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.