Security devices based on liquid crystals doped with a colour dye

Carrasco-Vela, Carlos; Quintana, Xabier; Otón, Eva; Geday, Morten Andreas; Otón, J. M.

doi:10.2478/s11772-011-0049-8

Cited by 16 publications

(20 citation statements)

References 5 publications

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“…[11][12][13] The use of multiple cells with a variety of surface alignment orientations containing guest-host mixtures can yield devices with complex polarised absorption properties, and such systems have been proposed for use in security devices. [14] Electrically switched guest-host devices have also been suggested for use within applications outside of displays, such as in smart windows using polymerdispersed liquid crystal hosts that enable the transmittance of the windows to be electrically controlled. [15] Incorporating fluorescent dye molecules into these smart windows, and using the windows themselves as waveguides, potentially enables light absorbed by the windows in their absorbing state to be used for solar energy conversion.…”

Section: Introduction To Guest-host Systemsmentioning

confidence: 99%

Dyes as guests in ordered systems: current understanding and future directions

Sims

2016

Liquid Crystals

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The optical properties of dyes dissolved in liquid crystals have led to their proposed use in a diverse range of practical applications. Such guest-host systems are typically required to fulfil a range of criteria relating to their absorption properties, degree of alignment and stability, but concurrently satisfying these requirements has proven a barrier to their widespread use. In this article, many of the proposed applications and their requirements are discussed, and an outline of some of the most prevalent classes of dye proposed in the context of guest-host systems is given, along with a summary of recent reports of dyes that exhibit thermotropic mesophases. Theoretical approaches to describing the alignment within guest-host systems are outlined, and possible strategies for the future rational design of guest-host systems are discussed. ARTICLE HISTORY

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Section: Introduction To Guest-host Systemsmentioning

confidence: 99%

Dyes as guests in ordered systems: current understanding and future directions

Sims

2016

Liquid Crystals

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“…[2] The properties of the photoswitch may also be used to modulate the amount of light passing through as ample on account of ac hangei nt he chromophoric properties, which is of relevance in eyewear technologies. [3] Another topic of interesti nt he field of liquid-crystal technology is doping of liquid-crystal host systemsw ith guest dyes, [4] where-by the absorbance of polarized light is different when parallel or perpendicular to the host director.S uch devices have aw ide range of potential applicationsi ncluding displays, [5] high-performance thin-film polarizers, [6] optically controlled diffraction gratings, [7] securityd evices, [8] switchable solar windows, [9] and 3D imaging for biological applications. [10] The degree to which alignment occurs is described by the dichroic orderp arameter,w hich is am easure of how well the dye alignsw ith the director for the liquid crystal,a nd how well the transition dipole moment is alignedw ith the long axis of the dye molecule.…”

Section: Introductionmentioning

confidence: 99%

Photoswitching of Dihydroazulene Derivatives in Liquid‐Crystalline Host Systems

Petersen

Jevric

Mandle

et al. 2017

Chemistry A European J

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Photoswitches and dyes in the liquid crystalline nematic phase have the potential for use within a wide range of applications. A high order parameter is desirable in order to maximize the change in properties induced by an external stimulus. A set of photochromic and non-photochromic dyes were investigated for these applications. It was found that a bent-shaped 7-substituted dihydroazulene (DHA) photoswitch exhibited liquid crystalline properties. Further investigation demonstrated that this material actually underwent two distinctive reaction pathways upon heating to a deactivated form via a 1,5-sigmatropic shift and to a linear 6-substituted DHA. In addition, elimination of hydrogen cyanide from these photoactive DHAs gave both bent and linear azulene dyes. In a nematic host, which has no absorbance around 350 nm, it was found that only the linearly shaped DHA derivative possessed nematic properties; however, both 6-and 7-substituted DHAs were found to have high order parameters. In the nematic host, ring opening of either DHA to the corresponding vinylheptafulvene (VHF) resulted in a decrease in dichroic order parameter and an unusually fast back reaction to a mixture of both DHAs. Likewise, only the linearly shaped azulene derivative showed mesomorphic properties. In the same nematic host, high order parameters were also observed for these dyes.

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“…How− ever, on the other hand, photonic applications based on these materials have already been extensively researched; covering many diverse fields. Nanotechnology works are dealing with carbon nanotubes applications and liquid crys− tal -nanoparticles interactions [2], security is treating cryp− tographic applications [3] and optical communications are handling optical components that are easily integrated in optical fibre systems. Some examples are modulators or fil− ters [4], distributed sensors [5], beam steering devices [6], aberration correction spatial light modulators [7], bio−optics applications [8] and optical lenses [9].…”

Section: Introductionmentioning

confidence: 99%