Phototunable Azobenzene Cholesteric Liquid Crystals with 2000 nm Range

White, Timothy J.; Bricker, Rebecca L.; Natarajan, Lalgudi V.; Tabiryan, Nelson V.; Green, Lisa; Li, Quan; Bunning, Timothy J.

doi:10.1002/adfm.200900396

Cited by 142 publications

(101 citation statements)

References 49 publications

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“…In the past decade, a number of light responsive chiral dopants which can change their HTP either upon isomerization or helical inversion have been used to tune the position of a cholesteric reflection notch over a wide range. [116][117][118] A light responsive system which can change its reflection bandwidth based on the intensities of light would be very attractive. First steps for such a responsive system in the visible and infrared regions have been taken by White et al using a chiral azobenzene photoisomer doped in a Ch-LC cell.…”

Section: Outlook and Future Challengesmentioning

confidence: 99%

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

324

220

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(IR), here defined as light with wavelengths between 700 nm and 2500 nm, accounts for around 50% of the total energy emitted by the sun reaching Earth (Figure 1b), [3,4] and this light produces interior heating but is invisible to the unaided eye.The absorption of sunlight by building materials and passage of IR through transparent surfaces such as windows is responsible for much of the interior overheating of office rooms, automobile interiors, greenhouses, and other similar spaces. The use of artificial cooling and heating systems will only increase with the continued influence of global climate change, with energy used for cooling systems surpassing energy used for heating around the year 2070, and a 40 fold increase in air cooling energy use is expected by 2100. [5] By controlling the influx of radiant heat transfer, calculations show that more than 50% of the energy used in lighting, heating and cooling could be saved by deploying better control systems over only 18% of available window stock. [6] In areas with human inhabitants employing windows, more aspects must be considered than simply reducing the use of energy in the room: any switchable window used in, for example, a commercial office space has several other requirements that must be met before it may be installed. Among these requirement are reasonably fast switching speeds [7] (although for IR control, relatively longer times compared to visible light switching should be acceptable), good optical transparency with minimum haze, an acceptable device lifetime, [8] and functionality over a range of exterior temperatures. Controlling the excess of solar energy without compromising the visible transparency of the window is an important consideration for human health: maintaining inside/outside contact and daylighting are vital in retaining well-being and productivity, as well as providing economic and aesthetic gain by reducing the need for artificial lighting systems. [9,10] These are challenging goals for a window to realize.A number of materials have been developed over the past few decades to maintain indoor temperatures. Many of these focus on the opaque structural building elements like walls and roofing. [10][11][12][13] Other solutions target the transparent window, employing external mechanical shutters and blinds, [14] phase change materials (PCMs), [15] thermochromic materials, [16] aerogels, [17] trapped gas in fluid membranes, [18] and even phononic materials, [19] among other options. Indeed, controlling heat passage through the window in response to changing climate conditions is a great challenge; ideally, one would accomplish Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or trans...

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Section: Outlook and Future Challengesmentioning

confidence: 99%

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

324

220

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“…In CLC, the birefringent molecules self-assemble with the director (crystalline) axis arranged in a spiral, with a pitch on the order of the optical wavelength stretching from the UV to the infrared regime, as seen in Figure 12. As a result, CLC's possess not only the advantageous features of liquid crystals such as fabrication ease and low cost, and a very wide spectral dynamic range of operation [68,69], but also the 1-D photonic crystals' unique ability to enhance the nonlinear ultrafast all-optical responses of the CLC constituent molecules [mostly due to the nematic constituent], in addition to the dispersion effect at the photonic band-edges. A typical magnitude of the non-resonant nonlinear index coefficient n 2 is in the order of 10 −14 -10 −13 cm 2 /W, but owing to the photonic crystal band-edge enhancement, the magnitude of the effective n 2 can be as large as 10 −12 -10 −11 cm 2 /W.…”

Section: Ultrafast Pulse Modulations Based On Cholesteric Liquid Crysmentioning

confidence: 99%

Ultrafast Optical Signal Processing with Bragg Structures

Liu

Malomed

et al. 2017

Applied Sciences

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Abstract:The phase, amplitude, speed, and polarization, in addition to many other properties of light, can be modulated by photonic Bragg structures. In conjunction with nonlinearity and quantum effects, a variety of ensuing micro-or nano-photonic applications can be realized. This paper reviews various optical phenomena in several exemplary 1D Bragg gratings. Important examples are resonantly absorbing photonic structures, chirped Bragg grating, and cholesteric liquid crystals; their unique operation capabilities and key issues are considered in detail. These Bragg structures are expected to be used in wide-spread applications involving light field modulations, especially in the rapidly advancing field of ultrafast optical signal processing.

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“…[14,26] Recently, we reported the synthesis of a planar chiral azobenzene consisting of a di-A C H T U N G T R E N N U N G oxynaphthalene moiety that was cyclically bonded at the meta positions of azobenzene by bismethylene spacers, which was successfully employed as a chiroptical switch in commercially available liquid crystals, giving rise to phototunable reflection colors.…”

Section: Introductionmentioning

confidence: 99%

“…[1,12] Moreover, the intriguing science behind photoinduced chirality is also attracting the attention of many researchers owing to its the possible applications in chiral sensors [13] and switches. [14] Following studies by le Bel [15] and Van't Hoff [16] that demonstrated the potential usefulness of l-or r-circular polarized light (l-or r-CPL), several attempts have been made to achieve enantiomeric enrichment using CPL. Among the various photocontrolled chiral induction processes, reversible enantio-differentiating photoisomerization is known to take place in a number of compounds for which photoresolution and photoracemization occur with CPL and normal light, respectively.…”

Section: Introductionmentioning

confidence: 99%

Induction of Molecular Chirality by Circularly Polarized Light in Cyclic Azobenzene with a Photoswitchable Benzene Rotor

Hashim

Thomas

Tamaoki

2011

Chemistry A European J

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New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3'-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed.

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Phototunable Azobenzene Cholesteric Liquid Crystals with 2000 nm Range

Cited by 142 publications

References 49 publications

Infrared Regulating Smart Window Based on Organic Materials

Infrared Regulating Smart Window Based on Organic Materials

Ultrafast Optical Signal Processing with Bragg Structures

Induction of Molecular Chirality by Circularly Polarized Light in Cyclic Azobenzene with a Photoswitchable Benzene Rotor

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