It has long been recognised that coordination compounds have unique optical, electronic and magnetic properties.   Photochromism refers to the reversible colour change of a compound upon irradiation with light.

In their Dalton Transactions Perspective, Shoko Kume and Hiroshi Nishihara from the University of Tokyo review photochromic transition metal complexes and their electronic, steric and metal-metal interactions which lead to these effects.   The authors conclude by looking at the development of new photochromic reactions involving metal-ligand bond rearrangements, with the potential for light-driven molecular machines.

Future work will create new materials with the ability to conduct and respond to electromagnetic fields and light, the authors say.

This Dalton Perspective features on the outside cover of issue 25 which shows how photochromic metal complexes provide new functionalities such as photoelectric conversion or photo-electro coupled memory through interplay of molecular components.