Dichroic Dyes for Liquid Crystal Applications
Dichroic dyes have a range of applications, including guest-host liquid crystal displays for electronic display devices and more recently in PDLC (polymer dispersed liquid crystals), for applications such as Smart / Privacy Glass, lenses and electronic displays.
Dichroic Dyes – How do they work?
What is dichroism?
A dichroic dye is effective because the light absorbed by the dye molecule is absorbed generally in one direction. Therefore if the dye is moved perpendicular to this absorbance, no light is absorbed and no colour effect is observed.
In a reflective guest-host system a dye-doped liquid crystal (LC) mixture is prepared by mixing the LC with the dichroic dye. This mixture is then applied between two glass substrates to create an LC cell.
In a nematic LC, in most cases the LC molecule has a rod-like structure and in most cases this rod-like structure must be replicated in the dye molecule in order to effect dichroism. When a magnetic or electric field is applied to the nematic LC, it becomes aligned along that field and the dye molecules align with the LC molecules. This effect allows for the light to either be absorbed or to pass directly through the LC material. Where light is absorbed, the wavelength of that absorbance caused by the dye molecule will cause a colour to be observed.
Dichroic Dyes – Standards supplied by CSS
CSS can supply a set of standard dichroic dyes including dichroic azo-dyes and anthraquinone dyes, to achieve specific colour effects. CSS also provide several standard mixtures of dyes to give a broad absorbance across the visual spectrum, These standard mixtures come as green, or black visual effect. In general we can supply dyes to absorb across wavelengths from ~350nm to ~800nm.
Dichroic Dyes – Research
CSS can also supply a number of research dyes in small amounts. These dyes may have different chromophores to the Azo / AQ dyes used in our standards and can have different physical properties. Over many years of collaborative work, we have found that each application often requires a different approach and a different type of dye, so being able to offer a selection of dichroic dyes is often useful to determine which class of dye is most useful.
This information then allows CSS to help design specific dyes to improve their performance in each application.
Using our expert dye knowledge we can modify the substituents around the central chromophore, to alter the λmax (the absorption maximum of the chromophore). Then by the addition of mesogenic groups we can improve the dichroic ratio and the dye solubility in a given medium, such as a liquid crystal matrix. This means that we can tailor the structure of any known dichroic dye compound to meet your requirements. We can even synthesise polymerisable dichroic dyes which can be used to “fix” patterns in polymeric liquid crystals.
Our knowledge of dichroic dyes and chromophores in general, allows us to extend our range of dyes to offer UV absorbers at ~350nm to IR absorbers up to around 850nm absorbance. We can even offer more cost efficient dyes, where slightly lower quality (98-99% purity) will suffice in your application.
At CS Solutions Ltd, we’re able to use our understanding of liquid crystals to incorporate appropriate mesogenic groups to your dye to improve it’s dichroic ratio and overall performance. Alternatively, we’re able to take a mesogen and incorporate a chromophore which absorbs at a given wavelength to allow you to explore a range of properties within your liquid crystal medium.
We are now expanding our catalogue of dichroic dyes in order to offer single colours (yellow, orange, red, magenta, blue and cyan) in both Azo and Anthraquinone forms, plus we can offer a series of homogenous black dichroic dyes for testing in your application.
We are constantly striving to improve our dichroic dye range and improve upon their absorption, solubility, dichroic ratio and thermal/photostability. Give CSS a call and see if we can help in your application.
Dichroic dyes available from CS Solutions
Here at CS Solutions we like to provide a tailored solution to give the best results in your applications. However, we realise that initially our customers often want an off-the-shelf dichroic dye to develop working prototypes and prove feasibility.
With this in mind, CSS have begun developing an UV to coloured to NIR absorbing dichroic dyes in a selection of chromophores. These chromophores include standard azo and anthraquinones, but also other more investigative structures that may suit your applications.
Dichroic Dyes – Quality
Working with dichroic dyes in electronic displays often means working to very high specifications (e.g. 99.0-99.9% organic purity) and our customers are continually impressed with the very high purity and oquality of the products we supply. Having worked on a number of contract research projects involving dichroic dyes, our team of chemists has developed the skills required to carry out difficult synthetic procedures and produce samples of the highest quality.
We can currently provide 100’s milligrams to gram samples of a selection of dyes of various colours, including yellow, red, magenta, blue and cyan. Our standard Azo dichroic dyes can be purchased in larger amounts (up to 100s grams) without loss of quality. We also provide dichroic black mixtures, and can customise mixtures to your specific requirements or other mixtures to provide you with the absorbance (or transmission) you require.
If you have any questions or wish to discuss placing an order please contact us using the form on the website and let us know what your requirements are.