Colorimetric and fluorescent pH and Cu2+ probes induced by photoisomerization of a maleonitrile-based Salen ligand.

Both photo-induced cis-trans-isomers of a maleonitrile-based Salen ligand can be used as pH probes covering a broad pH range through three different mechanisms but upon undergoing the formation of a stable complex and Cu(2+)-promoted hydrolysis, respectively, they exhibit totally different responses and mechanisms for sensing Cu(2+).