The effect of terminal halogen atom on the self-assembly of bisthienylethene-based rod-like molecules

Three novel rod-like molecules containing a bisthienylethene as pi-conjugate rigid core with a different type of terminal functional atom (H, Cl, Br) were constructed by using Suzuki coupling and Knoevenagel reactions. The effect of the terminal functional atom on self-assembly behaviors in both bulk state and solution states and solid structures was investigated by using differential scanning calorimetry, polarized optical microscopy, small-angle X-ray scattering diffraction, density functional theory calculations and field-emission scanning electron microscopy. The non-halogen substituted compound and chlorinated compound are non-mesogen, whereas the brominated compound can self-assemble into a monotropic single-layer smectic A phase. The non-halogen substituted compound cannot form organogel in the common organic solvents, the chlorinated compound can form yellow-green fluorescent oragnogels in ethyl acetate and acetone, with rod-like morphology and brominated compound can form yellow-green, yellow or orange fluorescent oragnogels in ethyl acetate, acetone, 1,4-dioxane and toluene with sheet-like morphology. In addition, the terminal halogen atom induced great changes in the orderliness of solid morphology. Therefore, tuning terminal halogen atom could well lead to the transition of self-assembly behaviors in bulk state and solution state, which provides a way to obtain different self-assembly materials.