The article represents a translation of Section 6.2 of the monograph authored by A.S. Burlov, V.G. Vlasenko, D.A. Garnovskiy, A.I. Uraev, E.I. Maltsev, D.A. Lypenko, and A.V. Vannikov, Electroluminescent Organic Light-Emitting Diodes Based on Metal Coordination Compounds, Rostov-on-Don: Yuzhn. Fed. Univ., 2015; ISBN 978-5-9275-1469-4 (see Additional Information), dedicated to reviewing the photoluminescence and electroluminescence properties of metal complexes based on (Zn, Cd, Al, Sc, Be, B) with azoles (2-(2-hydroxyphenyl)benzothiazoles, 2-(2-hydroxyphenyl)benzoxazoles, 2-(2-hydroxyphenyl)benzimidazoles, azaindoles, oxadiazoles, and their derivatives) as ligands. Modifying such ligands by introducing electron-donating substituents into various positions of the phenyl fragments leads to significant changes in their electroluminescence characteristics. Metal complex compounds with ligands of this type are widely used for creating OLED devices emitting white light.

This review article explores and analyzes published data on the photoluminescence and electroluminescence characteristics of rare earth element (REE) complex compounds, which are promising materials for creating highly efficient OLED devices. Distinguishing features of such compounds include their narrow emission bands, Stokes shift, long lifetime, and high quantum yields, enabling high resolution and color purity in constructed OLED devices. Using REE complexes as emissive layers in light-emitting diodes ensures significant color saturation and high device efficiency.

The article represents a translated, revised, and updated Section 6.3 of the monograph by A.S. Burlov, V.G. Vlasenko, D.A. Garnovskiy, A.I. Uraev, E.I. Maltsev, D.A. Lypenko, and A.V. Vannikov, Electroluminescent Organic Light-Emitting Diodes Based on Metal Coordination Compounds, Rostov-on-Don: Yuzhn. Fed. Univ., 2015; ISBN 978-5-9275-1469-4 (see Additional Information). This section is dedicated to reviewing the photoluminescence and electroluminescence properties of metal complexes based on bi- and polydentate ligands of the azomethine type (Schiff bases). Many metal complexes of Schiff bases find wide use as luminescent materials. One of the applications of these compounds is the use as emissive layers or dopants for manufacturing OLED. The photo- and electroluminescence properties of a series of the metal complexes with the ligands based on the derivatives of hydroxybenzaldehyde, 2-(N-tosylamino)benzaldehyde, 1‑phenyl-3-methyl-4-formylpyrazol-5-one, and some others are reviewed. The systematic categorization of these compounds extends beyond their photophysical properties to consider the electroluminescence characteristics observed in OLED devices employing them as the basis. By modifying known azomethine-type ligand systems, one can obtain metal complex compounds with exceptional thermal stability, solubility, and quantum efficiency. These characteristics enable their use as luminescent materials in highly efficient OLED devices.

The review is devoted to analysis of photo- and electroluminescent properties of metal complexes (Al, Be, Mg, Ga, In, Zn, and B) based on substituted quinoline derivatives. Literature data shows that changing the substituents in quinoline ligands and the metal complexing agent can affect the color and intensity of photoluminescence in the corresponding metal complexes. OLED devices fabricated based on these complexes have exhibited high brightness and efficient electroluminescence across a broad spectral range from red to blue. Furthermore, these compounds possess excellent electron-transport properties, enabling their utilization as conductive layers in OLEDs.

This review summarizes the results of the synthesis, photoluminescence, and electroluminescence of the main classes of cyclometallated iridium(III) complex compounds. The primary focus of the review is on heteroleptic iridium(III) complexes, which contain two equivalent C^N ligands and an additional auxiliary ligand. Numerous examples demonstrate that the selection and modification of the ligand systems in iridium(III) complexes, using various donor or acceptor groups, alter significantly their spectral characteristics, often achieving record levels of brightness and emission efficiency for OLED devices manufactured based on them.

β-Aminovinyl ketone (2-nitro-3-(8-quinolylamino)prop-2-enal) was synthesized by condensation of nitromalondialdehyde with 8-aminoquinoline. The reactions of β-aminovinyl ketone with copper, nickel, and cobalt acetates in methanol gave metal complexes. The spectral and magnetic characteristics of preparatively isolated compounds were studied. The structure of cobalt(II) chelate was determined on the basis of X-ray diffraction study (CIF file CCDC no. 2109263).

Azomethines were synthesized from 2,4,6-trimethylaniline, salicylaldehyde, and its 3(5)-halogen derivatives, as well as their complexes with zinc(II) (ZnL2). The structure and composition of the compounds were determined by elemental analysis, IR, 1H NMR, and X-ray spectroscopy. The ZnL2 complexes have a tetrahedral structure. The photoluminescent properties of azomethines and their zinc complexes in methylene chloride solutions and in solid state have been studied. The photoluminescence quantum yields of azomethines lie in the range 4.66–12.16%; for zinc complexes they decrease to 0.45–2.02%. The average photoluminescence lifetimes for azomethines and their complexes range from 2.00 to 2.87 ns. Azomethine, obtained from 2,4,6-trimethylaniline and dichlorosalicylic aldehyde, and its complex with zinc have significant protistocidal activity.

Осуществлен синтез комплекса Ni(II) на основе (4Z)-4-[(2-диэтиламиноэтиламино)мети­лен]-5-метил-2-фенилпиразол-3-она (НL) — продукта конденсации 5-гидрокси-3-метил-1-фенилпиразол-4-карбальдегида с N,N-диэтилэтилендиамином. Методами элементного анализа и ИК спектроскопии установлено, что комплекс никеля имеет состав Ni(L) CH3COO·CH3OH·H2O. Кристаллическое и молекулярное строение комплекса определено методом монокристальной рентгеновской дифракции. Из данных РСА следует, что в монохелатном комплексе Ni(II) реализуется искаженное октаэдрическое строение за счет связей с монодентатным ацетат-анионом и молекулами метанола и воды.

(4Z)-4-[(2-Furylmethylamino)methylene]-5-methyl-2-phenylpyrazol-3-one (HL) and its Cu(II), Ni(II), Co(II), Zn(II), and Pd(II) complexes with the ML2 composition are synthesized. The structures of the complexes are studied by elemental C,H,N analysis, IR spectroscopy, magnetochemical measurements, and quantum chemistry. The crystal structures of the copper(II) and cobalt(II) complexes are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2177619 and 2177622, respectively). Two deprotonated ligands are coordinated to the metal ions via the chelate mode by the nitrogen atom of the imino group and the oxygen atom of the hydroxy group of the ligand. The geometry of the copper(II) ion environment corresponds to a distorted planar square, whereas the cobalt(II) ion exists in a distorted tetrahedral environment. In the series of the compounds studied, fluorescence with a maximum at 431 nm and a quantum yield of 0.29 is observed for the Zn(II) complex in a solution of CH2Cl2. The synthesized enamine and metal complexes are tested for antibacterial, protistocidal, and fungistatic activities. All compounds are shown to have no fungistatic and antibacterial activities, and only a weak protistocidal activity is found for the copper and zinc complexes.

(4Z)-4-[(2-Diethylaminoethylamino)methylene]-5-methyl-2-phenylpyrazol-3-one (НL, product of the condensation of 5-hydroxy-3-methyl-1-phenylpyrazole-4-carbaldehyde with N,N-diethylethylenediamine) and its complexes CuL2 (I) and Co(L)CH3COO · CH3OH · H2O (II) are synthesized. The structures and compositions of the synthesized compounds are determined by elemental analysis, 1Н NMR and IR spectroscopy, and X-ray diffraction analysis (CIF files CCDC nos. 1971770 (I) and 1971772 (II)). Bis(chelate) pentacoordinated complex I has a distorted tetragonal pyramidal structure, and a distorted octahedral structure with the monodentate acetate anion and methanol and water molecules is observed for monochelate complex II.

The electrochemical oxidation of a zero-valent metals (copper, cobalt, nickel, zinc, and cadmium) (1–5) in an acetonitrile-methanol solution containing the equimolar amounts of 1,10-phenanthroline (phen) and the N, N, S-tridentate basic form of the Schiff base N-[2-[[3-methyl-1-phenyl-5-thioxo-pyrazole-4-ylidenemethyl]amino]phenyl]-4-methylbenzenesulfonamide (H2L) resulted in the formation of the mixed ligand complexes with a common formula [M(L)phen]. All compounds were characterized with C, H, N elemental analysis, FT-IR, 1H NMR, X-ray absorption spectroscopy and magnetic measurements. The structures of the complexes [Cu(L)phen] (1) and [Zn(L)phen] (4) were determined by X-ray single-crystal diffraction. In both complexes the metal centers are surrounded with imine and amide nitrogens, sulfur of thiol group of H2L and two nitrogens of phen used as co-ligand. The assignment and the nature of the bands in experimental UV–Vis spectra of adducts were analyzed using time-dependent (TD) DFT calculations.

1,10-Phenanthroline (Phen) adducts [M(L)Phen] in copper(II), cobalt(II), and zinc(II) chelates based on N,N,O-tridentate tosylamino-functionalized pyrazole-containing Schiff base (H2L), resulting from condensation of 2-tosylaminoaniline with 3-methyl-1-phenyl-4-formylpyrazol-5-ol, were obtained by electrosynthesis. The composition and structure of the mixed-ligand complexes were confirmed by elemental analysis, IR spectroscopy, and magnetochemical measurements. The structures of azomethine H2L and mixed-ligand copper(II) complex were determined by X-ray diffraction.

Novel Cu(II), Co(II), Ni(II), and Zn(II) complexes of 5-methyl-2-phenyl-4-[(4-phenylazo)anilinemethylylidene]- 2,4-dihydro-3H-pyrazole-3-thione and 5-methyl-4-[4-methyl-2-(4-methylphenylazo)anilinemethylylidene]- 2-phenyl-2,4-dihydro-3H-pyrazole-3-thione, i.e. ligands containing the phenylazo group in the ortho and para positions of the aniline fragment, were synthesized by the chemical and electrochemical methods. The complexes and ligands were characterized by IR, 1H NMR, X-ray absorption spectroscopy and magnetochemistry. The azo group of the ligands is not involved in coordination to the metal.

The reaction of 4-formyl-5-mercaptopyrazole with thiosemicarbazides in methanol has afforded novel disulfide derivatives of thiosemicarbazones, and their structure has been studied by NMR and IR spectroscopy. X-ray diffraction analysis of [5,5'-dithiobis(4-formyl-3-methyl-1-phenylpyrazole)]-4-allylthio-semicarbazone has shown that it exists as a dimer with two molecules linked via the disulfide S–S bridge between the heterocycles in the crystal.

The synthesis of a series of adducts of 2-amino-1-ethylbenzimidazole (L1) in Cu(II), Co(II), Zn(II) and Ni(II) chelates of the N, N, S tridentate basic form of the tosylamino functionalized pyrazol containing Schiff base N-[2-[[3-methyl-1-phenyl-5-thioxo-pyrazole-4-ylidenemethyl]amino]phenyl]-4-methylbenzenesulfonamide (H2L) with common formula [M(L)L1] was performed. The compounds were characterized with C, H, N elemental analysis, FT-IR, 1H NMR, X-ray absorption spectroscopy and magnetic measurements. Crystal structure of nickel complex [Ni(L)L1] showed that the 2-amino-1-ethylbenzimidazole co-ligand is coordinated through the endocyclic nitrogen atom of pyridine type. The assignment and the nature of the electronic transitions observed in the UV–Vis spectra of chelates were analyzed using time-dependent (TD) DFT calculations.

Copper, nickel, and cobalt complexes of the N,N,S-tridentate tosylamino-functionalized mercaptopyrazole Schiff base were obtained by an electrochemical method. The structure and composition of the metal chelates were characterized by C, H, N elemental analysis data and IR and 1H NMR spectroscopy. More data on the structures of the complexes were obtained by magnetochemical and X-ray absorption spectroscopy measurements. The mononuclear structure of the copper(II) complex was confirmed by X-ray diffraction (CIF file CCDC no. 1473320).