Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 9, Issue 23, Pages 5879-5887Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200304795
Keywords
antenna systems; energy transfer; macrocycles; porphyrinoids; self-assembly
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The bis-porphyrin system ZnP2, in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)15,20-diphenylporphyrin (4'-cisDPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP2(4'-cisDPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6 x 10(8) M-1 was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match between the two interacting units. The macrocycle was crystallized and studied by X-ray diffraction, which confirmed the excellent complementarity of the two components. Photoinduced energy transfer from the singlet excited state of the zinc porphyrin chromophores to the free-base porphyrin occurs with an efficiency of 98% (k(en) = 2 x 10(10)s(-1) in toluene, ambient temperature) with a mechanism consistent with a dipole-dipole process with a low orientation factor.
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