Methoxycarbazolyl-disubstituted dibenzofuranes as holes- and electrons-transporting hosts for phosphorescent and TADF-based OLEDs

Abstract

In the search of universal host materials for organic light emitting diodes a new series of bipolar host materials containing methoxy-substituted carbazoles as the electron-donating and dibenzofuran as an electron-accepting units were designed and synthesized. Different linking topologies and number of methoxy groups attached to carbazolyl moiety were used to understand the impact of the strength of the donor moiety on the thermal, optical, photophysical, electrochemical and electroluminescent properties. The synthesized compounds exhibited relatively high thermal stability with 5% weight loss temperatures exceeding 378°C and formed molecular glasses with high glass-transition temperatures ranging from 120 to 148°C. High triplet energy values of 2.86-2.96 eV were estimated for dilute THF solutions at 77K. Hole and electron drift mobilities estimated using time-of-flight technique in solid layers approached 10 −4 cm 2 V −1 s −1 at high electric fields exceeding 3.6 × 10 5 V cm −1 . The synthesized methoxy-carbazole based compounds were tested as hosts in electrophosphorescent and TADF organic light-emitting diodes reaching luminance of 53000 cd m −2 and external quantum efficiency of 12.5%, in the best case.

Beyond Woodward–Fieser Rules: Design Principles of Property-Oriented Chromophores Based on Explainable Deep Learning Optical Spectroscopy

“…The molecule shown in Figure 5e is originally developed as a host molecule for the TADF OLEDs exhibiting a small PLQY (Φ = 0.17) and fluorescing at 404 nm in tetrahydrofuran. 44 The PLQY of the molecule in toluene is predicted to be Φ = 0.35. As the average attribution of diethylamine groups is more positive for the PLQY than that of methoxy groups, the PLQY of the molecule can be improved by substituting methoxy groups with diethylamine groups.…”

“…The molecule shown in Figure e is originally developed as a host molecule for the TADF OLEDs exhibiting a small PLQY (Φ = 0.17) and fluorescing at 404 nm in tetrahydrofuran . The PLQY of the molecule in toluene is predicted to be Φ = 0.35.…”

Derivatives of Imidazole and Carbazole as Bifunctional Materials for Organic Light-Emitting Diodes

“…Consequently, these compounds can form a hybridized local charge transfer state (HLCT) [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ] that can be exploited for practical electroluminescent applications, including blue-emitting OLEDs. Recently, there has been a great deal of interest in the use of HLCT compounds including imidazole derivatives [ 34 , 38 ] as hosts in systems utilizing prompt fluorescent [ 34 ], TADF [ 39 ], phosphorescent [ 38 , 39 ] and HLCT [ 40 ] emitters. Such an approach results in triplet harvesting via host similarly to the principle of hyperfluorescence involving TADF host matrices [ 41 , 42 ].…”

Aryl-substituted acridanes as hosts for TADF-based OLEDs

“…Conventional hosts such as 1,3-bis(N-carbazolyl)benzene (mCP) and bis [2-(diphenylphosphino)phenyl] ether oxide (DPEPO), are generally used as hosts in blue phosphorescent OLEDs, are also widely applied in TADF-based OLEDs so far [20,21]. Although these hosts demonstrate relatively good results, it can be presumed that the further improvement of the performance of TADF-based OLEDs is possible, if some drawbacks of widely used hosts such as unipolar charge transport or uncomplimentary energy levels are overcome [22][23][24][25][26]. The only hole or electron-transporting property of hosts leads to charge recombination near the interface between the charge-transporting layer and the emissive layer, thus decreasing the device's efficiency [27].…”