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 orde r to mimic the array of tetrapyrrolic chromophores in the bacterial ph otosynthetic centres. The electronic properties of the dpp bridge have been tuned by complexation of copper(I) either in a homoleptic, entwi ned complex, or in a rotaxane complex whose threaded ring is a dpp-con taining macrocycle. Photoinduced electron transfer between the zinc po rphyrin excited state and the gold porphyrin cation has been studied b y laser flash spectroscopy and its rate has been shown to depend on th e 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 coppe r(I) complex.