Supramolecular Control of the Template‐Induced Selective Photodimerization of 4‐Methyl‐7‐ O ‐hexylcoumarin

A symmetric ditopic molecular receptor ( 3 ), containing two identical hydrogen‐bonding recognition subunits, was designed and synthesized. These subunits are capable of binding substrates with complementary donor and acceptor sites to form a supramolecular complex through hydrogen bonding. Receptor 3 was designed to accept two guest molecules, which are held in close proximity within the supramolecular species. The substrate molecule, 4‐methyl‐7‐ O ‐hexylcoumarin ( 1 c ), forms a 2:1 complex with a binding constant of 150  m −1 for the second substrate, passing first through a 1:1 complex with an affinity constant of 510  m −1 . The orientation of two molecules of 1 c when bound to the template leads to the selective formation of the trans‐syn [2+2] photoproduct 2 cB upon irradiation. Other photoproducts typically produced in the absence of the template are suppressed.