First Evidence of a Photoinduced Spin Change in an FeIII Complex Using Visible Light at Room Temperature

An iron(III) complex [Fe(salten)(Mepepy)]BPh4 containing only one photoisomerizable ligand (Mepepy) has been synthesized, it exhibits a thermally-induced spin crossover in the solid state and in solution {H2salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate); Mepepy = 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)ethene}. The photoisomerizations of both the free and coordinated Mepepy ligand have been observed at room temperature with visible-light irradiation and monitored by UV/Vis and 1H NMR spectrometries. trans-to-cis isomerization of only one photosensitive ligand in the iron(III) complex is sufficient to detect a partial spin change of the iron(III) ion. This photoinduced spin change is seen for the first time from a high-spin state to a low-spin state.