Chien‐Hong Cheng

A strategy of substituent engineering of DBA-based molecules is investigated via experimental and theoretical methods. A 1 nm-thick emitting layer OLED has been developed.

Three pyridine-carbonitrile (PPC) fluorophores with amine-type donors, carbazole, tert -butylcarbazole, and spiroacridine have been designed and synthesized. A high-performance green OLED based on SAcmPPC dopant exhibited an external quantum efficiency of 37.2%.

Herein, we report the nickel-catalyzed denitrogenative cyclization reaction of 1,2,3,4-benzothiatriazine-1,1-dioxides with arynes to generate the polysubstituted biaryl sultams with tolerance of a wide diversity of substituents on every subunit. The mechanistic study indicates that the reaction is initiated by the formation of a diradical species, which reacts with a nickel complex to form a nickelacycle intermediate and carries out the subsequent cyclization through insertion of an aryne.

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 ΔE_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.

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 ΔE_ST 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.

A unique strategy for the attainment of a discotic nematic (N_D) mesophase is reported consisting of a central benzene core to which are attached two 4-alkylphenyl and two 4-pentylbiphenyl moieties diagonally via alkynyl linkers. The rotational nature and incompatibility of unequal phenylethynyl units led to the disruption of π–π interactions within cores that aids to the realization of N_D phase and favors high solid-state emission. When used in OLEDs, compounds act as an efficient solid-state pure deep-blue emitter with Commission Internationale de L’Eclairage (CIE_x,y) coordinates of (0.16, 0.07).