Exploration of electronically interactive cyclic porphyrin arrays

We have explored a variety of covalently and non-covalently assembled cyclic porphyrin arrays mainly as biomimetic models of light harvesting antenna in photosynthetic systems. The key reaction is Ag(I)-promoted coupling reaction of 5,15-diaryl zinc(II) porphyrin that provides a meso–meso linked diporphyrin. An advantage of this coupling reaction is its extremely easy extension to higher porphyrin arrays, since longer porphyrin arrays have practically the same reactivity as that of the monomer. On the basis of this strategy, we have prepared cyclic porphyrin arrays including directly meso–meso linked porphyrin rings CZ4–CZ8, large porphyrin wheels C12ZA and C24ZB, and three-dimensional porphyrin boxes D1–D3. Efficient excitation energy transfer along these cyclic porphyrin arrays has been revealed by the time-resolved transient absorption and fluorescence measurements.