Dataset Information

High Triplet Energy Host Materials for Blue TADF OLEDs-A Tool Box Approach.

ABSTRACT: The synthesis of stable blue TADF emitters and the corresponding matrix materials is one of the biggest challenges in the development of novel OLED materials. We present six bipolar host materials based on triazine as an acceptor and two types of donors, namely, carbazole, and acridine. Using a tool box approach, the chemical structure of the materials is changed in a systematic way. Both the carbazole and acridine donor are connected to the triazine acceptor via a para- or a meta-linked phenyl ring or are linked directly to each other. The photophysics of the materials has been investigated in detail by absorption-, fluorescence-, and phosphorescence spectroscopy in solution. In addition, a number of DFT calculations have been made which result in a deeper understanding of the photophysics. The presence of a phenyl bridge between donor and acceptor cores leads to a considerable decrease of the triplet energy due to extension of the overlap electron and hole orbitals over the triazine-phenyl core of the molecule. This decrease is more pronounced for the para-phenylene than for the meta-phenylene linker. Only direct connection of the donor group to the triazine core provides a high energy of the triplet state of 2.97 eV for the carbazole derivative CTRZ and 3.07 eV for the acridine ATRZ. This is a major requirement for the use of the materials as a host for blue TADF emitters.

SUBMITTER: Rodella F

PROVIDER: S-EPMC7403631 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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High Triplet Energy Host Materials for Blue TADF OLEDs-A Tool Box Approach.

Rodella Francesco F Bagnich Sergey S Duda Eimantas E Meier Tobias T Kahle Julian J Athanasopoulos Stavros S Köhler Anna A Strohriegl Peter P

Frontiers in chemistry 20200729

The synthesis of stable blue TADF emitters and the corresponding matrix materials is one of the biggest challenges in the development of novel OLED materials. We present six bipolar host materials based on triazine as an acceptor and two types of donors, namely, carbazole, and acridine. Using a tool box approach, the chemical structure of the materials is changed in a systematic way. Both the carbazole and acridine donor are connected to the triazine acceptor via a para- or a meta-linked phenyl ...[more]

PMID: 32850669

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Project description:Development of emissive materials for utilization in organic light-emitting diodes (OLEDs) remains a highly relevant research field. One of the most important aspects in the development of efficient emitters for OLEDs is the efficiency of triplet-to-singlet exciton conversion. There are many concepts proposed for the transformation of triplet excitons to singlet excitons, among which thermally activated delayed fluorescence (TADF) is the most efficient and widespread. One of the variations of the TADF concept is the hot exciton approach according to which the process of exciton relaxation into the lowest energy electronic state (internal conversion as usual) is slower than intersystem crossing between high-lying singlets and triplets. In this paper, we present the donor-acceptor materials based on 2-pyridone acceptor coupled to the different donor moieties through the phenyl linker demonstrating good performance as components of sky-blue, green-yellow, and white OLEDs. Despite relatively low photoluminescence quantum yields, the compound containing 9,9-dimethyl-9,10-dihydroacridine donor demonstrated very good efficiency in sky-blue OLED with the single emissive layer, which showed an external quantum efficiency (EQE) of 3.7%. It also forms a green-yellow-emitting exciplex with 4,4',4″-tris[phenyl(m-tolyl)amino]triphenylamine. The corresponding OLED showed an EQE of 6.9%. The white OLED combining both exciplex and single emitter layers demonstrated an EQE of 9.8% together with excellent current and power efficiencies of 16.1 cd A-1 and 6.9 lm W-1, respectively. Quantum-chemical calculations together with the analysis of photoluminescence decay curves confirm the ability of all of the studied compounds to exhibit TADF through the hot exciton pathway, but the limiting factor reducing the efficiency of OLEDs is the low photoluminescence quantum yields caused mainly by nonradiative intersystem crossing dominating over the radiative fluorescence pathway.

Dataset Information

High Triplet Energy Host Materials for Blue TADF OLEDs-A Tool Box Approach.

Publications

High Triplet Energy Host Materials for Blue TADF OLEDs-A Tool Box Approach.

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