Exposure of the ground form to hexane vapors reverted to the original compound. The powder Xray diffraction (PXRD) of the as-prepared compound exhibits reflection peaks indicating its crystalline nature while the ground form did show any significant reflection peaks, pointing to its amorphous state (Figure ). Thus, the change in luminescence upon grinding is due to a crystalline to amorphous transition. The high-contrast mechanochromism was exploited in an invisible ink application where filter paper was coated with tBuCz-PA and only where pressure was applied does the text "TADF" appear upon excitation with a UV torch, as shown in Figure .