“Colored” inorganic dopants for inducing liquid crystal chiral nematic and blue phases: monitoring of dopant–host interaction by Raman spectroscopy

Abstract

A new ruthenium complex that effectively induces chiral nematic and blue phases upon doping with a nematic liquid crystal was developed. The red-colored dopant exhibits strong Raman scattering in solution and nematics even at low concentrations. Further measurements at various concentrations strongly suggested homogeneous dispersion of the dopant in chiral nematics.

Comprehensive Understanding of Host- and Guest-Dependent Helix Inversion in Chiral Nematic Liquid Crystals: Experimental and Molecular Dynamics Simulation Study

“…The Δ isomer of Ru-per induces left-handed helices in all of the hosts investigated, whereas that of Ru-para1 induces left-handed helices (vice versa for Λ isomers). 58,59,61 According to polarized UV−vis spectroscopy and MD simulation, 58,60 the elongated ligand was confirmed to align with the ordering direction of host LCs (Figure 4). That is, the para and per types have almost 90°difference in orientation in LC media (Figure 4).…”

“…We also experimentally verified that Ru-para1 is homogeneously distributed in the N* media, based on Raman scattering measurements. 61 Almost 90°difference in orientation and a homogeneous distribution of dopants in the LC media lead to opposite helix inductions, according to the surface chirality model, which is a physical theory developed by Ferrarini, Nordio, and co-workers. 27,48,93−101 In this model, the HTP of a chiral dopant is treated in terms of the dopant molecular structure and represented by the following equation…”

“…We recently confirmed that Ru-para1 molecules are basically homogeneously distributed in N* media based on Raman scattering measurements. 61 Thus, it is reasonable to consider that metal complexes are monodispersed for all binary systems examined in this study. Second, we assume that the five used nematics afford the same excluded volume effect for a dopant to make the analysis simple.…”

Highly Miscible Hybrid Liquid-Crystal Systems Containing Fluorescent Excited-State Intramolecular Proton Transfer Molecules

“…Light-emitting liquid-crystal displays (LE-LCDs) − have received great attention as energy-efficient alternatives to conventional LCDs since polarized light emission from LC molecules enables one of the polarizers to be removed. One convenient approach to obtain LE-LCDs is doping of luminescent molecules in a nematic LC host. − The miscibility (solubility and compatibility) between host and guest (dopant) molecules , is the primary issue in the system. The other problem is the well-known aggregation-caused quenching (ACQ): the decrease of the photoluminescence quantum yield when the concentration of fluorescent dopants is increased. , Owing to the characteristic large Stokes shift, some ESIPT chromophores are fluorescent in the visible region despite being composed of noncolored, small aromatic structures.…”

“…One convenient approach to obtain LE-LCDs is doping of luminescent molecules in a nematic LC host. 19−23 The miscibility (solubility and compatibility) between host and guest (dopant) molecules 24,25 is the primary issue in the system. The other problem is the well-known aggregationcaused quenching (ACQ): the decrease of the photoluminescence quantum yield when the concentration of fluorescent dopants is increased.…”