Dramatic Substituent Effects on the Photoluminescence of Boron Complexes of 2‐(Benzothiazol‐2‐yl)phenols

Substituents can induce dramatic changes in the photoluminescence properties of N,O‐chelated boron complexes. Specifically, the boron complexes of 2‐(benzothiazol‐2‐yl)phenols become bright deep blue‐ and orange‐red‐emitting materials depending on amino substituents at the 5‐ and 4‐positions of 2‐(benzothiazol‐2‐yl)phenol, respectively. Absorption and emission data show that the resulting boron complexes have little or small overlap between the absorption and emission spectra and, furthermore, X‐ray crystal structures for both the blue and orange‐red complexes indicate the absence of π–π stacking interaction in the crystal‐packing structures. These features endow the boron complexes with bright and strong photoluminescence in the solid state, which distinguishes itself from the typical boron complexes of dipyrromethenes (BODIPYs). A preliminary study indicates that the blue complexes have promising electro‐optical characteristics as dopant in an organic light‐emitting diode (OLED) device and show chromaticity close to an ideal deep blue. The substituent effects on the photoluminescent properties may be used to tune the desired emission wavelength of related boron or other metal complexes.     

Synthesis and photoluminescence of iridium complexes with benzothiazol-2-yl carbazole derivative ligand

Two new iridium(III) complexes containing benzothiazol-2-yl carbazole derivative as a cyclometalated ligand (L) and picolinate (pic) or acetylacetonate (acac) as the ancillary ligand, Ir(III) bis(3-(benzothiazol-2-yl)-9-butyl-carbazole)(picolinate) [Ir(L)₂(pic)] and Ir(III) bis(3-(benzothiazol-2-yl)-9-butyl-carbazole)(acetylacetonate) [Ir(L)₂(acac)], were synthesized and characterized by elemental analysis, ¹H NMR, FT-IR, and UV–Vis absorption spectra. Both the iridium(III) complexes emit intense green–yellow emissions, indicating that they are useful for the fabrication of organic light-emitting diodes.     

基于三萘苯的溶液可加工螺旋形寡聚物的合成及其在蓝光有机电致发光器件中的应用

近年来,人们在有机电致发光材料和器件结构方面取得了巨大的进步。然而由于蓝光材料具带隙宽的内禀属性,在发光效率、色纯度和稳定性上仍然面临巨大挑战。本文将螺旋形三萘苯共轭体系引入电致发光材料领域,它独特的螺旋形分子结构和易于化学修饰的特点有利于抑制聚集体和基激缔合物的形成。通过SiCl₄催化的环三缩合反应和Suzuki偶联反应,我们设计合成了以三萘基苯为核心,萘、蒽和三苯胺为取代基团的系列螺旋形蓝光寡聚物,并系统地研究了它们的热学、光物理和电化学性质。研究发现,萘和三苯胺取代的寡聚物1, 3, 5-三(3-(1-甲氧基萘-2-基)-4-甲氧基萘-1-基)苯(TNNB)和1, 3, 5-三(3-(4-(N, N-二苯胺基)苯基)-4-甲氧基萘-1-基)苯(TPANB)具有最好的热稳定性。在溶液中,这两种材料都具有深蓝发射,发射峰分别为382和415 nm;在薄膜中, TNNB的发射峰仅有1 nm的红移,而TPANB甚至产生了6 nm的蓝移。以这些寡聚物为发光材料,通过旋涂法制备的有机电致发光器件结果表明,基于TNNB的器件获得了最大亮度达到5273 cd·m^-2,色坐标(0.17, 0.11)的纯蓝光器件。     

Synthesis, structures, and luminescent properties of phenol-pyridyl boron complexes

Syntheses of the four mixed phenol-pyridine derivatives 1,6-bis(2-hydroxyphenyl)pyridyl boron naphthalene (1), 1,6-bis(2-hydroxy-5-methylphenyl)pyridyl boron naphthalene (2), 1,6-bis(2-hydroxyphenyl)pyridyl boron 2-methoxylbenzene (3), and 1,6-bis(2-hydroxy-5-methylphenyl)pyridyl boron 2-methoxylbenzene (4) are reported. The structures of the boron compounds 1, 3, and 4 were determined by single-crystal X-ray diffraction. The molecular packing is characterized by intermolecular pi...pi and hydrogen-bonding interactions. DSC analysis demonstrates that 1 and 2 have good thermal stability with higher glass transition temperatures (Tg) and melting points (Tm) than 3 and 4. Boron complexes 1-4 display bright blue luminescence in solution and the solid state. White and blue electroluminescent (EL) devices were fabricated successfully using these boron compounds.     

Photochromic dihetarylethenes. 10. Photochromic 1,2-bis[2-(benzothiazol-2-yl)-3-thienyl]- and 1,2-bis[2-(benzothiazol-2-yl)benzothiophen-3-yl]ethenes

Dithienylethenes containing the thiophene rings with benzothiazolyl substituents in position 2 were synthesized. 1,2-Bis[2-(benzothiazol-2-yl)benzothiophen-3-yl]hexafluorocyclopentene and 1,2-bis[2,5-di(benzothiazol-2-yl)-3-thienyl]hexafluorocyclopentene possess photochromic properties. The open forms of 1,2-bis(2-benzothiazolylhetaryl)ethenes fluoresce, but introduction of the benzothiazole rings into dihetarylethenes significantly lowers the fatigue resistance of photochromes and favors thermal reversibility.     

Theoretical study on photophysical properties of phenolpyridyl boron complexes

Organoboron complexes have potential application in organic light-emitting devices (OLEDs). Our group has synthesized four phenolpyridyl boron complexes (Inorg. Chem. 2006, 45, 2788), which can function as an electron transport materials (ETM), white and blue emitters, and exhibit high efficiency and stability. To reveal the relationship between the properties and structures of these functional materials, theoretical analysis of spectral properties and electronic structures of these complexes was systematically characterized with the B3LYP and 6-31G* basis set. The calculated absorption and emission spectra of these systems are in good agreement with the experimental ones. It is clear seen that these transitions are charge transferred along 2,6-bis(2-hydroxyphenyl)pyridyl boron moiety, and the contribution of boron atom in these compounds to the main transition orbitals is vanishingly small. The substitution of methyl and methoxyl for hydrogen does not change the absorption wavelengths and transition natures, but influences the radioactive efficiencies and electron transport properties, which are observed and discussed in detail. Furthermore, large red shifts of fluorescence are caused by replacing the hydrogen with CN or NO2 groups, which indicates that they are potential candidates as green-light-emitting materials. These results are favorable to further understanding the photophysical properties of this kind of complexes.     

Towards deep‐blue phosphorescence: molecular design and property prediction of iridium complexes with pyridinylphosphinate ancillary ligand

A series of iridium complexes ( 1 – 5 ), which consist of two 2‐(2,4‐difluorophenyl)pyridine (dfppy)‐based primary ligands and one pyridinylphosphinate ancillary ligand, have been investigated theoretically for screening highly efficient deep‐blue light‐emitting materials. Compared with the reported dfppy‐based emitter 1 , the designed iridium complexes 3 – 5 with the introduction of a stronger electron‐withdrawing (–CN, –CF₃ , or o‐carborane) group and a bulky electron‐donating (tert‐butyl) group in dfppy ligands can be achieved to display the emission peaks at 443, 442, and 447 nm, respectively. The electronic structures, absorption and emission properties, radiative and nonradiative processes of their excited states, and charge injection and transport properties of the iridium complexes are analyzed in detail. The calculated results show that designed iridium complexes have comparable radiative and nonradiative rate constants with 1 , and are expected to have similar quantum efficiency with 1 . Meanwhile, these designed complexes keep the advantages of the charge transport properties of 1 , indicating that they are potential iridium complexes for efficient deep‐blue phosphorescence. This work provides more in‐depth understanding the structure–property relationship of dfppy‐based iridium complexes, and shed lights on molecular design for deep‐blue phosphorescent metal complexes.     

Synthesis,Structure, and Luminescence Properties of Boron Complex with 4-Bromo-2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenoxide Ligand

Russian Journal of General Chemistry - A boron complex with 4-bromo-2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenoxide ligand has been synthesized, and its photoluminescence properties in...     

Lanthanide complexes with substituted naphtholate ligands: extraordinary bright near-infrared luminescence of ytterbium

A series of Pr, Nd, Ho, Er, Tm, and Yb complexes with 3-(2-benzoxazol-2-yl)-2-naphtholate and 3-(2-benzothiazol-2-yl)-2-naphtholate ligands was synthesized. The structure, as well as the photo- and electroluminescent properties of these complexes were studied. An extraordinary bright emission of Yb³⁺ was detected. To explain the phenomenon, a novel excitation mechanism involving intramolecular electron transfer was proposed.     

Bicyclic dioxetanes bearing a 4-(benzoazol-2-yl)-3-hydroxyphenyl moiety: chemiluminescence profile for base-induced decomposition in aprotic medium and in aqueous medium

Four bicyclic dioxetanes bearing a 4-(benzothiazol-2-yl)-3-hydroxyphenyl or 4-(benzoxazol-2-yl)-3-hydroxyphenyl group were synthesized. These dioxetanes underwent base-induced decomposition with accompanying emission of light with high efficiency in NaOH/H₂O as well as in tetrabutyl ammonium fluoride (TBAF)/acetonitrile. Among them, benzothiazol-analogs decomposed faster in the aqueous solution than in acetonitrile.     

Highly Luminescent Pincer Gold(III) Aryl Emitters: Thermally Activated Delayed Fluorescence and Solution‐Processed OLEDs

Herein are described the synthesis, photophysical properties and applications of a series of luminescent cyclometalated Au^III complexes having an auxiliary aryl ligand. These complexes show photoluminescence with emission quantum yields of up to 0.79 in solution and 0.84 in thin films (4 wt % in PMMA) at room temperature, both of which are the highest reported values among Au^III complexes. Thermally activated delayed fluorescence (TADF) is the emission origin for some of these complexes. Solution‐processed OLEDs made with these complexes showed sky‐blue to green electroluminescence with external quantum efficiencies (EQEs) of up to 23.8 %, current efficiencies of up to 70.4 cd A⁻¹, and roll‐off of down to 1 %, highlighting the bright prospect of Au^III‐TADF emitters in OLEDs.     

Synthesis and antimicrobial studies of new pyridine derivatives

2-(p-Acetylaminobenzenesulfonylamido)-substituted benzothiazoles were prepared from 2-amino-substituted benzothiazoles and p-acetamidobenzenesulfonyl chloride using a mixture of pyridine and Ac₂O, which formed an electrophilic N-acetyl- pyridinium complex facilitating condensation to give the desired products by removal of HCl. 2-[4-(Substituted benzothiazol-2-yl)aminosulfonylanilino]pyridine-3-carboxylic acids (synthesized from 2-chloropyridine-3-carboxylic acid and the corresponding substituted 2-(p-aminobenzenesulfonylamido)benzothiazole in 2-ethoxyethanol using Cu-powder and K₂CO₃) were then converted to acid chlorides, which on further reaction with piperazine and 4-methoxyphenylpiperazine yielded the corresponding 2-[4-(substituted benzothiazol-2-yl)amino-sulfonyl]anilino-3-(piperazinocarbonyl) pyridine and 2-[4-(substituted benzothiazol-2-yl)amino-sulfonyl]anilino-3-[(4-methoxyphenyl)piperazin-1-yl-carbonyl]pyridine. The structures of the new compounds have been established on the basis of their elemental analyses as well as IR, ¹H NMR, and mass-spectral data. All the compounds have been screened for antimicrobial activity and found to possess considerable antibacterial activity.     

Three-coordinate organoboron compounds BAr2R (Ar = mesityl, R = 7-azaindolyl- or 2,2'-dipyridylamino-functionalized aryl or thienyl) for electroluminescent devices and supramolecular assembly

Eight novel three-coordinate boron compounds with the general formula BAr(2)L, in which Ar is mesityl and L is a 7-azaindolyl- or a 2,2'-dipyridylamino-functionalized aryl or thienyl ligand, have been synthesized by Suzuki coupling, Ullmann condensation methods, or simple substitution reactions (L = p-(2,2'-dipyridylamino)phenyl, 1; p-(2,2'-dipyridylamino)biphenyl, 2; p-(7-azaindolyl)phenyl, 3; p-(7-azaindolyl)biphenyl, 4; 3,5-bis(2,2'-dipyridylamino)phenyl, 5; 3,5-bis(7-azaindolyl)phenyl, 6; p-[3,5-bis(2,2'-dipyridylamino)phenyl]phenyl, 7; 5-[p-(2,2'-dipyridylamino)phenyl]-2-thienyl, 8). The structures of 1, 3, and 5-7 have been determined by X-ray diffraction analyses. These new boron compounds are bright blue emitters. Electroluminescent devices using compound 2 or 8 as the emitter and the electron-transport layer have been successfully fabricated. Molecular orbital calculations (Gaussian 98) have established that the blue emission of compounds 1-8 originates from charge transfer between the pi orbital of the ligand L and the p(pi) orbital of the boron center. The ability of these boron compounds to bind to metal centers to form supramolecular assemblies was demonstrated by treatment of compound 2 with Zn(O(2)CCF(3))(2), which generated a 1:1 chelate complex [2.Zn(O(2)CCF(3))(2)] (10), and also by treatment of compound 4 with AgNO(3), yielding a 2:1 coordination compound [(4)(2).Ag(NO(3))] (11). In the solid state, compounds 10 and 11 form interesting head-to-head and tail-to-tail extended structures that host solvent molecules such as benzene.     

Synthesis,structure, and luminescence properties of complex ZnLCl<Superscript>b2</Superscript> (L is 2-(3,5-dimethylpyrazol-1-yl)-4-methylquinoline)

A complex ZnLCl^b2 (L is 2-(3,5-dimethylpyrazol-1-yl)-4-methylquinoline) was synthesized. According to X-ray diffraction data, the Zn^p2+ ions in mononuclear molecules of the obtained complex coordinate two N atoms of the bidentate chelating ligand L and two Cl atoms. The coordination polyhedron Cl2N^b2 represents a distorted tetrahedron. In solid state at 300 K, the ligand L exhibits weak photoluminescence in the visible spectral range. The complex ZnLCl^b2 exhibits bright blue photoluminescence.     

Étude comparative de la décarboxylation des acides (benzothiazolyl-2)-acétique, -3-propionique, -glyoxylique et -pyruvique

Benzothiazol-2-yl glyoxylic acid and α-amino-benzothiazol-2-yl acetic acid hydrochloride undergo decarboxylation at room temperature. This facile decarboxylation seems to depend on the following requirements: (a) the formation of a planar zwitterion; (b) a distance of about 2.2 Å between the charges of the zwitterion; (c) the stabilisation of the intermediate carbanion. In fact the following compounds which do not fulfil these three conditions do not decarboxylate at room temperature: α-hydroximino benzothiazol-2-yl acetic acid, α-amino benzothiazol-2-yl acetic acid as internal salt, benzothiazol-2-yl acetic acid, 3-(benzothiazol-2-yl)-propionic acid and benzothiazol-2-yl pyruvic acid.     

BORAZANs: tunable fluorophores based on 2-(pyrazolyl)aniline chelates of diphenylboron

The reaction between 2-pyrazolyl-4-X-anilines, H(pzAnX), (X = para-OMe (L1), Me (L2), H (L3), Cl (L4), CO2Et (L5), CF3 (L6), CN (L7)) and triphenylboron in boiling toluene affords the respective, highly emissive N,N'-boron chelate complexes, BPh2(pzAnX) (X = para-OMe (1), Me (2), H (3), Cl (4), CO2Et (5), CF3 (6), CN (7)) in high yield. The structural, electrochemical, and photophysical properties of the new boron complexes can be fine-tuned by varying the electron-withdrawing or -donating power of the para-aniline substituent (delineated by the substituent's Hammett parameter). Those complexes with electron-withdrawing para-aniline substituents such as CO2Et (5), CF3 (6), and CN (7) have more planar chelate rings, more 'quinoidal' distortion in the aniline rings, greater chemical stability, higher oxidation potentials, and more intense (phiF = 0.81 for 7 in toluene), higher-energy (blue) fluorescent emission compared to those with electron-donating substituents. Thus, for 1 the oxidation potential is 0.53 V versus Ag/AgCl (compared to 1.12 V for 7), and the emission is tuned to the yellow-green but at an expense in terms of lower quantum yields (phiF = 0.07 for 1 in toluene) and increased chemical reactivity. Density functional calculations (B3LYP/6-31G*) on PM3 energy-minimized structures of the ligands and boron complexes reproduced experimentally observed data and trends and provided further insight into the nature of the electronic transitions.     

Ordered dispersion of ZnO quantum dots in SiO2 matrix and its strong emission properties

ZnO nanoparticles in the form of quantum dots (QDs) have been dispersed in SiO₂ matrix using StÖber method to form ZnO QDs-SiO₂ nanocomposites. Addition of tetraethyl orthosilicate (TEOS) to an ethanolic solution of ZnO nanoparticles produces random dispersion. On the other hand, addition of ZnO nanoparticles to an already hydrolyzed ethanolic TEOS solution results in a chain-like ordered dispersion. The photoluminescence spectra of the as-grown nanocomposites show strong emission in the ultraviolet region. When annealed at higher temperature, depending on the sample type, these show strong red or white emission. Interestingly, when the excitation is removed, the orderly dispersed ZnO QDs-SiO₂ composite shows a very bright blue fluorescence visible by naked eyes for few seconds indicating their promise for display applications. The emission property has been explained in the light of structure–property relationship.     

Highly efficient yellow-emitting iridium(III) complexes based on fluorinated 2-(biphenyl-4-yl)-2H-indazole ligands: Syntheses,structures, properties,and density functional theory calculations

Two new iridium (III) complexes ( Ir1-Ir2 ) bearing different fluorinated 2-(biphenyl-4-yl)-2H-indazole-based compounds as cyclometalated ligands and Xantphos as an ancillary ligand were synthesized and fully characterized. The ultraviolet (UV)–vis absorption, photoluminescence, and electrochemistry properties were studied. The single crystal structures of Ir1-Ir2 were determined by X-ray diffraction, showing each adopts the distorted octahedral coordination geometry. To gain insights into the lowest energy electron transitions and the lowest triplet excited states, density functional theory calculations were used to further investigate the origination. Two complexes emit yellow photoluminescence with quantum yields of 49.7–72.5% in solution at room temperature. Their Commission Internationale de L'Eclairage color coordinates are (0.42, 0.53) and (0.39, 0.47), respectively.     

Synthesis and structure of cobalt(II) 1-aryl-3-aryl(alkyl)-5-(benzothiazol-2-yl)formazanates

New mono- and binuclear cobalt(II) complexes based on 1-aryl-3-aryl(alkyl)-5-(benzothiazol-2-yl)formazans were synthesized. The structure of the synthesized compounds was determined by electronic and IR absorption spectroscopy, mass spectrometry, and X-ray crystallography.     

Nucleophilic substitution of fluorine atoms in 2,6-difluoro-3-(pyridin-2-yl)benzonitrile leading to soluble blue-emitting cyclometalated Ir(III) complexes

New functionalized phenylpyridine ligands and their derived heteroleptic cyclometalated Ir(III) complexes have been synthesized. The complexes possess a combination of important properties: (i) blue emission, (ii) good photoluminescence quantum yields, and (iii) good solubility in organic solvents, making them very attractive as phosphorescent dopant emitters for solution-processable light-emitting devices.