Synthesis, complexation properties and spectroscopic studies of the cation-induced conformational changes of some new oligooxaethylene-spacered diporphyrin arrays

New linear diporphyrin arrays and a heteroleptic diad have been synthesized in good yield. H-1 NMR, UV-visible and fluorescence studies reveal that th e receptors bind to alkali and alkaline-earth metal ions to give a supramol ecular complex in which the ion is nestled within the oligooxaethylene fram ework. The formation of the host-guest complexes promotes a change in the g eometry of the system toward a topology in which the two tetrapyrrolic macr ocycles tend to face together. This is evidenced by the mutual ring current anisotropy effect exerted by the porphyrinic platforms, and by the blue sh ift and broadening of the relative UV-visible bands (Soret). In particular, the changes observed allow the complexation process to be monitored at ver y low concentrations. The association constants lie within the range 25-1 x 10(5) M-1 (CD3CN-CDCl3 1 : 1) depending on either the nature of the diporp hyrinic receptors or that of the interacting metal ions. The heteroleptic d iad shows a very efficient energy transfer process (>99%) between the two d ifferent macrocycles in a variety of solvents that is not altered by comple xation with metal ions. The systems reported present interesting properties as switchable biomimetics.