Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated.Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtos...

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Hydrogen Bonding in the Electronic Excited State

Bioactive species, including reactive oxygen species (ROS, including O2˙-, H2O2, HOCl, 1O2, ˙OH, HOBr, etc.), reactive nitrogen species (RNS, including ONOO-, NO, NO2, HNO, etc.), reactive sulfur species (RSS, including GSH, Hcy, Cys, H2S, H2S n , SO2 derivatives, etc.), ATP, HCHO, CO and so on, are a highly important category of molecules in living cells. The dynamic fluctuations of these molecules in subcellular microenvironments determine cellular homeostasis, signal conduction, immunity and metabolism. However, their abnormal expressions can cause disorders which are associated with diverse major diseases. Monitoring bioactive molecules in subcellular structures is therefore critical for bioanalysis and related drug discovery. With the emergence of organelle-targeted fluorescent probes, significant progress has been made in subcellular imaging. Among the developed subcellular localization fluorescent tools, ROS, RNS and RSS (RONSS) probes are highly attractive, owing to their potential for revealing the physiological and pathological functions of these highly reactive, interactive and interconvertible molecules during diverse biological events, which are rather significant for advancing our understanding of different life phenomena and exploring new technologies for life regulation. This review mainly illustrates the design principles, detection mechanisms, current challenges, and potential future directions of organelle-targeted fluorescent probes toward RONSS.

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Fluorescent probes for organelle-targeted bioactive species imaging

In this tutorial review, we will explore recent advances in the construction and application of Forster resonance energy transfer (FRET)-based small-molecule fluorescent probes. The advantages of FRET-based fluorescent probes include: a large Stokes shift, ratiometric sensing and dual/multi-analyte responsive systems. We discuss the underlying energy donor–acceptor dye combinations and emphasise their applications for the detection or imaging of cations, anions, small neutral molecules, biomacromolecules, cellular microenvionments and dual/multi-analyte responsive systems.

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Förster resonance energy transfer (FRET)-based small-molecule sensors and imaging agents.

Fluorescence imaging is a powerful approach for noninvasive and real-time visualization and tracking of biomolecules and biological processes in living systems. The fluorescent chemosensors with dual/triple interplaying sensing mechanisms tend to provide diverse fluorescence signals or amplify the response signals, which are propitious to simultaneously track multiple analytes or to improve the selectivity and sensitivity of the chemosensors. Thus, the development of dual/triple sensing mechanism-based chemosensors has attracted great interest recently. This review highlights the representative cases of the fluorescent chemosensors with dual/triple interplaying sensing mechanisms published since 2010, and these chemosensors are classified according to the types of the interplaying sensing mechanisms, including ICT-FRET, PET-FRET, PET-ICT-ESIPT, etc.

Fluorescent chemosensors manipulated by dual/triple interplaying sensing mechanisms

The sensing of hydrogen sulfide (H2S) has become a long-time challenging task. In this work, we developed a general strategy for sensing of H2S utilizing postsynthetic modification of a nano metal–organic frameworks (MOF) UiO-66-(COOH)2 with Eu3+ and Cu2+ ions. The nano MOF Eu3+/Cu2+@UiO-66-(COOH)2 displays the characteristic Eu3+ sharp emissions and the broad ligand-centered (LC) emission simultaneously. Because H2S can strongly increase the fluorescence of Eu3+ and quench the broad LC emission through its superior affinity for Cu2+ ions, the MOF Eu3+/Cu2+@UiO-66-(COOH)2 exhibits highly sensitive turn-on sensing of H2S over other environmentally and biologically relevant species under physiological conditions. Furthermore, this approach for fluorescent turn-on sensing of H2S is expected to extend to other water-stable MOFs containing uncoordinated −COOH.

Xin Wang

Papers

A mitochondria-targeted fluorescent probe for ratiometric detection of endogenous sulfur dioxide derivatives in cancer cells