Cyclic dimer of a fused porphyrin zinc complex as a novel host with two -electronically coupled binding sites

Upon complexation with 4,4-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two -electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1:1 and 1:2 inclusion complexes.