Tracking anharmonic oscillations in the structure of β-1,3-diacetylpyrene.

A recently discovered β polymorph of 1,3-diacetylpyrene has turned out to be a prominent negative thermal expansion material, with a linear thermal expansion coefficient of -199 (6) MK at room temperature. Its unique properties can be linked to anharmonic oscillations in the crystal structure that can be attributed to several weak C-H..

On the importance of low-frequency modes in predicting pressure-induced phase transitions.

The occurrence of ultra-low frequency oscillation mode as observed by means of periodic DFT calculations at point in a molecular crystal at ambient conditions can be a valuable predictor of imminent pressure-induced phase transition. We illustrate it with a series of polymorphs of diacetyl-pyrenes, for two of which such soft-modes indicated the trajectory of pressure-induced structural reorganization at ≈0.8 GPa.

Evolution of structure and spectroscopic properties of a new 1,3-diacetylpyrene polymorph with temperature and pressure.

A new polymorph of 1,3-diacetylpyrene has been obtained from its melt and thoroughly characterized using single-crystal X-ray diffraction, steady-state UV-Vis spectroscopy and periodic density functional theory calculations. Experimental studies covered the temperature range from 90 to 390 K and the pressure range from atmospheric to 4.08 GPa.