Enhancement of host-guest interactions using rationally designed macrocyclic boronic esters with a naphthalene core.

Efficient inclusion of electron-deficient aromatic guest molecules in an organic solvent utilizing π-stacking interactions was achieved by using two kinds of macrocyclic boronic esters, 1,4-naph-[2+2] and 1,5-naph-[2+2], which were easily prepared by self-assembly of 1,4-naphthalenediboronic acid (3) or 1,5-naphthalenediboronic acid (4) and racemic tetrol 1 with an indacene framework in a protic solvent. The X-ray crystallographic analyses revealed that the tilt angles of the two naphthalene rings are different: that of 1,4-naph-[2+2] is about 15° and that of 1,5-naph-[2+2] is about 0°. Owing to the parallel alignment of two aromatic rings, 1,5-naph-[2+2] has a much higher binding ability than 1,4-naph-[2+2]. This knowledge could be useful for the design of the new host molecules in organic solvents.