Piezochromic Luminescence of Donor-Acceptor Cocrystals: Distinct Responses to Anisotropic Grinding and Isotropic Compression.

Piezochromic luminescent materials that exhibit distinct luminescence responses to different types of mechanical stresses have been emerging as new kinds of materials which are rarely investigated. Herein, we report a donor-acceptor (D-A) charge-transfer (CT) cocrystal, which shows distinct hypochromatic and bathochromatic shifts upon anisotropic grinding and isotropic compression, respectively. Detailed spectroscopic and structural analyses revealed that the hypochromatic shifted emission under grinding is attributable to a structural reorganization from a loosely segregated-stack to a mixed-stack, while the bathochromatic shifted emission originates from the formation of a tighter packing structure. We present rare evidence of a distinct luminescent response to anisotropic grinding and isotropic compression on the basis of structural rearrangement in a D-A cocrystal, and thus enriches our insight into piezochromic luminescence.