Derivatives of Phenyl Pyrimidine and of the Different Donor Moieties as Emitters for OLEDs.

Two derivatives of phenyl pyrimidine as acceptor unit and triphenylamino or 4,4'-dimethoxytriphenylamino donor groups were designed and synthesized as emitters for organic light-emitting diodes (OLEDs) aiming to utilize triplet excitons in the electroluminescence. Thermogravimetric analysis revealed high thermal stability of the compounds with 5% weight loss temperatures of 397 and 438 °C. The theoretical estimations and photophysical data show the contributions of local excited and charge transfer states into emission. The addition of the methoxy groups led to the significant improvement of hole-transporting properties and the bathochromic shift of the emission from blue to green-blue spectral diapason. It is shown that mixing of the compounds with the organic host results in facilitation of the delayed emission. The singlet-triplet energy splitting was found to be too big for the thermally activated delayed fluorescence. No thermal activation of the long-lived emission was detected. No experimental evidence for triplet-triplet annihilation and room temperature phosphorescence were detected making the hot exciton mechanism the most probable one. The OLEDs based on the compounds reached the maximum external quantum efficiency of up to 10.6%.

Synthesis and properties of quinazoline-based versatile exciplex-forming compounds.

Three compounds, bearing a quinazoline unit as the acceptor core and carbazole, dimethyldihydroacridine, or phenothiazine donor moieties, were designed and synthesized in two steps including a facile copper-catalyzed cyclization and a nucleophilic aromatic substitution reaction. The photophysical properties of the compounds, based on theoretical calculations and experimental measurements, as well as the electrochemical and thermal properties, are discussed. The synthesized compounds form glasses with glass-transition temperatures ranging from 116 °C to 123 °C. The ionization potentials estimated by cyclic voltammetry of the derivatives were in the range of 5.22-5.87 eV. The 3,6-di-tert-butylcarbazole-substituted quinazoline-based compound forms a sky-blue emitting exciplex in solid mixture with the acceptor 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine as well as an orange emitting exciplex with the donor 4,4',4″-tris[3-methylphenyl(phenyl)amino]triphenylamine. A white OLED based on these versatile exciplex systems with a relatively high maximum brightness of 3030 cd/m2 and an external quantum efficiency of 0.5% was fabricated.

Synthesis and Performance in OLEDs of Selenium-Containing Phosphorescent Emitters with Red Emission Color Deeper Than the Corresponding NTSC Standard.

The synthesis of new iridium(III) complexes containing a 2-(benzo[b]selenophen-2-yl)pyridine ligand is reported along with their photophysical, thermal, electrochemical and electroluminescent properties. These complexes are characterized by deep red phosphorescence with photoluminescence quantum yields exceeding 31% in the solid state. Solid layers of the complexes were characterized by ionization potentials of 5.17-5.27 eV and electron affinities of 2.87-2.95 eV. Their thermal and electrochemical stabilities were proved by cyclic voltammetry and thermogravimetric analysis. Deep red selenium-based iridium phosphorescent emitters were used in red electroluminescent devices which were characterized by a deep red color with Commission Internationale de l'Eclairage (CIE 1931) chromaticity coordinates (x, y) of (0.69, 0.31). This color is deeper than that defined by the red color standard (0.67, 0.33) of the National Television System Committee (NTSC) or CIE 1931 of (0.68, 0.32) of the widely known red phosphorescent emitter bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2(acac)). Using newly developed deep red iridium complexes, white hybrid wet-processable light-emitting devices were fabricated, the electroluminescence of which was characterized by a white color with a color rendering index (CRI) reaching 85. White hybrid OLEDs were obtained by mixing blue fluorescence, green thermally activated delayed fluorescence, and red phosphorescence. They showed a maximum brightness exceeding 10000 cd/m2 and a high external quantum efficiency of 6.3% as for solution-processed white devices.