Molecular Recognition Properties of Biphen[4]arene

Abstract Biphen[ n ]arenes ( n =3, 4) are a new family of macrocyclic hosts. Here, we describe the molecular recognition behavior of hydroxylated biphen[4]arene (OHBP4) for the first time. A series of cationic guests with different sizes and shapes, including quaternary ammonium salts ( 1⋅ PF 6 and 2⋅ PF 6 ), pyridinium‐based guests ( 3⋅ 2 PF 6 – 6⋅ 2 PF 6 ), and cobaltocenium hexafluorophosphate ( 7⋅ PF 6 ), were chosen as model guest molecules. OHBP4 exhibits good selectivity towards the 2,7‐dibutyldiazapyrenium bis(hexafluorophosphate) ( 4⋅ 2 PF 6 ) axle to form a [2]pseudorotaxane‐type complex. In contrast, hydroxylated biphen[3]arene (OHBP3) cannot bind with this big guest. In addition, OHBP4 strongly interacts with adamantane derivative 2⋅ PF 6 and cobaltocenium 7⋅ PF 6 , which have tridimensional shape and relatively large size. The association constant of the 7 + ⊂OHBP4 complex in 1:1 (v/v) [D 6 ]acetone/CD 2 Cl 2 solution is up to 3100±300 m −1 .