1,2‐Dihydrophosphete: A Platform for the Molecular Engineering of Electroluminescent Phosphorus Materials for Light‐Emitting Devices

The discovery and molecular engineering of novel electroluminescent materials is still a challenge in optoelectronics. In this work, the development of new π‐conjugated oligomers incorporating a dihydrophosphete skeleton is reported. Variation of the substitution pattern of 1,2‐dihydrophosphete derivatives and chemical modification of their P atoms afford thermally stable derivatives, which are suitable emitters to construct organic light‐emitting diodes (OLEDs). The optical and electrochemical properties of these new P‐based oligomers have been investigated in detail and are supported by DFT calculations. The OLED devices exhibit good performance and current‐independent CIE coordinates.     

Luminescent Platinum(II) Complexes of 1,3‐Bis(N‐alkylbenzimidazol‐ 2′‐yl)benzene‐Type Ligands with Potential Applications in Efficient Organic Light‐Emitting Diodes

A series of luminescent platinum(II) complexes of tridentate 1,3‐bis(N‐alkylbenzimidazol‐2′‐yl)benzene (bzimb) ligands has been synthesized and characterized. One of these platinum(II) complexes has been structurally characterized by X‐ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. Computational studies have been performed on this class of complexes to elucidate the origin of their photophysical properties. Some of these complexes have been utilized in the fabrication of organic light‐emitting diodes (OLEDs) by using either vapor deposition or spin‐coating techniques. Chloroplatinum(II)? bzimb complexes that are functionalized at the 5‐position of the aryl ring, [Pt(R‐bzimb)Cl], not only show tunable emission color but also exhibit high current and external quantum efficiencies in OLEDs. Concentration‐dependent dual‐emissive behavior was observed in multilayer OLEDs upon the incorporation of pyrenyl ligand into the Pt(bzimb) system. Devices doped with low concentrations of the complexes gave rise to white‐light emission, thereby representing a unique class of small‐molecule, platinum(II)‐based white OLEDs.     

Luminescent Pincer Platinum(II) Complexes with Emission Quantum Yields up to Almost Unity: Photophysics,Photoreductive CC Bond Formation,and Materials Applications

Luminescent pincer‐type Pt^II complexes supported by C‐deprotonated π‐extended tridentate R? C^N^N? R′ ligands and pentafluorophenylacetylide ligands show emission quantum yields up to almost unity. Femtosecond time‐resolved fluorescence measurements and time‐dependent DFT calculations together reveal the dependence of excited‐state structural distortions of [Pt(R? C^N^N? R′)(C?C‐C₆F₅)] on the positional isomers of the tridentate ligand. Pt complexes [Pt(R‐C^N^N? R′)(C?C‐Ar)] are efficient photocatalysts for visible‐light‐induced reductive C? C bond formation. The [Pt(R‐C^N^N? R′)(C?C‐C₆F₅)] complexes perform strongly as phosphorescent dopants for green‐ and red‐emitting organic light‐emitting diodes (OLEDs) with external quantum efficiency values over 22.1 %. These complexes are also applied in two‐photon cellular imaging when incorporated into mesoporous silica nanoparticles (MSNs).     

Near‐IR Emitting Iridium(III) Complexes with Heteroaromatic β‐Diketonate Ancillary Ligands for Efficient Solution‐Processed OLEDs: Structure–Property Correlations

Three NIR‐emitting neutral Ir^III complexes [Ir(iqbt)₂(dpm)] ( 1 ), [Ir(iqbt)₂(tta)] ( 2 ), and [Ir(iqbt)₂(dtdk)] ( 3 ) based on the 1‐(benzo[b]thiophen‐2‐yl)‐isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6‐tetramethyl‐3,5‐heptanedionate; tta=2‐thienoyltrifluoroacetonate; dtdk=1,3‐di(thiophen‐2‐yl)propane‐1,3‐dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR‐emitting, solution‐processed phosphorescent organic light‐emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1 ) with negligible efficiency roll‐off values, exceeding the highest reported values for solution‐processible NIR emitters.     

Blue‐Light‐Emitting Conjugated Polymers Derived From 2,7‐Carbazoles

Blue‐light‐emitting 2,7‐carbazole‐based conjugated copolymers have been prepared by Yamamoto or Suzuki cross‐coupling reactions. By introducing highly substituted aromatic comonomers, fully soluble high‐molecular‐weight copolymers have been obtained. Moreover, these amorphous polymeric materials exhibit good thermal stability and interesting redox properties. All these features make these new conjugated polymers highly promising for the development of single‐polymer‐layer blue‐light‐emitting diodes.

     

Synthesis and Characterization of Luminescent Cyclometalated Platinum(II) Complexes of 1,3‐Bis‐Hetero‐Azolylbenzenes with Tunable Color for Applications in Organic Light‐Emitting Devices through Extension of π Conjugation by Variation of the Heteroatom

A series of luminescent cyclometalated platinum(II) complexes of N^C^N ligands [N^C^N=2,6‐bis(benzoxazol‐2′‐yl)benzene (bzoxb), 2,6‐bis(benzothiazol‐2′‐yl)benzene (bzthb), and 2,6‐bis(N‐alkylnaphthoimidazol‐2′‐yl)benzene (naphimb)] has been synthesized and characterized. Two of the platinum(II) complexes have been structurally characterized by X‐ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. In dichloromethane solution at room temperature, the cyclometalated N^C^N platinum(II) complexes exhibited rich luminescence with well‐resolved vibronic‐structured emission bands. The emission energies of the complexes are found to be closely related to the electronic properties of the N^C^N ligands. By varying the electronic properties of the cyclometalated ligands, a fine‐tuning of the emission energies can be achieved, as supported by computational studies. Multilayer organic light‐emitting devices have been prepared by utilizing two of these platinum(II) complexes as phosphorescent dopants, in which a saturated yellow emission with Commission International de I′Eclairage coordinates of (0.50, 0.49) was achieved.     

A Versatile Triphenylamine/Fluoranthene‐Based Derivative as a Nondoped Green‐Emitting,Hole‐Transporting Interlayer for Electroluminescent Devices

A new triphenylamine‐bridged fluoranthene derivative, 4‐(7,10‐diphenylfluoranthen‐8‐yl)‐N‐[4‐(7,10‐diphenylfluoranthen‐8‐yl)phenyl]‐N‐phenylaniline (BDPFPA), with a high glass transition temperature of 220 °C has been synthesized and characterized. BDPFPA is a highly fluorescent and versatile material that can be used as a nondoped green emitter and as a hole transporter. BDPFPA was used in a standard trilayer device as the emitting layer, which showed a low turn‐on voltage (<3 V) and a high efficiency of 11.6 cd A^?1. The device also shows little efficiency roll‐off at high brightness. For example, the efficiency can still be maintained at 11.4 cd A^?1 (5.4 lm W^?1) at a brightness of 10 000 cd m^?2. These results are among the best reported for nondoped fluorescent green organic light‐emitting diodes. A simple bilayer device, in which BDPFPA serves as a hole‐transporting layer, has a maximum power efficiency of 3.3 lm W^?1 and the performance is nearly 40 % higher than that of an N,N′‐bis(1‐naphthyl)‐N,N′‐ diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB)‐based standard device.     

Blue‐emitting poly(1,3‐phenylenevinylene) derivatives: Effect of substitution patterns on optical properties

Blue‐emitting poly{[5‐(diphenylamino)‐1,3‐phenylenevinylene]‐alt‐(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene)} ( 3 ), poly{[5‐bis‐(4‐butyl‐phenylamino)‐1,3‐phenylenevinylene]‐alt‐(1,3‐phenylene vinylene)} ( 4 ), and poly(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene) ( 5 ) were synthesized by the Wittig–Horner reaction. Although polymers 3–5 possess fluorescent quantum yields of only 13–34% in tetrahydrofuran solution, their films appear to be highly luminescent. Attachments of substituents tuned the emission color of thin films to the desirable blue region (λ_max = 462–477 nm). Double‐layer light‐emitting‐diode devices with 3 and 5 as an emissive layer produced blue emission (λ_em = 474 and 477 nm) with turn‐on voltages of 8 and 11 V, respectively. The external quantum efficiencies were up to 0.13%. © 2005Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2800–2809, 2005     

A Stable and High‐Efficiency Blue‐Light Emitting Terphenyl‐Bridged Ladder Polysiloxane

A novel blue‐light emitting terphenyl‐bridged ladder polysiloxane ( TBLP) was prepared by the condensation of a tetrasilanol monomer via a ladder supramolecular structure. TBLPs emit narrow blue light (420 nm) with high quantum yields (0.96) in diluted solution and shows no evident fluorophore aggregation in the solid state, indicating that the terphenyls are well isolated due to confinement of the ladder‐rungs. In addition, it has excellent emission stability at high temperature based on TGA, DSC and annealing experiments. Overall, TBLPs can be considered as a potential material for fabricating stable and high‐efficiency blue‐light emitting optoelectronic devices.

     

A New Class of Blue‐Emitting Materials for LED Applications: Triarylamine N‐Functionalised 2,7‐Linked Carbazole Polymers

Attachment of triarylamino‐functional groups at the 9‐position of 2,7‐linked carbazole polymers results in blue‐emitting materials with two independent redox processes that were attributed to the triarylamino groups and the polymer backbone, respectively. This new class of blue‐emitting conjugated polymers was prepared via a Suzuki cross‐coupling reaction and showed low turn‐on voltages in electroluminescent devices as a result of their low ionisation potentials. The photophysical, electrochemical and electroluminescent properties of these materials are discussed.

     

2,5‐Difluorenyl‐Substituted Siloles for the Fabrication of High‐Performance Yellow Organic Light‐Emitting Diodes

2,3,4,5‐Tetraarylsiloles are a class of important luminogenic materials with efficient solid‐state emission and excellent electron‐transport capacity. However, those exhibiting outstanding electroluminescence properties are still rare. In this work, bulky 9,9‐dimethylfluorenyl, 9,9‐diphenylfluorenyl, and 9,9′‐spirobifluorenyl substituents were introduced into the 2,5‐positions of silole rings. The resulting 2,5‐difluorenyl‐substituted siloles are thermally stable and have low‐lying LUMO energy levels. Crystallographic analysis revealed that intramolecular π–π interactions are prone to form between 9,9′‐spirobifluorene units and phenyl rings at the 3,4‐positions of the silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with a certain extension of π conjugation, respectively. With increasing substituent volume, intramolecular rotation is decreased, and thus the emissions of the present siloles gradually improved and they showed higher fluorescence quantum yields (Φ_F=2.5–5.4 %) than 2,3,4,5‐tetraphenylsiloles. They are highly emissive in solid films, with dominant green to yellow emissions and good solid‐state Φ_F values (75–88 %). Efficient organic light‐emitting diodes were fabricated by adopting them as host emitters and gave high luminance, current efficiency, and power efficiency of up to 44 100 cd m^?2, 18.3 cd A^?1, and 15.7 lm W^?1, respectively. Notably, a maximum external quantum efficiency of 5.5 % was achieved in an optimized device.     

Tetraaryl‐Substituted Benzo[1,2‐b:4,5‐b′]dipyrroles: Synthesis,Properties, and Applications to Hole‐Injection Materials in OLED Devices

Yes, HIMs can! A series of 2,3,6,7‐tetraarylbenzo[1,2‐b:4,5‐b′]dipyrroles (BDPs) were synthesized using zinc‐mediated double cyclization. Organic light‐emitting diodes consisting of BDP:PPB as a hole‐injection layer could be driven at a lower voltage than a PEDOT:PSS‐based device. Correlation of the IP values with the driving voltage shed some light on the mechanism of hole‐injection processes.

     

Enhancement of Photostability in Blue‐Light‐Emitting Polymers Doped with Gold Nanoparticles

A dramatic increase in the photostability of a blue‐light‐emitting polymer, poly(9,9‐dioctylfluorene), was achieved by the addition of 5–10 nm gold nanoparticles. The optical absorption band of the gold nanoparticles was tuned to resonate the triplet exciton ground state bandgap energy of the polymer. Photo‐oxidation rate of poly(9,9‐dioctylfluorene) was effectively reduced by doping the polymer with very small amounts (≈10⁻⁶–10⁻⁵ volume fraction) of the gold nanoparticles.

Retarded photo‐oxidation in PDOF nanocomposite films with various doped gold nanoparticles.     

Twist versus Linkage Mode: Which One is Better for the Construction of Blue Luminogens with AIE Properties?

Two new blue luminogens, Py‐4MethylTPE and Py‐4mTPE, constructed with a pyrene core and tetraphenylethene peripheries, have been successfully obtained. These two luminogens show AIE and AEE effects, respectively, as a result of minor differences in their structures. An OLED device based on Py‐4mTPE exhibits a good performance (η_C,max=4.02 cd A^?1, λ_EL,max=436 nm) and reveals the powerful effect of a different linkage mode for the construction of blue AIE luminogens.     

Highly Efficient Near‐Infrared Delayed Fluorescence Organic Light Emitting Diodes Using a Phenanthrene‐Based Charge‐Transfer Compound

Significant efforts have been made to develop high‐efficiency organic light‐emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) emitters with blue, green, yellow, and orange–red colors. However, efficient TADF materials with colors ranging from red, to deep‐red, to near‐infrared (NIR) have been rarely reported owing to the difficulty in molecular design. Herein, we report the first NIR TADF molecule TPA‐DCPP (TPA=triphenylamine; DCPP=2,3‐dicyanopyrazino phenanthrene) which has a small singlet–triplet splitting (ΔE_ST) of 0.13 eV. Its nondoped OLED device exhibits a maximum external quantum efficiency (EQE) of 2.1 % with a Commission International de L′Éclairage (CIE) coordinate of (0.70, 0.29). Moreover, an extremely high EQE of nearly 10 % with an emission band at λ=668 nm has been achieved in the doped device, which is comparable to the most‐efficient deep‐red/NIR phosphorescent OLEDs with similar electroluminescent spectra.     

Deep Red to Near‐Infrared Emitting Rhenium(I) Complexes: Synthesis,Characterization, Electrochemistry,Photophysics, and Electroluminescence Studies

A series of triarylamine‐containing tricarbonyl rhenium(I) complexes, [BrRe(CO)₃(N^N)] (N^N=5,5′‐bis(N,N‐diaryl‐4‐[ethen‐1‐yl]‐aniline)‐2,2′‐bipyridine), has been designed and synthesized by introducing a rhenium(I) metal center into a donor‐π‐acceptor‐π‐donor structure. All of the complexes showed an intense broad structureless emission band in dichloromethane at around 680–708 nm, which originated from an excited state of intraligand charge transfer (³ILCT) character from the triarylamine to the bipyridine moiety. Upon introduction of the bulky and electron‐donating pentaphenylbenzene units attached to the aniline groups, the emission bands were found to be red shifted. The nanosecond transient absorption spectra of two selected complexes were studied, which were suggestive of the formation of an initial charge‐separated state. Computational studies have been performed to provide further insight into the origin of the absorption and emission. One of the rhenium(I) complexes has been utilized in the fabrication of organic light‐emitting diodes (OLEDs), representing the first example of the realization of deep red to near‐infrared rhenium(I)‐based OLEDs with an emission extending up to 800 nm.     

Electronic Structure Calculations for Hole‐Transporting Triphenylamine Derivatives in Polymer Light‐Emitting Diodes

Hole‐transporting polymers based on polyethene‐triphenylamine derivatives are investigated with respect to their UV/Vis spectra. Two substituents, N‐phenyl‐1‐naphthylamine and carbazole, are examined as their respective polymer light‐emitting diodes (PLEDs) show very different luminous efficiencies. In order to identify the origin of these phenomena electronic structure calculations based on TD‐DFT were performed using monomer models of the hole‐transporting polymers. In experiment these hole‐transporting polymers show very specific differences in their absorption and emission (fluorescence and phosphorescence) spectra. The analysis of the simulated absorption and emission spectra, the MOs as well as the ground and excited state geometries give explanations for the different optical performances of the corresponding PLEDs.

     

New 3π‐2Spiro Ladder‐Type Phenylene Materials: Synthesis,Physicochemical Properties and Applications in OLEDs

New routes to ladder‐type phenylene materials 1 and 2 are described. The oligomers 1 and 2 , which possess a “3π‐2spiro” architecture, have been synthesized by using extended diketone derivatives 3 and 10 as key intermediates. The physicochemical properties of the new blue‐light emitter 2 were studied in detail and compared with those of the less‐extended 1 . Owing to the recent development of fluorenone derivatives and their corresponding more conjugated analogues as potential electron‐transport materials in organic light‐emitting diodes (OLEDs) and as n‐type materials for photovoltaic applications, we also report herein the thermal, optical and electrochemical behavior of the key intermediates, diketones 3 and 10 . Finally, the application of dispiro 2 as a new light‐emitting material in OLEDs is reported.