Novel photocontrollable photonic crystals based on porous silicon prepared by electrochemical etching are elaborated and their great potential for creation of photoswitchable materials is demonstrated. For this purpose, silicon‐based photonic porous wafers are filled with photochromic liquid crystalline (LC) nematic mixture formulated by 4‐pentyl‐4′‐cyanobiphenyl and a specific azobenzene derivative. Results of electron paramagnetic resonance spectroscopy reveal that molecules of LC mixture are aligned along the etched channels in silicon plate, i.e., in normal direction. UV irradiation (375 nm) of the resulting composite causes a shift of photonic band gap to longer wavelengths by ≈10 nm. This phenomenon is explained by isothermal photoinduced nematic–isotropic phase transition associated with the bent‐shaped Z isomer formation of the azobenzene compound. During this transition, effective refractive index slightly increases as the initial homeotropic alignment of LC molecules transforms to the isotropic nonaligned state. This process is completely reversible under visible light action (428 nm) and can be repeated many times. Obtained photonic crystal photochromic LC composites can be considered as new promising material for photonic applications.

中文翻译：

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基于多孔硅填充光致变色液晶混合物的光控光子晶体

阐述了通过电化学刻蚀制备的基于多孔硅的新型可控光子晶体，并证明了其在创建可光开关材料方面的巨大潜力。为此，在硅基光子多孔晶片中填充由4-戊基-4'-氰基联苯和特定的偶氮苯衍生物配制的光致变色液晶（LC）向列混合物。电子顺磁共振波谱的结果表明，LC混合物的分子沿硅板中的蚀刻通道排列，即法线方向。所得复合材料的紫外线照射（375 nm）导致光子带隙向更长波长移动≈10nm。这种现象可以通过等温光致向列-各向同性相变与弯曲形Z来解释。偶氮苯化合物的异构体形成。在此过渡过程中，有效折射率随LC分子的初始垂直排列转变为各向同性非排列状态而略有增加。在可见光作用下（428 nm），该过程是完全可逆的，可以重复多次。获得的光子晶体光致变色LC复合材料可以被认为是光子应用的新材料。