Structures and Chromogenic Properties of Bisimidazole Derivatives

Two imidazole derivatives, 2,2‘-(2,5-thiophenediyl)bis[4,5-diphenyl-1H-imidazole] (1) and 2,2‘-(1,4-phenylene)bis[4,5-diphenyl-1H-imidazole] (3), were synthesized and crystallized from different solvents. The crystal solvates have different colors, and some of these compounds show piezochromism, photochromism, and thermochromism in the solid state and show solvatochromism, halochromism, and photochromism in solution. The X-ray crystal structures of bisimidazole derivatives of lophine and the spectroscopic properties and photochemistry of these compounds in solutions are reported. The thermal behavior of the crystalline compounds was studied by a calorimetric method, and it was shown that upon heating the crystal solvates lose the solvent molecules, and the color is changed to the original color of the nonsolvate parent compound. The conclusion is that hydrogen bonding is responsible for the different colors.