We have assessed the potential of light-responsive bent-core liquid crystals as candidate materials for energy conversion and storage applications. Samples comprise two chromophore bent-core compounds containing either one (IP33) or two (IP31) azobenzene groups, and their 5% (molar) mixtures with one non-chromophore bent-core compound (NG75), which was also measured as a reference material. The pristine compounds and their mixtures were introduced in thin transparent Indium Tin Oxide (ITO) cells, and were characterised by polarised optical microscopy, UV-visible spectrophotometry, impedance spectroscopy, and ferroelectric analysis, under different conditions of electrical fields and UV irradiation. All materials display smectic C polar phases (SmCP) except IP31, which forms columnar phases (Col), and IP33, IP31 and their mixtures exhibit light-responsiveness when irradiated at 365 nm due to reversible trans-to-cis photoisomerisation of the azobenzene units. All the bent-core based materials exhibit, at least, two dielectric relaxations, associated to different modes of molecular reorientation under weak alternating electrical fields (1 Vrms), as well as ferroelectric response that leads to permanent polarisation under the application of strong alternating fields (~ 75 kV·cm-1) at frequencies associated to the Goldstone-mode (1 Hz). Samples show considerable conductivity values and relaxor behaviour for liquid crystals, which can be tuned by application of UV light. In addition, we have induced in IP31 isothermal phase transitions from columnar to smectic phases (via the isotropic melt), by a combination of light and electrical stimuli. Our results confirm the potential of these bent-core compounds as light-harvesters for energy applications.
IDC would like to thank the Universitat Politècnica de València (UPV), for the FPI grant (PAID-2019-SP20190013), the Generalitat Valenciana (GVA) and the European Social Fund (ESF), for the FPI grant (ACIF/2020/233) and the mobility grant (CIBEFP/2021/53). NFKA would like to thank Universiti Teknologi MARA (UiTM) for sponsoring her academic sabbatical leave and allowing her to work on this project. AMF would like to thank the Carnegie Trust for the Universities of Scotland, for the Research Incentive Grant RIG008586, the Royal Society and Specac Ltd., for the Research Grant RGS\R1\201397, the Royal Society of Chemistry for the award of a mobility grant (M19- 0000), and the Scottish Government and the Royal Society of Edinburgh for the award of a SAPHIRE project. The authors from INMA greatly appreciate financial support from projects of the Spanish Government PGC2018-093761-B-C31 [MCIU/AEI/FEDER, UE] and the Gobierno de Aragón/FEDER (research group E47_20R). Thanks are given to the nuclear magnetic resonance, mass spectrometry, and thermal analysis services of the INMA (Univ. Zaragoza-CSIC)
- bent-core liquid crystals
- dielectric spectroscopy
- energy storage