KR102495682B1 - Chiral nanoporous template and method of manufacturing for them - Google Patents

Abstract

A fabrication method based on a bottom-up template for fabricating a chiral nanoporous template providing a chiral environment for nematic liquid crystals is provided. The chiral nanoporous template in the present invention can be applied to applications such as chirooptic modulators and switches, and biological sensors.

Description

Chiral nanoporous template and method for manufacturing the same {CHIRAL NANOPOROUS TEMPLATE AND METHOD OF MANUFACTURING FOR THEM}

The present invention relates to a chiral nanoporous template and a method for preparing the same, and more specifically, to a template prepared with a chiral material by a physical method without chemical method by filling an achiral material.

Chirality is abundant in nature and plays a significant role in the origin of biological systems. Chirality has been extensively studied in the fields of chemistry, physics, biology, pharmacy and medicine. In general, helical aggregates (or chiral superstructures) are formed from chiral molecules. As an example, proteins and deoxyribonucleic acid (DNA) are helical aggregates, leading to the formation of chiral superlattice structures from chiral molecules in the solid state as well as in fluids.

On the other hand, macroscopic spontaneous chiral segregation was reported for the first time in 1997 in an achiral bent-core (BC) liquid crystal (LC) molecule. Chirality-related studies in these achiral LC molecules have been one of the most exciting topics not only in the LC field but also in the broader material science field. One of these macroscopic chiral phases, the helical nanofilament (HNF) phase (also called the B4 phase), is the lowest-temperature mesophase of many BC-LCs. ), and it has been found to have a helical superlattice structure even though it is composed of only achiral molecules. Subsequent studies have suggested that the HNF phase is not LC, but rather semicrystalline, but the problem of breaking the chiral symmetry of the HNF phase has prompted many chemists and physicists to engage in profound research on chirality. It has affected.

Recently, attempts have been made to produce chiroptical materials using binary systems of BC-type nematic (N) LCs and rod-like nematic (N) LCs. It has been shown that nanoscale phase separation occurs in this mixed system between a semi-crystalline HNF phase and a nematic liquid crystal (N-LC) phase. As a result of previous studies, the structural chirality of the HNF phase affects the structure of the isolated rod-shaped N-LC phase, and the self-assembled chiral superlattice related to the chirality of the HNF phase. form a structure

Thus, a substantial chirooptic effect in achiral N-LC is induced, the chirality of the binary mixture is modified, and the strength of the chirality is amplified. An interesting approach based on this phenomenon has recently been reported. Circularly polarized luminescence (CPL) was observed in an achiral mixture of rod-shaped guest molecules and BC host molecules mixed with fluorescent dyes. This CPL is clear evidence that N-LC molecules separated from HNF form a chiral nanospace (ie, a chiral superlattice structure).

Republic of Korea Patent No. 1825597

The present invention is to implement a chiral polymeric material by transferring chirality (or chiral information) from an HNF phase to an achiral molecule.

That is, chiral nanospaces separated from HNF are fixed using a polymer stabilizer, and chiral nanospaces stabilized with the polymer are used as a useful template to provide chiroptical effects.

In order to achieve the object to be solved, a chiral nanoporous template according to one embodiment of the present invention includes a polymer network structure composed of a reactive mesogen compound; and a plurality of nanopores formed on the polymer network structure.

The reactive mesogen compound may be composed of a nematic liquid crystal (N-LC) and a reactive monomer, and the nematic liquid crystal (N-LC) may be 4-cyano-4'-pentylbiphenyl, and the reactive monomer may be 2 -methyl-1,4-phenylene bis(4-(((4-(acryloyl oxy)butoxy)carbonyl)oxy)benzoate).

The chiral nanoporous template may have an inverse helical nanofilament structure.

In addition, a method for preparing a chiral nanoporous template according to one embodiment of the present invention includes preparing a precursor mixture including a bent nucleus molecule, a reactive mesogen compound, and a photoinitiator; preparing a template by photocuring the precursor mixture; removing the bent nuclear molecule on the template; and drying the template.

The bent nuclear molecule may have a helical nanofilament phase as a nanofission phase, and the bent nuclear molecule may be 1,3-phenylene bis[4-(4-eptyloxyphenyliminomethyl)-benzoate ].

The reactive mesogen compound may be composed of a nematic liquid crystal (N-LC) and a reactive monomer, and the nematic liquid crystal (N-LC) may be 4-cyano-4'-pentylbiphenyl, and the reactive monomer may be 2 -methyl-1,4-phenylene bis(4-(((4-(acryloyl oxy)butoxy)carbonyl)oxy)benzoate).

The photoinitiator may be 2,2-dimethoxy-2-phenylacetophenone (DMPAP).

The photocuring may be performed at 80 to 120 °C.

Removal of the bent nuclear molecule may be performed using 1,2-dichlorobenzene.

According to one aspect of the present invention, a bottom-up based template manufacturing method for manufacturing a chiral nanoporous template providing a chiral environment is provided.

In addition, according to the present invention, a chiral nanoporous template can be prepared from an achiral material (molecule) without a complicated manufacturing process through a bottom-up self-assembly method.

In addition, the chiral nanoporous template of the present invention can be provided for applications such as chirooptic modulators and switches, and biological sensors.

1A is a flowchart of a method for manufacturing a chiral nanoporous template according to an embodiment of the present invention.
Figure 1b shows a schematic diagram of a manufacturing process of a chiral nanoporous template according to an embodiment of the present invention.
Figure 2 shows SEM images and schematic diagrams of each cross section in the manufacturing process of a chiral nanoporous template according to an embodiment of the present invention.
FIG. 3A shows typical Polarized Optical Microscopy (POM) images of a film at each stage of a fabrication process of a chiral nanoporous template at room temperature (RT) according to an embodiment of the present invention.
3b to 3d show three different LC materials (8CB (Sigma-Aldrich), BYLC 53XX (BaYi) for each step of the manufacturing process of the chiral nanoporous template at room temperature (RT) according to an embodiment of the present invention. Space Co.) and MLC-7029 (Merck)), polarized optical microscopy (POM) images of the chiral nanoporous template when refilled to stage 3 (see Fig. 1b) are shown.
Figure 4a shows typical CD spectra measured for single domains (monodomains) at each step of the fabrication process of a chiral nanoporous template at room temperature (RT) according to an embodiment of the present invention.
FIG. 4B shows CD spectra rotated at various azimuth angles (α=0, 30, 60, and 90°) after refilling the chiral nanoporous template with an achiral compound according to an embodiment of the present invention.
Figure 5 shows two images in the N phase (at room temperature (RT) and Iso phase (at 120 ° C) after refilling the achiral compound in the chiral nanoporous template according to an embodiment of the present invention). CD spectra for two enantiomeric domains (FIG. 5(a)) and CD spectra for two enantiomers under various electric field conditions at room temperature (RT) (FIG. 5(b)) are shown.
Figure 6 is a chiral nanoporous template refilled with achiral N-LC doped with pyrromethene-based fluorescent dye (PM580) to further demonstrate the functionality of the chiral nanoporous template according to an embodiment of the present invention. A schematic diagram (Fig. 6 (a)) and a circular polarization intensity difference ( I _left - I _right (Fig. 6 (b))) are shown.
Figure 7 (a) shows the chiral domains corresponding to the N phase and the Iso phase refilled with the achiral compound in the chiral nanoporous template according to an embodiment of the present invention. I _left - I _right | 7(b) shows the domain | I _left - I _right | shows the spectrum.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings and the contents described in the accompanying drawings, but the present invention is not limited or limited by the embodiments.

Terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, "comprises" and/or "comprising" means that a stated component, step, operation, and/or element is present in the presence of one or more other components, steps, operations, and/or elements. or do not rule out additions.

As used herein, “embodiments,” “examples,” “aspects,” “examples,” and the like should not be construed as indicating that any aspect or design described is preferred or advantageous over other aspects or designs. It is not.

The terms used in the description below have been selected as general and universal in the related technical field, but there may be other terms depending on the development and / or change of technology, convention, preference of technicians, etc. Therefore, terms used in the following description should not be understood as limiting technical ideas, but should be understood as exemplary terms for describing the embodiments.

In addition, in certain cases, there are also terms arbitrarily selected by the applicant, and in this case, their meanings will be described in detail in the corresponding description section. Therefore, terms used in the following description should be understood based on the meaning of the term and the contents throughout the specification, not simply the name of the term.

Meanwhile, terms such as first and second may be used to describe various components, but the components are not limited by the terms. Terms are used only to distinguish one component from another.

In addition, when a part of a film, layer, region, composition request, etc. is said to be "on" or "on" another part, not only if it is directly above the other part, but also if there is another film, layer, region, or component in the middle thereof. The case where the etc. are interposed is also included.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless explicitly specifically defined.

Meanwhile, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, the terminology used in this specification is a term used to appropriately express the embodiment of the present invention, which may vary according to the intention of a user or operator or customs in the field to which the present invention belongs. Therefore, definitions of these terms will have to be made based on the content throughout this specification.

A polymer network structure composed of a reactive mesogen compound (RMC) according to one embodiment of the present invention; and a plurality of nanopores formed on the polymer network structure.

The reactive mesogen compound may be a photoreactive nematic liquid crystal (N-LC) compound, and the reactive mesogen compound may be composed of a nematic liquid crystal (N-LC) and a reactive monomer.

The nematic liquid crystal (N-LC) may be a rod-like nematic liquid crystal (N-LC) compound, and the nematic liquid crystal (N-LC) is 4-cyano-4'-pentylbiphenyl (5CB ), 4-n-octyl-4'-cyanobiphenyl (8CB), BYLC53XX (from BaYi Space Co.) or MLC-7029 (from Merck).

The reactive monomer may be 2-methyl-1,4-phenylene bis(4-(((4-(acryloyl oxy)butoxy)carbonyl)oxy)benzoate).

The chiral nanoporous template may have an inverse helical nanofilament structure.

1A is a flowchart of a method for manufacturing a chiral nanoporous template according to an embodiment of the present invention.

Referring to FIG. 1A, a method for preparing a chiral nanoporous template according to an embodiment of the present invention prepares a precursor mixture including bent-core (BC) molecules, a reactive mesogenic compound (RMC), and a photoinitiator. Step (S110); preparing a template by photo-curing the precursor mixture (S120); removing the bent nuclear molecule on the template (S130); and drying the template (S140).

S110 is a step of preparing a precursor mixture as a material for preparing a template through photocuring, wherein the precursor mixture includes a bent nucleus (BC) molecule, a reactive mesogenic compound (RMC) and a photoinitiator, and more specifically, a bent nucleus It is based on a binary mixture of molecules and a reactive mesogen compound, and may include a small amount of a photoinitiator in the binary mixture.

The bent nuclear molecule may have a helical nanofilament phase (B4 phase) as a nanofission phase, and the bent nuclear molecule may be 1,3-phenylene bis[4-(4-eptyloxyphenyliminomethyl)- benzoate]. The helical nanofilamental network of the bent-nuclear molecule was utilized as a three-dimensional template, and thus the final product, a chiral nanoporous template, had an inverse helical nanofilament (or 'inverse nanohelix') structure (inverse helical nanofilament). structure).

The reactive mesogen compound is a photoreactive nematic liquid crystal (N-LC) compound, and the reactive mesogen compound may be composed of a nematic liquid crystal (N-LC) and a reactive monomer.

The nematic liquid crystal (N-LC) may be a rod-like nematic liquid crystal (N-LC) compound, and the nematic liquid crystal (N-LC) is 4-cyano-4'-pentylbiphenyl (5CB ), 4-n-octyl-4'-cyanobiphenyl (8CB), BYLC53XX (from BaYi Space Co.) or MLC-7029 (from Merck).

The reactive monomer may be 2-methyl-1,4-phenylene bis(4-(((4-(acryloyl oxy)butoxy)carbonyl)oxy)benzoate).

The photoinitiator may be 2,2-dimethoxy-2-phenylacetophenone (DMPAP).

The photoinitiator may be included in an amount of 0.5 to 1 wt% in the precursor mixture.

S120 is a step for preparing a template from the precursor mixture, and the template may be formed through photocuring using UV light on the precursor mixture, and the template may be in the form of a film.

In S120, the precursor mixture may be filled in a cell made of upper and lower glass to perform photocuring, and the distance between the upper and lower glass of the cell may be 1 to 10 μm.

The photocuring temperature in S120 may be performed in a temperature range in which phase separation of the precursor mixture is implemented, and more specifically, the photocuring may be performed at 80 to 120 ° C., preferably It may be carried out at 100 ° C. The photo-curing temperature range is 80 to 120 ° C., more preferably 100 ° C. .

S130 is a step of removing an unpolymerized material present on the photocured and manufactured template, and more specifically, a step of removing the bent nuclear molecules that do not participate in the photopolymerization reaction during the manufacturing process of the template.

The bent nucleus molecules do not participate in the photopolymerization reaction on the template and occupy a certain space (nanospcace) on the template, and by removing the bent nucleus molecules, the polymer network (polymer network) on the template is It forms nanopores as a network.

The bent nuclear molecule is phase-transformed into an HNF phase during photopolymerization, and the nanopore formed by removing the bent nuclear molecule has an inverse HNF structure, which is derived from a chiral supramolecular structure that is HNF. A novel chiral supramolecular polymer network is formed.

Removal of the bent core molecules may be performed using an organic solvent that dissolves the bent core molecules, and the organic solvent may be 1,2-dichlorobenzene.

S140 is a step of providing a chiral nanoporous template as a final product by drying the template from which the bent nuclear molecules are removed. At this time, the provided chiral nanoporous template may be in the form of a nanoporous film.

More specifically, S140 may be to completely evaporate and remove residual solvent by drying at room temperature (25 ° C.) for 24 hours (h).

More specifically, in the case of the manufacturing method of the chiral nanoporous template of the present invention,

The nano-separated rod-like N-LC was synthesized as a photopolymerizable reactive mesogen and photopolymerized with BC molecules. BC molecules of the HNF phase are removed from the prepared template after photopolymerization, and thus only a polymer network having "inverse HNF" remains on the template. A nanoporous film (nanoporous template) with such an inverted HNF structure has the ability to memorize and transfer chirality, which could be useful for chirooptic applications. When the inverse HNF structure of these nanoporous templates was filled with achiral N-LC, a clear and strong circular dichroism (CD) appeared. Due to the stimulus-responsive nature of the filled N-LC, the CD signal can be easily modulated by applying an electric field or heat. This is according to the “washout-refill method” and is intended to implement a photonic crystal structure based on a stimulus-tunable polymer templated from cholesteric LC or bluephase LC.

In addition, CPL can be implemented by filling the inverse HNF structure on the nanoporous template with achiral N-LC doped with a fluorescent dye. CPL intensity may be modulated by an external stimulus similar to a CD signal. Such chirooptic properties were realized in a system composed of only achiral molecules. In addition, a chiral template obtained from achiral molecules through a bottom-up self-assembly methodology does not require a complicated fabrication process.

Hereinafter, the present invention will be described in more detail through examples. These examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited by these examples.

ready yes. Chiral nanoporous template composite materials

The mixture used for preparing the template in the present invention is a bent-core (BC) molecule (P7: 1,3-phenylene bis[4-(4-eptyloxyphenyliminomethyl)-benzoate]) and a reactive mesogen compound; RMC).

BC molecule (P7) is a method according to Kumazawa et al. (Important Role Played by Interlayer Steric Interactions for the Emergence of the Ferroelectric Phase in Bent-Core Mesogens. J. Mater. Chem. 2004, 14, 157-164.) synthesized

RMC is a nematic liquid crystal (N-LC) (5CB: 4-cyano-4'-pentylbipenyl) and a reactive monomer (LC242: 2-methyl-1,4-phenylene bis(4-(((4-(acryloyl oxy) It is composed of butoxy)carbonyl)oxy)benzoate)).

The mixture further includes a photoinitiator (DMPAP: 2,2-dimethoxy-2-phenylacetophenone).

LC242 was purchased from BASF, and 5CB and DMPAP were purchased from Sigma-Aldrich.

The mixing ratio of the mixture in the present invention is shown in Table 1 below.

mixture P7 RMC
(LC242:5CB=67 wt%:33 wt%) DMPAP Mixing ratio (wt%) 49.5 49.5 One

P7 and RMC were dissolved together in chloroform and mixed through sonication. Then, in order to remove the solvent (chloroform), it was heated and dried. Upon cooling, the order of the phases of neat P7 and RMC is Iso-(170 °C)-B2-(154 °C)-B7-(144 °C)-HNF (helical nanofilament) and Iso-(120 °C)-N-, respectively. (80 ℃) -Cryst.

To fill the nanopores of the template, an achiral mixture of N-LC (HTW109100-100, HCCH) was used. The sequence of phases upon cooling was Iso-(120 °C)-N-(-40 °C)-Cryst. In addition, three other LC materials (8CB (Sigma-Aldrich), BYLC 53XX (BaYi Space Co.) and MLC-7029 (Merck)) were filled into the nanoporous film. Among them, MLC-7029 has negative dielectric anisotropy.

The emissive N-LC mixture for Circular Polarizer (CPL) experiments is a pyrromethene-based fluorescent dye (PM580: [[(4-butyl-3 ,5-dimethyl-1H-pyrrol-2-yl)(4-butyl-3,5-dimethyl-2H-pyrrol-2-ylidene)methyl]-methane](difluoroborane)) was doped with 0.5 wt %. The PM580 was purchased from Exciton.

The chemical structure of P7 may be represented by Formula 1 below.

[Formula 1]

The chemical structure of LC242 may be represented by Formula 2 below.

[Formula 2]

The chemical structure of 5CB may be represented by Formula 3 below.

[Formula 3]

The chemical structure of PM580 may be represented by Formula 4 below.

[Formula 4]

manufacturing example. Preparation of Chiral Nanoporous Templates

A binary mixture is prepared by mixing the BC molecule (P7) and the RMC (CB5 + LC242) of the above preparation. At this time, DMPAP is added as a photoinitiator to the binary mixture to prepare a precursor mixture, The mixing ratio of the precursor mixture is the same as the mixing ratio in Table 1 above. P7 and RMC (CB5 + LC242) were dissolved together in chloroform and mixed through sonication. Then, in order to remove the solvent (chloroform), it was heated and dried.

The sequence of nanosegregated phases of the binary mixture in the precursor mixture prior to photocuring is Iso-(140 °C)-<HNF/Iso>-(120 °C)-<HNF/N>-( 80 °C) - <HNF/Cryst>. To describe the nanosegregated phases of the binary mixture composed of P7 and RMC, the notation for the binary mixture composed of P7 and RMC is <phase of P7(BC molecule)/phase of RMC(rod- like molecule)>, for example, <HNF/N> indicates that P7 is located in the HNF phase, while RMC is located in the N phase.

A liquid crystal (LC) cell with a gap of 2 μm composed of two parallel slide quartz substrates without surface treatment is fabricated, and the LC cell is not absorbed in the near-ultraviolet (UV) region. and no fluorescence is present.

The LC cell is filled with a precursor mixture containing P7 and RMC. The two-component mixture filled in the LC cell (sample) was irradiated at 100 °C for 10 minutes (min) using UV light from a low pressure mercury lamp (254 nm, 30 mW/cm ² ). Then, photocuring is performed to produce a template. As the temperature range of <HNF/N> of the nano-fragmented phase of the binary mixture in the precursor mixture was confirmed at 80 to 120 °C, photocuring was performed at 100 °C.

Photocured template to remove P7 and residual unpolymerized RMC by immersing the LC cell in 1,2-dichlorobenzene (purity 99%) at 150 °C for 24 h (h). was washed. At this time, the organic solvent 1,2-dichlorobenzene (purity 99%) was used for its high boiling point temperature and selective dissolvability of the BC molecule (P7). The laminated structure can withstand temperatures of up to 150 °C.

Thereafter, the remaining solvent in the LC cell was completely evaporated by drying at room temperature (25 °C) for 24 hours (h).

measurement example. Ultra High Resolution Field Emission Scanning Electron Microscope (UHR-FE-SEM) observation

UHR FE-SEM (S-5500, Hitachi) observations were performed to confirm the nanoscopic morphology of the chiral nanoporous template before and after removal of HNF. To check the internal structure of the sample, the sample LC cell was disassembled and then a thin (~5 nm) layer of osmium was sputtered on the exposed surface.

measurement example. Polarized optical microscopy (POM) observation

POM analysis was performed using a polarized optical microscope (OPTIPHOT-POL, Nikon) and images were recorded in transmission mode using a camera with two linear polarizers.

measurement example. Circular Dichroism (CD) measurement

Solid CD spectra were obtained in the chiral domain at different electric field intensities and temperatures using the microspot CD device built into the J-720WI spectropolarimeter (Jasco). (chiral domains). To measure the CD signals of small chiral domains, focal-reducing optics were installed in the CD spectrometer. Typical beam diameters are smaller than chiral domains, less than 10 μm. The thickness of the quartz LC cell used for CD measurements is less than 2 μm.

measurement example. Measuring circularly polarized light (CPL)

A custom-made device was installed for CPL measurements using monodomains. A non-polar white light from an LDLS system (EQ-99X, Energyq) was used. The light was intensively focused on the sample after being monochromated using a band-pass filter (525 nm). The polarization of the emission output was modulated using a photoelastic modulator (PEM) (PEM-100 I/FS50, HINDS) oscillating at a frequency of about 50 kHz. The modulated polarization signal was converted into an intensity-modulated signal using a linear polarizer and then sensed as a modulated current by a photomultiplier tube (PMT) (H6780, Hamamatsu).

Then, the 1f alternating current (AC) component of the modulated signal was analyzed using a lock-in amplifier (7265, signal recovery) using the reference frequency of the PEM. Circular differences ( I _left - I _right ) and ( I _left + I _right ) were inferred from the AC and DC components of the modulated signal, respectively. Spectroscopic CPL was measured using an n-line Fastie-Ebert monochromator (Edmund Optics) set just before the PMT.

experimental example.

Synthesis of chiral compounds using chiral nanoporous templates

In order to specify the measurement steps in various experimental examples to be described later, the manufacturing process of the chiral nanoporous template in the above-described manufacturing examples and the process of filling the achiral compound to prepare the chiral compound in the prepared template It is summarized below with reference to FIG. 1B.

Referring to FIG. 1B, a small amount of photoinitiator was added to the two-component mixture of BC (Bent-Core) molecule (P7) and photoreactive N-LC compound (RMC). The mixture is introduced into an LC cell composed of two parallel slides of quartz. At this time, the LC cell is not absorbed in the near-ultraviolet (UV) region and does not emit fluorescence. .

RMC is composed of a rod-like photoreactive mesogen (LC242, 50 wt %) and a nematogen (5CB, 50 wt %). Pure LC242 was very viscous and did not separate at all from the HNF phase, so it was diluted with 5CB.

UV light over the temperature range (80 ~ 120 ℃) where nanosegregation of the binary mixture filled in the LC cell occurs (BC is HNF phase, RMC is N phase) A template is prepared through photocuring using This procedure is referred to as stage 1 (see FIG. 1B).

Then, the template was immersed in an organic solvent (1,2-dichlorobenzene) at an elevated temperature of 150 °C to dissolve BC molecules and residual unpolymerized RMC. Thereafter, residual solvent was removed at room temperature (RT) (stage 2 (see FIG. 1b)).

Finally, the template is refilled with another commercially available achiral helical N-LC (HTW109100-100, HCH) at room temperature (RT) to prepare a chiral compound (stage 3 (Fig. see 1b)).

measurement example. Ultra High Resolution Field Emission Scanning Electron Microscope (UHR-FE-SEM) observation

In order to observe the morphologies of the photocured chiral nanoporous template (preparation example), ultrahigh-resolution field-emission scanning electron microscopy (UHR FE-SEM) was used to observe the morphologies. A cross section of the chiral nanoporous template prepared in Preparation Example was observed.

Figure 2 (a) shows BC molecules (HNF phase) before removal (stage 1, see FIG. 1b) and Figure 2 (b) shows BC molecules (HNF phase) after removal (stage 2, see Figure 1b) UHR FE-SEM images of were shown.

Referring to (a) of FIG. 2 , in stage 1, the BC molecules (HNF phase) filled in the space within the template and the photocured synthetic polymer coexisted, so it looked almost homogeneous and flat.

On the other hand, referring to (b) of FIG. 2, in stage 2, nano-pores are clearly observed in the micrograph, and through this, BC molecules (HNF phase) on the chiral nanoporous template )) was removed through washing, and only the template polymer network remained due to the removal of BC molecules. Although the polymer wall appeared to be slightly eroded, warped walls were observed in some places, indicating the formation of an inverse HNF structure. The estimated half-pitch of this inverse helix is ~100 nm, which can be compared to a typical HNF phase. The nanopore size was tens to hundreds of nanometers in diameter estimated from the interstices in the polymer network, which also coincided with the general diameter of the HNF phase of the BC system.

Therefore, the morphological chirality of the chiral nanoporous template is transferred from the original HNF network in stage 2 to the polymer (RMC) constituting the chiral nanoporous template, as shown in FIG. 2(c). it can be seen that

measurement example. Polarized optical microscopy (POM) observation

FIG. 3a shows polarized light microscopy (POM) images of the chiral nanoporous template at room temperature (RT) in stage 1, stage 2, and stage 3 (see FIG. 1b) of the manufacturing process of the chiral nanoporous template.

Referring to Fig. 3a, in stage 1, two different regions can be clearly distinguished by slightly crossing the polarizers, while very low birefringence for the crossed-Nicols condition. got dark vision The incidence ratio of these two regions was approximately 50:50.

It can be seen that the two optically active regions are two enantiomeric domains with opposite chirality.

Since achiral BC molecules are known to exhibit unavoidable chirality degeneracy (i.e., optical segregation) through spontaneous symmetry through in-layer tilt, each domain's Chirality is considered to be related to the handedness of HNF nuclei formed initially during the separation process.

In stage 2, the two chiral domains are almost indistinguishable under the POM. Because the absorption band of photocured synthetic polymers is much shorter than the visible wavelengths, the visible region is too small to be perceived by the naked eye.

However, at stage 3, two enantiomeric regions were reproduced with signs of the same optical activity as stage 1. In stage 3, the chiroptical properties are due to the pores filled with N-LC. Therefore, chirality is transferred from inverse HNF to packed N-LC, i.e., a photocured synthetic polymer film with a nanoporous inverse HNF structure exhibits chirality to another achiral medium. It can act as a chiral template that can be used to transfer. This trend was consistently observed when refilling nanoporous films with N-LC materials, whether for positive or negative dielectric anisotropy.

In this regard, additionally, using three different LC materials (8CB (Sigma-Aldrich), BYLC 53XX (BaYi Space Co.) and MLC-7029 (Merck)), refilling stage 3 (see Fig. 1b) Polarized light microscopy (POM) images of the chiral nanoporous templates as they were were shown in Fig. 3b (8CB), Fig. 3c (BYLC 53XX), and Fig. 3d (MLC-7029), respectively.

experimental example. Circular Dichroism (CD) measurement

In order to more clearly observe the chiroptical features, microscopic CD observation was performed. CD spectroscopy was performed to confirm the existence of a chiral superstructure. Therefore, only relative information, not quantified information, needs to be obtained from CD measurement. In particular, a CD signal appears when a chiral superlattice structure is generated, and similarly, a CD signal does not appear when a chiral superlattice structure is not present. FIG. 4a shows typical CD spectra measured at room temperature (RT) for monodomains in stage 1, stage 2, and stage 3 (see FIG. 1b).

Referring to FIG. 4a , in stage 1, mirror inversion associated with two enantiomeric domains was confirmed in the CD spectrum. These CD signals are mainly due to BC molecules and N-LC molecules upon HNF formation. This was confirmed by the disappearance of the CD signal in stage 2. On the other hand, a smaller but well-shaped CD signal (Fig. 4a inset) was observed in the range of 300 to 350 nm, which corresponds to the absorption wavelength of the photocured polymer. This confirms that the photocured polymer has a chiral superlattice structure generating a CD signal. That is, the structural chirality of the HNF phase was successfully transferred not only to the surface morphology of inverse HNF but also to the internal structure of the photocured polymer. That is, while chirality (or chiral information) is transferred from the nanoporous film to a specific achiral N-LC phase, chirality is not only transmitted, but also chirality is amplified. A slight rotation of the cell azimuthally alters the CD spectrum, eliminating the possibility of artifact signals due to birefringence.

In stage 3, the CD signal reappeared due to the chiral templating effect of the chiral nanoporous film (chiral nanoporous template). In particular, the CD intensity of stage 3 tends to be greatly improved compared to the case of values with the same sign of stage 1. That is, transfer of chirality (or chiral information) from the chiral nanoporous template to the achiral N-LC phase was further amplified.

Figure 4b shows CD spectra rotated at various azimuth angles (α = 0, 30, 60, and 90°) in stage 3. Referring to FIG. 4B , rotating the sample (chiral nanoporous template) at an azimuthal angle changes the CD spectrum, and artifact signals due to birefringence can be removed.

When refilling the nanoporous film with N-LC molecules, the template polymer (inverse HNF, Fig. 2(c)) forms a network that acts as a porous nanoconfinement medium with a large internal area, The refilled N-LC molecules are trapped in nanoscale interstitial volumes between polymers. Around templated polymers, N-LC molecules can be affected by the polymer surface.

The chiral transfer from the nanoporous film to the refilled achiral N-LC molecules can be explained as follows: the refilled N-LC molecules are aligned along the grooves of the template polymer network and the template polymer It can be seen that it is fixed to the surface (templated polymer surfaces). When the N-LC molecules are aligned parallel to each other and perpendicular to the axis of the template polymer network, the N-LC molecules assemble into a helicoidal structure along the axis of the template polymer network. That is, the direction of inclination of the N-LC molecules with respect to the axis of the template polymer network is formed around the axis of the template polymer network, thereby generating a chiral superlattice structure. It can be seen that this helical structure is somewhat similar to the distorted N-LC structure rather than the helical structure of conventional cholesteric LC.

In addition, the amplified CD signal after N-LC molecules are refilled into the nanoporous film can be explained as follows: The chiral superlattice structure of the template polymer network is, in this case, the superlattice structure of the N-LC molecules. It can be transmitted directly by chirality. Since the chiral signals of the template polymer network (stemming from the HNF phase) and the superlattice structure (stemming from the refilled N-LC molecules) are identical, the CD signal is amplified. These results can be easily expected due to the contribution of the long-range orientation order of N-LC molecules. That is, the macroscopic chirality of the refilled nanoporous film can be amplified to the bulk regions through a confined N-LC medium having a long-range orientation order independent of the polymer surface.

As described above, the stage 3 nanoporous film has two enantiomeric domains in the N-LC phase at room temperature (RT) and shows a distinct CD spectrum with enantiomerism. However, when the nanoporous film was heated to an isotropic (Iso) phase temperature (120 °C), the CD signal almost disappeared (Fig. 5(a)). This suggests that long-range ordering of LCs plays an important role in CD signal induction. The CD signal was restored when the nanoporous film was cooled back to room temperature (RT), i.e., when the phase was converted to the N-LC phase. This is representative of a temperature-modulated chiroptic function.

Figure 5 (a) is the CD spectrum for two enantiomeric domains in the N phase (at room temperature (RT)) and the Iso phase (at 120 ° C) in stage 3 (see Fig. 1b). is shown. Figure 5(b) shows the CD spectra of the two enantiomers under various electric field conditions at room temperature (RT) in stage 3 (see Figure 1b).

In (inset) of FIG. 5 (b), POM images corresponding to two phases are shown. While two chiral domains can be clearly identified in the N phase using slightly uncrossed polarizers, it is difficult to identify the domain boundaries in the Iso phase. These two chiral domains are again distinguishable after the Iso phase cools back to the N phase. These POM observations are consistent with the CD measurement results.

Stimuli-responsive modulation is also performed by applying an electric field. Figure 5(b) shows typical CD spectra for two enantiomeric domains under various electric fields at room temperature (RT). Also, as shown in the top inset of Fig. 5(b), the CD intensity is plotted as a function of the applied electric field. This means that the N-LC molecules anchored in the polymer network can play an important role in the formation process of the chiral superlattice structure. The CD intensity was constant within a certain range, which means that the refilled N-LC molecules were strongly immobilized on the surface of the template polymer network. Conversely, since the reorientation of N-LC molecules (in nanopores) decomposes the chiral superlattice structure, the CD intensity rapidly decreases as the electric field is increased above the threshold value. Therefore, it can be seen that a kind of Fredericksz transition occurred in N-LC. When the electric field was removed, the nanopore's N-LC molecules reassembled into the initial chiral superlattice structure, restoring their CD-active state. This was again clearly confirmed by the POM observation (bottom inset of Fig. 5(b)), where a sufficiently strong electric field aligns the N-LC molecules (α > 0) parallel to the electric field, which is ortho- In the crossed-Nicols condition, birefringence is reduced, which tends to further reduce brightness. While the two enantiomeric domains can be clearly distinguished in the absence of an electric field, a distinct textural change is observed with the uncrossed polarizer as the boundary of the enantiomeric domains gradually disappears as the strength of the electric field increases. can do. When a sufficiently strong electric field is applied, the enantiomeric domain boundaries become virtually indistinguishable to the naked eye. When the applied electric field is removed, the two chiral domains (enantiomeric domains) are restored, and this conversion process can be repeated. Typical modulation (applying the electric field) and relaxation (after removing the electric field) times are both about 10-20 ms. Since molecular dynamics occur in hundreds of nano-sized pores, rapid reactions can be observed.

experimental example. Measuring circularly polarized light (CPL)

In order to further demonstrate the functionality of the chiral nanoporous template (chiral nanoporous film) prepared in Preparation Example, a chiral N-LC doped with a pyrromethene-based fluorescent dye (PM580) was used. After filling, the CFL emissivity was investigated (Fig. 6 (a)). When chirality is transferred to a fluorescent achiral N-LC to form a chiral superlattice structure, a CPL signal is generated. Fig. 6(b) shows circular images of two enantiomeric domains of a chiral nanoporous template packed with fluorescent N-LC (at RT) excited using nonpolarized 525 nm light. It shows the polarization intensity difference ( I _left - I _right ). where I _left and I _right are the intensities of the left- and right-circularly polarized emission, respectively. The CPL spectra obtained from the two enantiomeric domains are mirror images of each other. In addition, a luminescence dissymmetry factor g _lum defined as 2 ( I _left - I _right )/( I _left + I _right ) was used to quantify the CPL level. For most small organic chiral molecules, the luminescence asymmetry constant is generally in the range of 10 ⁻⁵ to 10 ⁻³ . The estimated g _lum for this experiment was 2 Х 10 ^-3 to 3 Х 10 ^-3 for the two domains (Fig. 5(b), see inset). The detected CPL originated from a chiral superlattice structure formed by the fluorescent N-LC, thus this result further confirms the transfer of chirality.

(a) of FIG. 7 shows the respective | I _left - I _right | 7(b) shows the spectrum of the domain under various electric field conditions at room temperature (RT) in stage 3 (see FIG. 1b). I _left - I _right | shows the spectrum.

Figure 7(a) is a typical | I _left - I _right | Shows a comparison of spectra. Similar to the CD signal, the CPL signal almost disappeared when the nanoporous film was heated to the Iso phase region (120 °C). As expected, the CPL signal reappeared upon cooling to room temperature (RT), i.e. upon re-entering the N-LC phase. In addition, this confirms that the chiral superlattice structure formed by N-LC in the nanopore plays an important role in inducing the CPL signal. CD and CPL signals were inactivated in the cooled solid state from the N-LC phase. The solid state has positional ordering as well as long-range directional ordering. The formation of chiral superlattice structures influenced by the grooves of the template polymer can be hindered by the strong localization inherent in the solid state. Therefore, the phenomena observed in the present invention were not observed in nanoporous films filled with solid-state molecules.

Modulation of the CPL signal by electric stimulation is also possible. As shown in (b) of FIG. 7, as the applied electric field increases, | I _left - I _right | decreased, because the chiral superlattice structure was continuously collapsed in the nanopore through the reorientation of N-LC molecules. When the electric field was removed, the nanopore's LC molecules restored their superlattice structure to return to their initial CPL active state.

Finally, the advantages of the present invention compared to previous studies are as follows.

First, the nano-separated BC molecules and N molecules in the HNF phase tend to further separate into macroscopic aggregates over time, thereby degrading their chiroptical properties. However, the HNF network of the present invention was stabilized by photocross-linking of the N region, and further nanoseparation was suppressed.

Second, the active temperature range for stimuli-responsive chiroptical properties is broadened due to the use of LC molecules with a wide N temperature range including room temperature (RT), whereas the CPL in previous studies was 50 This was possible only at temperatures above °C.

Therefore, the photo-cross-linking method greatly improves the stability and reliability of the system, which was relatively poor in previous studies.

conclusion

A chiral nanoporous template with excellent functionality was fabricated based on spontaneous nanoscale segregation in an achiral binary system of BC molecules and reactive mesogenic compounds. The formation of an inverse nanohelical structure by photocrosslinking, which serves as a template for N-LC, was confirmed by scanning electron microscopy (SEM). These chiral nanotemplates are simply composed of achiral molecules and can be easily fabricated by a simple bottom-up methodology without a complicated fabrication process. It has been demonstrated that these chiral nanoporous films can act as three-dimensional nanomolds that give rise to chirooptic properties, ie, stimulus-responsive CD and CPL. This methodology can be used as a strategy to construct new chiroptical materials that can be applied to various applications including chiroptical modulators and switches, biological sensors, and the like.

On the other hand, the embodiments of the present invention disclosed in this specification and drawings are only presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art that other modified examples based on the technical idea of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims (14)

A polymer network structure composed of a reactive mesogen compound; and
A chiral nanoporous template comprising a plurality of nanopores formed on the polymer network structure.
According to claim 1,
The reactive mesogenic compound is a chiral nanoporous template, characterized in that composed of a nematic liquid crystal (N-LC) and a reactive monomer.
According to claim 2,
The nematic liquid crystal (N-LC) is a chiral nanoporous template, characterized in that 4-cyano-4'-pentylbiphenyl.
According to claim 2,
The reactive monomer is a chiral nanoporous template, characterized in that 2-methyl-1,4-phenylene bis (4-(((4- (acryloyl oxy) butoxy) carbonyl) oxy) benzoate).
According to claim 1,
The chiral nanoporous template has an inverse helical nanofilament structure.
Preparing a precursor mixture comprising a bent nuclear molecule, a reactive mesogen compound and a photoinitiator;
preparing a template by photocuring the precursor mixture;
removing the bent nuclear molecule on the template; and
Method for producing a chiral nanoporous template comprising the step of drying the template.
According to claim 6,
The method for producing a chiral nanoporous template, characterized in that the bent nuclear molecule has a helical nanofilament phase as a nanodisruption phase.
According to claim 6,
The bent nucleus molecule is a method for producing a chiral nanoporous template, characterized in that 1,3-phenylene bis [4- (4-eptyloxyphenyliminomethyl) -benzoate].
According to claim 8,
The reactive mesogenic compound is a method for producing a chiral nanoporous template, characterized in that composed of a nematic liquid crystal (N-LC) and a reactive monomer.
According to claim 9,
The method for producing a chiral nanoporous template, characterized in that the nematic liquid crystal (N-LC) is 4-cyano-4'-pentylbiphenyl.
According to claim 9,
The reactive monomer is a method for producing a chiral nanoporous template, characterized in that 2-methyl-1,4-phenylene bis (4-(((4- (acryloyl oxy) butoxy) carbonyl) oxy) benzoate).
According to claim 6,
The photoinitiator is a method for producing a chiral nanoporous template, characterized in that DMPAP (2,2-dimethoxy-2-phenylacetophenone).
According to claim 6,
The photocuring is a method for producing a chiral nanoporous template, characterized in that carried out at 80 to 120 ℃
According to claim 6,
The removal of the bent nuclear molecule is a method for producing a chiral nanoporous template, characterized in that using 1,2-dichlorobenzene (1,2-dichlorobenzene).

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