Alignment Of Dye Research Articles

In-situ homeotropic alignment of dye doped liquid crystal molecules on multilayered self assembled nanoparticles in confined cells for next generation display devices

The in-situ homeotropic alignment (HA) of pure liquid crystal (LC) and dye doped LC molecules was prepared on the multilayered self assembled silica nanoparticles (SNPs) deposited on the substrates in a confined empty ITO cell. The LC and azo dye mixtures with (0.0625–0.5 wt%) concentrations show the uniform in-situ HA of nematic LC (NLC) over SNPs coated surface. The surface morphology with mapping of elements and functionality of the SNPs coated ITO glass substrate were confirmed by “field emission scanning electron microscope (FESEM)” and “X-ray photoelectron spectroscopy (XPS)”. Polarized optical microscopic textures and conoscopic view of pure and dye doped LC mixtures in SNPs coated confined cells, confirmed the HA of LC molecules and exhibited the uniform black textures under crossed polarizers. The electro-optic behaviour of dye doped homeotropically aligned LC (HALC) cells was compared to pure SNPs coated HALC cell. The results showed that on increasing the azo dye concentration (0.0625–0.25 wt%), the threshold (Vth) and operating (Vo) voltages were found decreased. However, on further increase of dye concentration to 0.5 wt%, Vth and Vo were observed relatively increased. The contrast ratio (CR) was found improved in dye doped HALCs with maximum CR at lowest dye concentration (0.0625 wt%). The UV results exhibit higher absorbance of the dye doped HALC cells with increasing the dye concentration. Also, the band gap values showed that the addition of even small amount of dye, it reduced the value of band gap in HALC cell.

Dichroic Dipole Antenna Membranes from Aligned Linear BOPHY Dyes

AbstractLinear dyes are molecular mimics of dipole antennas that receive UV–vis light. In this work the assembly of linear dyes via the Langmuir technique to achieve uniform dye alignment for optically anisotropic molecular dipole antenna arrays is presented. The molecular orientations in these arrays are quantified from Langmuir isotherms, topography data, and from polarization‐ and angle‐dependent UV–vis transmission spectra. It is achieved the smallest angles by which the transition dipole moment orientation deviates from vertical alignment (16°–30°) in the antenna arrays that have been reported in literature so far. The resulting maximum absorption contrast between grazing and vertical incidence amounts to 75%. This high optical anisotropy enables application as anisotropic receiver arrays in optical communication, as optical layers for privacy applications, or other applications building on dichroic dye layers.

The structural studies of 2-[(4-tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) incorporated γ ray irradiated chitosan films for optoelectronic applications

Herein, versatile biopolymer chitosan films doped with 2-[(4-‑tert-butylphenyl)-5–(4-biphenyl)]-1, 3, 4- oxadiazole (PBD) a known OLED material were prepared by intercalation method. These films witnessed crosslinking which in turn exhibited exciting properties due to gamma irradiation with varied dosages. The radical mediated crosslinking of NH2 group with t‑butyl group was envisaged by the increased crystallinity of the films. The XPS analysis showed the formation of the bond between dopant and polymer backbone. The changes in binding energies of unirradiated and irradiated CHPBD films for N1s from 399.08 eV (1° amine) to 400.7 eV (2°amine), supported reaction of NH2 group with t‑butyl group of PBD in crosslinking of dopant and polymer matrix with the formation of CN linkage. In PXRD, peaks centered around 21.24° for pristine chitosan film, but for the unirradiated CHPBD, it was shifted to the lower angle16.09° to form amorphous film. However, for the irradiated CHPBD shifting to the higher angle 22.9°, 23.08°, 27.23° suggesting that dopant had chemically interacted with the polymer matrix. The Young's modulus, tensile strength indicated supportive properties. An interesting change in UV absorption behavior was observed for the unirradiated CHPBD exhibiting λmax at 290 nm with a hypsochromic shift with respected to dopant (λmax,309 nm). This indicated weak head-to-head alignment of dyes in an unirradiated matrix; whereas irradiation brought about changes through chemical crosslinking in the architecture of films with a redshift to 309 nm. Hyperchromism was also the effect of irradiation on films. The unirradiated films exhibited emission maxima around 369 nm whereas irradiated films showed 412 nm. Hence, a simple method was developed for the preparation of blue emissive biopolymeric materials.

Correlating Optical and Electrical Dipole Moments To Pinpoint Phosphorescent Dye Alignment in Organic Light-Emitting Diodes.

Understanding the morphology of organic materials within optoelectronic thin film devices is of crucial importance for the development of state-of-the-art organic light emitting diodes (OLEDs). In this context, the preferential alignment of organometallic Ir complexes has been in the focus of research to benefit from the improved light-outcoupling efficiencies. Although the emissive dipole orientation has been identified from an optical point of view and molecular dynamic simulations give first insights into film morphologies, new experimental techniques are necessary to pinpoint the exact alignment of phosphorescent dye molecules. In this work, optical characterization of luminescent thin films was combined with electrical measurements on bilayer devices to elucidate the orientation distribution of both, electrical and optical dipole moments of phosphorescent guest-host systems. The results not only confirm previous suggestions for the alignment mechanism of organometallic dyes but also disclose a direct correlation between the degree of electrical and optical dipole alignment, thus opening a roadway for achieving higher light-outcoupling efficiency in OLEDs.

A Rationally Designed, General Strategy for Membrane Orientation of Photoinduced Electron Transfer-Based Voltage-Sensitive Dyes

Voltage imaging with fluorescent dyes offers promise for interrogating the complex roles of membrane potential in coordinating the activity of neurons in the brain. Yet, low sensitivity often limits the broad applicability of optical voltage indicators. In this paper, we use molecular dynamics (MD) simulations to guide the design of new, ultrasensitive fluorescent voltage indicators that use photoinduced electron transfer (PeT) as a voltage-sensing switch. MD simulations predict an approximately 16% increase in voltage sensitivity resulting purely from improved alignment of dye with the membrane. We confirm this theoretical finding by synthesizing 9 new voltage-sensitive (VoltageFluor, or VF) dyes and establishing that all of them display the expected improvement of approximately 19%. This synergistic outworking of theory and experiment enabled computational and theoretical estimation of VF dye orientation in lipid bilayers and has yielded the most sensitive PeT-based VF dye to date. We use this new voltage indicator to monitor voltage spikes in neurons from rat hippocampus and human pluripotent-stem-cell-derived dopaminergic neurons.

Dyes in Liquid Crystals: Experimental and Computational Studies of a Guest-Host System Based on a Combined DFT and MD Approach.

Practical applications of guest–host liquid crystal systems are critically dependent on the alignment of the guest species within the liquid crystal host. UV/Vis absorption spectroscopy shows that the 1,5-dihydroxy-2,6-bis-(4-propylphenyl)-9,10-anthraquinone dye aligns within the E7 nematic host, giving an experimental dichroic ratio of 9.40 and dye order parameter of 0.74. This alignment was modelled by using a combination of density functional theory (DFT) and molecular dynamics (MD) computational approaches that do not require the input of experimental data. Time-dependent DFT calculations show that the electronic transition dipole moment is highly aligned with the long molecular axis of the dye. Fully atomistic MD simulations show that the long axis of the dye is less highly aligned within the E7 host, indicating that this contribution limits the overall dye alignment and, thereby, the potential practical applications of this particular system. Importantly, this study demonstrates an experimental and combined DFT and MD computational approach that may be applied generally to guest–host systems, providing a potential route to their rational design.

67.3: Photo‐stable Azo Dye Photoalignment Polymer Surface for In Plane Switching Liquid Crystal Displays

A photo‐stable azo dye photoalignment surface for liquid crystal is proposed and demonstrated. The alignment surface has a structure of stacking a thin photo‐polymerisable liquid crystal polymer on top of an azo dye photoalignment layer. The liquid crystal polymer acts as a passivation layer for the azo dye alignment layer. The alignment direction of the azo dye cannot be rewritten once the liquid crystal polymer is polymerized. Hence, the synthetic alignment surface is robust, highly reproducible and has excellent stability. In addition, measurement results show the alignment properties of this synthetic alignment surface are comparable to conventional polyimide. As a result, the proposed alignment layer is suitable for in plane switching liquid crystal display which requires high anchoring energy and very small residual direct current.

New photosensitizers containing the dipyridoquinoxaline moiety and their use in dye-sensitized solar cells

New Ru(II) polypyridyl complexes containing two N, N bidentate ligands, [Ru(phendione)2dpq(COOH)2](BF4)2 (L101), {Ru(phendione)[dpq(COOH)2]2}(BF4)2 (L102) and [Ru(phendione)dpq(COOH)2 (SCN)2](L103), (phendione=5,6 dione-1,10-phenanthroline and dpq(COOH)2=6,7-dicarboxylicdipyrido[2,2-d:2′,3′f]quinoxaline) have been synthesized and characterized, and attached to a TiO2 substrate to be tested as solar cell sensitizers. We found that the solar to electricity conversion efficiency of cell is strongly affected by the type of ancillary ligand, the efficiency of L102 (with one phendione moiety) adsorbed on TiO2 nanocrystalline films being 2.5 times as large as that of L101 (with two phendione moieties) adsorbed on the same films. The effect of ancillary ligand on the photovoltaic performance of the complexes was compared to results of computational methods by ab initio DFT molecular dynamics simulations and quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in L101–103/TiO2-anatase nanostructures. It is found that the primary process in the interfacial electron-transfer dynamics involves an ultrafast (τ1=6fs) electron-injection. The concepts of attribute ancillary ligand substitution and HOMO–LUMO alignment of dye with conduction band of semiconductor and electrolyte redox state are shown very helpful for tuning the photovoltaic properties and the rational architecture of polypyridyl photosensitizer with anticipated good properties.

Lasing and waveguiding in smectic A liquid crystal optical fibers

We demonstrate a new class of soft matter optical fibers, which are self-assembled in a form of smectic-A liquid crystal microtubes grown in an aqueous surfactant dispersion of a smectic-A liquid crystal. The diameter of the fibers is highly uniform and the fibers are highly birefringent. They are characterized by a line topological defect in the core of the fiber with an optical axis pointing from the defect core towards the surface. We demonstrate guiding of light along the fiber and Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the fiber. The light guiding as well as the lasing threshold are significantly dependent on the polarization of the excitation beam. The observed threshold for WGM lasing is very low (≈ 75μJ/cm(2)) when the pump beam polarization is perpendicular to the direction of the laser dye alignment and is similar to the lasing threshold in nematic droplets. The smectic-A fibers are soft and flexible and can be manipulated with laser tweezers demonstrating a promising approach for realization of soft photonic circuits.

Dye alignment in luminescent solar concentrators: I Vertical alignment for improved waveguide coupling

Luminescent solar concentrators (LSCs) use dye molecules embedded in a flat-plate waveguide to absorb solar radiation. Ideally, the dyes re-emit the absorbed light into waveguide modes that are coupled to solar cells. But some photons are always lost, re-emitted through the face of the LSC and coupled out of the waveguide. In this work, we improve the fundamental efficiency limit of an LSC by controlling the orientation of dye molecules using a liquid crystalline host. First, we present a theoretical model for the waveguide trapping efficiency as a function of dipole orientation. Next, we demonstrate an increase in the trapping efficiency from 66% for LSCs with no dye alignment to 81% for a LSC with vertical dye alignment. Finally, we show that the enhanced trapping efficiency is preserved for geometric gains up to 30, and demonstrate that an external diffuser can alleviate weak absorption in LSCs with vertically-aligned dyes.

Dye alignment in luminescent solar concentrators: II Horizontal alignment for energy harvesting in linear polarizers

We describe Linearly Polarized Luminescent Solar Concentrators (LP-LSCs) to replace conventional, purely absorptive, linear polarizers in energy harvesting applications. As a proof of concept, we align 3-(2-Benzothiazolyl)-N,N-diethylumbelliferylamine (Coumarin 6) and 4-dicyanomethyl-6-dimethylaminostiryl-4H-pyran (DCM) dye molecules linearly in the plane of the substrate using a polymerizable liquid crystal host. We show that up to 38% of the photons polarized on the long axis of the dye molecules can be coupled to the edge of the device for an LP-LSC based on Coumarin 6 with an order parameter of 0.52.

Controlling Light Emission in Luminescent Solar Concentrators Through Use of Dye Molecules Aligned in a Planar Manner by Liquid Crystals

AbstractA luminescent solar concentrator (LSC) is a potential low‐cost enhancement of the standard large‐area silicon photovoltaic panels for the generation of electricity from sunlight. In this work, guest–host systems are investigated using anisotropic fluorescent dyes and liquid crystal mesogens to control the direction of emitted light in the LSC. It is determined that up to 30% more light is emitted from the edge of an LSC waveguide with planar dye alignment parallel to the alignment direction than from any edge of an LSC with no alignment (isotropic). The aligned samples continue to show dichroic performance after additions of both edge mirrors and rear scattering layer.

Temperature-induced chirality reversal of induced circular dichroism of premicellar aggregates of acridine orange derivatives and dodecanoyl-l-threonine in aqueous solution

Circular dichroism (CD) and absorption spectra were measured for acridine orange derivatives: 3,6-bis(dimethylamino) acridine (AO), 3,6-bis(dimethylamino)-10-methylacridinium bromide (C1AO), and 3,6-bis(dimethylamino)-10-dodecylacridinium bromide (C12AO) in aqueous dodecanoyl-l-threonine (C12Thr) solutions at 30, 40, 50, and 60 °C and pH 8–9. CD spectra were not induced for AO and C1AO in C12Thr aqueous solutions. Induced circular dichroism (ICD) based on the exciton interaction was found for premicellar aggregates of C12AO with C12Thr, but the micellar aggregates failed to induce CD for solubilized C12AO at a higher concentration than C12Thr critical micelle concentration. The maximum ICD intensity was observed for 1:1.2 aggregates of C12AO and C12Thr. The ICD spectrum indicated positive chirality at 30 °C, but negative chirality at 50 °C. The chirality transition occurred at 40∼45 °C. The slow change in both the absorption and ICD spectra is ascribed partly to the rearrangement of dye alignment and partly to the growth of the aggregate; the system reaches final phase separation after a few days.

Hydrogen‐Bond‐Directed Head‐to‐Tail Orientation of Dipolar Merocyanine Dyes: A Strategy for the Design of Electrooptical Materials

Two merocyanine dyes are assembled by multiple hydrogen bonds with summation of their dipole moments (see formula; R=2-ethylhexyl). It exhibits a strongly increased degree of dye alignment in an electric field according to electrooptical absorption spectroscopy.

Using “Internal Free Volume” to Increase Chromophore Alignment

Triptycenes have general applicability for increasing the alignment of fluorescent and dichroic dyes in LC hosts. Dyes containing varying numbers of triptycenes were synthesized to study the effect of free-volume alignment of triptycenes on the alignment of dyes. These dyes were designed such that multiple triptycenes could be incorporated and the triptycene-free volume is coincident to the aspect ratio of the dye, allowing a cooperative effect to increase their overall average alignment. With increasing triptycene incorporation, a stepwise increase in the alignment parameters of each dye was seen. It was also found that the attachment of one triptycene group has a negligible effect on the optical switching response times of the dyes. This can be a powerful tool for designing dyes with higher alignments for a variety of applications including guest-host reflective LCDs and holographic data storage.

Simultaneous Near-Field Optical Birefringence and Fluorescence Contrast Applied to the Study of Dye-Doped Polymer-Dispersed Liquid Crystals

The local optical and electrooptical properties of dye-doped polymer-dispersed liquid crystal (PDLC) thin films are explored by near-field scanning optical microscopy (NSOM). Detailed information on the mechanisms for dye alignment and electric-field-induced dye reorientation in localized sample regions is sought. Dye reorientation is predicted to occur by two distinct processes: (i) via its interactions with the liquid crystal host and (ii) via the direct interactions of its permanent and induced dipole moments with the applied field. The liquid crystal is doped with a nearly isotropically aligned BODIPY dye so that contributions of both reorientation mechanisms can be explored. An order parameter of 0.10 ± 0.02 is measured for BODIPY in bulk aligned samples, suggesting that host−guest interactions are very weak. Simultaneously recorded birefringence (transmission) and fluorescence NSOM images confirm that the dye is apparently not well aligned, even on submicrometer length scales. Surprisingly, NSOM studies of dye reorientation prove that host−guest interactions still play a substantial role in controlling the dye reorientation process. The field dependence of dye reorientation is found to be correlated with liquid crystal reorientation, varying spatially across individual droplets. Analysis of the simultaneously recorded birefringence and fluorescence data shows that the dye is strongly reoriented via its interactions with the reorienting liquid-crystal host and also via its independent interactions with the applied field. The former mechanism is manifested as a rotation of the dye alignment axis while the latter leads to a field-dependent increase in the local dye order parameter. “Bistable” alignment of the dye in the nematic host is proposed as a possible explanation for the apparent coupling of the two reorientation mechanisms.

Mechanisms of a remanent optical alignment of dyes in a gel matrix

We present the mechanisms of a remanent alignment of polarizable molecules dispersed in a solid silica gel matrix, when submitted to powerful, femtosecond, linearly polarized, optical pulses emitted from a dye laser. This alignment can be related to third-order nonlinearities of the dopants through an orientational optical Kerr effect. Its remanence results from the strong interactions the dopants share with their host matrix, particularly through hydrogen bonds. We expose here the detailed mechanism of this phenomenon, considering that such a rotation of large chromophores may not be compatible at first sight with subpicosecond pulse durations. Through several experiments, we show that this apparent contradiction is solved once analyzed, by the structure of the excitation pulses, which cannot be simply described as ‘‘femtosecond pulses’’, but consist of two temporal components—a femtosecond one and a nanosecond one—playing different but essential roles in the process.

Dichroism of Dyed Fibres as a Means of Studying Micellar Arrangement

WHY certain types of dyes are adsorbed by cellulose in a definite oriented manner, and how the orientation or alignment of the micelles or crystalline portions is reflected or imitated by such dye molecules as well as how this dye alignment may manifest itself through the phenomenon of dichroism, or of polarized fluorescence, have been discussed.1 Although, for reasons which will shortly appear, the quantitative studies made by the author have been based solely on polarized fluorescence, 2 the phenomenon of dichroism may also be used to advantage in fibre structure studies. This article takes up its use as a quantitative tool, and its advantages and disadvantages when compared with the polarized fluorescence method.