Reversible Mechanochromic Luminescence at Room Temperature in Cationic Platinum(II) Terpyridyl Complexes

Reversible mechanochromic
luminescence in cationic platinum­(II)
terpyridyl complexes is described. The complexes [Pt­(Nttpy)­Cl]­X2 (Nttpy = 4′-(p-nicotinamide-N-methylphenyl)-2,2′:6′,2″-terpyridine,
X = PF6 (1), SbF6 (2), Cl (3), ClO4 (4), OTf (5), BF4 (6)) exhibit different colors
under ambient light in the solid state, going from red to orange to
yellow. All of these complexes are brightly luminescent at both room
temperature and 77 K. Upon gentle grinding, the yellow complexes (4–6) turn orange and exhibit bright red
luminescence. The red luminescence can be changed back to yellow by
the addition of a few drops of acetonitrile to the sample. Crystallographic
studies of the yellow and red forms of complex 5 suggest
that the mechanochromic response is likely the result of a change
in intermolecular Pt···Pt distances upon grinding.