Interplay between polarity and chirality in the electric-field-responsive columnar phase of a dipeptide derivative

We studied unconventional polar switching associated with an electro-optical response in the columnar oblique phase of a dipeptide derivative. Slow and careful cooling allows us to obtain a large monodomain with the column axis perpendicular to the substrates. The cross-section of the columns is birefringent, and the principal axis rotates about the column axis by applying an electric field parallel to the column axis, yielding the following characteristics: (1) the rotation angle exhibits linear dependence on an applied electric field; (2) the rotational sense is reversed by reversing the field direction; and (3) the optical isomers exhibit opposite rotational sense. A second-harmonic generation (SHG) signal was observed only under an electric field. We observed a dependence of the SHG intensity and infrared (IR) absorption on the incidence angle. Asymmetric and symmetric variations were observed when the sample was rotated about the slow and fast in-plane optical axes, respectively. From these experimental results, we proposed a model of molecular packing in the columnar phase; the molecules stack with their molecular planes tilted from the column axis, and the polar order is cancelled within the neighboring columns.