Structurally simple thienodipyrandione-containing reversible fluorescent switching piezo- and acido-chromic materials

We report here the structure-property correlations of a series of anthracene/pyrene derivatives grafted on a rigid, planar, and well conjugated endo-cyclic alkenyl lactone (thienodipyrandione) that exhibited aggregation induced emission. Unlike typical vinylene based solid-state fluorescence materials, rigid thienodipyrandione moieties can bestow a higher order of conformational twist as well as enhanced intermolecular interactions by C-H center dot center dot center dot O interactions due to the presence of a carbonyl group that leads to enhanced thermal stability. Compounds TDAn and TDAnPh exhibit distinct piezofluorochromic properties in which emission colors can be switched by grinding and heating. Based on a variety of spectroscopic techniques including XRD, DSC, and NMR, the observed piezochromic emission is attributed to the result of phase transition from structural crystalline (order) to amorphous (disorder) state or vice versa. Most uniquely, one of the anthracene derivatives, TDAn, displayed specific acido-fluorochromism whereas the other congener, TDAnPh, did not, even though they are structurally very similar. Crystal structure analysis revealed that a combination of various secondary interactions such as C-H center dot center dot center dot O, pi-pi and C-H center dot center dot center dot pi interactions all play key roles in the supramolecular assemblies to display such distinctive features. The current study has disclosed a class of new stimuli-responsive materials with great potential in applications for micro-environmental sensing, optical switching and recording.