Jeong-A Seo

Long lifetime blue phosphorescent organic light-emitting diodes with an exciton blocking layer

An acridine derived compound, 9,9-dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-dihydroacridine (PCZAC), was newly designed as a hole transport type high triplet energy material for application as a hole transport type exciton blocking layer of blue phosphorescent organic light-emitting diodes. The PCZAC compound provided a high triplet energy of 2.99 eV and a high glass transition temperature of 101 °C for high efficiency and long lifetime. PCZAC showed an improved quantum efficiency and more than 8 time improvement of the lifetime of blue phosphorescent organic light-emitting diodes.

The Effect of the Substitution Position of Dibenzofuran on the Photophysical and Charge‐Transport Properties of Host Materials for Phosphorescent Organic Light‐Emitting Diodes

Dibenzofuran has been used as a high-triplet-energy core structure of organic materials for phosphorescent organic light-emitting diodes (PHOLEDs) because of its high triplet energy of 3.14 eV. As it has strong electron-withdrawing oxygen linkage in the molecular structure, and has been used as a core structure of electron-transport materials or electron-transport-type host materials. The dibenzofuran core has been modified at the 2or 4position to synthesize various derivatives for use in PHOLEDs. The 2-position of dibenzofuran was modified simply by bromination using N-butylsuccinimide or bromine, while the 4-position of dibenzofuran was substituted with functional groups by direct lithiation owing to the electronwithdrawing character of oxygen in dibenzofuran. Several high-triplet-energy host materials have been developed by using this method. However, the 3-position of dibenzofuran could not be directly functionalized, and no organic material with substituent at the 3-position of dibenzofuran has been reported for use in PHOLEDs. Therefore, no systematic investigation about the relationship between the substitution position of dibenzofuran and device performances of PHOLEDs has been carried out. The synthesis of a dibenzofuran derivative with a substituent at the 3-position may thus enable the systematic study of the effect of substitution position of dibenzofuran on material characteristics and device performance. Herein, we synthesized high-triplet-energy host materials based on dibenzofuran and phenylcarbazole derived from a dibenzofuran intermediate with a substituent at 2-, 3and 4positions, and the relationship between the substitution position of dibenzofuran and material properties of host materials was systematically investigated. Furthermore, the device performances of green and blue PHOLEDs doped with phosphorescent dopants were also compared. It was shown that substitution at the 3-position of dibenzofuran is useful to lower the driving voltage, while substitution at the 2-position is effective in achieving a high triplet energy and high quantum efficiency. Three host materials, 9-(3-(dibenzo ACHTUNGTRENNUNG[b,d]furan-2-yl)phenyl)-9H-carbazole (2-DFPCz), 9-(3-(dibenzoACHTUNGTRENNUNG[b,d]furan-3-yl)phenyl)-9H-carbazole (3-DFPCz) and 9-(3-(dibenzoACHTUNGTRENNUNG[b,d]furan-4-yl)phenyl)-9H-carbazole (4-DFPCz) were synthesized by a Suzuki coupling reaction of brominated dibenzofuran with 3-(9H-carbazol-9-yl)phenylboronic acid. Brominated benzofuran and carbazole intermediates were prepared according to a previously reported procedure. 2-DFPCz was also synthesized by a previously reported procedure. The synthesis of the three host materials is shown in Scheme 1 (a detailed synthetic method is described in the Supporting Information).

Unconventional Molecular Design Approach of High-Efficiency Deep Blue Thermally Activated Delayed Fluorescent Emitters Using Indolocarbazole as an Acceptor

Unconventional blue thermally activated delayed fluorescent emitters having electron-donating type indolocarbazole as an acceptor were developed by attaching carbazolylcarbazole or acridine donors to the indolocarbazole acceptor. Three compounds were derived from the indolocarbazole acceptor. The indolocarbazole-acridine combined products showed efficient delayed fluorescent behavior and a high quantum efficiency of 19.5% with a color coordinate of (0.15, 0.16) when they were evaluated as thermally activated delayed fluorescent emitters in deep blue fluorescent devices. This is the first demonstration of the use of electron-donating carbazole-derived moieties as efficient acceptor units of blue thermally activated delayed fluorescent emitters.