Abstract
The piezochromic fluorescence (FL) of a distyrylpyrazine derivative, 2,3-diisocyano-5,6-distyrylpyrazine (DSP), was investigated in this study. Depending on the recrystallization method, DSP afforded two different crystals with green and orange FL emission. The orange color FL emission crystal (O-form) was easily converted to the green color FL emission one (G-form) by manual grinding. The G-form was also converted to a slightly different orange color FL emission crystal (RO-form) by a weak UV irradiation. When the RO-form was ground again, the G-form was regenerated. The FL colors changed between the G- and RO-forms over several ten times by repeated mechanical grinding and UV irradiation. The FL, UV–visible, 1H-NMR and XRD results showed that the O (or RO)-to-G transformation induced by mechanical stress results from the change of degree of molecular stacking from dense molecular stacking structure to relatively loose molecular stacking structure, whereas the G-to-RO reconversion by UV irradiation results from return to dense molecular stacking structure again due to lattice movement (lattice slipping) allowed by photocycloaddition in solid-state.
Highlights
The piezochromic fluorescence (FL) of a distyrylpyrazine derivative, 2,3-diisocyano-5,6distyrylpyrazine (DSP), was investigated in this study
When the crystal was manually ground using a mortar and/or pestle, the orange FL emission was changed to green emission (G-form shown in Fig. 1), the same as the color of crystal obtained by recrystallization from benzene
It was assumed that a certain phase transition occurred due to mechanical stress, which resulted in the crystal structure change
Summary
The piezochromic fluorescence (FL) of a distyrylpyrazine derivative, 2,3-diisocyano-5,6distyrylpyrazine (DSP), was investigated in this study. We report a unique PCFL-active metachromatic material, which recover its original FL emission by UV irradiation unlike the restoration of original color by thermal annealing or recrystallization.
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