Asynchronous piezochromic fluorescence and phosphorescence behavior observed in an organic dual emission crystal

Mechanochromic luminescence (MCL) is attracting much attention due to its promising applications and academic importance. However, the present studies mainly focus on fluorescent dyes, and investigations on organic phosphorescent materials are still lack. In the current work, a new organic room temperature phosphorescence‒fluorescence dual emission crystal with well-separated emission peaks is used to investigate the MCL behaviors by the diamond anvil cell technique in conjunction with the spectroscopic measurements. The results demonstrate the remarkably asynchronous piezochromic fluorescence and phosphorescence behavior in both emission colors and intensities. The theoretical analyses and calculations indicate that the high pressure induced molecular conformation and stacking structure changes can differently influence the energy levels and distributions of singlet and triplet excited states, which is responsible for the interesting photo-physical properties. This work provides a new perspective of understanding the effect of molecular confined environments on organic light emitting properties.