ИСТИНА

Creation of the self-assembled liquid crystalline (LC) hybrid composites is one of the hot topics in modern materials science associated with a wide range of possible applications of such “smart” materials. One of the most promising properties predetermining this interest is the combination of unique optical properties of LC systems with specific optical or mechanical features of the different matrices. This report describes our results on the design and investigation of hybrid composites based on two types of matrices: (i) porous cholesteric polymer networks and (ii) one-dimensional photonic crystals based on porous silicon. Filling these matrices with low-molar-mass photochromic LC mixtures or LC copolymers enables us obtaining composites with photovariable optical properties. The first type of the polymer scaffolds is prepared by the photopolymerization of the cholesteric mixtures containing mesogenic mono- and diacrylates followed by removing the low-molar-mass components that allows preparing highly porous cholesteric networks. Filling these scaffolds with photochromic LC mixtures capable of the isothermal photoinduced N-I phase transition results in cholesteric films with phototunable position and width of selective light reflection peak. Maximal photoinduced shift of the selective light reflection peak reaches ca. 100 nm. For such composites the possibility of holographic gratings recording and photocontrol of luminescence polarization is demonstrated. The second type of the composites presents photosensitive one-dimensional photonic crystals based on electrochemically etched porous silicon filled with low-molar-mass photochromic LC mixtures or glass-forming azobenzene-containing substances (low-molar-mass and polymeric). UV-irradiation of the composites filled with photochromic LC mixtures induces spectral shift of the photonic band gap in visible spectral range to the longer wavelength with maximal amplitude ca. 10 nm. This shift is associated with isothermal N-I transition of the mixture inside silicon pores and completely reversible by blue light irradiation. For the composites with the azobenzene containing glass-forming compounds polarized visible light results in a noticeable split (up to 25 nm) of the cavity mode of the photonic structure. Such split is explained by the photoinduced orientation of the chromophores in direction perpendicular to the polarization of the incident light. Initial spectra could be easily recovered by heating of the samples above glass transition temperature or by the irradiation with circularly polarized light. LC hybrid composites based on organic and inorganic porous matrices obtained and studied in this work can be considered as promising materials for the applications in photonics and optoelectronics. Acknowledgements: This research was supported by the Russian Science Foundation.