First evidence of a photoinduced spin change in an Fe-III complex using visible light at room temperature

An iron(III) complex [Fe(salten)(Mepepy)]BPh4 containing only one photoisom erizable ligand (Mepepy) has been synthesized, it exhibits a thermally-indu ced spin crossover in the solid state and in solution {H(2)salten = 4-azahe ptamethylene-1,7-bis(salicylideneiminate); Mepepy = 1-(pyridin-4-yl)-2-(N-m ethylpyrrol-2-yl)ethene}. The photoisomerizations of both the free and coor dinated Mepepy ligand have been observed at room temperature with visible-l ight irradiation and monitored by UV/Vis and H-1 NMR spectrometries. trans- to-cis isomerization of only one photosensitive Ligand in the iron(III) com plex is sufficient to detect a partial spin change of the iron(III) ion. Th is photoinduced spin change is seen for the first time from a high-spin sta te to a low-spin state.