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.
Efficient visible-to-ultraviolet (UV) triplet-triplet annihilation upconversion (TTA-UC) with large anti-Stokes shift is highly promising for solar-powered and indoor applications. Nonetheless, the excitation wavelength is confined to the blue region (< 450 nm) mainly due to large energy loss during triplet sensitization, resulting in reduced photon utilization efficiency in practical scenarios. Herein, a series of multiple resonance thermal activated delayed fluorescence (MR-TADF) compounds are developed as purely organic sensitizers for the purpose of energy-loss reduction, which also feature intense absorbance at visible region, high intersystem crossing efficiencies, and long triplet lifetimes. By pairing the MR-TADF sensitizers with appropriate acceptors, green-to-UV TTA-UC systems were realized with anti-Stokes shift up to 1.05 eV, upconversion quantum yield up to 8.6% and threshold excitation intensity as low as 9.2 mW cm -2 in solution. The TTA-UC pairs were applied as internal or external source of UV photons to trigger energy-demanding photopolymerization and photoligation reactions even under excitation of low-power-density green LED light, revealing the broad utility
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.