Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show great potentials for high color purity organic light-emitting diodes (OLEDs). However, the simultaneous realization of high photoluminescence quantum yield (PLQY) and high reverse intersystem crossing rate (k RISC ) is still a formidable challenge. Herein, a novel asymmetric MR-TADF emitter (2Cz-PTZ-BN) is designed that fully inherits the high PLQY and large k RISC values of the properly selected parent molecules. The resonating extended π-skeleton with peripheral protection can achieve a high PLQY of 96 % and a fast k RISC of above 1.0 × 10 5 s À 1 , and boost the performance of corresponding pure green devices with an outstanding external quantum efficiency (EQE) of up to 32.8 % without utilizing any sensitizing hosts. Remarkably, the device sufficiently maintains a high EQE exceeding 23 % at a high luminance of 1000 cd m À 2 , representing the highest value for reported green MR-TADF materials at the same luminescence.

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) material, which possesses the ability to achieve narrowband emission in organic light‐emitting diodes (OLEDs), is of significant importance for wide color gamut and high‐resolution display applications. To date, MR‐TADF material with narrow full width at half‐maximum (FWHM) below 0.14 eV still remains a great challenge. Herein, through peripheral protection of MR framework by phenyl derivatives, four efficient narrowband MR‐TADF emitters are successfully designed and synthesized. The introduction of peripheral phenyl‐based moieties via a single bond significantly suppresses the high‐frequency stretching vibrations and reduces the reorganization energies, accordingly deriving the resulting molecules with small FWMH values around 20 nm/0.11 eV and fast radiative decay rates exceeding 108 s−1. The corresponding green OLED based on TPh‐BN realizes excellent performance with the maximum external quantum efficiency (EQE) up to 28.9% without utilizing any sensitizing host and a relatively narrow FWHM of 0.14 eV (28 nm), which is smaller than the reported green MR‐TADF molecules in current literatures. Especially, the devices show significantly reduced efficiency roll‐off and relatively long operational lifetimes among the sensitizer‐free MR‐TADF devices. These results clearly indicate the promise of this design strategy for highly efficient OLEDs with ultra‐high color purity.

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In the last decades, organic light-emitting diodes (OLEDs) have been rapidly developed and occupy an important position in the lighting and display market. Early conventional fluorescent OLEDs materials can only...

As an important class of stimuli‐responsive material, piezochromic organic materials have been widely investigated in recent years. To promote their further applications as pressure sensors, realizing a high sensitivity and big color contrast, especially under high external pressure, is of great importance. Herein, two pure cis/trans isomers, E‐ANTCN and Z‐ANTCN, based on anthracene and cyano substituted double bond are achieved. The molecular structures are determined by nuclear Overhauser effect spectroscopy, correlation spectroscopy, and X‐ray diffraction. At ambient conditions, both of them show typical mechanochromic characteristics under grinding−heating or grinding−fuming treatments. E‐ANTCN displays a sensitivity of 0.83 nm GPa−1 and a color contrast of 5 nm in a high‐pressure experiment, while Z‐ANTCN shows a much enhanced sensitivity of 22.64 nm GPa−1 and bigger color contrast of 110 nm, indicating the potential as a good colorimetric sensor for external pressure. The two cyano groups in the same side of double bond in Z‐ANTCN induce more intense intermolecular interactions with a resultant spatial packing mode being mainly responsive for its good sensing performance. This study fills the gap for a piezochromic property and high‐pressure experiment of E/Z isomers and provides useful information for the investigation of molecular structural changes under isotropic and anisotropic treatments.