Molecular stacking alteration commonly involves the interchanges of H-and J-aggregation (sometimes X-aggregation may be involved). For instance, Peng Chong Xue and co-workers reported that the original crystal of a benzothiazole derivative with phenothiazine moiety (CBVP) displayed yellow emission at 560 nm. After being ground, the emission 596 nm H-aggregates. The original emission could be recovered by fuming, exhibiting a reversible luminescence color change from yellow to orange-red with a spectral shift of 36 nm under mechanical force stimuli (Figure ). UV absorption and single crystal analysis confirmed that the reversible mechanochromism is due to the transition of H-aggregates to Jaggregates after grinding.