Photoinduced electron transfer in supramolecular complexes of a π-extended viologen with porphyrin monomer and dimer

A pi-extended viologen has been synthesized, forming supramolecular complexes with a freebase tetraphenylporphyrin (H2TPP) and the cofacial porphyrin dimer with an anthracene spacer [H-4(DPA)] through pi-pi interaction in benzonitrile (PhCN). Formation of the H2TPP-BHV2+ supramolecular complex was probed by UV-vis and fluorescence spectra. The fluorescence of H2TPP was strongly quenched by electron transfer from the singlet excited state ((H2TPP)-H-1*) to BHV2+ in the supramolecular complex. The transient absorption spectrum of the charge-separated (CS) state (H2TPP center dot+ and BHV center dot+) was successfully detected by the laser flash photolysis measurements of the H2TPP-BHV2+ supramolecular complex in PhCN. The lifetime of the CS state of the supramolecular complex was determined as 0.37 ms in PhCN at 298 K. The H-4(DPA)-BHV2+ supramolecular complex was formed with a larger formation constant as compared to the H2TPP-BHV2+ supramolecular complex because of the stronger pi-pi interaction of BHV2+ with the cofacial porphyrin dimer and the lifetime of the CS state was determined to be 0.59 ms in PhCN at 298 K.