Distinct stimuli-responsive behavior for two polymorphs of 9,10-Bis(phenylethynyl)anthracene under pressure based on intermolecular interactions

Abstract Two polymorphs of 9,10-bis(phenylethynyl)anthracene (OC and RC) were obtained and they were characterized by multi spectroscopies including X-ray diffraction, absorption, fluorescence and Raman. The single-crystal structure analysis shows that RC has richer intermolecular interactions (C–H … π and C–H⋯H–C) than OC, which accounts for different spectroscopic behaviors of RC from OC in high pressure studies. Under mechanical grinding, two polymorphs have similar spectral changes in their fluorescence as significant enhancement and slight blue-shifts of the shoulder emission bands at lower wavelength, except that RC shows more sensitive to grinding than OC. During the compression process applied by diamond anvil cell (DAC), OC and RC both demonstrate remarkable red-shifts with increasing pressure, while RC shows a smaller shifting rate than OC. These spectral phenomena reveal that the richer intermolecular interactions in RC can be easily destroyed upon grinding. This work provides the in-depth insight into the mechanism of mechanochromism and the structure-property relation, and proves again that the intermolecular interactions play the key role in modulating the photo-physical properties.