Vapochromic and Mechanochromic Phosphorescence Materials Based on a Platinum(II) Complex with 4-Trifluoromethylphenylacetylide

Planar platinum­(II) complex Pt­(Me3SiCCbpyCCSiMe3)­(CCC6H4CF3-4)2 (6) with 5,5′-bis­(trimethylsilylethynyl)-2,2′-bipyridine
and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence
vapochromic and mechanochromic properties and a thermo-triggered luminescence
change. Solid-state 6 is selectively sensitive to vapors
of oxygen-containing volatile compounds such as tetrahydrofuran (THF),
dioxane, and tetrahydropyrane (THP) with phosphorescence vapochromic
response red shifts from 561
and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm (THP), respectively.
Upon being mechanically ground, desolvated 6, 6·CH2Cl2, and 6·1/2CH2ClCH2Cl exhibit significant
mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while
vapochromic crystalline species 6·THF, 6·dioxane, or 6·THP affords a mechanoluminescence
blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to
645 nm, respectively. When the compounds are heated, a thermo-triggered
luminescence change occurs, in which bright yellow luminescence at
561 and 608 nm turns to red luminescence at 667 nm with a drastic
red shift. The multi-stimulus-responsive luminescence switches have
been monitored by the changes in emission spectra and X-ray diffraction
patterns. Both X-ray crystallographic and density functional theory
studies suggest that the variation in the intermolecular Pt–Pt
interaction is the key factor in inducing an intriguing luminescence
switch.