Mechanofluorochromic Anthryl Phosphonate/Benzoic Acid Cocrystals with a Large Blue Shift: The Role of P=O⋅⋅⋅H Interactions.

Organophosphonates have a rich and diverse chemistry, but their mechanofluorochromic features have rarely been documented. Herein, we report on cocrystals of anthranylphosphonate with (E)-4-(2-(anthracen-9-yl)vinyl)benzoic acid that exhibit reversible mechanofluorochromic properties with large blue shifts. Anisotropic grinding (or pressure of just 25 kPa) maintains the co-crystals emission features but leads to a pronounced 59 nm (2087 cm-1 ) blue-shift. Such an impressive blue-shift for a cocrystal has not been reported to date. The underlying causes for the blue-shift were validated by X-ray diffraction (powder and single crystal) studies and Hirshfeld surface analysis. Twisted molecular conformations and P=O⋅⋅⋅ H/C=O⋅⋅⋅H/C⋅⋅⋅H noncovalent interactions afford molecular arrangements via slip-stacks with two different pitch angles and relatively larger interlayer distances. The new compound was established as a potential medium for optical recording and security display.