Assembly of Photopolymerizable Discotic Molecules on an Aligned Polyimide Layer Surface to Form a Negative Retardation Film with an Oblique Optical Axis

Abstract

Ultraviolet (UV) polymerizable discotic liquid‐crystalline (DLC) molecules (2,3,6,7,10,11‐hexakis(4′‐acryloy‐m‐alkyloxybenzoyoxy)triphenylene [HAHBT‐m, where m was the number of methylene units, and here m = 6 (HAHBT‐6)]) were assembled to form a negative retardation film with an oblique optical axis on a specifically designed rubbing‐aligned polyimide layer surface [6FDA‐11CBBP (where 11 is the number of methylene units in the side chains)]. The side chains of this polyimide were terminated by cyanobiphenyl groups. Surface‐enhanced Raman scattering (SERS) and optical second harmonic generation results showed that rubbing caused a surface structural re‐arrangement in the alignment layer resulting in a negative pre‐tilt angle (θs) of –8.5° (which was in the direction opposite to the rubbing direction). The molecular topology at the rubbed surface was governed by a stable fold‐like bent structure of the cyanobiphenyl side chains, in which the CN groups preferentially pointed down towards the surface. When the DLC molecules were deposited onto the alignment surface and polymerized via UV irradiation to generate a new optical film, an oblique optical axis with an average tilt angle of –18.6° with respect to the film normal was detected using ellipsometric measurements. This tilted optical axis was developed by the DLC molecules being wedged on top of the cyanobiphenyl groups when in the bent conformation. Furthermore, the tilt angle difference between the θs at the alignment surface and at the air interface of the DLC molecules was attributed to a splay deformation of the DLC molecules along the film surface normal. Optical modeling has also confirmed our experimental observations.

Discotic Liquid Crystals for Opto-Electronic Applications

“…This is due to the anisotropy of boundary tension between the mesophase and the nanogrooves’ walls . An aligned polyimide layer surface was also used to assemble triphenylene-based DLCs …”

Construction of Topological Macromolecular Side Chains Packing Model: Study Unique Relationship and Differences in LC-Microstructures and Properties of Two Analogous Architectures with Well-Designed Side Attachment Density

“…Since Pugh et al reported the effect of molecular architecture with branched systems on the thermal behavior; branched LC polymers have attracted considerable attention. Despite of extensive research on SCLCPs, related works about the effect of topology on LC properties have been seldom reported. ,− The effect of diverse topology on the physical and biological properties, such as the switching time of LC, drug-loading capacity/drug-release rate, solution property, birefringence induction and photoinduced anisotropy has been investigated. Meanwhile, a few researches focus on the influence of topology on thermal and mesophase behavior, , polymer with branched topology in Rao’s work showed a higher glass transition temperature ( T g ) compared with linear polymers, while Zhao et al developed a SCLCP with cyclic topology that exhibited a lower T g , in addition, many research results indicated that the diverse topology could lead to varied mesophases such as smectic A, smectic C, and columnar phases etc .…”

Self-Assembly of Chemically Linked Rod−Disc Mesogenic Liquid Crystals

“…This enables these molecules to be useful in developing compensation films with a tilted optical axis and negative birefringence to improve the viewing angle of LC displays. They can also be utilized in field-effect transistors and photovoltaic devices due to their extraordinary one-dimensional (1D) electrical/photo conductivity. − …”