Effect of pressure on the luminescence of 9,10-dichloroanthracene crystals

Luminescence spectra of β-9,10-dichloroanthracene have been studied at room temperature in the pressure range ≈ 0–10 GPa. The initial shift to lower energies of the excimer emission is linear (≈500 cm⁻¹/GPa) up to ≈3 GPa. Above this pressure a sharper emission grows at the high-energy side at the expense of the excimer luminescence. The suppression of the excimer state at pressures above ≈ 7 GPa is attributed to the strong repulsive interactions between the molecular pair. The new emission is thought to arise from a more loosely bound configuration in the excited state which could originate from a crystal phase change around 3 GPa.