Hole Localization or Delocalization? An Optical, Raman, and Redox Study of Lanthanide Porphyrin-Phthalocyanine Sandwich-Type Heterocomplexes

Abstract

A systematic electrochemical, redox, optical absorption, and resonance Raman spectroscopic study of 22 gadolinium and cerium double- and triple-decker tetraphenylporphyrin-phthalocyanine (TPP-Pc) complexes is reported. The work is aimed at elucidating the extent of the localization or delocalization among the chromophore ligands in the mixed complexes, where there exists a charge imbalance between the metal centers and the dianion Pc/TPP ligands, as well as in different oxidation states for these types of complexes. For mixed double- and triple-decker complexes, [vert bar]Pc(M)TPP[vert bar] and [vert bar]TPP(M)TPP[vert bar] (where M = Gd[sup III], Ce[sup IV]), in which the metal cannot be oxidized, it appears that the ligand preferentially oxidized is the Pc moiety. This perfentially localized hole in the phthalocyanine results in new near-infrared transitions which show maxima around 1200-1300 nm for the double-decker complexes and shifts to 1800-2300 nm for the triple-decker derivatives. In this case, the removal of an electron from a complex redox orbital which is rich in Pc character is easily identified by the accompanying changes in the optical absorption characteristic of a Pc[sup [sm bullet][minus]] species and is also seen in FT Raman spectra (excited at 1064 nm) by a significant (>15 cm[sup [minus]1]) upshift of a redox-sensitivemore » Raman band at ca. 1500 cm[sup [minus]1]. 33 refs., 13 figs., 2 tabs.« less