The molecule is an organic cation that is phenothiazin-5-ium substituted by dimethylamino groups at positions 3 and 7. The chloride salt is the histological dye 'methylene blue'. It is a conjugate acid of a 3,7-bis(dimethylamino)phenothiazine.
[7-(dimethylamino)phenothiazin-3-ylidene]-dimethylazanium