JP5526382B2 - Process for producing conjugated polymer film using nematic liquid crystal electrolyte and conjugated polymer film having optical anisotropy - Google Patents

Description

  The present invention relates to a method for producing a conjugated polymer film by electrolytic polymerization using a liquid crystal electrolyte and a conjugated polymer film having optical anisotropy.

  Conjugated polymers have received much attention both in chemistry and physics and in applications in semiconductor devices. For example, in conjugated polymers such as polyacetylene and poly-p-phenylene, a π-electron cloud spread in one dimension is formed by alternately connected single bonds and double bonds, thereby making it electrically conductive (semiconductor) and electrochromic. In addition, electronic characteristics such as luminescence are exhibited.

  Among these, a linear conjugated polymer composed of one polymer chain has anisotropy in intramolecular conduction. However, in the aggregated (aggregated) state, the direction of the polymer chain is random, and is isotropic as a whole and does not exhibit anisotropy.

  On the other hand, when the direction of the polymer chain is aligned, it will have anisotropy as a whole, and various interesting properties such as optical anisotropy and electrical anisotropy will be expressed. Various studies have been made to control the orientation of the main chain of the linear conjugated polymer. Conventionally, for example, methods such as stretching, magnetic field alignment, electric field alignment, and introduction of liquid crystal groups have been proposed.

  On the other hand, the present inventors have so far studied the synthesis of a conjugated polymer film by electrolytic polymerization in a cholesteric liquid crystal field (see Patent Document 1). According to this technology, the synthesized conjugated polymer film is affected by the cholesteric liquid crystal field to form a regular spiral structure, which reveals that the entire polymer film exhibits chiral characteristics. Yes.

Japanese Patent Laid-Open No. 2008-2223016

  Against this background, the present inventors tried to apply the electropolymerization technique using the liquid crystal electrolyte accumulated so far to a nematic liquid crystal electrolyte that has not been sufficiently studied. We investigated the synthesis of conjugated polymer films with new optical and electrical properties.

  The present invention has been made in view of the circumstances as described above, and a novel method for producing a conjugated polymer film by electrolytic polymerization using a liquid crystal electrolyte and a conjugate having optical anisotropy using the same. It is an object to provide a polymer film.

  The present invention is characterized by the following in order to solve the above problems.

  1: The following formula (I):

(In the formula, two A _{1 s} each independently represent a monovalent aromatic ring-containing group, n A _{2 s} each independently represent a divalent aromatic ring-containing group, and n is an integer of 0 to 3 And a conjugated polymer film having an orientation is synthesized by electrolytic polymerization of a conjugated aromatic monomer represented by formula (1) in a nematic liquid crystal electrolyte.

  Second: The method for producing a first conjugated polymer film according to the above, wherein a conjugated polymer film is synthesized on the electrode substrate by electrolytic polymerization using a rubbing-treated electrode substrate.

  Third: A conjugated polymer film obtained by the first or second manufacturing method and having linear dichroism.

  According to the present invention, a conjugated aromatic monomer forms an ordered structure by an anisotropic reaction field of a nematic liquid crystal whose molecular axis is aligned in one direction, and the synthesized conjugated polymer has a main chain having an orientation. become. Thereby, a conjugated polymer thin film having optical anisotropy and further electrical anisotropy can be obtained.

2 is a polarizing microscope photograph (× 50) under crossed Nicols of a nematic liquid crystal electrolyte (in a polymerization cell) in Example 1. FIG. FIG. 3 is a polarizing micrograph (× 50) under crossed Nicols of a conjugated polymer film polymerized in a nematic liquid crystal electrolyte (without rubbing treatment) in Example 1. FIG. It is a polarization microscope photograph (x50) under crossed Nicols of the conjugated polymer film obtained in Example 2 ((a) is 45 °, (b) is parallel to the analyzer, and (c) is the polarizer. Parallel, x50 each. It is the photograph which piled up the polarizing plate on the conjugated polymer film obtained in Example 2 ((a) is an orientation direction and a polarizing plate perpendicular | vertical, (b) is an orientation direction and a polarizing plate in parallel). It is the photograph which piled up the polarizing plate on the reduced conjugated polymer film ((a) is the orientation direction and a polarizing plate perpendicular, (b) is the orientation direction and a polarizing plate are parallel). 2 is a polarization absorption spectrum of a conjugated polymer film obtained in Example 2. The change by the polymerization time of the polarization | polarized-light absorption spectrum of the conjugated polymer film obtained in Example 2 is shown. (A) is a UV-vis spectrum of 6CB and a monomer (in THF), and (b) is a polarized absorption spectrum of the monomer in a nematic liquid crystal.

  Hereinafter, the present invention will be described in detail.

  In the present invention, a conjugated aromatic monomer represented by the above formula (I) is electrolytically polymerized in a nematic liquid crystal electrolytic solution to synthesize a conjugated polymer film having orientation.

In the conjugated aromatic monomer represented by the formula (I), the aromatic ring-containing group of A ₁ has a hydrocarbon aromatic ring or a heteroaromatic ring as the aromatic ring.

Examples of the hydrocarbon aromatic ring include a monocyclic ring such as a six-membered ring or a polycyclic ring containing the ring, such as a C ₆ -C ₁₈ hydrocarbon aromatic ring such as a benzene ring and a naphthalene ring. It is done.

  Examples of the heteroaromatic ring include a monocyclic ring such as a 5-membered ring and a 6-membered ring containing a heteroatom such as nitrogen, oxygen, and sulfur, or a polycyclic ring containing this, such as a thiophene ring and a pyridine ring. , Pyrrole ring, furan ring, imidazole ring, oxazoline ring, thiazole ring, pyrazoline ring, pyridine ring, pyridazine ring, pyrimidine ring and the like.

These hydrocarbon aromatic rings and heteroaromatic rings may have a substituent. Examples of the substituent include a halogen atom, a hydroxyl group, an amino group, a cyano group, a C ₁ -C ₆ alkyl group, a C ₂ -C ₆ alkenyl group, a C ₇ -C ₁₈ arylalkyl group, and a C ₁ -C ₆ alkoxy group. C ₂ -C ₆ alkoxycarbonyl group, C ₆ -C ₁₀ aryloxy group, C ₂ -C ₈ dialkylamino group, C ₂ -C ₈ acyl group and the like. In addition, a divalent substituent substituted with 2 atoms of a hydrocarbon aromatic ring or a heteroaromatic ring, for example, a C ₁ -C ₆ alkylene group, or ₁ to 3 in the main chain of a C ₁ -C ₆ alkylene group It may be one introduced with a heteroatom.

Further, between the adjacent A ₁ and A ₂ or A ₂ and A _2,, C ₁ -C ₆ alkylene group or a C ₁ -C ₆ 2 such as the main chain of the alkylene group which hetero atoms are introduced, A valent substituent may be shared.

In the conjugated aromatic monomer represented by the formula (I), the aromatic ring-containing group of A ₂ is a divalent group having a hydrocarbon aromatic ring or a heteroaromatic ring as the aromatic ring. Examples of the hydrocarbon aromatic ring and heteroaromatic ring include those exemplified above for A ₁ .

  Specific examples of the conjugated aromatic monomer include 2,7-di (2-furyl) fluorene, bithiophene, terthiophene, bipyridine, 1,4-di (2-thienyl) phenylene, 2,5-di ( 2-thienyl) pyridine, 3,4-ethylenedioxythiophene (EDOT) or a dimer or trimer thereof, 4,4′-di (2-furyl) biphenyl, and the like.

  If one type is selected as the conjugated aromatic monomer, a homopolymer can be obtained, and if two or more types are selected, a mixed conjugated polymer can be obtained.

  A nematic liquid crystal electrolyte used for electrolytic polymerization has nematic liquid crystal and a supporting electrolyte as essential components.

  The nematic liquid crystal forming the reaction field is not particularly limited, and various types can be used. For example, a thermotropic liquid crystal capable of realizing a liquid crystal form without including a solvent can be used, and the liquid crystal forming group (mesogen) may be either a main chain type or a side chain type. The structure of such a liquid crystal is not particularly limited. For example, a structure in which two benzene rings are connected by a linking group containing a double bond such as trans-stilbene, azoxybenzene, or nitrone, or a linking group such as biphenyl or cyclohexane. Illustrated. Furthermore, it is preferable that a flexible substituent such as an alkyl group or an alkoxy group is introduced at the end of the mesogenic group, and further, a substituent having an aliphatic chain, a rigid straight chain, or an asymmetric structure may be introduced. Good. Since the length of these substituents also affects the transition temperature of the liquid crystal, it may be appropriately selected in consideration of the temperature of electrolytic polymerization.

  Among them, those that can maintain the liquid crystal state at room temperature or higher and have a wide temperature range exhibiting a liquid crystal phase, specifically, for example, 6CB (4-cyano-4'-n-hexylbiphenyl) represented by the following formula is preferable. Can be used.

  In addition, for example, 5CB, 7CB, 8CB (these numbers at the beginning indicate the carbon number of the alkyl group), alkylazobenzene, phenylazomethine compounds, and the like can be used.

  The supporting electrolyte is not particularly limited as long as it does not inhibit the electropolymerization reaction and gives sufficient conductivity to the liquid crystal. Generally, the supporting electrolyte is appropriately selected from various ionic salts used in the electrochemical reaction according to the applied voltage and the like. can do. Specific examples include tetrabutylammonium perchlorate (TBAP) and lithium perchlorate.

  As a device for electrolytic polymerization, for example, a cell structure as in the embodiment can be used, but the present invention is not limited to this, and various configurations having electrodes can be employed.

  In the present invention, the blending ratio of the above aromatic conjugated monomer, nematic liquid crystal, and supporting electrolyte is not particularly limited. For example, aromatic conjugated monomer: 1 to 8 mol%, nematic liquid crystal: 90 to 96 mol%, supporting Electrolyte: Can be in the range of 0.1 to 1.0 mol%. The applied voltage in the electropolymerization can be appropriately selected according to the kind of the conjugated aromatic monomer, the liquid crystal reaction field used, the electrode material, and the like, and is not particularly limited. For example, the voltage is 1 to 5 V, the energization time is 1 Considering minutes to 5 hours. Note that the temperature is in a temperature range in which a nematic liquid crystal phase is obtained.

  The electrode used for the electropolymerization is not particularly limited, and examples thereof include a transparent glass electrode such as indium oxide and tin (ITO), a metal electrode such as gold, silver, and platinum, and a carbon electrode. These are appropriately selected according to the type of monomer, the type of liquid crystal, etc., or the amount of the target polymer.

  In particular, a conjugated polymer film in which the polymer main chain is uniformly oriented can be obtained by synthesizing a conjugated polymer film on the electrode plate using an electrode having a polymer film rubbed on the surface of the electrode plate. Can be obtained.

  For example, a polymer film (polyvinyl alcohol or the like) is applied to the electrode surface of the ITO substrate and rubbed in one direction with a soft cloth. As a result, fine grooves are formed in the polymer, and liquid crystal molecules can be aligned in one direction along the grooves.

  In the present invention, the orientation of the polymer main chain by the electropolymerization in the liquid crystal can be controlled by performing the electropolymerization in a state where the aromatic conjugated monomer is dissolved in the nematic liquid crystal electrolyte. That is, in the nematic liquid crystal, the rod-like monomer of formula (I) is aligned along the director of the liquid crystal. The synthesized conjugated polymer film is affected by the molecular arrangement of the nematic liquid crystal in the growth process during electropolymerization, and exhibits an optical structure similar to that of the nematic liquid crystal electrolyte. Thus, the polymer main chain can be grown along the orientation of the liquid crystal molecules by electropolymerization using nematic liquid crystal as a reaction field.

  Then, the liquid crystal molecules are uniformly aligned by the rubbing-treated electrode substrate, whereby a conjugated polymer film having macroscopic orientation can be synthesized. Thus, the conjugated polymer film having orientation exhibits linearly polarized light perpendicular to the orientation direction to the electrode substrate. Moreover, this conjugated polymer film shows a color change of the polymer in the oxidation-reduction process (dope-dedope) while maintaining linear dichroism.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.

  First, 2,7-di (2-furyl) fluorene was synthesized as an aromatic monomer, and this monomer was combined with tetrabutylammonium perchlorate as a supporting electrolyte and 6CB (4-cyano-4'-n-) as a nematic liquid crystal. A solution in hexylbiphenyl) was used as a liquid crystal electrolyte. The composition ratio was monomer: supporting electrolyte: nematic liquid crystal = 0.5: 0.5: 99.0 by mass ratio.

  This liquid crystal electrolyte is injected into two transparent glass (ITO glass) electrodes with a spacer of 12μm in thickness, and polymerization is performed by applying a constant voltage of DC 4.0V in the temperature range (20 ° C) showing the liquid crystal phase. Thus, a polymer thin film was obtained on the anode substrate.

  This polymer thin film was washed with hexane and dried. FIG. 1 is a polarizing microscope (POM) photograph under a crossed nicols of a nematic liquid crystal electrolyte (in a polymerization cell), and FIG. 2 is a polarizing microscope photograph of the synthesized conjugated polymer film. Thus, the electrolyte before polymerization exhibits a schlieren pattern unique to nematic liquid crystals, and the synthesized conjugated polymer film of poly (2,7-di (2-furyl) fluorene) also exhibits birefringence. A schlieren pattern peculiar to nematic liquid crystals was also observed.

  Next, electrolytic polymerization was performed in the same manner as in Example 1 except that the surface of the glass substrate electrode was subjected to an orientation treatment in one direction by rubbing. The rubbing was performed by applying a polymer film (polyvinyl alcohol) to the electrode surface of the glass substrate and rubbing it in one direction with absorbent cotton.

  The synthesized polymer thin film was observed with a polarizing microscope and a polarization absorption spectrum, and the optical anisotropy was examined. Further, the polarization absorption spectrum of the liquid crystal electrolyte in the cell subjected to the alignment treatment was also measured in the same manner.

  FIG. 3 shows a polarization micrograph of the synthesized conjugated polymer film ((a) is 45 °, (b) is parallel to the analyzer, (c) is parallel to the polarizer), and FIG. 5 shows the synthesized conjugated polymer film. It is the photograph which piled up an analyzer and a polarizer ((a) is the orientation direction and a polarizing plate perpendicular, (b) is the orientation direction and a polarizing plate are parallel). FIG. 6 is a photograph in which an analyzer and a polarizer are superimposed on a reduced conjugated polymer film ((a) is an orientation direction and a polarizing plate perpendicular, and (b) is an orientation direction and a polarizing plate are parallel).

  As described above, when the substrate subjected to the alignment treatment by rubbing was used, birefringence was exhibited, but no schlieren pattern was observed.

  Next, when the polarization absorption spectrum of the polymer thin film on the substrate subjected to the alignment treatment is measured (FIGS. 6 and 7), the absorption is more when the incident polarization is parallel to the rubbing direction than when it is perpendicular. It was large and found to exhibit linear dichroism.

  From these results, it is considered that the main chain of the polymer extends along the molecular orientation of the liquid crystal.

  Further, from the result of the polarization absorption spectrum of the nematic liquid crystal electrolyte in the cell using the alignment treatment substrate (FIG. 8), the same linear dichroism as the polymer thin film was observed in the absorption band derived from the monomer. This suggests that during polymerization, the monomer is aligned along the director of the nematic liquid crystal, and the anisotropic alignment state of the monomer in this liquid crystal is the orientation of the polymer main chain after polymerization. It is thought that this is induced.

Claims (2)

Formula (I):
(In the formula, two A _{1 s} each independently represent a monovalent aromatic ring-containing group, n A _{2 s} each independently represent a divalent aromatic ring-containing group, and n is an integer of 0 to 3 A conjugated aromatic monomer represented by formula (1) is electropolymerized in a nematic liquid crystal electrolyte using a rubbed electrode substrate, and a conjugated polymer film having orientation is synthesized on the electrode substrate. A process for producing a conjugated polymer film characterized by A conjugated polymer film obtained by the production method according to claim 1 and having linear dichroism.