A series of half-sandwich type ruthenium(II) complexes, [(η⁶-mesitylene)Ru(NHC-L)Cl]PF₆ (NHC = N-heterocyclic carbene, L = azole and imine ligand), containing the dithienylethene moiety has been synthesized and characterized by ¹H NMR, X-ray crystallography and electronic absorption spectroscopy. These complexes show photochromic properties upon UV photo-irradiation to generate the closed forms of the dithienylethene moiety.