Antisolvent-mediated modulation of π-π stacking enables fluorescence switching in anthracene-based crystal polymorphs.

Tuning the antisolvent ratio in a binary solvent system programs the stacking motif of a chloroanthracene (pClBA) into two distinct polymorphs. The thermodynamically stable form exhibits face-to-face π-π stacking, weak emission, and [4+4] photocycloaddition, whereas the kinetically trapped form adopts slipped stacking with bright fluorescence and remains inert upon light irradiation.