Light‐Switchable Metal Complexes: Introducing Photoresponsive Behaviour Through Azoheteroarenes

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.

Incorporating Photoresponses into Porous Liquids

“…MLCT bands are typically broad and intense, therefore charge transfer events often outcompete direct photoconversion, preventing switching to the metastable state. [34] Strategies to avoid MLCT include selection of metal ions less prone to charge transfer, and separation of the metal from the electron acceptor. For example, in the case of azoarenes, coordination at a remote position relative to the azo bond.…”

“…For example, in the case of azoarenes, coordination at a remote position relative to the azo bond. [34] Once a photoswitch has been selected, there are several methods that allow photoresponsive molecules to be incorporated into porous materials (Figure 4). [35] The first involves the addition of a photoresponsive guest molecule (Figure 4i).…”

Multiple control of azoquinoline based molecular photoswitches

“…1–4 In particular, the change in the molecular shape of azobenzene upon photoactivation offers a powerful strategy for manipulating guest recognition, 5–8 molecular machines, 9–12 supramolecular assemblies, 13–16 and nanoparticles. 17–20 Azoheteroarenes obtained by replacing one or both phenyl with a heteroaryl, 21–24 such as pyridine, 25–28 pyrazole, 29–31 imidazole, 32–34 and thiazole, 35–37 are recently generating strong interest. Many research efforts have focused on the extension of new heterocycles and the modulation of their photoswitching properties through substituent effects.…”

Photocontrol of catalysis in CuAAC reactions by air stable Cu(i) complexes of phenylazopyrazole-incorporated ligands

“…1–6 The resultant photoresponsive catalysts reversibly control the steric/electronic environment at the catalytically active center by light, thereby influencing the reactivity and/or selectivity of catalytic reactions. 7–9 Despite significant advancements in organic photoswitchable catalysts, 1–6 designing metal-containing analogues presents unique challenges. 7–18 In such complexes, photoisomerization behavior and stability of the photoswitched states are often suppressed due to metal coordination.…”

“…7–9 Despite significant advancements in organic photoswitchable catalysts, 1–6 designing metal-containing analogues presents unique challenges. 7–18 In such complexes, photoisomerization behavior and stability of the photoswitched states are often suppressed due to metal coordination. 9 In addition, competitive photo-triggered processes such as decoordination of the metal center or energy transfer processes add further complexity.…”