Acid-base-induced fac → mer isomerization of luminescent iridium(iii) complexes.

Luminescent Ir(C^N) complexes (C^N = cyclometalated arylpyridine ligand) exist in the form of two stable isomers with distinct photophysical and electrochemical properties: and . Herein, we show that -Ir(C^N) complexes can be converted into the thermodynamically less stable forms by a consecutive reaction with first acid and then base. The chemically induced isomerization is fast, quantitative, and stereoselective, and it can be inversed by light. The new isomerization process opens the possibility to use highly luminescent Ir(C^N) complexes as molecular switches.