Study of Cr→SmA phase transition and hydrogen bonding in four-ring bent-core liquid crystal

Monitoring structural fluctuations of discotic liquid crystal during phase transitions

The discotic liquid crystal 4-((2, 3, 4-tris (octyloxy) phenyl) diazenyl) benzoic acid, hereafter referred as DLC A8, exhibited in dimeric form has been studied using a combination of quantum chemical approaches and vibrational spectroscopy. This study investigates the structural alteration of DLC A8 associated with phase transition. The phase transitions of DLC A8 are Iso → Discotic nematic → Columnar → Crystalline, which have been investigated using differential scanning calorimetry (DSC) accompanied with polarized optical microscopy (POM). Monotropic columnar mesophase was observed during the cooling cycle while discotic nematic mesophase was observed in both the heating and cooling cycles. Density functional theory (DFT) along with IR and Raman spectroscopic techniques were utilized to study the dynamics of molecules during phase transition. To predict the most stable conformation of the molecule, one-dimensional PES scans have been performed along 31 flexible bonds using DFT/B3LYP/6-311G++(d,p) method. Vibrational normal modes were analyzed in detail, taking potential energy contribution into account. The spectral analysis of FT-IR and FT-Raman was done by deconvoluting the structural sensitive bands. The agreement between the calculated IR and Raman spectra and the observed FT-IR and Raman spectra at room temperature confirms our theoretically predicted molecular model of investigated discotic liquid crystal. Moreover, our studies have unraveled the existence of intact intermolecular H-bonding of dimers throughout the phase transitions.

Advanced Functional Luminescent Metallomesogens: The Key Role of the Metal Center

The use of liquid crystals for the fabrication of displays incorporated in technological devices (TVs, calculators, screens of eBook's, tablets, watches) demonstrates the relevance that these materials have had in our way of living. However, society evolves, and improved devices are looked for as we create a more efficient and safe technology. In this context, metallomesogens can behave as multifunctional materials because they can combine the fluidic state of the mesophases with properties such as photo and electroluminescence, which offers new exciting possibilities in the field of optoelectronics, energy, environment, and even biomedicine. Herein, it has been established the role of the molecular geometry induced by the metal center in metallomesogens to achieve the self-assembly required in the liquid-crystalline mesophase. Likewise, the effect of the coordination environment in metallomesogens has been further analyzed because of its importance to induce mesomorphism. The structural analysis has been combined with an in-depth discussion of the properties of these materials, including their current and potential future applications. This review will provide a solid background to stimulate the development of novel and attractive metallomesogens that allow designing improved optoelectronic and microelectronic components. Additionally, nanoscience and nanotechnology could be used as a tool to approach the design of nanosystems based on luminescent metallomesogens for use in bioimaging or drug delivery.