A Ferroelectrically Switchable Columnar Liquid Crystal Phase with Achiral Molecules:  Superstructures and Properties of Liquid Crystalline Ureas

Abstract

Novel columnar liquid crystalline compounds N,N'-bis(3,4,5-trialkoxylphenyl)ureas 1a-c (R = n-C(8)H(17), n-C(12)H(25), and n-C(16)H(33)) were synthesized, and their phase transitions were measured by differential scanning calorimetery. The superstructures were investigated by X-ray diffraction, polarized light optical microscopy, and IR spectroscopy. The compounds exhibited both rectangular and hexagonal columnar phases in which the urea molecules in each column were stacked in one direction with strong hydrogen bonds. To confirm the ferroelectric switching, optoelectronic experiments were carried out, and the hexagonal columnar phases of 1b and 1c gave a sharp peak of spontaneous polarization in response to an applied triangular wave electric field (0.1-18 Hz). This is the first example of ferroelectrically switchable columnar liquid crystal phases generated by achiral molecules.

Phase-Transitions in Langmuir-Blodgett and Cast Films of a Ferroelectric Liquid Crystal

“…This can supply reliable results even from spectra with a rather low signal-noise ratio. 16,17 In a previous research, temperature-dependent polarized and polarization angle-dependent IR spectra of a FLC of sec-butyl-6-(4-(nonyloxy)benzoyloxy)-2-naphthoate (FLC-1) in Sm-C* were measured 15 and several phase transitions were detected. 18 Their presence was further confirmed by temperature-dependent ultraviolet (UV), IR spectroscopy and X-ray diffraction.…”

“…[10][11][12][13] These three methods yield slightly different values but reinforce each other for characterization of LC phase transitions. [6][7][8][9][10][11][12]15 In spectral measurements, IR spectroscopy does permit the precise monitoring of subtle changes in the absorption band characteristics, such as frequencies, intensities and bandwidths, of specific functional groups. 14,15 Thus, IR spectroscopy is unique for exploring liquid crystalline phases because it elucidates the relationship between the molecular groups and the thermal behavior of LCs.…”

“…[6][7][8][9][10][11][12]15 In spectral measurements, IR spectroscopy does permit the precise monitoring of subtle changes in the absorption band characteristics, such as frequencies, intensities and bandwidths, of specific functional groups. 14,15 Thus, IR spectroscopy is unique for exploring liquid crystalline phases because it elucidates the relationship between the molecular groups and the thermal behavior of LCs. If such information about changes in band features is clear at different temperatures, these changes can be attributed to the conformation number changes of the molecules among different phases.…”

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

“…1 Hydrogen bonding is polar, thus sequential hydrogen bonds make a column polar. [2][3][4][5][6][7] If the direction of the hydrogen bonds can be reversed by an external electric field, the column could become ferroelectric. Even without reversing the hydrogen-bond direction, hydrogen-bonded chains may exhibit interesting polar properties.…”

Orthohalogen substituents dramatically enhance hydrogen bonding of aromatic ureas in solution

“…Its direct synthetic accessibility and its HB donor ability have been exploited in the fields of anion complexation, 2 organocatalysis 3 and foldamer conformational control. 4 Moreover, the self-complementarity of the phenylurea synthon is a reliable design motif for crystal engineering, 5 organogelators, 6 liquid crystals, 7 supramolecular polymers, 8 nanostructured polymers, 9 self-assembled capsules 10 and monolayers. 11 The effect of various electron withdrawing substituents on urea assembly is well-known, 12 but the case of halogen atoms in ortho position of the phenylurea moiety has rarely been investigated, probably because such substitution was shown to favour intramolecular HBs.…”