摘要
Organic ferroelectrics (OFEs) are an attractive topic in material science because of their usefulness in modern technologies. There are a variety of OFEs that have been developed through various approaches using various materials. To further design and understand OFEs, it is essentially important to evaluate the dynamical behaviors of individual molecules during polarization switching. Although recent developments in theoretical calculations offer powerful tools to predict how molecules assemble into complex structures at the molecular level, it is still too difficult to determine the dynamics in response to external stimuli at the functional group level. Here, this study adopts infrared-visible sum-frequency generation (IV-SFG) to probe the electric-field-induced dynamics at the functional group level and reports on the switching mechanism of the bulk ferroelectricity and paraelectricity in an organic system for the first time. This paper demonstrates an IV-SFG study on a recently-discovered polar columnar liquid crystal system of tapered-paraffinic-wedge molecules, whose favorable wet-processability may provide a suitable design for “paintable” organic ferroelectrics. Dynamic motions of dipoles, such as of phthalonitriles and amides, are successfully probed. In ferroelectric compounds, the phthalonitriles are responsible both for the ferroelectric and paraelectric switching, whereas the amides only for the ferroelectric switching.