Facile Generation of Thermally Activated Delayed Fluorescence and Fabrication of Highly Efficient Non‐Doped OLEDs Based on Triazine Derivatives

Abstract

As eries of donor-acceptor-donor triazine-based molecules with thermally activated delayedf luorescence (TADF) properties were synthesized to obtain highly efficient blue-emitting OLEDs with non-doped emitting layers (EMLs). The targeted molecules use at riazinec ore as the electron acceptor,a nd ab enzene ring as the conjugated linker with different electrond onors to alternate the energy level of the HOMO to further tune the emission color.T he introduction of long alkyl chains on the triazine core inhibits the unwanted intermolecular D-D/A-A-type p-p interactions, resulting in the intermolecularD -A charget ransfer.T he weak aggregation-causedq uenching (ACQ) effectc aused by the sup-pressed intermolecular D-D/A-A-type p-p interaction further enhancest he emission.T he crowded molecular structure allows the electrond onor and acceptort ob en early orthogonal, thereby reducing the energy gap between triplet and singlet excited states (DE ST ). As ar esult, blue-emitting devices with TH-2DMAC and TH-2DPAC non-doped EMLs showed satisfactory efficiencies of 12.8 %a nd 15.8 %, respectively,w hichi so ne of the highest external quantum efficiency (EQEs) reported for blue TADF emitters( l peak < 475 nm), demonstratingt hat our tailored molecular designsare promising strategies to endow OLEDs with excellent electroluminescent performances.

Dicyano-Imidazole-Based Host Materials Possessing a Balanced Bipolar Nature To Realize Efficient OLEDs with Extremely High Luminance

“…1.0 × 10 4 M –1 cm –1 ) and similar spectral characteristics and negligible solvent effects, which can be attributed to the spin-allowed acceptor-centered π → π* electronic transition of the dicyano-imidazole unit. The relatively low-intensity broadband at 290–350 nm can be presumably assigned to the combination of π → π* and n → π* electronic transitions of carbazole and intramolecular CT (ICT) from the carbazole fragment to the dicyano-imidazole moiety. − Compared to imM- o -Cz and imM- m -Cz , the conjugate system is more continuous because of the better planarity of the structure of imM- p -Cz , thus showing a higher intensity of ICT absorption. In addition, the corresponding optical energy band gaps evaluated using the absorption onset for imM- o -Cz , imM- m -Cz , and imM- p -Cz were 3.59, 3.54, and 3.40 eV, respectively.…”

Modulating the Electron‐Donating Ability of Acridine Donor Units for Orange–Red Thermally Activated Delayed Fluorescence Emitters

“…reported a blue TADF emitter, 9,9‐diphenyl‐10‐[4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)phenyl]‐9,10‐dihydroacridine (TH‐2DPAC), with DPAc as the donor unit. A nondoped blue OLED device with this emitter achieved a maximum EQE of 15.8 % [25] . Ge et al.…”

Recent progress in thermally activated delayed fluorescence emitters for nondoped organic light-emitting diodes

“…Moreover, it functions as a highly efficient host for green and yellow TADF OLEDs. Kippelen et al 120 further modified the molecule by introducing two tBu-substituted OXD moieties (134). Due to effectively restricted exciton quenching derived from the steric tBu group, 134 pristine neat film exhibits a high PLQY of 0.71.…”

“…Chang et al 134 modified the TRZ unit with a long alkyl chain to inhibit unwanted intermolecular D–D/A–A-type π–π interactions and accordingly designed two D–A-type TADF emitters 155 and 156. Owing to the nature of the electron-donating ability of the alkyl chain, the LUMO of the modified TRZ unit can be slightly weakened, generating blueshifted emission.…”