The influence of positional isomerism of a cyano group of pyrene-based rod-like mesogens on mesomorphism, dual-state emission and multiple applications

Abstract

Two novel cyanostilbene-based rod-like mesogens 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 the cyano group of cyanostilbene unit on the liquid crystalline characteristics, photophysical characteristics, and mechanochromism characteristics was studied by using polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, absorption spectra, photoluminescence spectra, density functional theory calculation and time-dependent density functional theory calculation. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits a monotropic smectic C phase, whereas the mesogen in which the cyano group is far away from the phenylpyrene unit exhibits an enantiotropic smectic C phase. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits more distinct positive solvatochromism due to more distinct intramolecular charge transfer. The mesogen in which the cyano group is adjacent to the phenylpyrene unit exhibits aggregation-induced emission behavior, but the mesogen in which the cyano group is far away from the phenylpyrene unit exhibits dual-state emission behavior. Reversible mechanochromism behavior could be achieved in both mesogens due to twisted molecular configurations. In addition, the rewritable luminescent paper and bioimaging applications were also achieved. These results demonstrated that the distinct molecular design could endow organic molecules with multifunctional properties and potential applications.