N-BP, the emission is structureless and broad indicating prominent electronic coupling between molecular orbitals of donor and acceptor in the latter case. Fluorescence quantum yields of phenyl-linked dyads are found to be higher than directly linked perylene-amine derivatives. High quantum yield (0.79) in non-polar hexane and polar DMSO (0.66) is observed for P-Ph-N-CBZ. It is interesting to note that the fluorescence lifetimes of these dyads are increasing while fluorescence quantum yields are decreasing with increasing polar solvents, suggesting that the emission has a significant contribution from the 1CT state. Dipole moments estimated from DFT studies and photophysical methods are higher for phenyl-linked dyads than those directly attached which is also consistent with their solvatochromism properties. Weaker electronic coupling in phenyl-linked dyads resulted due to the long distance between donor and acceptor in phenyl-linked dyads. Furthermore application in OLEDs was shown for P-Ph-N-CBZ and P-Ph-N-BP. OLEDs of P-Ph-N-BP showed a peak emission at 568 nm resulting in an amber device. A high luminance of 4.3 × 103 Cd/m2 at a current density of 100 mA/cm2 and a maximum EQE of 4.2% with a low turn on volatage of ∼ 4 V was obtained for these devices. Thus, our results show that weaker charge transfer takes place in perylene based donor–acceptor dyads resulting in bright OLED devices.

Synthesis and Characterization of PPY-PANI-ZnO Hybrid Nanocomposites for OLEDs Applications as Electron Transport Layer

Synthesis and Characterization of PPY-PANI-ZnO Hybrid Nanocomposites for OLEDs Applications as Electron Transport Layer

Hybrid Polymeric Nanocomposites Based High Performance Oleds: A Review

This review reports the recent significant progress for achieving the synthesis of various types of polymer-based nanocomposites and understanding of the basic principle which determine their optical, electronic and magnetic properties. Some of the polymeric nanocomposite materials show remarkable electrical as well as optical properties regarding towards interest for applications in OLEDs. Nanoparticles which are basically inorganic, plays important role in the opto-electronic field. A nanoparticle with conjugate polymer matrix makes polymer nanocomposite and that nanocomposite used as an active emissive layer between the structures of optoelectronic device like OLEDs, OPVs etc. Application of such polymeric nanocomposite materials are discussed in this present communication with their success and failure, towards their optical as well as electrical properties in the fabrication of OLEDs.

Recent advances in the syntheses of anthracene derivatives.

Anthracene and anthracene derivatives have been extensively studied over the years because of their interesting photophysical, photochemical, and biological properties. They are currently the subject of research in several areas, which investigate their use in the biological field and their application in OLEDs, OFETs, polymeric materials, solar cells, and many other organic materials. Their synthesis remains challenging, but some important preparative methods have been reported, especially in the last decade. This review presents an update of the recent strategies that have been employed to prepare anthracene derivatives. It encompasses papers published over the last twelve years (2008–2020) and focuses on direct and indirect methods to construct anthracene and anthraquinone frameworks.

P‐13.6: Design, Synthesis and OLEDs Application of a Novel Blue Phosphorescent Material with High Quantum Efficiency

P‐13.6: Design, Synthesis and OLEDs Application of a Novel Blue Phosphorescent Material with High Quantum Efficiency

Study on Electron Transport Characterization in TPBi Thin Films and OLED Application

Study on Electron Transport Characterization in TPBi Thin Films and OLED Application

Enhancement of performance of OLEDs using double indolo[3,2-b]indole electron-donors based emitter

Recently, considerable efforts have been devoted to the improvement of fluorescent OLEDs because of their affordable cost and metal-free materials. Indolo[3,2-b]indole derivatives with a large planar rigid structure and great photophysical properties have attracted attentions as materials in a variety of organic electronics but their applications as OLEDs are still limited. Herein, we reported two new fluorescent OLEDs, i.e., 10,10'-(sulfonylbis(4,1-phenylene))bis(5-ethyl-5,10-dihydroindolo[3,2-b]indole) (DHID-DPS) and 2,8-bis(10-butylindolo[3,2-b]indol-5(10H)-yl)dibenzo[b,d]thiophene 5,5-dioxide (DHID-DBS), with a distorted donor-acceptor-donor structure bearing indolo[3,2-b]indole moieties as electron-donors. The DHID-DPS exhibited a smaller singlet-triplet energy gap (ΔEST = 0.18 eV) than DHID-DBS (ΔEST = 0.33 eV). In addition, DHID-DPS demonstrated the fluorescence quantum yield in doped films reaching to 32% as well as the evidence of thermally activated delayed fluorescence (TADF) properties. As a result, the optimized doped OLED by using DHID-DPS as an emitter achieved a maximum external quantum efficiency of 3.86% with a blue-green fluorescence as well as a high brightness up to 12860 cd m−2. This suggested that indolo[3,2-b]indole derivatives are potential candidates for donor moieties in OLED applications.

Dendrimer applications: a brief review

: Dendrimers are highly branched three-dimensional macromolecules with a highly controlled structure, a single molecular weight, numerous controllable dendritic branches and peripheral functionalities, as well as the tendency to adopt an ellipsoid or spheroid shape once a certain size is reached. These features have made them attractive for application in pharmaceutical and medicinal chemistry in gene transfection, as medical imaging agents, and as drug carriers in potential drug delivery agents. The incorporation of metallic species into dendritic molecules has also been reported; the focus has been on organometallic dendrimers with metallic species only at specific positions of the molecules, such as the core, dendritic branches and the periphery, studied for their magnetic, electronic, and photo-optical or catalytic properties. Dendrimers have been investigated for optoelectronic applications (adsorption, emission, laser emission, nonlinear optics) through the encapsulation of active units by dendritic branches, core and peripheral. This review briefly discusses their use in nanomedicine, cancer treatment, treatment of other diseases, tissue repair, catalysis and applications in OLEDs and solar cells.

Blue Emissive fac/mer‐Iridium (III) NHC Carbene Complexes and their Application in OLEDs

AbstractThe photophysical and electrochemical properties of N‐heterocyclic carbene complexes of Iridium (III) (Ir(C^C:)3, where C^C: = N‐phenyl,N‐methyl‐pyrazinoimidazol‐2‐yl (pmpz), N,N‐di‐p‐tolyl‐pyrazinoimidazol‐2‐yl (tpz)) are reported. Facial and meridional isomers of Ir(pmpz)3 are prepared, but only the facial isomer can be isolated for Ir(tpz)3. The fac‐Ir(pmpz)3 and fac‐Ir(tpz)3 complexes have emission maxima at 465 nm in polystyrene, whereas the emission maximum of mer‐Ir(pmpz)3 is redshifted to 495 nm. The emission energies and photoluminescent quantum yield (ΦPL) in solution decrease on going from nonpolar to polar solvents; however, all the complexes are efficient emitters in polystyrene at room temperature (ΦPL = 88–96%) and 77 K. Blue phosphorescent organic light emitting diodes employing fac‐Ir(tpz)3 as an emissive dopant achieves a high external electroluminescence efficiency (≈18 ± 1%) and brightness (29 000 cd m−2) at low current density.