New Molecular Design Concurrently Providing Superior Pure Blue, Thermally Activated Delayed Fluorescence and Optical Out-Coupling Efficiencies

Simultaneous enhancement
of out-coupling efficiency, internal quantum
efficiency, and color purity in thermally activated delayed fluorescence
(TADF) emitters is highly desired for the practical application of
these materials. We designed and synthesized two isomeric TADF emitters,
2DPyM-mDTC and 3DPyM-pDTC, based
on di­(pyridinyl)­methanone (DPyM) cores as the new electron-accepting
units and di­(tert-butyl)­carbazole (DTC) as
the electron-donating units. 3DPyM-pDTC, which is
structurally nearly planar with a very small ΔEST, shows higher color purity, horizontal ratio, and quantum
yield than 2DPyM-mDTC, which has a more flexible
structure. An electro­luminescence device based on 3DPyM-pDTC as the dopant emitter can reach an extremely high external
quantum efficiency of 31.9% with a pure blue emission. This work also
demonstrates a way to design materials with a high portion of horizontal
molecular orientation to realize a highly efficient pure-blue device
based on TADF emitters.