Visible light irradiation of the readily available sandwich complex [(C5H5)Fe(C6H6)]BF4 with multidentate salicylate dyes such as Aluminon, Alumocresone, Chrome Azurol S, or Eriochrome Cyanine R produced intesively colored iron(III) complexes. Similar reaction can proceed on paper, cotton, or polyacrylamide hydrogel to give colored pH-sensitive patterns.
![Graphical abstract: Patterning of various materials by the photochemical reaction of [(C5H5)Fe(C6H6)]+ complex with salicylate dyes](http://hg.y866.cn/compound/lib/scimg/usr/1/D0NJ04221H.jpg)
