Tailoring Liquid Crystalline Self-Assembly and Photophysical Properties of Unsymmetrical Fluorenones via Polar Terminal Groups.

In this work, a series of novel unsymmetrical fluorenone derivatives bearing various head groups (H, Br, NO2, NH2, and CN) was synthesized and investigated with respect to their mesomorphic and photophysical properties. Depending on the head group, SmA, N, or SmC phases with phase widths of up to 145 K were observed, except for the NH2-substituted derivative. All mesomorphic derivatives exhibited bright yellow to orange fluorescence in the solid state and solution with quantum yields of up to 35%. Notably, the nitrile derivative showed thermally induced color and emission color shift from yellow to orange, which was not reversible upon cooling to room temperature. These results revealed that the mesomorphic and photophysical properties of the examined fluorenone derivatives are strongly dependent on the headgroup and, in the latter case, can be significantly influenced by the presence and nature of solvent or temperature.