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

Abstract

2-(Anthracenyl)-4,5-bis(2,5-dimethyl(3-thienyl))-1H-imidazole (anbdtiH) has been synthesized. Its three solid-state structures, anbdtiH·CH₃Cl (1), anbdtiH·2CH₃OH (2) and anbdtiH₂·CF₃COO·CH₃OH·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 π⋯π 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 Δλ = 83 nm for 1, a red-shift of Δλ = 20 nm for 2, and a blue-shift of Δλ = 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⋯N_imidazole hydrogen bonds by a grinding–heating process. Moreover, compound 3 can undergo a solid-state [4π + 4π] 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.