No abstract

As one of the most attractive purely organic luminescent materials, thermally activated delayed fluorescence (TADF) luminophores have drawn wide attention in the last decade. The long‐lived delayed fluorescence resulting from the reverse intersystem crossing from excited triplet state (T1) to excited singlet state (S1) in the TADF luminophores gives rise to long lifetimes ranging from nanoseconds to milliseconds, which offers a new strategy for time‐resolved luminescence imaging (TRLI) and sensing. However, the sensitivity of the T1 state in TADF luminophores to triplet oxygen remains a significant challenge for their application. This progress report summarizes the recent developments of efficient purely organic TADF luminophores and novel aggregation‐induced delayed fluorescence (AIDF) luminophores for TRLI and sensing in vitro and in vivo. The molecular design strategies, photophysical properties of the luminophores, and their application in specific imaging and sensing within the time domain are presented. Newly emerged organic materials with AIDF behavior open a new door for developing long‐lived emitters for high signal‐to‐noise ratio (SNR) imaging and sensing in the oxygenic atmosphere.

During the last few years, organoboron‐based thermally activated delayed fluorescence (TADF) materials have received extensive attention in optoelectronic area, owing to the unique electronegativity of boron atom. Herein, many research progress of organoboron‐based TADF materials for organic optoelectronic devices is summarized. This review comprehensively documents the organoboron‐based TADF materials according to the emission colors from blue to red‐near‐infrared (red‐NIR), covering the molecular design strategies, photophysical properties, and optoelectronic performance in organic light‐emitting diodes (OLEDs). The current progress and future challenges in this fast‐growing fields are reviewed systematically, providing instructive guidance for the future research on high‐performance TADF‐OLEDs.

The blue multi‐resonance thermally activated delayed fluorescence materials, simultaneously realizing narrow full‐width at half‐maximum, high external quantum efficiency (EQE), and low efficiency roll‐off, remains a formidable challenge. Herein, three novel emitters, namely PTZBN1, PTZBN2, and PTZBN3, are designed by gradual peripheral modification in boron/nitrogen (B/N) embedded polycyclic skeleton, which exhibit progressively hypsochromic‐shifted emission from 490 nm (PTZBN1) to 468 nm (PTZBN3) with photoluminescence quantum yields up to 98%. In particular, the incorporation of sulfone unit in the boron/nitrogen (B/N) embedded polycyclic skeleton provides a simple but effective tactic for narrowband blue emission. The organic light‐emitting diodes based on PTZBN2 achieve one of the‐state‐of‐the‐art EQEs of 34.8% with electroluminescence (EL) peak at 478 nm. Impressively, PTZBN3‐based device exhibits not only a high maximum EQE of 32.0% with EL peak at 468 nm, but also low efficiency roll‐off.

Scheme 1. Molecular design strategy for narrowband emission circularly polarized thermally activated delayed fluorescence (CP-TADF) emitters.

Thermally activated delayed fluorescence (TADF) conjugated polymers usually show broad emission spectra due to the large structure relaxation, which is not desirable for high‐quality organic light‐emitting diode (OLED) displays. Herein, through attaching multiple resonance (MR) induced emitting moiety as pendant onto the polycarbazole backbone, TADF conjugated polymers with narrowband emission are demonstrated. The obtained conjugated polymers exhibit typical TADF characteristics with narrowband emission with full‐width at half‐maximums (FWHMs) of 33–43 nm. The solution‐processed devices employing these polymers as emissive layers realize excellent performances with maximum external quantum efficiency (EQE) of 17.5 %, emission peak at 496 nm and FWHM of 34 nm.

AIE-active chiral polymer enantiomers (S-/R-P) can emit green circularly polarized electroluminescence (CP-EL) with gEL up to 0.024 without alignment layers and chiral dopants, which represents the first example of CP-OLEDs based on AIE-active main-chain chiral polymers.

Developing organic thermally activated delayed fluorescence (TADF) emitters with high efficiency and narrowband emissions is crucial and challenging for high-quality organic light-emitting diodes (OLEDs). Here, three multiresonance TADF emitters DPACzBN1, DPACzBN2, and DPACzBN3 are designed via a peripheral decoration strategy and synthesized through a lithium intermediate cascade borylation reaction (15% yield for DPACzBN1) or a more efficient lithium-free direct borylation reaction (45% yield for DPACzBN2 and 75% yield for DPACzBN3). All the emitters exhibit a similar blue emission with small full-width at half maximum (fwhm) values as low as 20 nm in toluene solutions. The introduction of the diphenylamino moiety into the parent molecule DPACzBN1 can not only maintain the high photoluminescence quantum yields over 90% but also narrow the bandwidth and enhance the rate constant of the reverse intersystem crossing process, as well as suppress the spectral broadening in devices. Benefiting from the excellent TADF properties and good inhibition of spectral broadening, TADF OLEDs based on DPACzBN3 achieve the highest maximum external quantum efficiency of 27.7% and the smallest fwhm of 24 nm among the three emitters.