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

Abstract

A π-extended viologen has been synthesized, forming supramolecular complexes with a freebase tetraphenylporphyrin (H₂TPP) and the cofacial porphyrin dimer with an anthracene spacer [H₄(DPA)] through π–π 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 (¹H₂TPP^*) to BHV²⁺ in the supramolecular complex. The transient absorption spectrum of the charge-separated (CS) state (H₂TPP^•+ and BHV^•+) 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 H₄(DPA)-BHV²⁺ supramolecular complex was formed with a larger formation constant as compared to the H₂TPP-BHV²⁺ supramolecular complex because of the stronger π–π 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.