Portal de Periódicos da CAPES

Photo-driven effects in twist-bend nematic phases: Dynamic and memory response of liquid crystalline dimers

2021; Elsevier BV; Volume: 344; Linguagem: Inglês

10.1016/j.molliq.2021.117680

1873-3166

Daniel Zaton, Alexia Karamoula, Grant J. Strachan, John M. D. Storey, Corrie T. Imrie, Alfonso Martínez‐Felipe,

Molecular spectroscopy and chirality

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¯, and 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.