Azoheteroarenes are an emerging class of photoswitch that offer distinct features such as efficient photoisomerization, variable stability of the photoswitched states, and bidirectional photoswitching. This Review overviews different classes of azoheteroarene-coordinated metal complexes reported in the literature. It also surveys their achievements in optical, magnetic properties, metallo-supramolecular chemistry, and catalysis, as well as the use of light to control them. (Image adapted from: Inorg. Chem. Front. 2022, 9, 2315–2327).

Abstract

Azoheteroarenes are emerging classes of photoswitches with versatile scaffolds that offer distinct features such as efficient photoisomerization, tunable stability of the photoswitched states, and bidirectional photoswitching. Moreover, the heteroatoms of such photoswitches exhibit coordination ability to bind to the metal centers. The resulting azoheteroarene-based metal complexes can be designed and developed to tune various metal-based properties towards intriguing applications such as in optics, magnetic properties, data storage applications, and catalysis. Despite the diverse utility of azopyridines in such contexts, other azoheteroarenes, particularly the state-of-the-art five-membered heterocycle-based photoswitches, remain under-explored. In this Review, we describe the diverse classes of azoheteroarene-coordinated metal complexes reported in the literature and survey their photoswitching behaviour and applications. Furthermore, we identify potential azoheteroarene candidates for building photochrome-coupled metal complexes and supramolecular architectures for maximizing the photo-tuning of metal-related properties.

A photo-induced transformation, specific to the nanometric size and different from the well-documented photo-induced electron transfer in molecules and large size coordination polymers, is evidenced in 5 nm nanocrystals of an alkali cation free CoFe Prussian blue analog by SQUID magnetometry and X-ray absorption spectroscopy.

Abstract

The discovery of a photomagnetic effect in a CoFe Prussian blue analog (PBA) has triggered a growing interest for photo-switchable bimetallic cyanide-bridged systems. Nevertheless, in between cyanide-bridged extended coordination polymers and discrete molecules, the photo-switching phenomena are much less well known in nano-sized materials. A photo-induced transformation, specific to the nanometric size, is evidenced by magnetometry and by X-ray absorption spectroscopy at the Co and Fe K-edges in an alkali cation free Prussian blue analog. The nanoparticles before irradiation can be described as having a core-shell structure, the core being made of the well-known fcc-Co^II(HS)Fe^III structure of CoFe PBAs while the shell contains Co^II ions in octahedral geometry and significantly distorted Fe(CN)₆ entities. Irradiation induces a change of the local structures around the transition metal ions, which remain in the same oxidation state, with different behaviors of the Co and Fe sub-lattices.

The Front Cover shows various luminescent nano-assemblies flying into cells and lighting them for cell imaging. Non-covalent interaction and binding enable the formation of dynamic supramolecular self-assemblies, realizing in situ control of luminescence and loading capacity for diagnosis, drug delivery, and treatment. More information can be found in the Review Article by Xu-Man Chen, Quan Li and co-workers.

Let's see… Recent advances in the development and application of supramolecular luminescent nano-assemblies based on different functional building blocks in cell imaging are reviewed. These supramolecular luminescent nano-assemblies have wide applications in targeted imaging of specific organelles, drug delivery, and therapy.

Abstract

Supramolecular luminescent nano-assemblies for cell imaging have recently attracted increasing interest, not only because of their outstanding photophysical properties, but also because of their easy fabrication through supramolecular strategies, good biocompatibility, high stability to photo- and micro-environments in cells, and facile combination of imaging and synergistic therapy for cancers. Luminescence-based bioimaging has great advantages, such as high sensitivity, being non-invasive, and functioning in real-time, leading to its wide application in many fields, including disease research, drug research, cell markers, gene expression, gene function studies, and protein interaction. In this Review, recent progress in the application of macrocycle-mediated (e.g., cyclodextrins, cucurbiturils, calixarenes, and pillar[n]arenes) and functionalized amphiphilic molecule-based supramolecular luminescent nanoparticles in cell imaging, especially targeted cell imaging of specific organelles, is reviewed. The combination of imaging with drug delivery, gene delivery, and photodynamic therapy is also introduced.