Liquid Crystal Azodye Photoalignment: New Development

Commercial azodye photoalignment materials based on our development are now readily available [1]. Many new displays and photonics applications, have been proposed and demonstrated. In particular, the application of photoalignment to active optical elements in optical signal processing and communications is currently a hot topic in photonics research [2].

Photoalignment on azo-dyes developed by us possesses obvious advantages in comparison with the usually “rubbing” treatment of the substrates of liquid crystal display (LCD) cells. Possible benefits for using this technique include :

• Elimination of electrostatic charges and impurities as well as mechanical damage of the surface;
• A controllable pretilt angle and anchoring energy of the liquid crystal cell, as well as its high thermo and UV stability and ionic purity;
• Possibility to produce the structures with the required LC director alignment within the selected areas of the cell, thus allowing pixel dividing to enable new special LC device configurations for transflective, multi-domain, 3D and other new display types;
• Potential increase of manufacturing yield, especially in LCDs with active matrix addressing, where fine tiny pixels of a high resolution LCD screen are driven by thin film transistors on a silicone substrate;
• New advanced applications of LC in fiber communications, optical data processing, holography and other fields, where the traditional rubbing LC alignment is not possible due to the sophisticated geometry of LC cell and/or high spatial resolution of the processing system;
• Ability for efficient LC alignment on curved and flexible substrates;
• Manufacturing of new optical elements for LC technology, such as patterned polarizers and phase retarders, tunable optical filters, polarization non-sensitive optical lenses, with voltage controllable focal distance etc.

This technique of azodye photoalignment does not involve any photochemical or structural transformations of the molecules. As well the new photoaligning films are robust and possess rather good aligning properties such as anchoring energies and voltage holding ratios. They can be very useful for the new generation of the liquid crystals devices as well as in new photovoltaic, optoelectronic and photonic devices based on highly ordered thin organic layers. Examples of such applications are light emitted diodes (OLED), solar cells, optical data storage and holographic memory devices. The novel and highly ordered layer structures of organic molecules may exhibit certain physical properties, which are similar to the aligned LC layers.

[1] V. Chigrinov, A. Srivastava, H.S. Kwok, Azo-dye photoalignment materials, In a book “High Quality Liquid Crystal Displays and Smart Devices - Volume 2: Surface alignment, new technologies and smart device applications”. IET. 2019, 41-64. Stevenage, UK.

[2] Vladimir G. Chigrinov, Liquid Crystal Photonics, Nova Science Publishers, December 2014.