Achieving Deep-Blue Thermally Activated Delayed Fluorescence in Nondoped Organic Light-Emitting Diodes through a Spiro-Blocking Strategy

A deep-blue thermally
activated delayed fluorescence (TADF) emitter
TXADO-spiro-DMACF has been reported for nondoped organic light-emitting
diodes (OLEDs) by integrating an appropriate blocking unit with the
donor (D)–acceptor (A)–donor (D)-type TADF emitter via
a spiro linkage. Benefiting from the characteristic perpendicular
arrangement, the intermolecular interactions are expected to be weakened
to some degree. As a result, TXADO-spiro-DMACF shows a very small
bathochromic shift of 8 nm associated with a narrowed full width at
half maximum of 54 nm on going from solution to the film. The corresponding
nondoped device successfully achieves a bright deep-blue emission,
revealing Commission Internationale de l’Eclairage coordinates
of (0.16, 0.09) and a peak external quantum efficiency of 5.3% (5.3
cd/A, 5.9 lm/W). The results clearly indicate that spiro-blocking
is a promising strategy to develop deep-blue TADF emitters capable
of nondoped OLEDs.