High‐Performance Dibenzoheteraborin‐Based Thermally Activated Delayed Fluorescence Emitters: Molecular Architectonics for Concurrently Achieving Narrowband Emission and Efficient Triplet–Singlet Spin Conversion

Abstract

Thermally activated delayed fluorescence (TADF) materials, which enable the full harvesting of singlet and triplet excited states for light emission, are expected as the third-generation emitters for organic light-emitting diodes (OLEDs), superseding the conventional fluorescence and phosphorescence materials. High photoluminescence quantum yield (Φ PL ), narrow-band emission (or high color purity), and short delayed fluorescence lifetime are all strongly desired for practical applications. However, to date, no rational design strategy of TADF emitters is established to fulfill these requirements.Here, an epoch-making design strategy is proposed for producing high-performance TADF emitters that concurrently exhibiting high Φ PL values close to 100%, narrow emission bandwidths, and short emission lifetimes of ≈1 µs, with a fast reverse intersystem crossing rate of over 10 6 s −1 . A new family of TADF emitters based on dibenzoheteraborins is introduced, which enable both doped and non-doped TADF-OLEDs to achieve markedly high external electroluminescence quantum efficiencies, exceeding 20%, and negligible efficiency roll-offs at a practical high luminance. Systematic photophysical and theoretical investigations and device evaluations for these dibenzoheteraborin-based TADF emitters are reported here.

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

“…Finally, D-π-A triarylboranes with small singlet-triplet gaps are already proving useful in thermally activated delayed fluorescence (TADF) based materials. [42,[86][87][88][89][90][91][92][93][94][95][96][97][98] The use of trifluoromethylated aryl groups in three coordinate boron compounds for optical applications provides a very efficient tool to fine tune properties. Consequently, it is of the utmost importance to understand the electronic properties of these systems in detail.…”

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

“…Taking the phenothiaborin unit for example, Yasuda et al. recently discovered that the boron‐sulfur (BS) unit can largely enhance SOC (Figure ), despite that sulfur atom is normally considered not to be a heavy atom . The delayed fluorescence lifetime is therein reduced to a significant amount of merely 1 μs , which is among the shortest lifetimes in TADF species.…”

“…Ta king the phenothiaborin unit for example, Yasuda et al recently discovered thatt he boron-sulfur (BS) unit can largely enhance SOC (Figure 11), despite that sulfur atom is normally considered not to be ah eavy atom. [58] The delayedf luorescence lifetime is therein reduced to as ignificant amount of merely 1 ms,w hich is among the shortest lifetimes in TADF species. Both doped and non-doped OLEDs with these BS-containing TADF materials achievedh igh maximum EQE of 25.3 %w ith very small efficiency roll-off at al uminance of 100 cd m À2 and 1000cdm À2 .T his work provides an interesting strategy of introducing non-conventional "heavya toms" and enhanced SOC.…”

High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

“…E g calculated from the absorption onset is ≈2.9 eV for both 2PhCz2CzBn and 2tCz2CzBn. [35][36][37][38] In addition, the PL spectra of two emitters in solvents with various polarities reveal a significant bathochromic shift with the broadening in spectral shape ( Figure S10, Supporting Information), indicating the presence of strong solvatochromic effect for both 2PhCz2CzBn and 2tCz2CzBn. Particularly, both the emitters show narrowband blue emission with a FWHM of 64 nm.…”