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 (H 2TPP) and the cofacial porphyrin dimer with an anthracene spacer [H 4(DPA)] through π-π interaction in benzonitrile (PhCN). Formation of the H 2TPP-BHV 2+ supramolecular complex was probed by UV-vis and fluorescence spectra. The fluorescence of H 2TPP was strongly quenched by electron transfer from the singlet excited state ( 1H 2TPP *) to BHV 2+ in the supramolecular complex. The transient absorption spectrum of the charge-separated (CS) state (H 2TPP •+ and BHV •+) was successfully detected by the laser flash photolysis measurements of the H 2TPP- BHV 2+ 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)-BHV 2+ supramolecular complex was formed with a larger formation constant as compared to the H 2TPP-BHV 2+ supramolecular complex because of the stronger π-π interaction of BHV 2+ with the cofacial porphyrin dimer and the lifetime of the CS state was determined to be 0.59 ms in PhCN at 298 K. © 2012 The Royal Society of Chemistry.