Using the Photostationary State of Arylazopyrazoles to Control Phase Transitions of Liquid Crystals

Abstract The development of responsive molecules enables the design of novel smart materials for numerous applications. A series of new arylazopyrazoles is designed as dopants for commercially available liquid crystal hosts and their photoresponse in solution and mesophases is investigated. Furthermore, the solid‐state structure in single‐crystal diffraction is analyzed to gain insight into possible intermolecular interactions of the photoswitches with LC host materials, thus anticipating the effect of photoswitching in the LC phase. Additionally, 3,5‐difluorophenol is implemented as a hydrogen‐bond donor to tune the impact of the photoisomers on the mesogenic behavior. Unprecedented, reversible control of the distribution of E ‐ and Z ‐isomers at the photostationary state of different wavelengths (365, 460, and 520nm) is utilized to induce phase transitions of liquid crystals. This strategy allows for the controlled transition between smectic, nematic, and isotropic phases at isothermic conditions by irradiation with the corresponding wavelength ‐ a new concept in the design of photoresponsive materials.