2-(Anthracenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole: regulatable stacking structures, reversible grinding- and heating-induced emission switching, and solid-state photodimerization behavior

2-(Anthracenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (anbdtiH) has been synthesized. Its three solid-state structures, anbdtiH center dot CH3Cl (1), anbdtiH center dot 2CH(3)OH (2) and anbdtiH(2)center dot CF3COO center dot CH3OH center dot H2O (3), have been constructed by skillfully choosing CHCl3 or CH3OH as the solvent and using or not using CF3COOH, with the aim of modifying the intermolecular hydrogen bonds and/or pi center dot center dot center dot pi stacking interactions. The three distinct structures show significantly different solid-state luminescence behaviors, an orange-red emission at 603 nm for 1, a blue emission at 453 nm for 2, and a green emission at 533 nm for 3. Upon grinding, these emission wavelengths exhibit evident variations, a blue-shift of Delta lambda = 83 nm for 1, a red-shift of Delta lambda = 20 nm for 2, and a blue-shift of Delta lambda = 54 nm for 3. The emission color of 1 can be reversibly switched between orange-red and green upon regulation of the intermolecular (N-H)(imidazole)center dot center dot center dot N-imidazole hydrogen bonds by a grinding-heating process. Moreover, compound 3 can undergo a solid-state [4 pi + 4 pi] photodimerization reaction upon irradiation with sunlight, forming 3-dimer. Based on the crystal structures of 1-3, this work discusses the relationship between the molecular stacking mode and the luminescence behavior/photochemical reactivity.