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

Abstract

A new donor–acceptor (D–A) molecule, zinc 5-{N-[4-(1′-benzyl-4,4′-bipyridinium-1-ylmethyl)benzyl]-4-pyridinio}-10,15,20-triphenylporphyrinate tris(hexafluorophosphate) has been synthesized. The diad and its precursors have fully been characterised by ¹H and ¹³C 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 reductions is the benzyl viologen component of the molecule, whilst the third electron reduction process is associated with the porphyrin moiety. The first 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.