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 (<b>NT</b>_<b>6mer</b>) formed from π-conjugated <i>m</i>-phenylene–pyrimidinylene alternated macrocycle <b>1</b>_<b>6mer</b> that exhibit size-selective recognition toward a specific aromatic acid. In a series of guest molecules, a size-matched trimesic acid (<b>G3</b>) gives inclusion complexes (<b>NT</b>_<b>6mer</b>⊃<b>G3</b>) 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 (<i>K</i> = 1.499 × 10⁵ M^–1) of <b>NT</b>_<b>6mer</b> with <b>G3</b> suggested that the complex involved triple hydrogen-bonding interactions. The encapsulated guest <b>G3</b> 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, <b>1</b>_<b>6mer</b> could not form self-assembled nanotubes in CHCl₃ or tetrahydrofuran (THF) solution, leading to weak or no size-selective recognizability, respectively