Phototropic liquid crystals (PtLC) are a new class of materials possessing number of potential applications in photonics devices. However, so far a significant majority of PtLC materials has been realized by the doping a classical liquid crystal with a photochromic dye. The photochemical phase transition in such systems was investigated mainly by the monitoring of the changes in the transmittance. In this study, the photochemical phase transition of single-component phototropic liquid crystals was investigated using a holographic grating recording in combination with a polarized optical microscope. The cis–trans photoisomerization of compounds causes the isotropic-to-nematic (I–N) phase transition and so that the interference pattern can be mapped as a diffraction grating. The process of the grating build up was monitored by the first-order light diffraction, and simultaneously the area of the material exposed to the light was observed directly under a polarized microscope. The combination of the holographic technique with polarized optical microscopy has allowed to propose the mechanism of the I–N phase transition of LC compounds. It assumes three processes responsible for the grating formation. The results have a crucial importance in understanding the mechanism of photochemical phase transition of PtLCs, and thus they can be useful in construction of new optical devices.

Holographic grating recording in azobenzene-based polymers using a single coherent light of a specific wavelength (monophotonic recording) is the basis of the majority of the applications of this type of material. Here, we report a new approach to holographic recording that uses two light sources having different wavelengths during the recording process (biphotonic recording). The efficiency of the recording process was improved significantly compared to that of the monophotonic recording. The results, by presenting a simple way to increase the efficiency of the recording process, have important implications for the applications of azobenzene-based materials. They indicate how the performance of the already proposed devices can be improved, and they can open a new way to developing applications of this class of materials.

No abstract