Solid-state luminescence of tetraphenylpyrene derivatives: mechano/vapochromic luminescence of 1,3,6,8-tetra(4′-carboxyphenyl) pyrene

The effect of mechanical stress on the solid-state luminescence of 3, a carboxylic acid derivative of 1,3,6,8-tetraphenylpyrene (TPPy), is studied. Grinding the powdery solid of 3 in a mortar results in a blue shift of luminescence (from yellow to green) instead of the red shift observed for amide (1) and ester (2) derivatives of TPPy. The initial yellow luminescence is recovered by exposure to solvent vapour. In contrast, application of compressive stress using an oil press causes practically no change of the initial yellow luminescence of 3. The yellow luminescence is ascribed to the dimeric form of 3, while the green luminescence is ascribed to the monomeric state. The macroscale shear stress applied by grinding induces the dimer-to-monomer transition at the molecular level, which causes the blue shift of the luminescence. Based on the results, the mechanisms of macroscale compressive and shear stresses to induce alteration of nanoscale molecular packing and luminescent properties are discussed.