High-triplet-energy derivatives of indole and carbazole as hosts for blue phosphorescent organic light-emitting diodes. (April 2017)

• Record Type: Journal Article
• Authors: Gudeika, Dalius; Norvaisa, Karolis; Stanislovaityte, Egle; Bezvikonnyi, Oleksandr; Volyniuk, Dmytro; Turyk, Pavlo; Hladka, Iryna; Yashchuk, Valeriy M.; Grazulevicius, Juozas V.
• Is Part Of: Dyes and pigments. Volume 139(2017)
• Page Start: 487
• Page End: 497
• Publication Date: 2017-04
• Subjects: Cyclic voltammetry -- Triplet-energy level -- Host -- Hole and electron mobilities -- External quantum efficiency; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2016.12.041
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: The synthesis and characterization of a series of electro-active compounds containing carbazolyl and indolyl moieties are reported. All the synthesized derivatives were capable of glass formation with the glass transition temperatures ranging from 89 to 130 °C. They showed high thermal stability with the 5% weight loss temperatures ranging from 370 to 412 °C. The obtained compounds emit light in the deep blue region (350–366 nm) and their solutions exhibit moderately high fluorescence quantum yields in the range of 22.9–44.2%. The compounds exhibited high triplet-energy levels ranging from 2.70 to 3.06 eV. The solid-state ionization potentials of the synthesized compounds were found to be comparable (5.68–5.72 eV). They are characterized by equal values of the optical band gaps (3.53 eV). Cyclic voltammetry revealed two irreversible oxidation peaks with the onsets at 0.95 V and 1.35 V in the repeated cycles. 9-{4-[Bis(1-ethyl-2-phenyl-1 H -indol-3-yl)methyl]phenyl}-9 H -carbazole exhibited well balanced hole and electron mobilities reaching 1.3 × 10 −3 cm 2 /V × s at electric fields higher than 8.1 × 10 5 V/cm. The compounds were tested as hosts in electrophosphorescent devices. The best device showed turn-on voltage of 2.4 V (at 1 cd/m 2 ); maximum current efficiency of 44.7 cd/A, maximum brightness of 4500 cd/m 2 (at 7 V), maximum power efficiency of 38 l m/W, and external quantum efficiency of ca. 18%. Graphical abstract: Highlights: Derivatives of indole and carbazole were synthesized. Their glass transition temperatures range from 89 to 130 °C. Cyclic voltammetry revealed two irreversible oxidation peaks. Hole and electron mobilities reached 1.3 × 10 −3 cm 2 /V × s. Blue electrophosphorescent devices were fabricated and characterized.