Chromotropic Behavior of Lophine Nitro-Derivatives

The crystal and molecular structures of two novel derivatives of the lophine chromophore with different solvents of crystallization are presented and discussed. Phenol, 2-[4,5-bis(4-methoxyphenyl)-1H-imidazole-2-yl]-4-nitro (1) and phenol, 2-[4,5-bis(4-methyl-phenyl)-1H-imidazole-2-yl]-4-nitro (2) form inclusion compounds with various guest molecules. The guest molecules interconnect host molecules of 1 and 2 through hydrogen bonds. The inclusion compounds showed chromotropic properties upon trituration, heating, or using different solvents for crystallization. The thermochromic properties have been determined by the removal of the guest molecules. To clarify the relations between the color, thermochromic properties, and the role of host in crystal packing, we have determined and compared a single-crystal X-ray analysis of six crystal structures of the two compounds. Thermal behavior in the solid state and spectroscopic behavior at different pH values and at various solvents are presented and discussed.