Fluorescent bioprobes are powerful tools for analytical sensing and optical imaging, which allow direct visualization of biological analytes at the molecular level and offer useful insights into complex biological structures and processes. The sensing and imaging sensitivity of a bioprobe is determined by the brightness and contrast of its fluorescence before and after analyte binding. Emission from a fluorophore is often quenched at high concentration or in aggregate state, which is notoriously known as concentration quenching or aggregation-caused quenching (ACQ). The ACQ effect limits the label-to-analyte ratio and forces researchers to use very dilute solutions of fluorophores. It compels many probes to operate in a fluorescence "turn-off" mode with a narrow scope of practical applications. The unique aggregation-induced emission (AIE) process offers a straightforward solution to the ACQ problem. Typical AIE fluorogens are characterized by their propeller-shaped rotorlike structures, which undergo low-frequency torsional motions as isolated molecules and emit very weakly in solutions. Their aggregates show strong fluorescence mainly due to the restriction of their intramolecular rotations in the aggregate state. This fascinating attribute of AIE fluorogens provides a new platform for the development of fluorescence light-up molecules and photostable nanoaggregates for specific analyte detection and imaging. In this Account, we review our recent AIE work to highlight the utility of AIE effect in the development of new fluorescent bioprobes, which allows the use of highly concentrated fluorogens for biosensing and imaging. The simple design and fluorescence turn-on feature of the molecular AIE bioprobes offer direct visualization of specific analytes and biological processes in aqueous media with higher sensitivity and better accuracy than traditional fluorescence turn-off probes. The AIE dot-based bioprobes with different formulations and surface functionalities show advanced features over quantum dots and small molecule dyes, such as large absorptivity, high luminosity, excellent biocompatibility, free of random blinking, and strong photobleaching resistance. These features enable cancer cell detection, long term cell tracing, and tumor imaging in a noninvasive and high contrast manner. Recent research has significantly expanded the scope of biological applications of AIE fluorogens and offers new strategies to fluorescent bioprobe design. We anticipate that future development on AIE bioprobes will combine one- or multiphoton fluorescence with other modalities (e.g., magnetic resonance imaging) or functionalities (e.g. therapy) to fully demonstrate their potential as a new generation of theranostic reagent. In parallel, the advances in molecular biology will provide more specific bioreceptors, which will enable the development of next generation AIE bioprobes with high selectivity and sensitivity for molecular sensing and imaging.

The structural effects of ligands on the emission properties of Pt(ii) complexes and promising applications of luminescent Pt(ii) complexes in various areas are discussed.

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The synthesis, structures and photophysical properties of the charge-neutral Pt(II) complexes (1-6) and their Pd(II) (7) and Ni(II) (8) congeners supported by tetradentate dianionic bis[phenolate-(N-heterocyclic carbene)] ligands are described. The X-ray crystal structures of two solvatomorphs of 2, which has p-F substituents on the tetradentate ligand, have been determined. The photophysical properties of all the complexes were examined. In THF solutions, 1-4 display deep blue phosphorescence (l max ¼ $440-460 nm, F e ¼ 3-18% and s ¼ 0.5-3.5 ms). In solutions at room temperature, 5-8 show profoundly different luminescence properties from being virtually non-emissive (F e < 10 À3 ) for 6-8 to highly emissive (F e ¼ 15%) with much red-shifted phosphorescence (l max ¼ $530 nm) and a long emission lifetime (s ¼ 47.2 ms) in the case of 5. Time-dependent density functional theory (TDDFT) calculations reveal that the tetradentate bis(phenolate-NHC) ligands in 1-4 provide a rigid scaffold for preserving a tightly bound Pt(II) in a square-planar coordination geometry in the T 1 as in the S 0 states and the blue emission is derived from the T 1 state having predominant ligand (p Ar-O )-to-ligand (p* NHC ) charge transfer (LLCT) character. A switch of orbital parentage from LLCT to ligand-centred (LC) p-p* is responsible for the long emission lifetime and vibronically structured emission displayed by 5 when compared to that of 1-4 and 6. Both femtosecond time-resolved fluorescence (fs-TRF) and nanosecond time-resolved emission (ns-TRE) measurements were conducted on 2 and 4 to directly probe the excited-state dynamics after photoexcitation. Excellent thermal stability of the fluorine-free complex 4 and its higher emission quantum yield (relative to 1 and 3), and using 9-(4-tert-butylphenyl)-3,6bis(triphenylsilyl)-9H-carbazole (CzSi) as host material, led to the fabrication of highly efficient deep blue OLEDs with peak current efficiency of 24 cd A À1 and white organic light-emitting devices (WOLEDs) with peak current efficiency of 88 cd A À1 .

Robust charge-neutral Pt(II) complexes containing dianionic tetradentate bis(N-heterocyclic carbene) ligands exhibit intense blue phosphorescence in fluid solutions and in polymer films, and have been vacuum-deposited as a phosphorescent dopant in organic blue-light-emitting diodes.

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The “spontaneous oxidation-reduction reaction” strategy is used to inlay ultrafine Ru nanoparticles (∼1.5–2.0 nm) into a Ni(OH)2 nanoarray on Ni foam for efficient H2 evolution in 1.0 M KOH.

Butterfly‐like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation‐induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV‐type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one‐step catalyst‐free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal–organic frameworks (MOFs) due to their built‐in pyrazine coordination sites. OAP‐based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light‐emitting devices. This work builds on RIV‐type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.