First N‑Borylated Emitters Displaying Highly Efficient Thermally Activated Delayed Fluorescence and High-Performance OLEDs

Despite
the fast boom of thermally activated delayed fluorescence (TADF) emitters
bearing borane-based acceptor, so far, no TADF emitter with a direct
B–N linkage between N-donor and boryl acceptor has been reported.
The latter should simplify the molecular architecture and hence facilitate
the synthetic design and versatility. We report here the preparation
and characterization of a new series of N-borylated compounds with
functional acridine donor unit; namely: ACBM, PACBM, and SACBM. Spectroscopic
studies were performed to explore their photophysical properties that
exhibited prominent solvatochromism and thermally activated delayed
fluorescence. The time-dependent DFT calculation indicated the involvement
of substantial intramolecular charge transfer character for which
HOMO and LUMO are spatially separated. For compound SACBM, fabrication
of green emitting OLED gave CIE chromaticity of (0.22, 0.59) and maximum
external quantum efficiency, luminance efficiency and power efficiency
of 19.1%, 60.9 cd/A, and 43.6 lm/W, respectively, demonstrating for
the first time the highly efficient OLEDs using N-borylated TADF emitters.