Effects of a semiflexible linker on the mechanochromic photoluminescence of bis(Pt-salen) complex

We report the crystal structures and the photophysical properties of a dinuclear Pt complex (Pt2L2) with bis(salen) and 2-methylenepropane-1,3-diyl as the ligand and linker, respectively; the mononuclear analogue (PtL1) and the corresponding Ni and Pd complexes were also examined. Solution-state measurements indicate that the two salen units in the dinuclear complexes are nearly independent and the linker exerts only a minimal influence. Solid-state ultraviolet–visible spectra of the Pt complexes show a weak absorption band at 520 nm, which is absent in the solution-state spectra. From crystal structure analysis and polarization spectra, the weak band is attributed to the stacked molecular structure of the complex. In response to mechanical stimuli, Pt2L2 microcrystals and smeared thin films show photoemission of various colors (mechanochromic photoluminescence), whereas PtL1 does not show any substantial emission. We attribute the changes in emission color to the semiflexible linker, which contributes to the fragility of molecular packing in the crystals under shear stress.

We report the preparation of bis(Pt-salen) complex with a semiflexible isobutenylene linker. Under shear stress, the photoluminescence emission of the crushed complex crystals changed from yellow to orange. The linker could effectively collapse the molecular arrangement responsible for the characteristic intraligand and metal-to-ligand charge transfer emission from the complex.Figure optionsDownload as PowerPoint slide