Coordination chemistry-assembled multicomponent systems built from a gable-like bis-porphyrin: Synthesis and photophysical properties

Abstract

Multiporphyrinic assemblies were quantitatively formed, in one step, from a gable-like zinc(II) bis-porphyrin ZnP2 and free-base porphyrins bearing pyridyl groups. The different fragments are held together by axial 4′-N(pyridyl)-Zn interactions. Formation of a macrocycle ZnP 2•(4′-cisDPyP) and a bis-macrocycle (ZnP2) 2•(TPyP) is discussed. The macrocycle and the bis-macrocycle were crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity between the various components. Spectrophotometric and spectrofluorimetric titrations and studies reveal high association constants for both multiporphyrinic assemblies due to the almost perfect geometrical match between the interacting units. As expected, energy transfer from the zinc porphyrin component to the free-base porphyrin quenches the fluorescence of the zinc porphyrin components in both compounds. But while in ZnP 2•(4′-cis DPyP) sensitization of the emission of the free-base porphyrin was observed, in (ZnP2)2•(TPyP) excitation of the peripheral Zn porphyrin units does not lead to quantitative sensitization of the luminescence of the free-base porphyrin acceptor. An unusual HOMO-HOMO electron transfer reaction from ZnP2 to the excited TPyP unit was detected and studied. Various noncovalent multiporphyrinic assemblies could be built from a gable-like bis-Zn porphyrin. Both energy and electron transfer processes have been characterized in these assemblies. In the three-component system, unusual electron transfer from a Zn porphyrin to a free-base porphyrin was evidenced. © 2013 The American Society of Photobiology.