Orientation and Solvatochromism of Dyes in Liquid Crystals

Abstract

Citation for published item: ¦ lssonD vF yF nd zlewskiD wrek nd oertsD eF nd wsutniD eF nd voveD qF hF nd grossD qF rF nd floorD hF nd uyD eF tF nd oolhouseD eF hF nd wsutniD eF nd sudD eF @PHHQA 9yrienttion nd solvtohromism of dyes in liquid rystlsF9D woleulr rystls nd liquid rystlsFD RHP @IAF ppF RQESQF Further information on publisher's website: httpXGGdxFdoiForgGIHFIHVHGURRVITTVS Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The orientation and solvatochromism of some dye molecules in a liquid crystal have been investigated. Interactions with the host and the structure of the dye molecule affect the macroscopic alignment of dichroic dye molecules in a liquid crystal. It was observed that some dye molecules show a large bathochromic shift of their absorption maxima in the liquid crystal host relative to the situation in isotropic solvents. It is suggested that this is due to the occurrence of a much weaker reaction field in the anisotropic, rigid host. These dye molecules show little or no apparent order in the anisotropic host despite the observation of a reduction in the electro optic switching time when the dye is present. The highest degree of macroscopic alignment was observed for a merocyanine compound, which showed the smallest solvatochromic shift in the liquid crystal host. These results are discussed in terms of the steric, dipolar and hydrogen bond interactions between the guest and the host.

Guest–host interactions between dichroic dyes and anisotropic hosts

“…[4]). This observation is also consistent with our previous study [12]. It is notable that the shift in the absorption maxima is larger than that of the emission maxima relative to the viscous solvents DEG and glycerol.…”

“…Hosts employed were LCs and isotropic solvents for which previous studies had indicated the formation of H-bonds with these dyes [12]. These measurements confirmed that the spectral shifts of the chromophores in the LC are much larger than those in isotropic solvents of varying polarity and hydrogen bonding ability.…”

“…If H-bond formation occurs, what impact might it have on the LC structure? In parallel to these observations, we also found that the large spectral shifts were accompanied by low order parameters of the dyes in the LC host and for display applications, this constitute a serious problem [12]. There is therefore, a need to learn more about the solvatochromic effects of high dipole moment dyes, and what impact these might have on the host material, i.e.…”

“…The presence of conformational substates will also provide an explanation for the low order parameter and luminescence anisotropy, which was observed previously for MORPIP in Ref. [12]. For display applications this would mean that more rigid dye structures most be sought after, which can maintain a more homogenous conformations in the LC host.…”

“…We also observed dramatic solvatochromic effects with larger spectral shifts in absorption and luminescence in LCs than in isotropic solvents [12]. This suggests that the reaction field of the LCs must be very different from those of isotropic solvents [3,4].…”