(E)-2-[4-(Dimethyl-amino)styr-yl]-1-methyl-quinolinium 4-methyl-benzene-sulfonate monohydrate.

In the title compound, C(20)H(21)N(2) (+)·C(7)H(7)O(3)S(-)·H(2)O, the cation is essentially planar, as indicated by the dihedral angle of 2.79 (13)° between the quinolinium and the dimethylaminophenyl rings, and exists in the E configuration. The π-conjugated planes of the cation and the anion are inclined to each other at a dihedral angle of 66.95 (12)°. The cation is linked to the anion through C-H⋯O hydrogen bonds and the anion is further linked with the water mol-ecule by O-H⋯O hydrogen bonds, forming a three-mol-ecule unit. These units are arranged in a face-to-face manner into a ribbon-like structure along the b axis. The ribbons are stacked along the c axis. The crystal structure is further stabilized by C-H⋯π inter-actions involving the dimethyl-amino-phenyl and methyl-phenyl rings. A π-π inter-action with a centroid-centroid distance of 3.6074 (19) Å is also observed.