Hiding and revealing information using the mechanochromic system of a 2,5-dicarbazole-substituted terephthalate derivative

Abstract

A 2,5-dicarbazole-substituted terephthalate derivative consisting of two carboxylic acid groups was synthesized in order to investigate the influence of acidic and basic vapours on its mechanofluorochromic (MFC) behavior. UV-vis absorption and emission spectra and quantum chemical calculations indicated a molecular push–pull electronic structure and non-planar geometry, which resulted in molecular marked MFC behavior. Under mechanical force, the white solid became a yellow one and its cyan fluorescence was converted to yellow-green fluorescence. The color and fluorescence of the solid could be recovered by solvent or thermal annealing. Thus, a reversible MFC process was observed. When exposed to NH₃ vapor, both the pristine and ground solids emitted blue fluorescence, and the colors of the fluorescence were restored to the original cyan and yellow-green colors by fuming with HCOOH vapor. Therefore, as a smart and multiple stimuli-responsive material, this molecule could be applied in data protection. Information written by force can be hidden using NH₃ vapor, revealed using HCOOH, and then erased again using thermal annealing.