Multiresonance
thermal activated delayed fluorescence
(MR-TADF)
materials with an efficient spin–flip transition between singlet
and triplet excited states remain demanding. Herein, we report an
MR-TADF compound (BN–Se) simultaneously possessing
efficient (reverse) intersystem crossing (ISC/RISC), fast radiative
decay, close-to-unity quantum yield, and narrowband emission by embedding
a single selenium atom into a common 4,4′-diazaborin framework.
Benefitting from the high RISC efficiency accelerated by the heavy-atom
effect, organic light-emitting diodes (OLEDs) based on BN–Se manifest excellent performance with an external quantum efficiency
of up to 32.6% and an ultralow efficiency roll-off of 1.3% at 1000
cd m–2. Furthermore, the high ISC efficiency and
small inherent energy loss also render BN–Se a
superior photosensitizer to realize the first example of visible (λex > 450 nm)-to-UV (λem < 350 nm) triplet–triplet
annihilation upconversion, with a high efficiency (21.4%) and an extremely
low threshold intensity (1.3 mW cm–2). This work
not only aids in designing advanced pure organic molecules with fast
exciton dynamics but also highlights the value of MR-TADF compounds
beyond OLED applications.
Regulating the structure of p-type organic small molecules to generate thermoelectric composites for achieving a high power factor of 113.2 μW m−1 K−2.
Acridone derivatives with different terminal tertiary amine groups were first developed as good n-type thermoelectric composites, and a high power factor of 289.4 μW m−1 K−2 at 430 K was achieved.
Considering
that the development of p-type single-walled carbon
nanotube (SWCNT)/organic small molecule (OSM)-based thermoelectric
(TE) materials with high performance is lagging behind and only a
few structure–activity relationships of OSMs on SWCNT composites
have been reported, new structures need to be developed for the sake
of stimulating this scientific issue. Taking advantages of porphyrins
(such as their aromatic systems, facile structures, high stability,
and ease of processing), we first synthesized a series of free base
porphyrins with different substituents as potent p-type SWCNT-based
TE composites. Notably, SWCNT/Por-5F with electron-withdrawing groups
exhibits the highest power factor (PF) of 279.3 μW m–1 K–2 at room temperature (two times higher than
that of SWCNT/Por-NH2), which is among the highest values
for SWCNT/OSM-based p-type TE materials reported up to date. The carrier
transport behavior was demonstrated to obey the fluctuation-induced
tunneling (FIT) model in SWCNT/porphyrin composites, and we find that
the differences in log P values of the substituents
in porphyrins might contribute to the dramatic changes in the dispersion
degree of OSMs in SWCNT networks, subsequently affecting the TE properties
of our materials. This work provides a basis for improving the TE
performance of p-type SWCNT/OSM-based TE materials.
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