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.