Inhibition of Ligand Binding Ability of Three Porphyrins by an Organic Effector

A stimulus‐responsive receptor 1 was designed and prepared to control the ligand‐binding ability of three active sites, two zinc tetraphenylporphyrin units (P1) and one zinc diethynyldiphenylporphyrin unit (P2), with one effector molecule 2 . Bulky hexarylbenzene units were incorporated as shielding panels in the middle of the flexible side arms of 1 . Spectroscopic titrations indicated that a stable supramolecular complex 1 ⋅ 2 ( K 1 ⋅ 2 =6.7×10 6   m −1 ) was produced by the cooperative formation of multiple hydrogen and coordination bonds. As a result, the binding of a ligand to P1 was inhibited by 2 in a competitive manner. Additionally, the formation of 1 ⋅ 2 brought about conformational restriction of the side arms to cover both faces of P2 with the shielding panels. The binding constant of 4‐phenylpyridine with P2 in 1 ⋅ 2 decreased to 8.9 % of that in 1 . Namely, the ligand‐binding ability of P2 was inhibited according to an allosteric mechanism.