(E)-2-[4-(Dimethylamino)styryl]-1-methylpyridinium 4-methylbenzenesulfonate monohydrateThis paper is dedicated to Her Royal Highness Princess Chulabhorn Walailak of Thailand on the occasion of her 53rd Birthday Anniversary which fell on July 4th, 2010.

The cation of the title compound, C16H19N2+·C7H7O3S−·H2O, exists in the E configuration with respect to the C=C double bond and is essentially planar, the dihedral angle between the pyridinium and benzene rings being 3.55 (13)°. In the crystal, π-conjugated planes of cations and anions are inclined to each other at 84.30 (11)°. The crystal structure is stabilized by O—H...O hydrogen bonds and weak C—H...O interactions, which link the cations, anions and water molecules into chains along the b axis. These chains are stacked along the a axis by π–π interactions with centroid–centroid distances of 3.6032 (16) and 3.6462 (16) Å.