Organometallic color chemistry: studies on [FcCHCHC5H4NCH2C6H4(tBu)]X (X=BPh4−, ClO4−)

The title dyes, [FcCHCHC5H4NCH2C6H4(tBu)]X (X=BPh4−, ClO4−), developed for rapid screening of catalysts, are intensely colored, but bleach on exposure to visible light in solution. Detailed study shows that on irradiation these alkene dyes first undergo a trans–cis isomerization, then give an irreversible bleaching via decomposition. Both dyes show color dependence on the nature of the anion as a result of ion-pairing, which affects the intensity and position of the visible absorption. NMR, MS and EPR data are also reported.