Piezoluminescence and Liquid Crystallinity of 4,4′-(9,10-Anthracenediyl)bispyridinium Salts

Piezoluminescence and liquid crystallinity of anthracene-based bispyridinium salts were investigated in stimulus-responsive luminescent organic crystals and luminescent ionic liquid crystals. The salts possess an anthracene moiety as a fluorophore in their center, and the pyridiniums attached to the anthracene moiety are substituted with trialkoxybenzyl groups. Single crystals of the salts bearing two trimethoxybenzyl groups were obtained as solvates. Ethyl acetate, acetone, and dioxane solvates of the chlorides have almost the same crystal structures with one-dimensional channels. Grinding of the solvated crystals caused the extrusion of the included solvent molecules, which resulted in the red shifts of their fluorescence in the solid state. The dimethyl sulfoxide solvate of the hexafluorophosphate also showed piezoluminescene by grinding. Tris­(octyloxy)­benzyl and tris­(dodecyloxy)­benzyl derivatives exhibited rectangular columnar liquid crystals upon being heated for their bromide and tetrafluoroborate salts and upon being cooled for their hexafluorophosphate salts. Of these pyridinium salts, hexafluorophosphates showed characteristic solvent-dependent fluorescence.