Revealing the origin of excimer emission in anthracene crystals: The role of excitation wavelength and pressure

Understanding the formation mechanism of excimer emission in aromatic molecules is the fundamental to several areas of photochemistry, including photo-induced dimerization. In this study, we observed the formation process of excimer emission in anthracene crystals at normal pressure by varying excitation wavelength. It was found that the excimer emission in anthracene crystals was originated from photo-induced van der Waals (vdW) dimers of anthracene molecules. The formation and annihilation processes of the excimer emission were characterized during the pressure loading and unloading processes, which were assigned to the pressure-induced vdW dimers formation and annihilation. Note that the fluorescence spectrum of anthracene crystals was dominated by excimer emission at 5.88 GPa, the excitation wavelength dependence of excimer emission can be obtained. The observed frequency shift confirmed the role of excitation wavelength in fluorescence process. These findings have significant implications for understanding the origin of the excimer emission and open novel perspectives in the fluorescence research of aromatic molecules.