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

A series
of four novel deep-blue to sky-blue thermally activated delayed fluorescence
(TADF) emitters (2CzdOXDMe, 2CzdOXD4MeOPh, 2CzdOXDPh, and 2CzdOXD4CF3Ph) 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 (ΔEST)
between 0.25 and 0.46 eV resulting in delayed components ranging from
4.8 to 25.8 ms. The OLED device with 2CzdOXD4CF3Ph 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).