The photoresponsive behaviors of a smectic liquid crystal, 8CB, tuned by an azobenzene chromophore have been systematically investigated. For the smectic 8CB doped with the azobenzene chromophore, 4-n-hexyl-49-(1-bromopropyloxy)azobenzene (AB), the smectic phase could be switched to nematic and then to isotropic phase induced by the trans-to-cis photoisomerization of AB upon UV irradiation. For the smectic 8CB doped with AB and the chiral molecule, (S)-( 2)-1, 19-binaphthyl-2, 29-diol (BD), the smectic phase could be switched to the cholesteric phase and then to the isotropic phase. The initial phase could be recovered when the cis isomer changed to the trans isomer upon visible irradiation. The switching of the position of reflection band of the liquid crystal mixtures could be also realized by photoisomerization. The photoresponsive behaviors are dependent on the composition ratios and the temperature performed in the study.

Through the looking glass: A reflection color transition is demonstrated in a smectic liquid crystal doped with a photochromic azobenzene and a chiral agent with high helical twisting power. The reflection color can be switched reversibly due to the isomerization of azobenzene upon UV/visible irradiation.

The photocontrolled phase transitions and reflection behaviors of a smectic liquid crystal, 4-octyl-4'-cyanobiphenyl (8CB), tuned by a chiral azobenzene, are systematically investigated. For the smectic 8CB doped with the chiral azobenzene (1R)-(-)-4-n-hexyl-4'-menthylazobenzene (ABE), the initial smectic phase can be switched to cholesteric and then to isotropic upon UV irradiation due to the trans-to-cis photoisomerization of ABE; however, no reflection band is observed. For the smectic 8CB doped with ABE and the chiral agent (S)-(-)-1,1'-binaphthyl-2,2'-diol (BN), a reflection band located in the short-wavelength infrared region is observed, which disappears after further UV irradiation. For the smectic 8CB doped with ABE and a chiral agent with higher helical twisting power, (S)-2,2'-methylendioxy-1,1'-binaphthalene (DBN), a phototunable system with cholesteric pitch short enough to reflect visible light is demonstrated. With a given concentration of the chiral dopant DBN, a reversible reflection color transition is realized tuned by the isomerization of azobenzene. The reverse phase transition from isotropic to cholesteric and then to smectic can be recovered upon visible irradiation. The photocontrolled phase transitions in smectic liquid crystals and the corresponding changes in reflection band switched by photoisomerization of azobenzene may provide impetus for their practical application in optical memories, displays, and switches.