Abstract
We apply UV light to control the stability of twist-bend nematic phases, NTB, and conventional nematic phases, N, in three new liquid crystalline nonsymmetric dimers containing cyanobiphenyl and light-responsive azobenzene fragments connected by a hexyloxy spacer. The dynamic and static (5 kHz) dielectric responses of (E)-4'-(6-(4-((4-(ethoxy)phenyl)diazenyl)phenoxy)hexyl)-[1,1'-
biphenyl]-4-carbonitrile, CB6OAzO2, (E)-4'-(6-(4-((4-hexyloxy)phenyl)diazenyl)phenoxy)hexyl)-[1,1'-biphenyl]-4-carbonitrile, CB6OAzO6, and (E)-4'-(6-(4-((4-hexylphenyl) diazenyl)phenoxy)hexyl)-[1,1'-biphenyl]-4-carbonitrile, CB6OAz6, are measured at different temperatures, in planar and homeotropic alignments, by the application of bias and alternating electrical fields. The three CB6OAz(O)n dimers show high values of the dielectric
mean, 𝜀, an ̅ d dielectric anisotropy, Δ𝜀, due to the dipole moment associated with the cyanobiphenyl groups. The absence of the ether linkage to the terminal chain in CB6OAz6 reduces the NTB - N transition temperature and increases the bend elastic constant, K3, compared to those seen for CB6OAzO6. Isothermal phase transitions are promoted by light-irradiation, via trans-to-cis photoisomerisation of the azobenzene units, resulting in the disruption of the liquid crystal order and appearance of re-entrant nematic and isotropic phases at low temperatures. It is possible to control the dynamics and reversibility of these transitions by varying the chemical structure of the new dimers, the temperature and UV light dosage. This may be exploited in devices using multiple external stimuli.
biphenyl]-4-carbonitrile, CB6OAzO2, (E)-4'-(6-(4-((4-hexyloxy)phenyl)diazenyl)phenoxy)hexyl)-[1,1'-biphenyl]-4-carbonitrile, CB6OAzO6, and (E)-4'-(6-(4-((4-hexylphenyl) diazenyl)phenoxy)hexyl)-[1,1'-biphenyl]-4-carbonitrile, CB6OAz6, are measured at different temperatures, in planar and homeotropic alignments, by the application of bias and alternating electrical fields. The three CB6OAz(O)n dimers show high values of the dielectric
mean, 𝜀, an ̅ d dielectric anisotropy, Δ𝜀, due to the dipole moment associated with the cyanobiphenyl groups. The absence of the ether linkage to the terminal chain in CB6OAz6 reduces the NTB - N transition temperature and increases the bend elastic constant, K3, compared to those seen for CB6OAzO6. Isothermal phase transitions are promoted by light-irradiation, via trans-to-cis photoisomerisation of the azobenzene units, resulting in the disruption of the liquid crystal order and appearance of re-entrant nematic and isotropic phases at low temperatures. It is possible to control the dynamics and reversibility of these transitions by varying the chemical structure of the new dimers, the temperature and UV light dosage. This may be exploited in devices using multiple external stimuli.
| Original language | English |
|---|---|
| Article number | 117680 |
| Number of pages | 11 |
| Journal | Journal of molecular liquids |
| Volume | 344 |
| Early online date | 19 Oct 2021 |
| DOIs | |
| Publication status | Published - 15 Dec 2021 |
Bibliographical note
AMF would like to acknowledge the Scottish Government and the Royal Society of Edinburgh, for the award of one SAPHIRE project, the Carnegie Trust for the Universities of Scotland, for the award of the RIG008586 project, the Royal Society, for the Research Grant RGS\R1\201397, and the Royal Society of Chemistry, for the award of the mobility grant M19-0000. AMF and AK would also like to acknowledge the Carnegie Trust for the Universities of Scotland, for the award of one Carnegie Trust Vacation Scholarships. All authors would like to thank the School of Engineering and the Department of Chemistry of the University of Aberdeen, for financial support.Keywords
- twist-bend nematic phase
- azobenzene
- Light-responsive liquid crystals
- Trans-to-cis photo-isomerisation
- Isothermal phase transitions