This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

The electroluminescence of organic materials

Coordination complexes exhibiting room-temperature phosphorescence: Evaluation of their suitability as triplet emitters in organic light emitting diodes

The present invention relates to novel organic electroluminescent compounds exhibiting high luminous efficiency, and organic electroluminescent devices comprising the same. The organic electroluminescent compounds according to the invention are represented by Chemical Formula (1):

Novel organic electroluminescent compounds and organic electroluminescent device using the same

Metal chelates as emitting materials for organic electroluminescence

ion and completion of the cyclometalation reaction are feasible and produce the cyclometalated complex 205. Notably, addition of a strong acid reverts the cyclometalation and regenerates the agostic species 204. Small changes in the rhodium precursor significantly modify the product outcome and lead at fast rates to the cyclometalated complex 203, that is, the final oxidative addition product S. Similarly, alkene C-H bond activation has been observed to occur readily in a PCP ligand setting.348 Milstein and co-workers developed a procedure for preparing the cyclometalated PCP, PCN, or PCO pincer complexes 209 by rhodium-mediated cleavage of a strong Caryl-Calkyl bond (Scheme 87).32,349,350 Kinetically, Calkyl-H bond activation is competitive and complex 208 is formed as a second product at essentially similar rates. However, C-C bond cleavage appears to be the thermodynamically more favored process. Obviously, the higher energy required for Caryl-Calkyl bond activation (bond dissociation energy 427 kJ mol-1) compared to C-H bond breaking (368 kJ mol-1) is compensated by the stronger Rh-Caryl bond and the formation of two fiverather than six-membered metallacycles. Because rhodium-mediated Caryl-Calkyl and Calkyl-H bond activations in 206 are thermodynamically and kinetically very similar processes,351 subtle changes in the ligand parameters strongly affect the reaction outcome. For example, PPh2 donors induce C-H bond cleavage to afford 208d exclusively at ambient temperatures. C-C activation and formation of 209d is only induced upon heating under H2 atmosphere,352 presumably because these conditions allow the product selectivity to be controlled thermodynamically. In contrast, bulky PtBu2 donors as in 206a promote C-C bond activation already at room temperature, and the aryl complex 209a is the only product observed. Similarly, replacing one phosphine donor by a harder NEt2 group or the use of less basic phosphinite donors results in selective C-C bond cleavage at room temperature. These preferences suggest steric factors to play a more dominant role than electronic differences in determining the C-C vs C-H selectivity. Steric congestion induced by the donor substituents has been proposed to arrange the orbitals of the metal center to be directed toward the C-C bond rather than toward the C-H bond.353 Kinetic investigations have identified the coordination compound 207 as a common intermediate of Calkyl-H and the Caryl-Calkyl bond activation. On the basis of the similar rates for both cleavage processes and because of the absence of any detectable intermediate, formation of 207 and not C-H or C-C bond activation appears to be rate-limiting. While displacement of a weakly bound olefin ligand in the metal precursor may be fast, formation of the 8-membered metallacycle in 207 may be less favored, especially due to the potential for forming diand polymeric coordination compounds. It is worth noting that, upon substituting the PCP pincer ligand to a PCN donor array, the coordination complex 207c becomes stable at low temperature and has been spectroscopically characterized.354 As a consequence, the rate-determining step is shifted to a later stage on the reaction coordinate. Notably, slight modifications in the metal precursor, that is, utilization of [Rh(C2H4)(CO)(solv)2]BF4 instead of [RhCl(C2H4)2]2, alters the stability of the intermediates and produces complex 210 (Scheme 88).355 This complex may be represented by an agostic interaction of the C-C bond with the rhodium center, or alternatively by an arenium structure including an sp3-hybridized ipso carbon. Because of only weak Cipso-Rh interactions in solution (e.g., the absence of any 103Rh coupling), the agostic description is favored. The different product outcome has been presumed to originate from the reduced electron density at the cationic rhodium(I) center due to the strongly withdrawing CO ligand and the relatively weak Rh-N bond. This configuration Scheme 87 Scheme 86 Cyclometalation Using d-Block Transition Metals Chemical Reviews, 2010, Vol. 110, No. 2 603

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Cyclometalation Using d-Block Transition Metals: Fundamental Aspects and Recent Trends

White emission is important for applying organic EL devices to full-color displays and backlighting. In order to obtain white emission, the use of a white-light-emitting material which shows the white emission by itself is advantageous for these applications because of its high reliability and productivity. A device structure of indium-tin-oxide (ITO, anode)/hole transport layer/emitting layer/MgIn alloy (cathode) was employed. Bis(2-(2-hydroxyphenyl)benzothiazolate)zinc ( Zn(BTZ)2) was used as the emitting material. Zn(BTZ)2 showed greenish-white emission with a broad electroluminescent spectrum (half-width: 157 nm, peak wavelength: 486, 524 nm). It exhibited a high luminance of 10,190 cd/m2 at the applied voltage of 8 V because Zn(BTZ)2 has a good electron-transport property. As such, Zn(BTZ)2 is expected to serve as a new white-light-emitting material for organic EL devices.

https://iopscience.iop.org/article/10.1143/JJAP.35.L1339/pdf

White-Light-Emitting Material for Organic Electroluminescent Devices

A gallium complex (GaMq2Cl) consisting of two 2-methyl-8-hydroxyquinolines (Mq) and a chlorine was synthesized and used for the fabrication of organic light-emitting diodes (OLEDs). The photoluminescent peak of GaMq2Cl at 492 nm was as strong in intensity as that of tris(8-hydroxyquinolinato)aluminum (Alq3). The OLED using GaMq2Cl as an emitting material showed blue-green luminance of 10 490 cd/m2. When it was used as an electron transport material in a rubrene doped cell, an OLED with a high luminance of 27 700 cd/m2 was obtained. We found that GaMq2Cl also was useful as a host material.

Organic light-emitting diodes using a gallium complex

3- or 5-hydroxyflavone-metal complexes were synthesized and applied to organic light-emitting diodes (OLEDs) as an emitting material and an electron transport material. When bis(5-hydroxyflavonato)beryllium [Be(5Fla)2] was used as an emitting material, the OLED showed a luminance of 1900 cd/m2 with yellow. On the other hand, when used as an electron transport material in an organic three-layer cell, a high luminance of more than 10 000 cd/m2 was obtained. Furthermore, the turn-on voltage of the OLED could be lowered to 2.4 V and its lifetime was more than 1300 h. Be(5Fla)2 was found to have a good electron transporting capability and good stability.

Organic light-emitting diodes using 3- or 5-hydroxyflavone–metal complexes

A touch sensor includes a contact sensor and a pressure sensor. The contact sensor includes a first electrode and a first switching element connected to the first electrode, and detects a change in an electric potential when an object contacts a surface. The pressure sensor includes a second electrode and a second switching element connected to the second electrode, and detects a change in a pressure when an object depresses the surface. The touch sensor includes a plurality of the contact sensors and a plurality of the pressure sensors disposed regularly in an array.

Touch sensor, touch pad and input device

A luminescent organometallic compound having the chemical structure represented by the general formula (1) or (2): [in the general formulas (1) and (2), A and B represent ring structures, M represents a metallic atom, X represents a hetero atom other than carbon and hydrogen, Y represents at least one electron-attracting group connecting to ring structure B, Lb represents a unidentate or multidentate ligand, and p, q and r represent positive integers.]

Hiroyuki Fujii

Papers

White-Light-Emitting Material for Organic Electroluminescent Devices

Organic light-emitting diodes using a gallium complex

Organic light-emitting diodes using 3- or 5-hydroxyflavone–metal complexes

Touch sensor, touch pad and input device

Luminescent organometallic compound and light emitting device