A sterically hindered asymmetric D–A–D′ thermally activated delayed fluorescence emitter for highly efficient non-doped organic light-emitting diodes

Abstract

Thermally activated delayed fluorescence (TADF) materials have opened a new chapter for high-efficiency and low-cost organic light-emitting diodes (OLEDs). Herein, we describe a novel and effective design strategy for TADF emitters which includes introducing a carbazole donor unit at the ortho-position, at which the donor and acceptor groups are spatially in close proximity to guarantee the existence of intramolecular electrostatic attraction and through-space charge transfer, leading to reduced structural vibrations, suppressed non-radiative decay and rapid radiative decay to avoid excited state energy loss.As a result, a green TADF emitter (2Cz-DPS) showing high solid-state photoluminescence quantum efficiency (91.9%) and excellent OLED performance was produced. Theoretical simulations reveal that the non-adiabatic coupling accelerates the reverse intersystem crossing of 2Cz-DPS, resulting in a stateof-the-art non-doped OLED with an extremely high external quantum efficiency of 28.7%. S 1 and T 1 energy difference determined from theoretical simulations. m PL quantum yield measured under vacuum. n Energy gap calculated from the onset of absorption spectra. This journal isView Article Online a Turn-on voltage at a luminance of 1 cd m À2 . b Maximum luminance. c Maximum efficiency. d Efficiency achieved at 300 cd m À2 . e EL peak wavelength. f Full-width-at-half-maximum.This journal is

Structural Design of Blue‐to‐Red Thermally‐Activated Delayed Fluorescence Molecules by Adjusting the Strength between Donor and Acceptor

“…In 2019, Chi's group introduced two kinds of donors to construct a new type of DÀ A-D' type green TADF materials (4Cz-DPS and 2Cz-DPS, Figure 9). [60] By inserting a sulfonyldibenzene acceptor between phenothiazine and carbazole donors, the asymmetric TADF materials exhibits green emissions and excellent PLQYs. The PL of the 4Cz-DPS and 2Cz-DPS films were peaked at 530 and 520 nm, with the PLQYs of 74.7% and 65.3% under atmosphere, while 97.3% and 91.9% under vacuum, respectively.…”

Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

“…Importantly,N B-TAc-TRZ exhibits f of 3.9 10 À3 for S 0 !S 1 excitation, which is % 66 folds higher than that of NB-Ac-TRZ (f = 5.9 10 À5 ), implying that faceto-face alignment of acridan donor and triazine acceptor can result in higher oscillator strength than edge-to-face alignment. This observation can be supported by reduced density gradient (RDG) analysis [62,63] (Figure 5) where NB-TAc-TRZ with face-to-face donor-acceptor alignment shows enhanced cofacial p-p interactions (corresponding to the larger green region in RDG isosurface map (red dashed box) and more spikes in the scatter diagram (red dashed circles)) compared to NB-Ac-TRZ with edge-to-face alignment. On another hand, unlike S 0 !S 1 transitions,N TOsf or S 0 !T 1 transitions Figure 3.…”

Molecular Design of Non‐doped OLEDs Based on a Twisted Heptagonal Acceptor: A Delicate Balance between Rigidity and Rotatability

“…Undoubtedly, it is very challenging to develop fundamental concepts of molecular design for AIDF materials that can be applied to assemble efficient non‐doped OLEDs. Currently, the acceptors for the construction of efficient AIDF materials typically involve one strongly electron‐deficient acyclic fragment such as benzophenone (BP) and diphenylsulfone (DPS) . Their acyclic structure and good rotatability between the phenyl and carbonyl or sulfuryl units are beneficial to induce the AIE effect .…”