Reversible Dual-Stimulus-Responsive Luminescence and Color Switch of a Platinum Complex with 4-[(2-Trimethylsilyl)ethynyl]-2,2′-bipyridine

The square-planar diimine platinum(II) complex Pt(BpyCCSiMe(3))(CCC6H5)(2) (1, BpyCCSiMe(3) = 4-[(2-trimethylsilyl)ethynyl]-2,2-bipyridine) was prepared and characterized. In the solid state, 1 shows unusual reversible thermochromic and mechanochromic properties. When crystalline 12(CHCl3) is heated or ground, the bright yellow emission centered at ca. 544 (576, sh) nm changes to 722 nm, which corresponds to a thermo- and mechanochromic response redshift of ca. 146-178 nm. Once the heated or ground samples were exposed to organic vapors, they reverted to the original crystalline state, and the luminescence changed from red to yellow. The conversion between a triplet metal-to-ligand charge transfer/ligand-to-ligand charge transfer ((MLCT)-M-3/(LLCT)-L-3) emission state and a triplet metal-metal-to-ligand charge transfer ((MMLCT)-M-3) state is the reason for the luminescence change.