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-allcylbenzimidazol-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 equivalent to C-Th-DTE in the presence of sodium hydroxide. They have been characterized by 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 ((IL)-I-3,) 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.