Molecular recognition of viologen by zinc porphyrinic receptors with diarylurea sidearms. Toward construction of a supramolecular electron transfer system

A series of zinc porphyrinic receptors for a viologen substrate (hexyl viologen, HV²⁺) were synthesized, in which varying numbers of diarylurea moieties, from one to four, were appended at the porphyrin's meso positions. The increase in the number of the diarylurea moiety led to the increase in stability of the receptor-HV²⁺ complex, showing that the convergent dipoles set up on the porphyrin platform played an essential role in the complexation. In this system, formation of the stable electron donor-acceptor complex resulted in the effective electron transfer from the singlet excited state of the zinc porphyrin to HV²⁺.