Indazole derivatives are currently drawing more and more attention in medicinal chemistry as kinase inhibitors. 1H-indazole-3-carboxaldehydes are key intermediates to access to a variety of polyfunctionalized 3-substituted indazoles. We report here a general access to this motif, based on the nitrosation of indoles in a slightly acidic environment. These very mild conditions allow the conversion of both electron-rich and electron-deficient indoles into 1H-indazole-3-carboxaldehydes.

Cell Imaging Platforms (CIPs) are research infrastructures offering support to a number of scientific projects including the choice of adapted fluorescent probes for live cell imaging. What to detect in what type of sample and for how long is a major issue with fluorescent probes and, for this, the “hat-trick” “Probe–Sample–Instrument” (PSI) has to be considered. We propose here to deal with key points usually discussed in CIPs including the properties of fluorescent organic probes, the modality of cell labeling, and the best equipment to obtain appropriate spectral, spatial, and temporal resolution. New strategies in organic synthesis and click chemistry for accessing probes with enhanced photophysical characteristics and targeting abilities will also be addressed. Finally, methods for image processing will be described to optimize exploitation of fluorescence signals.

We report the preparation of gold nanoclusters (AuNCs) as a delivery vehicle for the clinically approved photodynamic and chemotherapeutic agents Protoporphyrin IX (PpIX) and doxorubicin (DOX), respectively, and their effect on tumor cells. DOX was attached to the gold nanoclusters through a singlet oxygen-cleavable linker and was therefore released after PpIX irradiation with red light, contributing, synergistically with singlet oxygen, to induce cell death. The doubly functionalized AuNCs proved more effective than a combination of individually functionalized AuNCs. Unlike free DOX, the photoactive nanosystem was non-toxic in the absence of light, which paves the way to introduce a spatiotemporal control of the anticancer therapy and could contribute to reducing the undesirable side effects of DOX.

Photoactive transition‐metal complexes are luminophores combining high photostability and long luminescence lifetimes. However, reduced optical performance in aqueous solutions has limited their use in biological systems. Herein, the physicochemical and photophysical properties and bioimaging compatibility of Re diimine complexes and near‐infrared (NIR) emitting Cy5 dyes coencapsulated in polymer nanoparticles (NPs) are investigated. By varying the polymers, NPs with sizes from 20 to 70 nm and encapsulating ≤ 40 wt.% of Re complexes, i.e., ≈11 000 Re complexes per NP, are obtained. The photoluminescence (PL) quantum yields of the Re complexes increase eightfold to ≈50% upon encapsulation (vs 6–7% in acetonitrile), resulting in PL brightness up to 10⁸ m⁻¹ cm⁻¹ and PL lifetimes of 3–4 µs. Coencapsulation of Cy5 yields very bright NIR emission upon Re complex excitation. Very close Re‐to‐Cy5 donor–acceptor distances down to ≤2 nm and FRET efficiencies over 90% are confirmed by PL lifetime measurements. The Re‐Cy5 NPs enter mammalian cells for high‐contrast PL imaging in both visible and NIR. This detailed characterization provides a better understanding of the photophysical properties of the transition‐metal‐dye FRET NPs and presents a vital step toward the efficient design of a new class of bright luminescent NP probes.