Vapor- and Mechanical-Grinding-Triggered Color and Luminescence Switches for Bis(sigma-fluorophenylacetylide) Platinum(II) Complexes

Square-planar bis(sigma-fluorophenylacetylide) platinum(11) complexes [Pt(Me3Si CbpyC C-SiMe3)-(C CC6H4F)(2)] (C CC6H4F-2 for 2, C CC6H4F-3 for 3, and C CC6H4F-4 for 4; Me3SiC CbpyC CSiMe3=5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine) were prepared and were characterized by spectroscopic and luminescence studies, and X-ray crystallography. The color and luminescence of crystalline complex 3 is specifically sensitive to CHCl3 vapor to afford 140-180 nm of luminescence vapochromic redshift, which is useful for specific detection of CHCl3 vapor. Complex 4 displays selective luminescence vapochromic properties to CH2Cl2 and CHCl3 vapors with a luminescence vapochromic shift response of ca. 150-200 nm. Interestingly, complexes 2-4 exhibit reversible, and naked-eye perceivable, mechanical stimuli-responsive color and luminescence changes. When solid species 2-4 are crushed gently or ground, the crystalline state is converted to an amorphous phase. Meanwhile, bright yellow-orange luminescence in the crystalline species is converted to dark red under UV light irradiation with 100-160 nm of mechanochromic shift response. A vapochromic or mechanochromic cycle was monitored by dynamic variations in emission spectra and X-ray diffraction (XRD) patterns. The halohydrocarbon vapor- or mechanical-grinding-triggered color and luminescence switches are most likely correlated to a shorted intermolecular Pt-Pt distance as that revealed in vapochromic species 4.0.5 CH2Cl2 by X-ray crystallography, thus leading to an increased contribution from intermolecular Pt-Pt interaction as demonstrated by DTF computational studies.