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.
Three 2,6‐diphenylpyridine‐3,5‐dicarbonitrile‐based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (3LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light‐emitting diodes based on them exhibit a record‐high external quantum efficiency of 39.8% without any optical extraction technique.
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 blueish-green TADF dopants, 35CzBPym, 35tCzBPym, 25CzBPym, and 25tCzBPym, containing benzoyl pyrimidine (BPym) as the acceptor and carbazoles (Czs) as the donors were designed, synthesized, and investigated. The as-prepared 35CzBPym and 25CzBPym isomers showed star and Y-shaped configurations as confirmed by a single-crystal X-ray diffractometer. Interestingly, Y-shaped emitters exhibit high photoluminescence quantum yields (PLQYs) (76-88%) together with small Δ
E
ST
(45-90 meV) values, leading to very efficient TADF. The strong intramolecular interactions between the nearby pyrimidine and carbazole planes and hydrogen bonds are crucial for enhancing molecular rigidity resulting in the high PLQY. Thus, an electroluminescent device based on 25tCzBPym shows bluish-green emission (500 nm) with a maximum EQE of 23.3% and a low-efficiency roll-off at high luminance of 1000 cd m
−2
(28%). Moreover, the present molecular design exhibits combined effects of intramolecular charge transfer, donor-acceptor interactions, and hydrogen bonding within the molecular structures, supported by the DFT calculations and single-crystal analyses.
Two pairs of constitutional isomeric TADF dopants (35CzBPym and 25CzBPym; 35tCzBPym and 25tCzBPym) containing benzoyl pyrimidine (BPym) as an acceptor and carbazoles (Czs) as donors were designed for high-efficiency OLEDs.
We report three yellow-green to yellow TADF dopants
26DAcBPy
,
25DAcBPy
and
26DPXZBPy
containing dibenzoyl pyridine as the acceptor and dimethylacridine (Ac) and phenoxazine (PXZ) as the donors with ...short delayed fluorescence lifetimes of 2.3 μs, 1.9 μs, and 1.0 μs, respectively. The crystal structures show that
26DAcBPy
and
26DPXZBPy
have a U shape conformation and
25DAcBPy
a linear chain structure. All three molecules show intramolecular hydrogen bonding between the pyridine nitrogen and the
o
-hydrogen of a phenyl ring. These conformations appear to be the result of hydrogen bonding, which leads to rigid structures and provides higher photoluminescence quantum yield. Lastly, these molecules show large dihedral angles between the donor group and the spacer phenyl unit leading to a well-separated HOMO and LUMO and small Δ
E
ST
values. Combined with the small Δ
E
ST
values, and good photoluminescence (PL) quantum yields, the
26DAcBPy
-based devices show a maximum efficiency of 23.1% with a mild efficiency roll-off.
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.
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.
