Deep-Blue Oxadiazole-Containing Thermally Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes

Abstract

A series of four novel deep-blue to sky-blue thermally activated delayed fluorescence (TADF) emitters (2CzdOXDMe, 2CzdOXD4MeOPh, 2CzdOXDPh, and 2CzdOXD4CFPh) have been synthesized and characterized. These oxadiazole-based emitters demonstrated bluer emission compared with the reference emitter 2CzPN thanks to the weaker acceptor strength of the oxadiazole moieties. The oxadiazole compounds doped in hosts (mCP and PPT) emitted from 435 to 474 nm with photoluminescence quantum yields ranging from 14-55%. The emitters possess singlet-triplet excited-state energy gaps (Δ E) between 0.25 and 0.46 eV resulting in delayed components ranging from 4.8 to 25.8 ms. The OLED device with 2CzdOXD4CFPh shows a maximum external quantum efficiency of 11.2% with a sky-blue emission at CIE of (0.17, 0.25), while the device with 2CzdOXD4MeOPh shows a maximum external quantum efficiency of 6.6% with a deep-blue emission at CIE of (0.15, 0.11).

Enhanced thermally activated delayed fluorescence through bridge modification in sulfone-based emitters employed in deep blue organic light-emitting diodes

“…Please do not adjust margins Please do not adjust margins significantly improved compared to our recently reported oxadiazole-based blue OLEDs (EQEmax = 4.7%; CIEx,y = 0.15, 0.12). 22 Devices A, B and C show maximum current and power efficiencies of 6.5, 17.1, 1.4 cd A -1 , and 5.9, 15.3, 1.1 lm W -1 , respectively. The use of pDTCz-2DPyS as the dopant resulted in a ca.…”

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

“…[52] Based on the 2CzPN scaffold, Zysman-Colman's group had successfully developed a range of deep blue TADF materials (2CzdOXDMe, 2CzdOXDPh, 2CzdOXD4CF3Ph and 2CzdOXD4MeOPh) by substituting the cyano acceptors with 1,3,4-oxadiazole (Figure 7). [53] The main reason is that the electron absorption ability of oxadiazole is weaker than that of the cyano group, which leads to the shift of electron density of LUMO towards the benzene bridge direction, giving rise to ΔE ST similar to 2CzPN. The change of acceptor has a little effect on the HOMO for these oxadiazole derivatives, therefore the TADF characteristics of the solid-state emitter have been maintained.…”

Acceptor Derivatization of the 4CzIPN TADF System: Color Tuning and Introduction of Functional Groups

“…Some molecular orbitals are formed partially delocalized over several carbazole moieties (HOMO, HOMO‐1, HOMO‐2, etc.). As reported by the Zysman‐Colman group, oxadiazoles are known to be weaker acceptor groups than nitriles . The oxadiazoles are expected to destabilize the LUMO, increasing its energy and the optical band gap.…”

“…reported a two‐step protocol, to replace the nitriles by oxadiazoles in 1,2‐bis(carbazol‐9‐yl)‐4,5‐dicyanobenzene (2CzPN) for deep‐blue emitters. These emitters exhibited emission maxima at 474 nm and 446 nm and maximum external quantum efficiencies (EQE) of 11.2 % and 6.6 %, respectively . Most recently, the Zysman‐Colman group expanded this concept to derivatives of another isomer of 2CzPN …”