Structure and piezochromism of chrysene at high pressures

Fluorescence materials have attracted great attention in the last decades because of their modulable fluorescence properties and broad applications. Molecular packing is one of the most important factors that determines organic molecular piezochromic fluorescence behavior. Herein, we systematically investigated the fluorescence, vibrational, and structural properties of chrysene up to 20 GPa by using multiple experimental techniques and ab-initio calculations. We find the obvious color-changing with increasing pressure. Meanwhile, the phase transition at a pressure of about 6.6 GPa has been identified from both the frequency shifts and the changes in intensity of the Raman modes. However, the structure of chrysene at ambient pressure remains stable to at least P∼20.2 GPa from both experimental and theoretical x-ray diffraction results. Further structural analysis indicates that the angle between two molecular planes decreases with pressure, resulting in the packing alteration. The combined results from the experiments and computations demonstrated that the observed phase transition at 6.6 GPa is probably a result of the change of molecular packing. Furthermore, the intermolecular interactions have changed correspondingly due to the change of the molecular packing, which results in the color-changing of chrysene under pressure. These results provide further evidence that the intermolecular interactions play the important role in tuning the photo-physical properties, and this work will contribute to understanding the relationship between molecular packing and piezochromism in fluorescence materials.