Abstract Azobenzene-linked, single-chain ammonium amphiphile (C12AzoC5N+Br−), C33H54N3O3Br, was crystallized from their solutions in water and ethanol. The crystals are triclinic with the space group P\bar1, Z=2, a=3.4243(6), b=0.8525(1), c=0.6073(1)nm, α=73.45(1), β=88.03(1), and γ=93.32(1)°. The structure was solved by the direct method and refined anisotropically by the block-diagonal least-squares procedure: R=0.06 for 2917 observed reflections (2θ<105°, Cu Kα, λ=0.154184 nm). The crystal structure consists of regularly stacking bimolecular layers in which C12AzoC5N+Br− molecules incline about 30° to the layer surface. As expected from spectroscopic analyses, the azobenzene chromophore shows a head-to-tail (J-like) aggregation between adjacent molecules. The pronounced planarity of the azobenzene chromophore found in this crystal structure enables parallel stacking of phenyl groups in the J-like aggregation.