Controlling Singlet–Triplet Energy Splitting for Deep‐Blue Thermally Activated Delayed Fluorescence Emitters

Abstract

The development of efficient metal-free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep-blue emission is still challenging. A new family of deep-blue TADF emitters based on a donor-acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep-blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2 % with CIE coordinates of (0.148, 0.098).

Triggering Thermally Activated Delayed Fluorescence by Managing the Heteroatom in Donor Scaffolds: Intriguing Photophysical and Electroluminescence Properties

“…The Fc/Fc + redox couple was used as an internal standard to calibrate the oxidation potentials of the compounds, and the relevant data are listed in Table . In general, the electron‐donor strength of the chromophores can be evaluated based on their oxidation potential . Therefore, to understand the effect of heteroatoms in the donor units based on their donor strength, the oxidation potentials of the donors were recorded.…”

“…Similarly, Adachi et al. reported a series of carbazole donors with methyl substituents on peripheral nuclear positions to develop efficient deep‐blue TADF emitters . They demonstrated that the ionization potentials of the donors have a profound impact on control of the Δ E ST value and TADF mechanism of the materials, which obviously dominated the performance of their devices.…”

“…In this regard, the development of donor–acceptor (DA)‐type bipolar systems with or without π‐conjugation linkers have been demonstrated as the most promising approach to ensure spatially partitioned HOMO and LUMO orbitals on the donor and acceptor units, respectively . It has been demonstrated that the nature of donor and acceptor units plays a vital role in determining the functional properties of the materials . For example, Park et al.…”

“…Therefore, the development of new and efficient donors for TADF emitters is highly desirable. Additionally, several molecular designs have been proposed for tuning the lowest excited singlet (S 1 ) and triplet (T 1 ) states and Δ E ST values of TADF emitters by managing the π linkers, the nature of the donor and acceptor units and their conjugation connectivity, the combination of DA units, the conjugation length, etc . However, systematic studies focused on the effect of the heteroatom in the donor scaffold on excited‐state energy, Δ E ST values, and TADF mechanism of the materials are scarce in the literature .…”

Molecular Engineering of Isomeric Benzofurocarbazole Donors for Photophysical Management of Thermally Activated Delayed Fluorescence Emitters

“…TADF emitters can harvest triplet excitons through an efficient up‐conversion process by reverse intersystem crossing (RISC) from the triplet excited state (T 1 ) to the singlet excited state (S 1 ) . TADF materials should have a sufficiently small energy gap between S 1 and T 1 (Δ E S−T ) for the RISC process, which is achieved by tuning the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) separation …”