Mechano-/seeding-triggered crystal-to-crystal phase transition in luminescent switching cocrystals.

Currently, there are only a few cases of both mechanical stimulation-induced and seeding-triggered fluorescence conversion in which the mechanism of phase transition remains less well investigated. Herein, the first report of a luminescent switch based on mechano-/seeding-triggered crystal-crystal phase transition in a cocrystal polymorphic system is present. Based on the structure analysis and theoretical calculations, the luminescent switching can be attributed to the orbital overlap of the chromophores and exciton coupling. Furthermore, a mechanism of the phase transition was proposed, in which the synthons undergo movements including slipping and twisting during the phase transition. The effects of heating, local mechanical stimulus, and seed contact on the transition were discussed. It was proposed that contacting seeds can lower the energy barrier of the phase transition by inducing the formation of intermediate transition states of synthons via molecular recognition. The energy barrier was found to be the key factor in such mechano-/seeding-triggered phase transition. Green-to-orange luminescent switching triggered by mechanical force and seed contacting in a cocrystal polymorphic system is demonstrated. Local seed contacting can arise domino-like phase transition, which may follow a mechanism of synthon transformation and energy barrier decreasing via molecular recognition. [Display omitted] • The first report of mechano-/seed-triggered luminescent switch in cocrystals is present. • Luminescent switch is based on the crystal-crystal transition involving large packing changes. • A mechanism is proposed to interpret the phase transition on both mechanical stimulation and seed contacting. • The work provides a strategy to design new mechanochromic luminescent materials. [ABSTRACT FROM AUTHOR]