Synthesis and Photochromic Studies of Dithienylethene-Containing Cyclometalated Alkynylplatinum(II) 1,3-Bis(N‑alkylbenzimidazol-2′-yl)benzene Complexes

Several photochromic cyclometalated alkynylplatinum­(II) complexes with tridentate 1,3-bis­(N-alkylbenzimidazol-2′-yl)­benzene (bzimb) ligands have been synthesized by the reaction of the corresponding chloroplatinum­(II) bzimb precursor complexes with the photochromic ligand TMS-CC-Th-DTE in the presence of sodium hydroxide. They have been characterized by ¹H NMR spectroscopy and positive-ion FAB or ESI mass spectrometry and confirmed by elemental analysis. One of the complexes has also been characterized by X-ray crystallography. Their photophysical, photochromic, and electrochemical properties have been studied. Upon photoexcitation, the yellow solutions in benzene display green phosphorescence originating from the triplet intraligand (³IL) excited state. All the cyclometalated alkynylplatinum­(II) bzimb complexes exhibit reversible photochromism with solution colors changing between yellow and purple upon photoirradiation. The thermal bleaching kinetics of complex 2 has been studied in toluene at various temperatures with the activation barrier for the thermal cycloreversion reaction determined.