Intramolecular charge transfer (ICT) is a fundamental mechanism that enables the development of numerous fluorophores and probes for bioimaging and sensing. However, the electron-withdrawing targets (EWTs)-induced fluorescence quenching is a long-standing and unsolved issue in ICT fluorophores, and significantly limits the widespread applicability. Here we report a simple and generalizable structural-modification for completely overturning the intramolecular rotation driving energy, and thus fully reversing the ICT fluorophores’ quenching mode into light-up mode. Specifically, the insertion of an indazole unit into ICT scaffold can fully amplify the intramolecular rotation in donor-indazole-π-acceptor fluorophores (fluorescence OFF), whereas efficiently suppressing the rotation in their EWT-substituted system (fluorescence ON). This molecular strategy is generalizable, yielding a palette of chromophores with fluorescence umpolung that spans visible and near-infrared range. This strategy expands the bio-analytical toolboxes and allows exploiting ICT fluorophores for light-up sensing of EWTs including N-acetyltransferases and nerve agents.

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Understanding the mechanisms of aggregation-induced emission (AIE) is essential for the rational design and deployment of AIEgens toward various applications. Such a deep mechanistic understanding demands a thorough investigation of the excited-state behaviors of AIEgens. However, because of considerable complexity and rapid decay, these behaviors are often not experimentally accessible and the mechanistic comprehension of many AIEgens is lacking. Herein, utilizing detailed quantum chemical calculations, we provide insights toward the AIE mechanism of 1-(N,N-dialkylamino)-naphthalene (DAN) derivatives. Our theoretical analysis, corroborated by experimental observations, leads to the discovery that modulating the formation of the twisted intramolecular charge transfer (TICT) state (caused by the rotation of the amino groups) and managing the steric hindrance to minimize solid-state intermolecular interactions provides a plausible explanation for the AIE characteristics of DAN derivatives. These results will inspire the deployment of the TICT mechanism as a useful design strategy toward AIEgen development.

A fluorescent probe (COU-LIP-1) for monitoring labile Fe(II) pools (LIP) with high selectivity and sensitivity was developed utilizing coumarin 343 as the fluorophore and 3-nitrophenylazanyl ester as both the reactive...

Photoacoustic imaging (PAI), a state‐of‐the‐art noninvasive in vivo imaging technique, has been widely used in clinical disease diagnosis. However, the design of high‐performance PAI agents with three key characteristics, i.e., near‐infrared (NIR) absorption (λabs>800 nm), intense PA signals, and excellent photostability, remains a challenging goal. Herein, we present a facile but effective approach for engineering PAI agents by amplifying intramolecular low‐frequency vibrations and enhancing the push‐pull effect. As a demonstration of this blended approach, we constructed a PAI agent (BDP1‐NEt2) based on the boron‐dipyrromethene (BODIPY) scaffold. Compared with indocyanine green (ICG, an FDA‐approved organic dye widely utilized in PAI studies; λabs=788 nm), BDP1‐NEt2 exhibited a UV/Vis‐NIR spectrum peaked at 825 nm, superior in vivo PA signal intensity and outstanding stability to offer improved tumor diagnostics. We believe this work provides a promising strategy to develop the next generation of PAI agents.