Charge transfer spectra and photoreactivity of (E)-1-ferrocenyl-2-(1-methyl-4-pyridiniumyl)ethylene cation

The electronic spectrum of (E)-1-ferrocenyl-2-(1-methyl-4-pyridiniumyl)ethylene (E-fmpe+) cation shows two long-wavelength absorptions near 570 and 370 nm which are assigned to metal-to-ligand charge transfer (MLCT) and intraligand charge transfer (ILCT) transitions, respectively. The complex displays a strong negative solvatochromism. MLCT as well as ILCT excitation leads to a trans/cis isomerization at the olefinic double bond. The complex is photochromic since the photoisomerization is thermally reversed. The ion pair E-fmpe+[Fe(CN)6]4− shows a photoactive outer-sphere charge transfer absorption at λmax=490 nm.