Synthesis, electrochemistry, and spectroelectrochemistry of a metalloporphyrin-viologen donor-acceptor diad

A new donor-acceptor (D-A) molecule, zinc 5-{N-[4-(1'-benzyl-4,4'-bipyridin ium-1-ylmethyl)benzyl]-4-pyridinio}-10,15,20-triphenylporphyrinate tris(hex afluorophosphate) has been synthesized. The diad and its precursors have fu lly been characterised by H-1 and C-13 NMR spectroscopy, mass spectrometry, UV/Visible spectroscopy and cyclic voltammetry. In situ UV/Visible and EPR measurements show that the site of the first and second electrochemical re ductions is the benzyl viologen component of the molecule, whilst the third electron reduction process is associated with the porphyrin moiety. The fi rst reduction process gave rise to an EPR signal due to the benzyl viologen radical, whilst the second caused the molecule to become diamagnetic. The third of these processes gave rise to a new EPR signal, which was found to correspond to the metalloporphyrin radical.