Photochromic Reactions in Coordination Compounds

Photochromic coordination compounds can be broadly divided into two different categories according to the photochromic reaction mechanisms, photo-induced linkage isomerization of the metal-ligand coordination and photochromism of the coordinated organic ligand. Different ambidentate ligands capable of forming different coordination modes with transition metal complexes have been designed to modify and tune the photochromic properties. On the other hand, the design of photochromic coordination compounds built on ligands of different organic photochromic families has received tremendous attention. Through coordination of these ligands into transition metal complexes, it opens up the photochromism from the triplet excited-state due to the strong spin-orbit coupling. By judicious design, efficient photosensitization of the photochromic ligands through intramolecular triplet-triplet energy transfer can be achieved. Moreover, photoswitching of the functional properties of the coordination unit through the photochromic reaction has also been demonstrated. In this chapter, the photochromic properties of these coordination compounds and their potential applications have been described.