Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid‐state lighting and full‐color displays. Here, the design and synthesis of three triarylamine‐pyridine‐carbonitrile‐based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔEST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light‐emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A–1, and a power efficiency of 136.3 ± 2.2 lm W–1. The highest device efficiency of 39.8% appears to be record‐breaking among TADF‐based OLEDs to date. In addition, the TPAmPPC‐based device shows superior operation lifetime and high‐temperature resistance. It is worth noting that the TPA‐PPC‐based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.
Though s-indacene is an intriguing antiaromatic
hydrocarbon of 12 π-electrons, it has been underrepresented
due to the lack of efficient and versatile methods to prepare stable
derivatives. Herein we report a concise and modular synthetic method
for hexaaryl-s-indacene derivatives bearing electron-donating/-accepting
groups at specific positions to furnish C
2h
-, D
2h
-, and C
2v
-symmetric
substitution patterns. We also report the effects of substituents
on their molecular structures, frontier molecular orbital (MO) levels,
and magnetically induced ring current tropicities. Both theoretical
calculations and X-ray structure analyses indicate that the derivatives
of the C
2h
-substitution
pattern adopt different C
2h
structures with significant bond length alternation depending
on the electronic property of the substituents. Due to the nonuniform
distribution of the frontier MOs, their energy levels are selectively
modulated by the electron-donating substituents. This leads to the
inversion of the HOMO and HOMO–1 sequences with respect to
those of the intrinsic s-indacene as theoretically
predicted and experimentally proven by the absorption spectra at visible
and near-infrared regions. The NICS values and the 1H NMR
chemical shifts of the s-indacene derivatives indicate
their weak antiaromaticity. The different tropicities are explained
by the modulation of the HOMO and HOMO–1 levels. In addition,
for the hexaxylyl derivative, weak fluorescence from the S2 excited state was detected due to the large energy gap between the
S1 and S2 states. Notably, an organic field-effect
transistor (OFET) fabricated using the hexaxylyl derivative exhibited
moderate hole carrier mobility, a result which opens the door for
optoelectronic applications of s-indacene derivatives.
The crystal structures show a U shape for 26DAcBPy and 26DPXZBPy and a linear chain conformation for 25DAcBPy; for the first time, we reveal that the conformations are the result of intramolecular hydrogen bonding of these molecules.
Thermally activated delayed fluorescence (TADF) emitters are highly useful to achieve 100% internal quantum efficiency (IQE) and high external quantum efficiency (EQE) by reverse intersystem crossing. Herein, four sky-blue to...
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