We prepared an orthogonal compact electron‐donor (phenoxazine, PXZ)‐acceptor (naphthalimide, NI) dyad (NI‐PXZ), to study the photophysics of the thermally‐activated delayed fluorescence (TADF), which has a luminescence lifetime of 16.4 ns (99.2 %)/17.0 μs (0.80 %). A weak charge transfer (CT) absorption band was observed for the dyad, indicating non‐negligible electronic coupling between the donor and acceptor at the ground state. Femtosecond transient absorption spectroscopy shows a fast charge separation (CS) (ca. 2.02∼2.72 ps), the majority of the singlet CS state is short‐lived, especially in polar solvents (τCR = 10.3 ps in acetonitrile, vs. 1.83 ns in toluene, 7.81 ns in n‐hexane). Nanosecond transient absorption spectroscopy detects a long‐lived transient species in n‐hexane, which is with a mixed triplet local excited state (3LE) and charge separated state (3CS), the lifetime is 15.4 μs. In polar solvents, such as tetrahydrofuran and acetonitrile, a neat 3CS state was observed, whose lifetimes are 226 ns and 142 ns, respectively. Time‐resolved electron paramagnetic resonance (TREPR) spectra indicate the existence of strongly spin exchanged 3LE/3CT states, with the effective zero field splitting (ZFS) |D| and |E| parameters of 1484 MHz and 109 MHz, respectively, much smaller than that of the native 3NI state (2475 and 135 MHz). It is rare but solid experimental evidence that a closely‐lying 3LE state is crucial for occurrence of TADF and this 3LE state is an essential intermediate state to facilitate reverse intersystem crossing in TADF systems.

Multiple-resonance (MR) thermal activated delayed fluorescence (TADF) emitters have attracted increasing attention in organic electroluminescence devices, owing to their superior quantum efficiency and narrowband emission for high color purity. However, MR-TADF materials often suffer from severe aggregation-caused quenching (ACQ) and efficiency roll-off problems due to their rigid planar structures and the lack of sufficient charge-transfer (CT) characters with inefficient reverse intersystem crossing (RISC). Herein, by attaching electron-rich triphenylamine (TPA) with twisted spatial conformation to the MR framework, two efficient narrowband MR-TADF emitters, namely BNCz-pTPA and BNCz-mTPA, are developed. The TPA substituent endows the new emitters with aggregation-induced emission enhancement (AIEE) for ACQ suppression. The unprecedented AIEE-MR-TADF emitters exhibit CT character in high-lying triplet excited states for faster RISC, while the locally-excited (LE) character of the first singlet excited state is retained for narrowband emission with high emission efficiency. An organic light-emitting diode (OLED) based on BNCz-pTPA exhibits a maximum external quantum efficiency of 27.3%with slow efficiency roll-off, demonstrating much higher performances than those of the BNCz-based OLED. This study may provide a simple but effective approach to constructing high-performance emitters for wide-colorgamut OLED displays.

Three novel tetraphenylethylene derivatives with different lengths of alkoxy chains, named TPEO1-PPI, TPEO4-PPI and TPEO6-PPI, are synthesized and fully characterized.

The development of anticancer therapy is significant to human health but remains a huge challenge. Photodynamic therapy (PDT), inducing the synergistic mitochondrial dysfunction in cancer cells is a promising approach but suffer from the low efficiency in hypoxic microenvironment and deep-seated tumors. Herein, to improve the outcomes of PDT for cancer treatment, a series of red fluorophores consisting of dual-cationic triphenylphosphoniumalkylated pyridinium and (substituted) triphenylamine are prepared as organelle-targeting antitumor photosensitizers (PSs) with aggregation-induced emission characteristics. These PSs can selectively accumulate at the mitochondria or lysosomes of cancer cells with both dark-and photo-cytotoxicity, making them possess excellent killing effect on cancer cells and efficient inhibition of tumor growth in living mice. This study brings about new insight into the development of powerful cancer treatment.

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Narrowband emitting fluorophores exhibit immense potentials for organic light-emitting diodes (OLEDs) with high color purity. However, it's still hard to simultaneously realize short-wavelength ultraviolet (UV) or near ultraviolet emission (NUV) while maintaining a narrowed full width at half maximum (FWHM) value, and rare work focus on such challenging pursuit. Herein, an ingenious synthetic method was devised to achieve emitters with coplanar structure. 11-(4,6-diphenyl-1,3,5-triazin-2-yl)indolo[3,2,1-jk]carbazole (ICZ-TAZ) was designed to realize narrowed UV emission both in photoluminescence (PL) and electroluminescence (EL) which benefited from the suppression of vibronic coupling. UV/NUV OLEDs based on ICZ-TAZ achieve external quantum efficiency (EQE) maximums of 3.26 % peaks @ 388 nm and 4.02 % peaks @ 406 nm with small FWHM of 32 nm and 46 nm, respectively, corresponding with reduced efficiency rolloff at luminance of 100 cd m À 2 .

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