High Pressure Kinetics of Azo Dyes in Nematic Liquid Crystals

The introduction of organic photochromes into nematic liquid crystals (LCs) enables the modulation of their macroscopic properties and gives rise to unique applications. In particular, azo compounds are the dyes of common choice for this task because of their clean and reversible isomerization. In this context, gaining a good insight into how the LC medium influences the kinetics of the isomerization process is essential to develop novel liquid-crystalline materials with specific capabilities. Herein, we report the measure for the first time of the pressure activation parameters for the cis-to-trans thermal isomerization reaction of azo dyes in this self-organized state of condensed matter. For this purpose, a novel setup has been developed, which can also be utilized for highly light-absorbing solutions. Initially, the mechanism of the thermal back reaction in the isotropic phase of the LC has been confirmed and compared with that observed in standard solvents (ΔV⧧ ≈ 0). Further increase in pressure or d...