Robust Supramolecular Nano‐Tunnels Built from Molecular Bricks**

Herein we report a linear ionic molecule that assembles into a supramolecular nano-tunnel structure through synergy of trident-type ionic interactions and π-π stacking interactions. The nano-tunnel crystal exhibits anisotropic guest adsorption behavior. The material shows good thermal stability and undergoes multi-stage single-crystal-to-single-crystal phase transformations to a nonporous structure on heating. The material exhibits a remarkable chemical stability under both acidic and basic conditions, which is rarely observed in supramolecular organic frameworks and is often related to structures with designed hydrogen-bonding interactions. Because of the high polarity of the tunnels, this molecular crystal also shows a large CO₂ -adsorption capacity while excluding other gases at ambient temperature, leading to high CO₂ /CH₄ selectivity. Aggregation-induced emission of the molecules gives the bulk crystals vapochromic properties.