<title>Alignment of coumarin-containing polymers for liquid crystal displays</title>

Abstract

Ill this paper, a range of polyrnethacrylate derivatives of hydroxycoumarin are investigated as photomduced alignment layers for liquid crystals, and their performance is compared with poiynyi cinnamate. For all the coumarin-containing polymers, the liquid crystal alignment direction is parallel to the polarization direction of the incident UV light at low fluences. At a critical fluence threshold, a sharp change to perpenthcular alignment is found. Molecular models and spectroscopy are used to explain this phenomenon as well as the fact that only perpendicular alignment is observed for polyvinyl cinnarnate. The azimuthal anchoring energies ofthe alignment layers are measured and values greater than 6 x io-5 j in2 are found. The incorporation of a flexible spacer into the coumarin sidechain results in stronger anchoring at low fluences. Exposure of the coumarin-containing alignment layers at oblique incidence gives pretilted alignment with pretilt angles up to 5.1°.

Large, Tunable Liquid Crystal Pretilt Achieved by Enhanced Out-of-Plane Reorientation of Azodye Thin Films

“…Changes to the concentration of BY alone show a significant change in the magnitude of the measured pretilt by a factor of 4 (compare rows 1 and 3). Despite this, even the smallest pretilt value in Table represents an increase over previously reported values for single photoalignment layers, where the materials used were E7 and 11-3233, respectively. , Further work will be necessary to optimize the process for specific applications.…”

“…Despite this, even the smallest pretilt value in Table 1 represents an increase over previously reported values for single photoalignment layers, where the materials used were E7 and 11-3233, respectively. 19,20 Further work will be necessary to optimize the process for specific applications.…”

“…These methods include double-polarized ultraviolet (UV) exposure of poly­(vinyl cinnamate) films, use of coumarin-substituted cinnamate derivatives, UV exposure of polyimides during imidization, oblique exposure of polyimide films with azobenzene backbone, and the method of photo-rubbing . The largest pretilt reported from these methods is 6° and exhibited limited tunability …”

“…18 The largest pretilt reported from these methods is 6°and exhibited limited tunability. 19 Of particular interest to this paper is the two-step exposure originally proposed by Chigrinov et al to obtain an LC pretilt angle using thin films of the azodye SD-1. 20 Using this method, a tunable pretilt angle from 2.5 to 5.5°was obtained.…”

VAN LCOS Microdisplays: A Decade of Technological Evolution

“…In the original report by Gibbons [24], polyimide films doped with photo-sensitive azo-dye compounds are used. Later on mainly poly-vinyl-cinnamate and its derivatives have been used [25]- [27], but also polyimides [28] and other reactive polymers [29]. Alignment of liquid crystal molecules is for most polymers triggered by a process of photodegradation.…”