The effect of positional isomerism of cyano group of the rod-like mesogens on the liquid crystalline and optical characteristics

Abstract Two novel cyanostilbene-based rod-like mesogens named BI-CN-4 and BI-CHO-4 consisting of one terminal pyrene and one terminal alkyl chain were prepared by Suzuki coupling and Knoevenagel reactions. The influence of the positional isomerism of cyano group of cyanostilbene unit on the liquid crystalline characteristics, photophysical characteristics, and mechanochromism characteristics is explored by using POM, DSC, XRD, UV spectra, PL spectra, DFT and TD-DFT calculations. BI-CN-4 in which the cyano group is adjacent to the phenylpyrene unit exhibits monotropic smectic C phase, whereas BI-CHO-4 in which the cyano group is far away from the phenylpyrene unit exhibits enantiotropic smectic C phase. BI-CN-4 exhibits more distinct positive solvatochromism due to more distinct intramolecular charge transfer. Both compounds exhibit AIE or AIEE behavior and reversible mechanochromism behavior due to twisted molecular configurations. These results demonstrated that the distinct molecular design could endow organic molecules with multifunctional properties and potentials.