Flat-panel displays have become a ubiquitous part of life, with the global market exceeding a value of 100 billion USD in 2019 with growth predicted to reach 190 billion USD by 2026. Devices produced by this industry include TVs, laptops, tablets, smart watches, amongst many others, which are essential and enhance our lives in all areas from domestic uses to commercial environments. A variety of technologies have been developed to produce display devices, the most prevalent of those, currently in the market utilise LC and OLED technologies. Fabrication of display devices is complex with many challenges to be overcome. Among the challenges is correcting the variety of optical imperfections observed in uncompensated devices.
Optical retardation films are widely used in the industry as corrective layers in display stacks to correct viewing imperfections. Several methods have been used to produce retardation films, films composed of liquid crystalline reactive mesogens have seen widespread use due to their versatility and thin lightweight form factor. Reactive mesogens are a specialised class of liquid crystals possessing polymerizable groups, allowing them to be polymerised to give a solid plastic films with anisotropic properties. A wide variety of optical properties can be produced through adjustments in formulation and LC alignment. However, like many materials, liquid crystals exhibit dispersion and to produce a single film with uniform retardation across the entire visible spectrum is challenging and remains costly to achieve. It has been previously demonstrated that it is possible to produce reactive mesogen films which exhibit reverse wavelength dispersion birefringence. Where, through careful molecular design, the refractive indices of the material are controlled to produce the effect of having lower birefringence at shorter wavelengths, emulating negative dispersion.
In this work, three novel classes of negative dispersion reactive mesogen additives are investigated and compared to a material currently in commercial use. In order to facilitate these studies extensive synthetic route development was required. Most notable from this work is the area of materials containing benzodithiophene cores, which were found capable of strong reverse wavelength dispersion birefringence. The effect was found to be tuneable, depending on the aryl substituents used and 11 novel homologues of these materials were produced, characterised and material properties examined.