Size-Selective Recognition by a Tubular Assembly of Phenylene–Pyrimidinylene Alternated Macrocycle through Hydrogen-Bonding Interactions

Study of artificial tubular assemblies as a useful host scaffold for size-selective recognition and release of guest molecules is an important subject in host–guest chemistry. We describe well-defined self-assembled nanotubes (NT 6mer ) formed from π-conjugated m-phenylene–pyrimidinylene alternated macrocycle 1 6mer that exhibit size-selective recognition toward a specific aromatic acid. In a series of guest molecules, a size-matched trimesic acid (G3) gives inclusion complexes (NT 6mer ⊃G3) in dichloromethane resulting in an enhanced and red-shifted fluorescence. 1H nuclear magnetic resonance (NMR) titration experiments indicated that the complex was formed in a 1:1 molar ratio. Density functional theory (DFT) calculations and the binding constant value (K = 1.499 × 105 M–1) of NT 6mer with G3 suggested that the complex involved triple hydrogen-bonding interactions. The encapsulated guest G3 molecules can be readily released from the tubular channel through the dissociation of hydrogen bonding by the addition of a polar solvent such as dimethylsulfoxide (DMSO). In contrast, 1 6mer could not form self-assembled nanotubes in CHCl3 or tetrahydrofuran (THF) solution, leading to weak or no size-selective recognizability, respectively.