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 (NT6mer) formed from pi-conjugated m-phenylene pyrimidinylene alternated macrocyde 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 (NT6mer superset of G3) in dichloromethane resulting in an enhanced and red-shifted fluorescence. H-1 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 x 10(5) M-1) of NT6mer 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.