Mechanically induced single-molecule white-light emission of excited-state intramolecular proton transfer (ESIPT) materials

Described herein is the first example of mechanically induced single-molecule white-light emission based on excited-state intramolecular proton transfer (ESIPT) materials. Mechanism of mechanochromism is clearly disclosed by powder and single crystal X-ray diffraction (XRD) data, infrared spectroscopy, and fluorescence up-conversion measurement, etc. 2-(2'-Hydroxyphenyl)oxazole (6b) with a herringbone packing motif exhibits a predominant keto-form emission, giving off yellowish-green fluorescence. Mechanical grinding transforms the herringbone packing motif into a brickwork packing motif, decreases intermolecular distances, which results in an enhanced intermolecular charge-transfer interaction, and therefore changes ESIPT dynamics, leading to an enhanced enol-form emission and white fluorescence. Herringbone-packing 6b is thermodynamically more stable than brickwork-packing 6b. Thus, the latter can convert to the former by solvent fuming or thermal annealing.