<p>Thermally activated delayed fluorescence (TADF) has been considered an
important development in organic light-emitting diodes (OLEDs) for
significantly enhancing efficiency of pure organic emitters. However, TADF is
often associated with boarder emission spectra not meeting the requirements of
modern high-performance flat-panel displays. A recent breakthrough in TADF
emitters is the development of multiple resonance (MR) emitters which have a
narrow spectral band width, i.e., good colour purities. However, so far
molecular design for MR emitters is still much restricted and their emission
peaks are covering only in
a
very limited range between ~ 460 to 510 nm. Herein, by exploiting a new
emitting mechanism of densely packed dimer enhanced MR TADF, we demonstrate for
the first time of highly efficient electroluminescence covering the RGB full
colour with narrow spectral widths using pure organic emitters. MR-structured
compounds with symmetry-forbidden n-π* transition for fluorescence are
employed. They form intimate molecular interaction in their dimer states,
leading to substantial changes in the S<sub>1</sub> electronic structure into
π-π* transition and much smaller singlet-triplet energy offset, which can
significantly enhance TADF characteristics. The fluorescence efficiency
increases tremendously to approach unity upon dimer formation. More
importantly, molecular relaxations are strongly restricted in the systems due
to their robust MR typed monomer frameworks as well as their strong dimer
interaction.<a> By applying these MR dimers in OLEDs, highly
efficient narrow emission spectra can be achieved with full-width at half
maximum of 32, 44, and 64 nm for blue, green, and red, respectively.
Particularly, the green OLED realizes a remarkable maximum external quantum efficiency
of 31%. Our strategies not only provide a pathway for realizing narrow emission
covering full RGB emission range via intermolecular emitting systems (dimers,
excimers, exciplexes, etc.</a>) for the first time, but also exploit a new
emitting mechanism leading to state-of-the-art performance among all reported
OLEDs.<b></b></p>
A Di-Carbazole-Based Dye as a Potential Sensitizer for Greenhouse-Integrated Dye-Sensitized Solar Cells
