Brilliant Yellow Research Articles

Cross-linked copolyimide-P84/CAU-10-H/branched polyethyleneimine membranes for organic solvent nanofiltration

The advancement of organic solvent nanofiltration (OSN) is often hindered by the inherent trade-off between permeance and rejection. In this study, we present a novel nanocomposite mixed matrix membrane (MMM) fabricated by integrating a compatible metal–organic framework (CAU-10-H) into a co-polyimide (P84) matrix. The resulting P84/CAU-10-H membrane was cross-linked using branched polyethyleneimine (PEI) to produce a P84/CAU-10-H/PEI MMM with robust resistance to harsh organic solvents, making it suitable for OSN applications. The integration of CAU-10-H, PEI, and P84 significantly enhanced the OSN performance, improving sieving efficiency and reducing fouling tendencies. The fabricated membrane exhibited outstanding permeance across various solvents, with values of 42.4, 45.4, 24.5, and 27.1 LMH/bar for methanol, acetone, N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO), respectively. Besides, the P84/CAU-10-H/PEI MMM demonstrated excellent rejection (Brilliant yellow (BY) > 90 %, Congo red (CR), Methyl blue (MB), Evans blue (EB), and Alcian blue (AB) > 99 %, respectively). In a 96-hour long-term test, the membrane demonstrated excellent stability and anti-fouling properties. This study presents a facile and viable approach for designing and constructing novel OSN MMMs.

A novel thioketal containing fluorescent dye for mercury(II) detection via Hg2+-triggered ACQ to AIE transformation

A novel thioketal containing fluorescent dye 1OS was elaborately designed for mercury(II) determination, which not only integrated the benefits of the remarkable specificity of Hg2+-promoted deprotection reaction and the robust emission of AIEgen in aggregated state, but also provided a surprising platform for ACQ-to-AIE switching, i.e. Hg2+-triggered ACQ to AIE transformation. Once encountered Hg2+ ions, the deprotection reaction happened immediately within seconds, accompanied with a conversion of 1OS (ACQ) to 1O (AIE). Excitedly, the probe shows remarkable selectivity and specificity towards Hg2+ both in solution, aggregated and solid states with significant fluorescence color change. When added trace Hg2+ ions into 1OS solution, its PL intensity declined completely with emission color changed from bright green to darkness with LOD as 0.36 μM. Oppositely, a “turn on” signal was achieved in the aggregated state (fw = 98 %), which exhibited a dramatically enhancement of PL intensity along with fluorescent emission altered from darkness to brilliant yellow. Other common metal cations gave no interference to the probe. Meanwhile, the constructed test strip could “turn on” signify Hg2+ in water solution.

Fabrication of azimuthally/radially symmetric liquid crystal plates using two-step photoalignments.

Fabrication of azimuthally/radially symmetric liquid crystal plates (A/RSLCPs) using two-step photoalignments with the two dichroic dyes methyl red (MR) and brilliant yellow (BY) is demonstrated. BY molecules coated onto a substrate and MR molecules doped in LCs in a cell can azimuthally and radially align LCs by illuminating radially and azimuthally symmetric polarized light with specific wavelengths, respectively. In contrast to the previous fabrication methods, the fabrication method proposed here can prevent the contamination/damage of photoalignment films on substrates. A method to improve the proposed fabrication to avoid generating undesirable patterns is also elucidated.

Photoalignment and Photofixation of Chromonic Mesophase in Ionic Linear Polysiloxanes Using a Dual Irradiation System

Photoalignment technology enables macroscopic alignment of liquid crystalline molecules and their aggregates in a non-contact process by irradiating photo-responsive liquid crystalline compounds with linearly polarized light. Because photoalignment techniques prevent dust generation and uneven stretching, and accomplish fine and complex patterning, they are involved in the practical process of fabricating display panels, and continue to be applied in the research and creation of various anisotropic materials. Brilliant yellow (BY), a chromonic liquid crystal, has attracted considerable attention as the photoalignment sublayer in recent years, because of its ability to induce a high dichroic nature among many photo-responsive liquid crystalline materials. However, its dichroism is not maintained after prolonged exposure to a humid environment because of its intrinsic strong hygroscopicity of ionic BY molecules. In this study, to overcome this drawback, the photoalignment and successive photo-fixation of the BY columnar phase is proposed using UV-curable ionic polysiloxane as a matrix. Visible light was used for the photoalignment of the BY columnar phase, and UV light for photo-fixation. Consequently, the columnar chromonic phase is found to retain its orientation even after 4 h of exposure to a highly humid environment.

Novel fluorescent probe based on dicoumarin for detection of hydrogen sulfide in real samples

AbstractA novel dicoumarin‐derived hydrogen sulfide (H2S) selective fluorescent “turn‐on” probe 3‐(2,4‐dinitrobenzenesulfonate)‐dicoumarin (DC‐HS) created by covalent bonding between the 2,4‐dinitrobenzenesulfonyl (DNBS) and the 3‐hydroxy‐dicoumarin (DC‐OH) units. Upon the addition of H2S, the probe DC‐HS solution's fluorescence significantly increased, and its appearance is changed from practically colorless to brilliant yellow. Probe DC‐HS also showed significant fluorescence amplification that was quantitatively detectable in the concentration range of 0–1.5 μM and had a low detection limit or limit of detection of 0.2 nM. Moreover, with a high recovery rate and excellent accuracy, the developed fluorescent molecule was used successfully for the analysis of H2S in red wine samples.

Potential of Polyalthia longifolia Branches as a Biosorbent to Remove Textile Brilliant Yellow Dye from Aqueous Media

This study was conducted to analyze the efficacy of Polyalthia longifolia branches as an effective biosorbent for elimination of textile dye stuff brilliant yellow. Different operating conditions were tested (adsorbent dose, dye concentration, contact time, pH and temperature) to investigate their relationship with adsorption strength of Polyalthia longifolia and subsequently to eliminate toxic color. The absorbent was also characterized by Fourier Transform Infrared (FTIR). Optimum adsorption was observed at pH 6. Model of kinetic explored the adsorption data showing pseudo 2nd order with high correlation coefficient R2 of 0.996. Langmuir model followed well to equilibrium data relative to Freundlich and Temkin models. Thermodynamic property was also observed, where Gibbs free energy, entropy and enthalpy were analyzed. Through Gibbs free energy it was found that absorbent has endothermic nature. Thermodynamic properties have depicted that adsorption process was natural, endothermic and suitable for treatment of toxic dye.

A dual-mode colorimetric/fluorescent probe based on perylene: Response to acidic pH values

BackgroundThe pH value plays critical roles in many chemical and physiological processes and exploring a more effective and sensitive method for the detection of pH is great need. MethodsA new “off-on” pH chemosensor, N,N-bis[(2-furan)-ethyl]-3,4,9,10-perylene tetracarboxylic diimide (FEPTD), was designed and synthesized by Schiff-base condensation reaction with 2-furaldehyde and perylene-3,4,9,10-tetracarboxylic acid dianhydriden as the starting materials. FEPTD as a fluorescent probe was used for highly detecting pH values on the basis of molecular fluorescence spectrophotometry with the excitation wavelength of 300 nm in EtOH/Buffer solutions. Meanwhile, FEPTD was also applied for the detection of H+ in test paper and cotton. Significant findsFEPTD exhibited excellent solubility and stability in EtOH/Buffer (V:V, 1:1) with obvious “off-on” fluorescence response towards pH changes due to photo-induced electron transfer (PET) processes. The linear response ranges of FEPTD for pH detection in acidic system are from 4.32 to 3.10 with pKa = 3.69. Moreover, FEPTD showed an evident naked-eye color changes, where pale pink solution of FEPTD turned deepened with the fluorescent color varying from colorless to brilliant yellow. 1H NMR titration and density function theory calculations proved the possible sensing mechanism. Finally, FEPTD was successfully applied for the detection of H+ in test paper and cotton.

Large rewritable liquid crystal pretilt angle by in situ photoalignment of brilliant yellow films

The ability to control the alignment of liquid crystals (LCs) is a challenge that is near-universal in LC research and applications. While several practical solutions exist for controlling the azimuthal (in-plane) alignment of LCs at an interface, control over the polar, or pretilt angle of the LC often requires a combination of materials or expensive and intricate processing. Here, we introduce a method for exerting control over large pretilt angles utilizing a two-step exposure method applied to Brilliant Yellow (BY) photoalignment films. We demonstrate that BY photoalignment films have the unique ability to enforce a large range of pretilt angles spanning homeotropic (90°) and planar (0°) anchoring conditions at the LC-substrate interface. The alignment is stable over time, rewritable, and patternable. Ultimately the control established here provides a powerful and low-cost means to align and take full advantage of the anisotropic and electro-optic properties of LCs for a wide range of applications.

Synthesis, structural and electrical conduction of some dual doped semiconductor oxides nanoparticles for photocatalytic degradation of Victoria blue-B and Brilliant yellow under solar light irradiation

In this study, the nanoparticles of undoped and dual (codoped) doped semiconductor oxides such as Bi2O3, Bi1.9Sm0.038Cu0.062O3; Co3O4, Co2.902Mn0.049Dy0.049O4; V2O5, V1.91Ni0.043Gd0.047O5; Cu2O, Cu1.927Mn0.036Yb0.037O; CeO2, and Ce0.938Ni0.028Zn0.034O2 were synthesized by tartarate and hydroxide coprecipitation method. The composition, structure, morphology, surface and optical properties of undoped and dual doped semiconductor oxides have been investigated by X-ray fluorescence spectroscopy (XRF), Energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), BET surface area analyzer and UV–Vis diffuse reflectance absorption spectra (UV–vis DRS). The XRD and SEM studies showcase monodispersion of undoped and dual (co-doped) doped semiconductor oxides in the average grain size range of 36–65 nm with a monoclinic structure for Bi2O3 and its doped oxide, cubic structure for Co3O4, Cu2O, CeO2 and their respective doped oxides and orthorhombic structure for V2O5 and its doped oxide. Rietveld refinements of XRD pattern and XPS results confirmed that the dual dopants exist in + 2 or + 3 states and successfully incorporated into the semiconductor oxide matrix. BET surface areas for these oxides were found in the range of 25.3–65.4 m2g−1. The band gap energy (Eg) of undoped and doped semiconductor had a direct transition to fall between 2.10 and 3.12 eV as estimated from the optical absorption data (UV–vis DRS) and found absorption band edge (λg) in the visible-light range. The d.c. electrical conductivity and thermo-electric power measurements for all compounds showed n-type semiconductor except undoped and doped Cu2O and Co3O4 compounds showed p-type semiconductivity. The photo catalytic activity of undoped and dual doped semiconductor oxides in the Victoria blue-B (VB) and Brilliant yellow (BY) solutions were studied in sunlight irradiation. A set of optimized conditions such as the amount of these oxides, initial dye concentration, pH, contact time and dopants on the photodegradation of these dyes were investigated in detail. The dual doped semiconductor oxides showed a noteworthy enhancement in the degradation of VB and BY dyes under exposure to sunlight. The enhanced photocatalytic activity can be attributed to the incorporation of multivalent dopants in semiconductor oxide matrix promoted the separation of photogenerated charges, inhibited the recombination of photogenerated carriers, and thus prolonged the charges lifetime to participate in the photocatalytic reaction. The kinetic measurements indicate the dominance of pseudo-first order rate constant for Victoria blue-B (VB) were higher than that of Brilliant yellow (BY) in all cases, indicating that the photocatalytic degradation of VB was easier and more rapid than BY dye during the adsorption and also ascribed to different molecular structure to these dyes. A tentative reaction mechanism has also been proposed for this photocatalytic reaction.

High accuracy OrMoSil (Polyvinylidene Fluoride)-supported colorimetric sensor: Novel approach for the calculation of the pH prediction error

pH colorimetric sensors with prediction error comparable to the potentiometric measurements in the working range of the indicator employed, were prepared. Bromothymol Blue (BB), Tetrabromophenol Blue (TBB), Cresol Red (CR) and Brilliant Yellow (BY) in PVDF (Polyvinylidene Fluoride)-supported OrMoSil (organically modified silicate) matrix, were used. Sensor preparation was reproducible. Signal was based on a suitably modified Hue coordinate from HSV (Hue, Saturation, Value) color space, H. Although H profile was not influenced by the indicator concentrations, the prediction error depended on the product of saturation and luminance, Δ. By using H, the response of every spot was less affected by shape and optical inhomogeneity. The H calibration held for all the spots of the same lot and remained identical in time giving an advantage with respect to a glass electrode requiring calibration before each set of measurements. The prediction errors both in solution and in the OrMoSil matrix were similar: for BB, spHi = 0.03 in both environments; for TBB, spHi = 0.02 in the sensing spot and 0.05 in solution; for CR, spHi = 0.11 in the sensing spot and 0.04 in solution; for BY, spHi = 0.17 in the sensing spot and 0.07 in solution. Indeed, H values of TBB and BB increased their variances near the inflection point where Δ has the minimum value (heteroscedastic behavior).

The formation of Gluconacetobacter xylinum cellulose under the influence of the dye brilliant yellow

The structural characteristics of the nascent fibril produced by Gluconacetobacter xylinum (G. xylinum) have been studied under the influence of the cellulose binding dye brilliant yellow (BY) by wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and 13C solid-state nuclear magnetic resonance. BY is found to be more effective at reducing crystallinity than fluorescent brightener 28 (FB28), pontamine fast scarlet 4 (S4B) and other dyes previously studied. Under static cultivation conditions, increasing concentrations of brilliant yellow in the growth media from 20, 50, 100 to 250 μM, result in decreasing cellulose crystallinity from 73 to 18%, respectively, as compared to 82% exhibited by the control. FTIR data indicate that the presence of BY is most effective at suppressing intra-molecular hydrogen bonding. After boiling in 70 vol% aqueous EtOH solution for 12 h, the extracted dye-altered cellulose becomes more ordered, which may be due to the extraction of BY from the BY-cellulose complex. FTIR data indicate that compared to control cellulose, the reclaimed brilliant yellow-altered cellulose contains more cellulose Iβ, where the FB28 and S4B altered cellulose remains principally Iα. Based on WAXD and NMR data we propose a dye-cellulose complex structure associated with BY. This model supports the hypothesis that microfibrils assemble through the hydrogen bonding of formed mini-sheets that consist of stacked glucan chains linked by van der Waals forces.

Fabrication and application of hierarchical porous carbon for the adsorption of bulky dyes

Abstract To enhance the removal efficiency of bulky dyes from water and wastewater, a hierarchical porous carbon (HPC) is developed and evaluated as a superior adsorbent in this study. Characterization of the prepared HPC demonstrates that it adopts an interconnected hierarchical porous structure. Macropores with 800–1000 nm diameters interconnect each other via inner windows, and mesopores with an average diameter of 8.1 nm locate in the interwalls of the macropores. The Brunauer-Emmett-Teller (BET) surface area and the pore volume of the HPC reach 1058 m2/g and 2.16 cm3/g, respectively. The adsorption kinetics and isotherms of HPC towards selected dyes are investigated and analyzed by theoretical models. Compared to the commercial activated carbon (AC) and mesoporous carbon (MC), HPC exhibits superior adsorption rate and capacity towards bulky dyes. For the adsorption of all the selected dyes in this study, the intraparticle diffusion rates of HPC keep 2–4 times as high as those of AC and 1.5–2 times as high as those of MC. The interconnected hierarchical porous framework of HPC strongly improves the diffusion rate of guest molecules through the porous network, and consequently accelerates the adsorption rate. A maximum adsorbed amount of 584.32 mg/g of brilliant yellow is achieved by HPC, which is nearly 6 times the capacity of AC. The opened macro/meso porous structure of HPC is assumed to enhance the accessibility of the inner surface to bulky molecules.

Photoisomerization and photoorientation of brilliant yellow in the thin film state

The features of photoisomerization and photoorientation of azo dye brilliant yellow (BY) in the thin film state are studied. The trans-cis-isomerization of the dye molecules is established to proceed upon irradiation of the films based on BY with a full light of an ultra-high pressure lamp DRT-1000 (UV / VID light), this reaction is described by the first-order reaction equation. Under the action of linearly polarized blue light (λ = 457 nm), an optical anisotropy arises in films of BY. Optically anisotropic films of BY with a high dichroic ratio (>10) are shown to be formed using N-methylpyrrolidone and N, N-dimethylformamide as solvents and cellulose acetate as the polymer matrix.

Adsorption of light green and brilliant yellow anionic dyes using amino functionalized magnetic silica (Fe3O4@SiO2@NH2) nanocomposite

Fe3O4@SiO2@NH2 nanocomposite was prepared for highly effective adsorption of two anionic dyes one of which is triarylmethane dye (light green, LG) and the other is azo dye (brilliant yellow, BY). The characterization results demonstrated that superparamagnetic Fe3O4 nanoparticles were covered with silica and functionalized with amino groups successfully without losing magnetic character. The effects of adsorbent dosage, contact time, pH, temperature, and dye molecular structure on the adsorption were investigated. Acidic pH was better for both LG and BY, on the other hand, alkaline pH was favorable to some extent for LG in comparison with BY due to the contribution of stacking effect in addition to electrostatic attraction. Kinetic data demonstrated that the driving force for adsorption process could be explained by pseudo-second order mechanism in both systems. The equilibrium data were more compatible with Langmuir isotherm than those of Freundlich isotherm and the maximum adsorption capacities of Fe3O4@SiO2@NH2 calculated from Langmuir isotherm model for LG and BY at 30 °C and natural pH of the solution were 40.2 and 35.5 mg g−1. Thermodynamic calculations related to temperature dependence demonstrated that the adsorption process was spontaneous and exothermic.

High Photoinduced Ordering and Controllable Photostability of Hydrophilic Azobenzene Material Based on Relative Humidity

Azobenzene materials provide an effective way for liquid crystal (LC) alignment besides traditional rubbing technology. A strong relationship between relative humidity (RH) and the photoalignment quality of hydrophilic azobenzene dye brilliant yellow (BY) has been investigated. Good photoalignment quality can only be ensured at about 40% RH or below. On the other hand, the photostability of the alignment layer is also influenced dramatically by RH. The rewritability can be guaranteed at extremely low RH (≤10%). It is gradually lost with increasing RH, and the alignment layer becomes photostable against further light exposure when at 40% RH or above. Therefore, the BY photoalignment layer can be tuned from rewritable to photostable by simply adjusting RH, and thus multistep photopatterned alignments can be obtained and reserved based on this method. Similar properties are also expected for other hydrophilic azobenzene photoalignment materials, where the specific RH values may vary correspondingly. The reason is due to the strong intermolecular interaction and J-aggregate formation of BY molecules with water insertion. Moreover, the lyotropic LC formed by J-aggregated BY molecules in aqueous solution is reported here.

An Excellent Photocatalytic Efficiency of ZnO under Visible Light for fast Removal of Organic Pollutant from aqueous solution

Solution combustion synthesized ZnO (SCSZ) and commercially available Degussa P-25 TiO2 was tested for the photocatalytic degradation of Brilliant Yellow (BY) under both UV/Solar light. Powder X-ray Diffraction (PXRD) results revealed crystalline wurtzite phase with P63mc space group for combustion derived ZnO. The scanning electron micrographs (SEM) of ZnO sample shows that the powder products are voluminous and porous. Diffused Reflectance Spectral studies indicated the extension of the band gap to the visible region for ZnO due to its smaller crystallite size. Fourier transform infrared spectra (FTIR) of as-formed SCSZ displayed strong band at 425 cm-1 which confirms the stretching vibration of Zn-O bond. SCSZ showed enhanced activity for the degradation of BY under UV/solar light compared to Degussa P-25 which was attributed to high crystallinity, large surface area of the sample and enhanced degree of hydroxylation on the surface of ZnO.

Synthesis of hexagonal mesoporous MgAl LDH nanoplatelets adsorbent for the effective adsorption of Brilliant Yellow

Hexagonal mesoporous MgAl layered double hydroxide (LDH) was synthesized through a simple hydrothermal method and was employed without calcination as adsorbent in the removal of the direct anionic azo dye, Brilliant Yellow (BY). The adsorbent was characterized by XRD, FT-IR, SEM and BET surface area. Hexagonal platelets of MgAl LDH were fabricated with nanometric building blocks. Batch experiments were carried out for study effects of contact time, amount of adsorbent, solution pH and solution temperature on the removal efficiency of BY. The adsorption of BY onto the MgAl LDH was pH dependent and the highest value of adsorption capacity was observed at pH=6. The equilibrium adsorption data were obtained using the Langmuir, Freundlich and Temkin isotherms. The results indicated that the experimental adsorption data were fitted to Langmuir and Freundlich models. The maximum adsorption capacity of BY onto the MgAl LDH was found to be 115mg/g. The kinetic data of adsorption were evaluated by pseudo-first order and pseudo-second order, which described well by pseudo-second order model. The negative values of ΔG° at all temperature indicated that the adsorption process was spontaneous. The values of ΔH° and ΔS° were calculated 19.3kJ/mol and 80.5J/mol·K, respectively. The positive value of ΔH° shows that the adsorption was endothermic, while positive ΔS° value reflects increased disorder at the solid–solution interface during the adsorption.

Application of magnetic isothiouronium polyurethane sorbent for the removal of acidic and basic dyes from wastewater

Commercial polyurethane foam (PUF) was coupled with magnetite nanoparticles (MNPs) through isothiouronium groups (IT) to prepare a new porous sorbent (PUF@IT@MNPs) with improved ionic character and better sorption affinity towards ionic molecules. PUF@IT@MNPs was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), thermal analysis (TGA), Brunauer-Emmett-Teller (BET) and FT-IR studies. PUF@IT@MNPs had an electrical conductivity (σ) value of 1.0 × 10−5 Ω−1m−1 and maximum ΔpH values of +0.3 and −3.5 at pH 1.4 and 9.7, pointing to the acidic character of the sorbent. FT-IR and TGA studies demonstrated that PUF@IT@MNPs contained different surface-active groups and had a composition of 40.90 wt % of Fe3O4. PUF@IT@MNPs had an improved stability in both acidic and alkaline solutions and high sorption efficiency for anionic (brilliant yellow, BY) and cationic (brilliant green, BG) dyes. The sorption capacities of PUF@IT@MNPs were 330, 328, 225 and 221 mg/g for I2, BY, BG, and MB. The average pore radius values of PUF@IT@MNPs were found to be 1.5 and 8.0 nm and the particle size was 21.4 nm. The sorption of BY was an exothermic process (ΔH = −15.51 kJ mol−1) while that of BG was endothermic (ΔH = 59.19 kJ mol−1).

Near-infrared chemodosimetric probes based on heptamethine cyanine dyes for the “naked-eye” detection of cyanide in aqueous media

Two simple chemodosimetric probes (P1 and P2) based on heptamethine cyanine dyes have been synthesized for highly sensitive and selective detection of cyanide anions (CN−) in aqueous media. The probes with an immobilized indolium salt as the specifically nucleophilic addition reaction site for CN− exhibit absorption bands in the near-infrared (NIR) region (650–850nm). Upon the addition of CN−, the probes display a blue-shifted spectrum and result in apparent color change from green to brilliant yellow that can be easily observed by the naked eye even in the presence of other interfering anions such as F−, AcO−, Br−, NO2−, Cl−, SO42− and I−. There are good linear relationships between the fluorescence intensity of the probes and CN− concentrations, and the detection limits for P1 and P2 are estimated to be 0.017μM and 0.2μM, respectively. The sensing mechanism of the nucleophilic addition is confirmed by 1H NMR and mass spectroscopic analysis. In addition, the probe P2 is employed for cell imaging and the detection of CN− in living cells L929 is successfully realized.

Effects of humidity and surface on photoalignment of brilliant yellow

ABSTRACTControlling and optimising the alignment of liquid crystals is a crucial process for display application. Here, we investigate the effects of humidity and surface types on photoalignment of an azo-dye brilliant yellow (BY). Specifically, the effect of humidity on the photoalignment of BY was studied at the stage of substrate storage before coating, during the spin-coating process, between film coating and exposure, and after exposure. Surprising results are the drastic effect of humidity during the spin-coating process, the humidity annealing to increase the order of the BY layer after exposure and the dry annealing to stabilise the layer. Our results are interpreted in terms of the effect of water on the aggregation of BY. The type of surface studied had minimal effects. Thin BY films (about 3 nm thickness) were sensitive to the hydrophilicity of the surface while thick BY films (about 30 nm thickness) were not affected by changing the surface. The results of this paper allow for the optimisation of the BY photoalignment for liquid crystal display application as well as a better understanding of the BY photoalignment mechanism.