Photoresponsive Liquid Crystal Research Articles

Optically controllable side-polished fiber attenuator with photoresponsive liquid crystal overlay

This study presents an optically controllable fiber-optic attenuator consisting of side-polished fiber (SPF) with a photoresponsive liquid crystal (LC) overlay operating in the telecommunication wavelength. Attenuation is controlled by a photochemical-induced phase transition of photoresponsive LC, which modulates the evanescent field leaked from the polished area. Before optical field illumination, the photoresponsive LCs are in the light-scattering state and attenuation is high. During photoirradiation, the formation of cis-azobenzene LC disrupts the nematic host and generates a light-transparent state in which the optical loss of the SPF attenuator decreases. The photoinduced tuning range is 15 dB at an environmental temperature of 45 degrees C, and a repeatable and reversible tuning is observed with a response time of less than 5 s. The proposed all-optical controllable attenuator has potential use as an optical signal modulator in an all-fiber telecommunication system.

Photoresponsive Liquid Crystals for Tuning and Aligning Nanostructures

The photoalignment of liquid crystalline azobenzene-containing polymers has been an active area of research, which intends to apply for optical elements such as rewritable optical memory, photorefractive and photomechanical devices. However, the photoalignment behavior is hardly studied in nano-confined environments. We introduce herein our current activities on the new types of photoalignment controls of azobenzene-containing liquid crystalline polymer materials; (i) polymer chains tethered (grafted) onto a substrate and (ii) nanostructures formed by a block copolymer. New platforms for the photoalignment technologies are anticipated in these photoactive thin film systems.

Light-Induced Deformation of Photoresponsive Liquid Crystals on a Water Surface

Photodeformation: Azobenzene derivatives showing a room-temperature liquid crystal (LC) phase exhibit photoinduced deformation on a water surface. While a droplet of a LC sample floating on the surface expands upon UV irradiation, a LC sample containing a solvent is condensed towards the center of the illuminated regions (see figure).

A photoresponsive liquid crystal based on (1-cyclohexenyl)phenyldiazene as a close analogue of azobenzene

A new photoresponsive calamitic liquid crystal molecule possessing (1-cyclohexenyl)phenyldiazene as a close analogue of azobenzene was synthesized and a comparative study with the corresponding azobenzene analogue carried out.

Light-controllable photoresponsive liquid-crystal photonic crystal fiber

We have developed all-optical modulation of photonic crystal fiber (PCF) by infiltrating photoresponsive liquid crystal (LC) into the voids within the cladding structure. The photo-induced phase transformation of the photoresponsive LC modulates the effective refractive index of the photoresponsive LC-filled cladding, thereby creating an environment of modifiable total internal reflection that tunes the output intensity of guided light upon the stimulus of optical field. The modulation range for the 632 nm wavelength is 10 dB and the response time for switching is less than 1 second by manually obstructing the pumping light path. In addition to altering the power of the pumping laser to actively tune the output intensity, the polarization direction of the pumping laser can also tune the output intensity by 5 dB.

Surface Plasmons of Metal Nanostructure Arrays: From Nanoengineering to Active Plasmonics

We developed cost-effective and high-throughput techniques to fabricate metal nanostructure arrays of various geometries on solid substrates. Surface plasmons of these nanostructure arrays were investigated both experimentally and theoretically. We systematically studied the effects of different parameters on the localized surface plasmon resonance of the nanostructure arrays. We further developed a few approaches to tailor surface plasmons for different applications. As an example of the applications of these nanostructure arrays, we demonstrated all-optical plasmonic switches/modulators based on long-range ordered Au nanodisk arrays and photoresponsive liquid crystals. The advantages of such arrays include low-cost, high-throughput, and tailorable plasmonic properties. These arrays can serve as a platform that will stimulate further progress in both fundamental research and engineering applications of plasmonics.

All-Optical Active Plasmonics Based on Ordered Au Nanodisk Array Embedded in Photoresponsive Liquid Crystals

ABSTRACTWe propose a new approach towards all-optical active plasmonics based on ordered Au nanodisk arrays embedded in azobenzene-doped liquid crystals (LCs). Upon photoirradiation, the doped LCs went through phase transition induced by trans-cis photoisomerization of the azobenzene molecules. The phase transition led to the change in the refractive index of the LCs experienced by incident light, and enabled reversible tuning of the localized surface plasmon resonance (LSPR) of the embedded Au nanodisks. The tuning utilized the sensitivity of the LSPR of the Au nanodisks to the change in the surroundings' refractive index. Experimental observations on both peak shift and intensity change of the LSPR matched those from discrete dipole approximation (DDA) calculations.

Control of the Optical Properties of Liquid Crystal-Infiltrated Inverse Opal Structures Using Photo Irradiation and/or an Electric Field

Tunable photonic band gap crystals were prepared by the infiltration of photoresponsive liquid crystals into inverse opal structure films. Tuning of their optical properties could be realized by means of photoinduced phase transition of liquid crystals. The photoinduced phase transition behavior could be evaluated by measuring the change in their optical properties under light irradiation, and it was clearly observed that the behavior varied with temperature and light intensity. The materials could store and display images that were created by the irradiation with UV light through a photomask. A great advantage of this technique is that the films themselves can display an image without the use of polarizers or other assistant materials, and they can also render a color display that can be selected by varying the lattice distance of the inverse opal structure. In addition, we achieved the control of their optical properties by the application of an electric field. Because the state induced by the electric field is different from that engendered by a photoinduced phase transition, it is now possible to switch among three states by a combination of these two techniques. The materials that we have developed have possibilities for practical applications in optical devices.

Design of Chiral Dimesogens Containing Cholesteryl Groups; Formation of New Molecular Organizations and Their Application to Molecular Photonics

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design of chiral dimesogens containing cholesteryl groups; formation of new molecular organizations and their application to molecular photonics.

Photoresponsive liquid crystals and organogels are finding increasing application in information technology and photonics. In this tutorial review, the authors describe how weak intermolecular interactions facilitate molecular organization of cholesterol-containing dimesogens to form such materials. Design considerations and photoresponsive properties of both organogels and glassy liquid crystals are discussed and their applications to molecular photonics highlighted. The review will be of value to readers interested in the development of new materials which respond to the different properties of light.

Photoresponsive liquid crystal display driven by new photochromic azobenzene-basedLangmuir–Blodgett films

We have used a new method to fabricate photochromic Langmuir–Blodgett (LB)films from a pure azobenzene derivative. The films are used to photoregulatenematic liquid crystals in the host–guest cell (LCD cell). We have demonstratedthat the photoresponsiveness of the LCD cell is well determined byphototriggering the active LB surface with alternating ultraviolet and visible lightillumination. The ‘on’ and ‘off’ states of the LCD display were assigned bythe appearance of the homogeneous ‘planar’ and ‘homeotropic’ texturesrespectively. The molecular dynamics of the LCD cell are explained in terms ofa model structure depicting photoresponsiveness against illumination.

Photoswitching of Helical Twisting Power by Chiral Diarylethene Dopants

Photochromic chiral compounds having two diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. Stable photoswitching of the photochromic dopants induced large pitch changes of chiral nematic liquid crystals composed of K-15 and a small amount of the chiral dopants.

Photoinduced pitch changes in chiral nematic liquid crystals formed by doping with chiral diarylethene

Chiral binaphthyl derivatives having two photochromic diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. These compounds showed thermally irreversible photochromic reactions. The circular dichroism (CD) spectra and the optical rotation values of the derivatives reversibly changed in methanol upon alternate irradiation with ultraviolet and visible light. Large photostimulated pitch changes of chiral nematic K-15 liquid crystals were observed on addition of the derivatives as dopants. The relation between the optical rotation and the twisting power force was discussed.

Phase Transition of a Liquid Crystal Induced by Chiral Photochromic Dopants

A chiral cyclohexane having two photochromic diarylethene unit was synthesized in an attempt to use it as a dopant for a photoresponsive liquid crystal. A stable photoswitching between nematic and cholesteric phases could be induced by the addition of a small amount of the chiral cyclohexane to a nematic liquid crystal 4-cyano-4′-penthylbiphenyl (K-15).

Photoswitching of Helical Twisting Power of a Chiral Diarylethene Dopant: Pitch Change in a Chiral Nematic Liquid Crystal

A chiral cyclohexane containing two photochromic diarylethene units was synthesized in an attempt to use it as a dopant for a photoresponsive liquid crystal. A stable photoswitching between nematic and cholesteric phases could be induced by the addition of a small amount of the chiral cyclohexane to a nematic liquid crystal 4-cyano-4‘-penthylbiphenyl (K-15).

Photoresponsive liquid crystals prepared from poly(biphenylyl vinyl ether‐alt‐maleic anhydride)s

AbstractPhotoresponsive groups (azobenzene and cinnamic acid derivatives) were incorporated into alternating copolymers of maleic anhydride and vinyl ethers with pendant 4′‐methoxy‐4‐biphenylyl moieties bound via ethylene glycol spacers. The resulting polymers were examined with respect to their liquid crystalline behavior and photochemical reactivity in relation to the isothermal phase transition behavior.