Effect of alkyl chain length on the luminescence on-off mechanochromic behavior of solid-state Gold(I) isocyanide complexes

Five phenylethyne(p-alkoxyphenyl isocyanide)gold(I) complexes with different alkyl chains (OR) in the para-position of the phenyl isocyanide have been successfully synthesized [where R = CH3 (5a), C2H3 (5b), C4H9 (5c), C6H13 (5d), and C10H21 (5e)] and structurally characterized by H-1 NMR, C-13 NMR, and HRMS. To our surprise, the as-prepared powders of these complexes exhibited different emission colors. The diversity of their mechanochromic luminescence properties has been investigated with photoluminescence spectroscopy, powder X-ray diffraction (XRD) analysis, and single-crystal XRD analysis. The results indicated the presence of weak intermolecular interactions in their crystal structures, and different alkyl chains had obvious impacts on their stacking arrangements and optical behavior. The luminescence quantum yield of 5c was as high as 49.3% in the solid state. Complexes 5a-5e each showed luminescence quenching after grinding.