Chemically Induced Breathing of Flexible Porphyrinic Covalent Cages

The synthesis of two flexible bis-porphyrin cages 3 and 4, incorporating respectively Zn­(II) porphyrins and free-base porphyrins, is reported. In both cages, the four covalent linkers that bind the two porphyrins are functionalized with two 1,2,3-triazolyl ligands. These cages were characterized by NMR and HRMS, and for cage 3 incorporating 1,4-diazabicyclo[2.2.2]­octane (DABCO), an X-ray crystallographic structure was obtained. Chemically induced conformational changes are studied and compared to those of two related cages with longer flexible linkers. Binding of four silver­(I) ions to the peripheral ligands opens the flattened structures in solution and locks the two porphyrins in a face-to-face disposition. Addition of an excess of acid fully expands the cages due to electrostatic repulsion between the positively charged sites. These two reversible processes allow for a chemically induced breathing of the flexible structures.