In this letter, we report the results of phototunable lasing in dye-doped cholesteric liquid crystals (DD–CLC). Photoexcitation of DD–CLC films gives rise to laser emission in the violet-UV range. Control of the structure of the chiral dopant driven by UV phototransformation is exploited in order to obtain a permanent variation of the cholesteric pitch. Laser emission wavelength tuning, by means of photoinduced shifting of the selective reflection band of the cholesteric liquid crystals is established. A tuning interval of about 35 nm, in the wavelength range of 385–415 nm, is observed.

tial for applications such as anisotropic building blocks for the preparation of colloidal crystals and photonic materials of unusual symmetry, colloidal liquid crystals, and biosensors.In summary, we have used a gel trapping technique as a generic method for preparing Janus particles by templating of particle monolayers at air±water or oil±water interfaces, followed by lifting off the particles with PDMS and subsequent deposition of gold. By replication of colloidal monolayers of repulsive particles at liquid surfaces we have also fabricated microporous surfaces and composite supraparticles. ExperimentalIn a typical procedure for the preparation of microporous surfaces or Janus particles, 30 lL of a latex particle suspension/isopropanol solution (50:50) was injected at the interface between a hot Gellan solution at 50 C (prepared by hydration of 2 % Gellan (Kelcogel, CPKelco, UK) in water at 95 C for 10 min) and a pre-warmed decane phase. After setting the gel at 25 C, the decane phase was replaced with PDMS (Sylgard 184, Dow Corning) and cured for 48 h. Then the solid elastomer was peeled off the gel and washed in hot water (95 C) for 10 min to remove Gellan residues from the surfaces. To fabricate PDMS with a microporous surface, the particles were removed by stretching the elastomer and collecting the released particles with a metal blade from the surface in the presence of a surfactant solution (1 mM C 12 E 5 ). Janus particles were produced by gold sputtering (NanoTech Seprep II Sputter coater) on the partially embedded particle monolayer on PDMS and subsequent mechanical removal of the particles from the interface.

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A new class of photoactive chiral liquid crystals based on a photoactive nematic host material and a photoinactive chiral dopant was utilized to investigate the behavior of the blues phases when trans-cis isomerization is induced. While the general behavior follows what has been observed in the cholesteric phase, the sensitivity of the blue phases to external parameters causes different behavior when these systems are exposed to UV radiation. The results for four different mixtures are reported and include (1) modulation of the blue phase selective reflection wavelength with low levels of UV and visible light, (2) conversion of one blue phase to another upon exposure to UV light, and (3) induction of blue phases due to UV irradiation when no blue phases are stable beforehand. It is also noted that the supercooled blue phase behaves differently from the other blue phases. All of these results can be understood qualitatively from the ratio of non-nematogenic cis isomers to nematogenic trans isomers and chiral molecules.

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