Robust Supramolecular Nano‐Tunnels Built from Molecular Bricks**

Abstract 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 CO 2 ‐adsorption capacity while excluding other gases at ambient temperature, leading to high CO 2 /CH 4 selectivity. Aggregation‐induced emission of the molecules gives the bulk crystals vapochromic properties.