WO2015192778A1

WO2015192778A1 - Light-emitting liquid crystal devices using aie materials

Info

Publication number: WO2015192778A1
Application number: PCT/CN2015/081750
Authority: WO
Inventors: Benzhong Tang; Dongyu ZHAO
Original assignee: The Hong Kong University Of Science And Technology
Priority date: 2014-06-18
Filing date: 2015-06-18
Publication date: 2015-12-23
Also published as: CN106461988B; CN106461988A

Abstract

Provided are a method of fabricating a luminescent liquid crystal device and two types of luminescent liquid crystal devices. The method comprises: synthesizing a luminescent liquid crystalline compound which comprises an aggregation-induced emission (AIE) luminogen and a mesogenic moiety; dissolving the luminescent liquid crystalline compound into a nematic liquid crystal to form a mixture; and preparing a liquid crystal (LC) cell by filling an empty LC cell with the mixture. One type of luminescent liquid crystal device comprises a patterned alignment, wherein a reversed dark and bright area is achieved upon UV irradiation when a polarizer is put in different directions. Another type of luminescent liquid crystal device comprises a patterned electrode, wherein no figures emit light upon UV irradiation at an electric field-off state.

Description

LIGHT-EMITTING LIQUID CRYSTAL DEVICES USING AIE MATERIALS

RELATED APPLICATIONS

The present patent application claims priority to provisional U.S. Patent Application No.61/998,085 filed June 18, 2014, which was filed by the inventor hereof and is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present described subject matter relates to the fabrication of light-emitting liquid crystal devices which do not require a LED (light emitting diode) back-light by using aggregation-induced emission (AIE) materials. This display paradigm has application in many areas, for example, anti-counterfeiting.

BACKGROUND

Liquid crystal displays (LCDs) are widely used for diverse purposes in many aspects of our life. Since LCD is a passive emission display device, it usually shows a narrow viewing angle and reduced brightness (Science, 1998, 279, 835) . Moreover, LCD devices have viewing angle dependence wherein the color or brightness changes according to a viewing direction or angle. Further, as a LCD display screen becomes larger, the viewing angle becomes narrower. The viewing angle dependence is due to the birefringence effect, i.e., the effect when the light is diagonally entered to the panel is different from the effect when the light is entered vertically to the panel.

Nowadays, LCDs with light-emittingproperties are suggested as the less energy consuming displays. The capability of luminescent liquid crystals (LC) to emit linear or circular polarized light when aligned may be utilized to construct bright, more efficient emissive LCDs. To realize this, strongly fluorescent materials with a dichroic property and strong emission are required (Adv. Funct. Mater. 2009, 19, 411； Org. Lett. 2008, 10, 3785) . However, many molecular emitters which are highly efficient and emissive in solution will suffer from heavy aggregation-caused quenching (ACQ) effects in the aggregate state, thereby being dim due to aggregate formation in the solid-state, which greatly limits their applications (J. Am. Chem. Soc. 2000, 122, 2474) .

Recently, a novel phenomenon of aggregation-induced emission (AIE) was discovered (Chem. Commun. 2001, 1740； Chem. Commun. 2009, 4332； Appl. Phys. Lett. 2007, 91, 011111) . Instead of quenching commonly observed in conventional luminophores, the light emission was induced by aggregate formation, turning them from weak fluorophores into strong emitters.

Introduction of AIE-active dyes into LCs may solve the aforementionedproblems. Until now, there have been some photo luminescent liquid crystal displays (LE-LCDs) using the luminescent molecules (J. Mater. Chem. 2004, 14, 1901) ； however, there are still no LCDs with the AIE liquid crystals that have been reported.

SUMMARY

In one exemplary embodiment, the present subject matter relates to a method of fabricating a luminescent liquid crystal device comprising synthesizing a luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety； dissolvingthe luminescent liquid crystalline compound into a nematic liquid crystal to form a mixture； andpreparing a liquid crystal (LC) cell by filling an empty LC cell with the mixture.

In another exemplary embodiment, the present subject matter relates to a luminescent liquid crystal device comprising a patterned electrode of liquid crystal cells, wherein the patterned electrode of liquid crystal cells comprises a LC cell fabricated with two rubbed substrates comprising a first glass substrate having a patterned ITO and another glass substrate having a uniform ITO； wherein the luminescent liquid crystal device comprises a luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety； wherein the luminescent liquid crystal compound is dissolved in a nematic liquid crystal to form a mixture； wherein a liquid crystal (LC) cell is prepared by filling an empty LC cell with the mixture； andwherein no figures emit light upon UV irradiation at an electric field-off state.

In yet another exemplary embodiment, the present subject matter relates to a luminescent liquid crystal device comprising a patterned alignment of liquid crystal cells, wherein the luminescent liquid crystal device comprises a luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety； wherein the luminescent liquid crystal compound is dissolved in a nematic liquid crystal to form a mixture； wherein a liquid crystal (LC) cell is prepared by filling an empty LC cell with the mixture； and wherein a reversed dark and bright area is achieved upon UV irradiation when a polarizer is put in different directions.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 showsabsorption spectra of TPE-PPE and TPE4Br in THF. [TPE-PPE] ＝10μM. [TPE4Br] ＝10μM.

Figure 2A shows fluorescence spectra of TPE-PPE in the THF/water mixtures with different fractions (f_w) of water； Excitation wavelength: 319 nm. [TPE-PPE] ＝ 10 μM.

Figure 2B is a plot of (I/I₀) values versus the compositionsof the aqueous mixtures. I₀ ＝ emission intensity in pure THF solution. The inset graph shows fluorescence images of TPE-PPE in THF and 10/90 THF/water mixture taken under UV illumination.

Figure 3 shows theDSC curve of TPE-PPE. Cr, Cr2: crystalline phases； S_m: smectic phase (temperature range: 218℃–228℃) ； I: isotropic phase.

Figure 4A showsthe POM image of TPE-PPE in the LC phase before UV irradiation.

Figure 4B showsthe POM image of TPE-PPE in the LC phase under UV irradiation at 365nm.

Figure 5A shows the transition electric dipole moments confirmed from the quantum chemistry calculations result.

Figure 5B shows molecular orbital amplitude plots of HOMO and LUMO energy levels of TPE-PPE calculated using the B3LYP/6-31G (d) basis set.

Figure 6 shows angular dependence of light transmittance passed through a LC cell filled with the LC mixture (Nematic LC PA0182 + 0.1 wt％ TPE-PPE) . This transmittance curve means that the LCs obtained the perfect planar orientation.

Figure 7A shows a schematic view of the experimental setup for photoluminescence measurements.

Figure 7B shows polar diagrams of PL intensity of the LC cell. The LC mixture ＝Nematic LC PA0182+0.1 wt ％ TPE-PPE. The arrow indicates the rubbing direction.

Figure 8A shows a schematic representation of the structure of the light-emitting LC cell in the electric field-off state under UV irradiation. The UV light source is polarized with the polarization direction perpendicular to the LC azimuthal direction.

Figure 8B shows a schematic representation of the structure of the light-emitting LC cell in the electric field-on state under UV irradiation. The UV light source is polarized with the polarization direction perpendicular to the LC azimuthal direction.

Figure 8C shows linearly polarized PL spectra of the LC cell in the electric field-off state (1KHz, 8v) . The LC mixture ＝ Nematic LC PA0182 + 0.1 wt ％ TPE-PPE. The circle and dot lines indicate the rubbing direction of the LC cell is parallel and vertical to the polarization direction of the detector, respectively.

Figure 8D shows linearly polarized PL spectra of the LC cell in the electric field-on state (1KHz, 8v) . The LC mixture ＝ Nematic LC PA0182 + 0.1 wt ％ TPE-PPE. The circle and dot lines indicate the rubbing direction of the LC cell is parallel and vertical to the polarization direction of the detector, respectively.

Figure 9A shows a schematic representation of the structure and photograph of the luminescent liquid crystal device with a patterned electrode in the electric field-off state under UV irradiationusing a light-emitting LC mixture. The LC mixture ＝Nematic LC PA0182 + 0.1 wt ％ TPE-PPE.

Figure 9B shows a schematic representation of the structure and photograph of the luminescent liquid crystal device with a patterned electrode in the electric field-on state under UV irradiation using a light-emitting LC mixture. The LC mixture ＝Nematic LC PA0182 + 0.1 wt ％ TPE-PPE.

Figure 10 shows the fabrication procedure of the luminescent liquid crystal device with a patterned photoalignment.

Figure 11 shows the structure and the photographs of the luminescent liquid crystal device with a patterned alignment in the electric field-off and field-on states under UV irradiation using light-emitting LC mixture. The LC mixture ＝ Nematic LC PA0182 + 0.1 wt ％ TPE-PPE.

Figure 12A shows circularly polarized PL spectra of the LC cell. The LC mixture ＝chiral nematic LC (N*LC) + 0.1 wt ％ TPE-PPE. The N*-LC samples ＝ SLC-1717 + CB15. The weight ratio of the N*LC samples is 50/50.

Figure 12B shows circularly polarized PL spectra of the LC cell. The LC mixture ＝chiral nematic LC (N*LC) + 0.1 wt ％ TPE-PPE. The N*-LC samples ＝ SLC-1717 + CB15. The weight ratio of the N*LC samples is 60/40.

Figure 12C shows circularly polarized PL spectra of the LC cell. The LC mixture ＝chiral nematic LC (N*LC) + 0.1 wt ％ TPE-PPE. The N*-LC samples ＝ SLC-1717 + CB15. The weight ratio of the N*LC samples is64/36.

Figure 12D shows circularly polarized PL spectra of the LC cell. The LC mixture ＝chiral nematic LC (N*LC) + 0.1 wt ％ TPE-PPE. The N*-LC samples ＝ SLC-1717 + CB15. The weight ratio of the N*LC samples is69/31.

DETAILED DESCRIPTION

Definitions

Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by someone ordinarily skilled in the art to which the present subject matter pertains. The following definitions are provided for the purpose of understanding the present subject matter and for constructing the appended patent claims.

Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, orcomprising specific process steps, it is contemplated that compositions of the presentteachings can also consist essentially of, or consist of, the recited components, and that theprocesses of the present teachings can also consist essentially of, or consist of, the recited processsteps.

In the application, where an element or component is said to be included in and/orselected from a list of recited elements or components, it should be understood that theelement or component can be any one of the recited elements or components, or the elementor component can be selected from a group consisting of two or more of the recited elementsor components. Further, it should be understood that elements and/or features of acomposition, an apparatus, or a method described herein can be combined in a variety ofways without departing from the spirit and scope of the present teachings, whether explicit orimplicit herein.

The use of the terms "include, " "includes" , "including, " "have, " "has, "or "having" should be generally understood as open-ended and non-limiting unless specifically statedotherwise.

The term “a” or “an” as used herein includes the singular and the plural, unless specifically stated otherwise. Therefore, the term “a, ” “an, ” or “at least one” can be used interchangeably in this application.

For purposes of better understanding the present teachings and in no way limiting the scope of the teachings, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about. ” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The use of the singular herein includes the plural (and vice versa) unless specificallystated otherwise. In addition, where the use of the term "about" is before a quantitativevalue, the present teachings also include the specific quantitative value itself, unlessspecifically stated otherwise. As used herein, the term "about" refers to a ±10％ variationfrom the nominal value unless otherwise indicated or inferred.

It should be understood that the order of steps or order for performing certainactions is immaterial so long as the present teachings remain operable. Moreover, two ormore steps or actions may be conducted simultaneously.

The phrase “aggregation induced emission” or “AIE” as used herein refers to the phenomenon manifested by compounds exhibiting enhancement of light-emission upon aggregation in the amorphous or crystalline (solid) states whereas they exhibit weak or almost no emission in dilute solutions. The use of the term “AIE” includes aggregation-induced emission and aggregation-enhanced emission unless otherwise indicated or inferred.

The phrase “emission intensity” as used herein refers to the magnitude of fluorescence/phosphorescence normally obtained from a fluorescence spectrometer or a fluorescence microscopy measurement.

The term “luminogen” as used herein refers to a chemical compound that manifests luminescence.

The term “fluorogen” as used herein refers to a chemical compound that manifests luminescence.

The following detailed description is provided to aid those skilled in the art in practicing the present subject matter. However, the following detailed description should not be constructed to unduly limit the present subject matter. Variations and modifications in the embodiments discussed may be made by these of ordinary skill in the art without departing from the scope of the present discovery.

A LCD as contemplated herein generally comprises a backlight module and a liquid crystal cell. Generally, the liquid crystal cell comprises two substrates and liquid crystal formed between these substrates, the liquid crystal comprising anisotropic molecules. To provide an orderly alignment of liquid crystal in the cell for the uniform brightness and the high contrast ratio of the liquid crystal cell, conventionally rubbing is carried out on alignment layers coating substrate. The rubbing is mechanical friction on the alignment layer so as to provide a pretilt of liquid crystal molecules defined by a polar angle and an azimuthal angle between the surface of alignment layer and the pretilt.

The liquid crystal cell is classified as a vertical aligned liquid crystal cell and a horizontal aligned liquid crystal cell depending on the pretilt angle. The vertical aligned liquid crystal cell typically defines a liquid crystal cell having a pretilt angle of an alignment layer larger than 60°, and the horizontal aligned liquid crystal cell typically refers to a liquid crystal cell having a pretilt angle of an alignment layer less than 5°.

There are several modes of liquid crystal cells, according to relationships between a first pretilt angle direction of a first alignment layer and a second pretilt angle direction of a second alignment layer facing the first substrate. A Twisted Nematic (TN) mode liquid crystal cell is when the first pretilt angle direction is perpendicular to the second alignment direction. An Electrically Controlled Birefringence (ECB) mode liquid crystal cell or bend mode liquid crystal cell is when the first pretilt angle direction and the second alignment direction are parallel with each other. Further, an In-Plane Switching (IPS) mode liquid crystal cell is when a pretilt angle direction is shifted depending on the voltage.

A twisted nematic liquid crystal display (TNLCD) is the conventionally used liquid crystal display, in which the transmittance is dependent according to the viewing angle at each gray level. While the transmittance is symmetrical in the horizontal direction, the transmittance is asymmetrical in the vertical direction. Thus, in the vertical direction, the vertical viewing angle becomes very limited, as the range with inverted image phenomenon occurs.

A multi-domain TNLC cell such as a two-domain liquid crystal cell may be used to overcome the aforementioned problems with inversion. The multi-domain liquid crystal cell has a wider viewing angle by providing more domains in each pixel, where the domains have different pretilts so as to compensate the viewing angle dependence of each domain.

Mechanical rubbing is the most popular process to obtain multi-domain liquid crystal cells. Rubbing is performed mechanically on the entire substrate coated with an alignment layer, such as polyimide, so that microgrooves are formed on the surface of the alignment layer. To divide two domains in a pixel, a photoresist is coated on the entire alignment layer surface, and the photoresist of one domain is removed by exposing light, thus a reverse rubbing process is carried out on one domain. The remaining photoresist is removed by exposing light, and thus two domains are provided on the substrate.

However, the rubbing process may cause dust particles or electrostatic discharge, thereby reducing the yield or damaging the substrate. Therefore, a photo-alignment method may simplify the alignment process as well as prevent damage of the substrate. Photo-alignment is the process in which a pretilt angle direction of the alignment layer is given by the irradiation of linearly polarized ultraviolet light. The alignment layer used in the photo-alignment method is mainly polyvinyl cinnamate (PVCN) . When ultraviolet light is irradiated into the photo-aligned layer coating the substrate, it causes cyclo-addition between the cinnamoyl groups of cinnamic acid side chains that belong to different photopolymers. Thereby, the direction of the photopolymer configuration, the pretilt of the alignment layer, is aligned uniformly.

In an embodiment, thepresent subject matter provides types of such light-emitting LC devices by using AIE luminogens and their molecular design strategies and preparation to enhance the properties of the LC devices.

One aspect of the present subject matter relates to a novel luminescent liquid crystalline compound TPE-PPE, consisting of a typical AIE-active dye with a tetraphenylethylene (TPE) core as a luminogen, as well as four mesogenic moieties. TPE-PPE exhibits AIE-active behavior in a THF/water mixture and thermotropic liquid crystalline characteristics. For example, by dissolving a very small amount of TPE-PPE into the nematic LC host PA0182, the linearly polarized emission can be obtained on the unidirectional orientated LC cell. The photoluminescence polarization ratio of the LC cell can reach 4.16 in the directions perpendicular and parallel to the rubbing direction. By dissolving TPE-PPE into chiral nematic LCs, the circularly polarized emission can be obtained.

Based on the emissive anisotropy of TPE-PPE, photo luminescent liquid crystal displays (LE-LCD) can be fabricated. The devices are comprised of liquid crystal cells. This approach simplifies device design, lowers the energy consumption and increases brightness of the LCD. The obtained LE-LCD has great potential application in anti-counterfeiting.

In an exemplary embodiment, the present subject matter relates to a method of fabricating a luminescent liquid crystal device comprising synthesizing a luminescent liquid crystalline compound comprising an AIE luminogen and a mesogenic moiety； dissolving the luminescent liquid crystalline compound into a nematic liquid crystal to form a mixture； and preparing a liquid crystal (LC) cell by filling an empty LC cell with the mixture.

In an exemplary embodiment, the AIE luminogen comprises a TPE core, comprising a backbone structure having a formula I:

In an exemplary embodiment, the luminescent liquid crystal compound comprises TPE-PPE, having a formula II:

wherein

R₁, R₂, R₃, and R₄ are independently selected from the group consisting of -C_nH_2n+1 and -OC_nH_2n+1；

n is an integer from 1-20； and

R₁, R₂, R₃, and R₄ can be the same or different.

In an exemplary embodiment, TPE-PPEis synthesized by a two-step method, as follows. The synthetic details are described in the EXAMPLES for further reference.

In an exemplary embodiment, the luminescent liquid crystalline compound aggregates upon addition of water.

In an exemplary embodiment, the luminescent liquid crystalline compound has a liquid crystal texture that can be observed under crossed polarizers, wherein at least two endothermic peaks emerge in a DSC curve.

In an exemplary embodiment, polarization emission of the mixture shows polarized luminescence upon UV irradiation.

In an exemplary embodiment, a dichroic ratio in two directions parallel and vertical to a rubbing direction of the liquid crystal cell is about 3.5 to 4.2. In an exemplary embodiment, a dichroic ratio in two directions parallel and vertical to a rubbing direction of the liquid crystal cell is about 4.16.

In an exemplary embodiment, the liquid crystal is a chiral nematic liquid crystal.

In an exemplary embodiment, polarization emission of the mixture shows circularly polarized luminescence upon UV irradiation.

In an exemplary embodiment, a maximum value range of dissymmetry factor of the LC cell reaches from -0.60 to 0.60. In an exemplary embodiment, a maximum value range of dissymmetry factor of the LC cell reaches -0.48.

In another exemplary embodiment, the present subject matter relates to a luminescent liquid crystal device comprising a patterned electrode of liquid crystal cells. In this regard, the patterned electrode of liquid crystal cells can comprise a LC cell fabricated with two rubbed substrates comprising a first glass substrate having a patterned ITO and another glass substrate having a uniform ITO. Further, the luminescent liquid crystal device can comprise a luminescent liquid crystalline compound comprising an AIE luminogen and a mesogenic moiety； wherein the luminescent liquid crystalline compound is dissolved in a nematic liquid crystal to form a mixture； wherein a LC cell is prepared by filling an empty LC cell with the mixture； andwherein no figures emit light upon UV irradiation at an electric field-off state.

In an exemplary embodiment, the figures will emit light in the device when voltage is applied to a cell.

In an exemplary embodiment, the present subject matter relates to a luminescent liquid crystal device comprising a patterned alignment of liquid crystal cells, wherein the luminescent liquid crystal device comprises a luminescent liquid crystalline compound comprising an AIE luminogen and a mesogenic moiety； wherein the luminescent liquid crystalline compound is dissolved in a nematic liquid crystal to form a mixture； wherein a LC cell is prepared by filling an empty LC cell with the mixture； andwherein a reversed dark and bright area is achieved upon UV irradiation when a polarizer is put in different directions. This occurs because there are two regions aligned orthogonally in this device. By rotating the polarizer, the parallel or perpendicular area of the device to the polarizer direction can be altered. The light emitting and the dark regions can then be switched.

In an exemplary embodiment, each liquid crystal cell has a same photo luminescent efficiency in all areas when voltage is applied to the cell.

In anexemplary embodiment, Figure 1 shows the UV-Vis absorption spectra of TPE4Br and TPE-PPE. TPE4Brshows an almost identical absorption profile to that of TPE-PPE with the peak at 320nm, which corresponds to the π-π transition of the TPE core. The absence of obvious electronic transitions beyond 330 nm strongly suggests the highly twisted TPE configurations herein. The absorption peaks at 360nm of TPE-PPE due to the triple bonds. When illuminated with a UV lamp, the THF solution of TPE-PPE does not emit any observable light. However, strong light is generated from its solid powders and films, indicating aggregation has turned on light emission processes of TPE-PPE.

In a further exemplary embodiment, whether the luminogen TPE-PPE is AIE-active is investigated. Water, a nonsolvent for the luminogen, is added to the THF solutions and the PL change is monitored (Figures 2A and 2B) . As shown in Figure 2A, the THF solution of TPE-PPE emits no light under UV illumination. However, addition of water into the THF solution has aggregated its molecules and enhanced its emission intensity. The emission is still weak in aqueous mixtures at low water fractions (～50％) , but becomes stronger afterwards. The photographs of solutions of TPE-PPE are given in the inset of Figure 2B as an example.

Water is a poor solvent for the luminogen TPE-PPE, thus it should have aggregated in the aqueous mixture with high water content. When aggregated, the restriction of intramolecular rotation (RIR) is activated and the radiative decay channel of the excitons becomes populated, leading to the enhancement of emission intensity. The polarity inside the aggregate is lower than the medium outside, due to the tightness of packing of hydrophobic molecules, which mainly gives rise to the blue shifted emission in the aggregate state than that in pure THF solution.

In one exemplary embodiment, the liquid crystalline properties were studiedwith the differential scanning calorimetry (DSC) and polarized optical microscopy (POM) . The DSCcurve of the TPE-PPEis shown in Figure 3. The endothermic peaks at 143℃, 218℃ and 228℃ are the crystal to crystal transformation, the melting point, and the clearing point of TPE-PPE, respectively. The LC phase exhibits in the temperature range of 218℃–228℃. Figure 4A shows the POM of TPE-PPE observed at 222℃, which is a smectic texture of disc liquid crystal. When observed under the crossed polarizers upon UV irradiation with 365 nm light, TPE-PPE shows both liquid crystalline texture and luminescence (Figure 4B) .

Quantum chemistry calculations were used to confirm the transition electric dipole moments. The ground state geometry (S0) was optimized at the level of the density functional theory (DFT) in the Gaussian 03 program, and then the time-dependent DFT method was applied to optimize the first single excited state geometry (S1) . The B3LYP functional and 6-31G (d) basis set were used. Figure 5A shows the result of the quantum chemistry calculations. Both the absorption and the emission electric dipole moment of TPE-PPE are in the direction parallel to the double bond. The molecular orbital amplitude plots of the HOMO andLUMO energy levels of TPE-PPE are shown in Figure 5B.

In an exemplary embodiment, in order to obtain the polarized PL, the planar oriented LC cell with two rubbed substrates was first fabricated, and then the alignment of the LCswas studiedby monitoring the light transmittance of the HeNe laser as a probe light through the aligned LC cell. The transmittance curve in Figure 6shows variation in the transmission intensity of the LC cells on rotating between crossed polarizers. The transmitted intensity changed periodically with a regular interval of 90°at all orientations of the cell (0°–360°) and in agreement with the transmittance of a uniaxial birefringent liquid crystal, meaning that the LCs obtained the perfect planar orientation.

In another exemplary embodiment, after the uniform alignment of the LC mixture was confirmed, polarized luminescence measurements wereperformed. A schematic view of the setup is given in Figure 7A. Figure 7B displays a polar diagram of the signal. As seen in Figure 7B, the rubbed film reveals a maximum signal value along the direction of 90°→270°, which lies perpendicular to the rubbing direction, but reveals a minimum signal value along the direction of 0°→180°, which is parallel to the rubbing direction. This anisotropic result confirms the polarization emission of the liquid crystals.

In an exemplary embodiment, the polarized fluorescence spectrum of the LC cell is shown in Figures8C and 8D. The circle and dot lines indicate the light emission is parallel and vertical with LC azimuthal direction. The dichroic ratio by this measurement can reach the values of 3.5-4.2, with the dichroic ratio by this measurement preferably 4.16, corresponding to the schematic illustration in Figure 8Awhich shows the electric field not applied on the LC cell. When the electric field was applied on the LC cell, the polarized emission disappeared, as shown the polarized fluorescence spectra in which the dichroic ratio reached to almost 1:1. The schematic representation of this status is shown in Figure 8B.

In an exemplary embodiment, by utilizing the results of the polarized photoluminescence measurements, luminescent liquid crystal displays (LE-LCD) were prepared. A LE-LCD is shown in Figures9A and 9B. The device with a patterned electrode was fabricated, filling with the LC mixture. The prepared LC cell was connected with an electric field power supply. In the structure, a UV lamp was used as the light source to illuminate the mixture material. A polarizer with the transmission direction parallel with the LC alignment direction was used to analyze the changing of photo luminescent efficiency. Figure 9A represents the state that no voltage is applied, whileFigure 9B represents the state that voltage is applied (1KHz, 8v) .

In another exemplary embodiment, another LE-LCD with patterned alignment was fabricated. The fabrication process is shown in Figure 10, in which a photoalignment technique was utilized. The device, as well as the structure, is shown in Figure 11. The prepared LC cell was connected with an electric field power supply. To test the performance of the device, a UV lamp was used as the light source to illuminate the mixture material. A polarizer was used to analyze the changing of photo luminescent efficiency.

Figure 11 shows schematic representation of the structure and photographs of the luminescent liquid crystal device with patterned alignment. There are two regions in the device which are aligned orthogonally by photoalignment treatment. Under UV irradiation, the region in which the rubbing direction is vertical to the polarizer will emit light. When the device is in the electric field-off condition, the regions with and without figures in the device will be alternately bright and dark, when viewed through the rotatable polarizer. When the electric field is applied, both regions are light-emitting and all of the figures in the two original displays disappear.

In an exemplary embodiment, the circularly polarized fluorescence spectra of the LC cells are shown in Figures12A-D. The degree of circular polarization is measured by the circular polarization dissymmetry factor:

g-factor ＝ 2 (I_L-I_R) / (I_L+I_R)

I_L and I_R are the intensities of left and right-handed circularly polarized light, respectively. The observed dissymmetry factor for the four samples wereg-factor is from -0.60 to 0.60, at their maximum wavelength of light reflection. The signs of the circular polarization reverse at the edge of the stop band.

EXAMPLES

Having described the present subject matter, the following examples are given to illustrate specific applications of the present subject matter, including the best mode now known to perform the present subject matter. These specific examples are not intended to limit the scope of the present subject matter described in this application.

Example 1: Synthesis of TPE4Br

Into a 250ml two-necked round-bottom flask equipped with a reflux condenser was placed 8g of Zinc dust (60 mmol) and 10.2g 4, 4-Dibromobenzophene (30mmol) . The flask was evacuated under vacuum and flushed with dry nitrogen three times, after which 120 ml of distilled THF was added. The mixture was cooled to 0℃, to which 0.33ml (30mmol) of titanium tetrachloride was slowly added. The mixture was slowly warmed to room temperature, then stirred for 0.5h, and then refluxed overnight. The reaction was quenched with 10％ potassium carbonate, and HCl was added until the solid turned to grey or white. The mixture was then extracted with dichloromethane for three times and the collected organic layer was washed by brine twice. The mixture was dried with 5g of anhydrous sodium sulfate. The crude product was condensed and recrystallized with hexane. A white solid was obtained in 85.4％ yield. Characterization data: ¹H NMR (400 MHz, DMSO-d₆, δ) : 7.28–7.26 (m, 8H, aromatic protons ortho to –Ar-Br) , 6.86, 6.84 (m, 8H, aromatic protons meta to –Ar-Br) .

Example2: Synthesis of TPE-PPE

Into a 250 ml two-necked flask were added 170 mg of PdCl₂ (PPh₃) ₂, 68 mg of CuI, 96 mg of PPh3, 1.944 g (3 mmol) of TPE4Br (1) , 2.6k g (5 mmol) of 4-Ethynylpropylbenzene, and 90 ml of TEA under nitrogen. The mixture was stirred at 80℃ for 24 h. The formed solid was removed by filtration and washed with acetone. The filtrate was concentrated by a rotary evaporator. The crude product was purified on a silica-gel column with hexane as eluent. A yellow solid was obtained in 61.3％ yield. ¹H NMR (400 MHz, CDCl3) , δ (TMS, ppm) : 7.42-7.28 (m,16H) , 7.15-6.99 (m, two 16H) , 2.58 (t, 8H) , 1.54 (m, 8H) , 0.93 (t, 12H) . HRMS (MALDI-TOF) : Calcd. for C10H60: 900.47. Found: 900.4686 [M+] .

Example 3: Preparation of the LC test cells

Firstly, two clean ITO glass substrates were prepared. The two glass substrates were then spin-coated with polyimide 3744 (with concentration 1wt％ in NMP) . Then the substrates were soft baked at 100℃ for 5 minutes to evaporate the solvent. Then the substrates were hard baked at 230℃ for 90 minutes. Then the substrates were rubbed to decide the azimuthal direction of the alignment layer. The two prepared substrates were assembled in anti-parallel direction to be an empty cell with a cell gap of 15 μm. Then the mixture of nematic LC with TPE-PPEwas filled into the empty cell to test the linearly polarized photo luminescence. The mixture of the chiral nematic LC/TPE-PPE was filled into the empty cell to test the circularly polarized photo luminescence.

Example 4: Experiment for testing the linearly polarized photo luminescence

The prepared LC cell was connected with an electric field power supply. In order to measure the photo luminescent property, a polarized UV light source with a polarization direction perpendicular with the LC azimuthal direction is used to illuminate the mixture material. Polarized fluorescence spectra were excited using a second-harmonic generation from a Ti:Sapphire mode-lock laser. The excitation laser source was intrinsically polarized so no extra polarizer was required. A rotatable polarizer in the angle range of 0°–360° was inserted between the sample and the detector. The excitation wavelength was 370nm. The polarized PL spectra of the LC cell were measured.

Example5: FabricationofLE-LCD with patterned electrode

Two clean glass substrates were prepared, one having a patterned ITO and the other having a uniform ITO. The two glass substrates were then spin-coated with polyimide 3744 (with concentration 1wt％ in NMP) . Then the substrates were soft baked at 100℃ for 5 minutes. Then the substrates were hard baked at 230℃ for 90 minutes. Then the substrates were rubbed to decide the azimuthal direction of the alignment layer. The two prepared substrates were assembled in anti-parallel direction to be an empty cell with a cell gap 15 μm. Then the mixture of nematic LC with TPE-PPE was filled into the empty cell. The prepared LC cell was connected with an electric field power supply. To test the performance of the device, the structure shown in Figures 9A and 9B was used.

Example6: Fabrication of LE-LCD with patterned alignment

Two clean glass substrates were prepared. The two glass substrates were then spin-coated with Photoalignment material sulfonic-dye-1 SD1 (with concentration 0.5 wt％ in dimethylformamide (DMF) ) . Then the substrates were soft bakedat 100℃ for 5 minutes to evaporate the solvent. The two prepared substrates were assembled to be an empty cell with a cell gap of 15 μm. Then polarized UV light is used to expose the empty cell to give a patterned alignment structure for the photoalignment material SD1. A two-step exposure is used. In the first step of exposure, the empty cell is exposed to a polarized UV light without a mask to give an initial alignment direction. In the second step of exposure, a mask is used to block some of the area, and the remaining area is exposed to a polarized UV light in the polarization direction that is perpendicular to the first time exposed light. In this case, the alignment direction in the newly exposed area will be changed by 90 degrees, and a patterned photoalignment structure is formed. Then the mixture of nematic LC with TPE-PPEis filled into the empty cell. This process is shown in Figure 10.

The prepared LC cell is connected with an electric field power supply. To test the performance of the device, a UV lamp is used as the light source to illuminate the mixture material. A polarizer is used to analyze the changing of photo luminescent efficiency. When the polarizer is put in different directions, a reversed dark and bright area can be achieved and the two conditions are shown in Figure 11. When voltage (1KHz, 8v) is applied to the cell, the cell has the same photo luminescent efficiency in all areas.

Example7: Experiment for testing the circularly photoluminescence

The basic setup of a circularly photoluminescence (CPL) experiment is as follows. The depolarized incident laser excites the sample at less than 10° from the direction of emission detection. The emission luminescence passes through a circular analyzer, which is comprised of a photoelastic modulator (PEM) followed by a linear polarizer oriented at 45° with respect to the crystal axis of the modulator. Subsequently the wavelength is resolved by the emission monochromator and detected by the photomultiplier.

With the information contained herein, various departures from precise descriptions of the present subject matter will be readily apparent to those skilled in the art to which the present subject matter pertains, without departing from the spirit and the scope of the below claims. The present subject matter is not considered limited in scope to the procedures, properties, or components defined, since the preferred embodiments and other descriptions are intended only to be illustrative of particular aspects of the presently provided subject matter. Indeed, various modifications of the described modes for carrying out the present subject matter which are obvious to those skilled in chemistry, biochemistry, or related fields are intended to be within the scope of the following claims.

Claims

A method of fabricatinga luminescentliquid crystal device comprising:

synthesizing a luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety；

dissolving the luminescent liquid crystalline compound into a nematic liquid crystal to form a mixture； and

preparing a liquid crystal (LC) cell by filling anempty LC cell with the mixture.
The method of claim 1, wherein the AIE luminogencomprises a TPE core, comprising a backbone structure having a formula I:
The method of claim 1, wherein the luminescent liquid crystalline compound comprises TPE-PPE, having a formula II:

wherein

R₁, R₂, R₃, and R₄ are independently selected from the group consisting of -C_nH_2n+1 and -OC_nH_2n+1；

n is an integer from 1-20； and

R₁, R₂, R₃, and R₄ can be the same or different.
Themethod of claim 1, wherein the luminescent liquid crystalline compound aggregates upon addition of water.
The method of claim 1, wherein the luminescent liquid crystalline compound has a liquid crystal texture that can be observed under crossed polarizers, whereinat least two endothermic peaks emerge in a DSC curve.
The method of claim 1, wherein polarization emission of the mixture shows polarized luminescence upon UV irradiation.
The method of claim 6, wherein adichroic ratio in two directions parallel and vertical to a rubbing direction of the liquid crystal cell is about 3.5 to 4.2.
The method of claim 7, wherein a dichroic ratio in two directions parallel and vertical to a rubbing direction of the liquid crystal cell is about 4.16.
The method of claim 1, wherein the nematic liquid crystal is a chiral nematic liquid crystal.
The method of claim 9, wherein polarization emission of the mixtureshows circularly polarized luminescence upon UV irradiation.
The method of claim 10, wherein a maximum value of dissymmetry factor of the LC cellreaches from -0.60 to 0.60.
The method of claim 11, wherein a maximum value of dissymmetry factor of the LC cell reaches -0.48.
A luminescent liquid crystal device comprisinga patterned electrode of liquid crystal cells, wherein the patterned electrode of liquid crystal cells comprises a LC cell fabricated with two rubbed substrates comprising a first glass substrate having a patterned ITO and another glass substrate having a uniform ITO；

wherein the luminescent liquid crystal device comprisesa luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety；

wherein the luminescent liquid crystalline compound is dissolved in a nematic liquid crystal to form a mixture；

wherein a liquid crystal (LC) cell is prepared by filling an empty LC cell with the mixture； and

wherein no figures emit light upon UV irradiation atan electric field-off state.
The luminescent liquid crystal device of claim 13, wherein the figures will emit light in the device when voltageis applied to a cell.
The luminescent liquid crystal device of claim 13, wherein the AIE luminogen comprises a TPE core, comprising a backbone structure having a formula I:
The luminescent liquid crystal device of claim 13, wherein the luminescent liquid crystal compound comprises TPE-PPE, having a formula II:

wherein

R₁, R₂, R₃, and R₄ are independently selected from the group consisting of -C_nH_2n+1 and -OC_nH_2n+1；

n is an integer from 1-20； and

R₁, R₂, R₃, and R₄ can be the same or different.
A luminescent liquid crystal device comprising a patterned alignment of liquid crystal cells,wherein the luminescent liquid crystal device comprises a luminescent liquid crystalline compound comprising an aggregation-induced emission (AIE) luminogen and a mesogenic moiety；

wherein the luminescent liquid crystalline compound is dissolved in a nematic liquid crystal to form a mixture；

wherein a liquid crystal (LC) cell is prepared by filling an empty LC cell with the mixture； and

wherein a reversed dark and bright area is achieved upon UV irradiation when a polarizer is put in different directions.
The luminescent liquid crystal device of claim 17, wherein each liquid crystal cell has a same photo luminescent efficiency in all areas when voltage is applied to the cell.
The luminescent liquid crystal device of claim 17, wherein the AIE luminogen comprises a TPE core, comprising a backbone structure having a formula I:
The luminescent liquid crystal device of claim 17, wherein the luminescent liquid crystal compound comprises TPE-PPE, having a formula II:

wherein

R₁, R₂, R₃, and R₄ are independently selected from the group consisting of -C_nH_2n+1 and -OC_nH_2n+1；

n is an integer from 1-20； and

R₁, R₂, R₃, and R₄ can be the same or different.