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

Abstract

The development of thermally activated delayed fluorescence (TADF) emitters with orange–red emission still lags behind that of their blue, green, and yellow counterparts. Recent research to address this problem mainly focused on developing new acceptor units. There were few donor units designed especially for orange–red emitters. Herein, with benzothiophene fused to a diphenylacridine donor unit, a new donor moiety, namely, 5,5‐diphenyl‐5,13‐dihydrobenzo[4,5]thieno[3,2‐c]acridine (BTDPAc), was designed and synthesized. Benefiting from the strong electron‐donating ability of the new donor moiety, a new TADF emitter, 2‐[4′‐(tert‐butyl)(1,1′‐biphenyl)‐4‐yl]‐6‐[5,5‐diphenylbenzo[4,5]thieno[3,2‐c]acridin‐13(5H)‐yl]‐1H‐benzo[de]isoquinoline‐1,3(2H)‐dione (BTDPAc‐PhNAI), shows an orange–red emission with a maximum at 610 nm in dilute toluene solution. Also, with the help of the diphenyl rings of the donor unit, high photoluminescence quantum yields were achieved for BTDPAc‐PhNAI over a wide concentration range. Consequently, an orange–red organic light‐emitting diode based on BTDPAc‐PhNAI achieved a high external quantum efficiency of nearly 20 %, which was comparable to state‐of‐the‐art device performances with similar emission spectra.

High‐Performance Orange–Red Organic Light‐Emitting Diodes with External Quantum Efficiencies Reaching 33.5% based on Carbonyl‐Containing Delayed Fluorescence Molecules

“…[ 13 , 14 , 15 , 16 ] In contrast, the device efficiencies of orange‐to‐red TADF materials with EL peaks over 560 nm remain far behind. [ 17 , 18 , 19 , 20 , 21 ] In order to realize efficient long‐wavelength EL emissions, strengthening intramolecular charge transfer (ICT) effect in a highly twisted D‐A framework is widely used in the design of TADF materials. [ 22 , 23 , 24 , 25 ] But according to the Franck–Condon transition principle, [ 26 ] the separation of HOMOs and LUMOs as well as strong ICT effect often leads to low radiative decay rate and weak oscillator strength, thereby resulting in decreased photoluminescence (PL) quantum yields ( Φ PL s).…”

On the Road Toward More Efficient Biocompatible Two‐Photon Excitable Fluorophores

“…Recently, phenoxazine, acridane, phenazasiline and phenothiazine have been used as very efficient donor cores in material chemistry. [22][23][24][25][26] However, these cores have never been extensively studied for their nonlinear properties and we decided to explore their potential to be used as donor cores for twophoton absorption (Figure 1).…”

“…In this work, we proposed to study a new family of quadrupolar dyes by enriching previous cores, to increase their two‐photon absorption properties. Recently, phenoxazine, acridane, phenazasiline and phenothiazine have been used as very efficient donor cores in material chemistry [22–26] . However, these cores have never been extensively studied for their nonlinear properties and we decided to explore their potential to be used as donor cores for two‐photon absorption (Figure 1).…”

1,4-Bis(trifluoromethyl)benzene as a new acceptor for the design and synthesis of emitters exhibiting efficient thermally activated delayed fluorescence and electroluminescence: experimental and computational guidance

“…As a result, different combinations of donors and acceptors have been explored in the design of TADF emitters. Common donors are carbazole, 5–7 phenoxazine, 8–10 phenothiazine, 11,12 and 9,9-dimethyl-9-10-dihydroacridine, 13–15 while common acceptors are triphenyltriazine, 9,16–18 sulfonyl groups, 19,20 and cyano groups. 21,22 Cyano and sulfonyl groups are strong electron-withdrawing moieties.…”