Derivatives of 2-Pyridone Exhibiting Hot-Exciton TADF for Sky-Blue and White OLEDs

Abstract

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.

Converting Conventional Host to TADF Sensitizer and Hot‐Exciton Emitter in Donor‐Adamantane‐Acceptor Triads for Blue OLEDs: A Computational Study

“…These materials utilize reverse intersystem crossing from higher triplet (T 2 , T n ) to singlet states, effectively harnessing non-radiative triplet excitons. [8] Later, Adachi et al introduced the fourth-generation hyperfluorescence approach to improve color purity and material stability in TADF emitters. By embedding a TADF sensitizer with a fluorescent emitter into a wide energy gap host matrix, excitons transfer between them, resulting in enhanced efficiency and overcoming emission broadening and stability issues in third-generation TADF emitters (refer to Figure 1, which illustrates the energy transfer mechanism occurring in hyperfluorescent OLEDs and hot-exciton emitters.).…”

Hybridized local and charge transfer dendrimers with near-unity exciton utilization for enabling high-efficiency solution-processed hyperfluorescent OLEDs

“…However, most of them failed to obtain high exciton utilization efficiency (>80%). 23,24 This is attributed to the competitive process between hRISC and internal conversion (IC). Furthermore, it is quite difficult to block the IC process from the T n to T 1 states, 25,26 leading to the non-radiative triplet excitons.…”

Modular Approach to Highly Substituted 3-Methylpyridones

“…Pyridone moiety is prevalent in a large range of natural products, pharmaceuticals and organic materials . Methyl groups are well understood to play a critical role in pharmaceutical molecules, especially those bearing heterocyclic cores .…”