PHOTOINDUCED ELECTRON-TRANSFER IN MULTIPORPHYRIN CLUSTERS AND ROTAXANES

A zinc(II) porphyrin and a gold(III) porphyrin dimer bridged by a 2,9-diphenyl-1,10-phenanthroline (dpp) spacer has been synthesized in order to mimic the array of tetrapyrrolic chromophores in the bacterial photosynthetic centres. The electronic properties of the dpp bridge have been tuned by complexation of copper(I) either in a homoleptic, entwined complex, or in a rotaxane complex whose threaded ring is a dpp-containing macrocycle. Photoinduced electron transfer between the zinc porphyrin excited state and the gold porphyrin cation has been studied by laser flash spectroscopy and its rate has been shown to depend on the nature of the bridging species lying in between the metal porphyrins : 55 ps in the dpp-bridged dimer, and 1 ps only in the rotaxane copper(I) complex.