JP4487079B2 - Optically active polyaniline, method for electrolytic synthesis thereof, and optically active electrochromic material - Google Patents

Description

  The present invention relates to an optically active polyaniline that can be synthesized from an aniline monomer and that can control an optical rotation angle by an external electric field, an electrolytic synthesis method thereof, and an optically active electrochromic (EC) material characterized by the method. It is.

  Electrochromic (EC) materials exhibit a color change when held under different potential conditions. Conductive polymers such as polythiophene, polypyrrole, poly (3,4-ethylenedioxythiophene) are known to provide a different approach to such EC materials than inorganic EC materials. When such a polymer is doped with ions, its conductivity ranges from a behavior characteristic of a semiconductor to a behavior characteristic of a metal. Doping is by an electrochemical procedure in which a polymer is utilized as an electrode for an electrolytic cell, which contains an electrolyte, which is a compound that can be ionized to become dopant ions. This process changes the electronic state of the polymer, resulting in EC characteristics. Polyaniline (PANI) is another promising conductive polymer. This is because it is chemically stable, has relatively high conductivity, and has interesting optical properties such as EC. EC here is caused by chemical and electrochemical doping. For example, preparation of camphorsulfonic acid (CSA) -doped PANI has been carried out by chemical oxidative polymerization (Non-patent Documents 1-3) and electrochemical polymerization (Non-patent Documents 4-5). A helical polyaniline is obtained.

  Polyaniline doped with CSA (PANI-CSA) is represented, for example, as:

さらに電気化学的重合過程における重合温度の変化によって、キラルなＰＡＮＩのらせん方向が変化することが知られている（非特許文献６）。また、最近では、光学活性を持つ成分を含む置換ＰＡＮＩの光学活性において、化学的ドーピングによって誘導される変化についての研究が行われている（非特許文献７）。
A.G. MacDiarmid et al., Synth. Met. 65, 103 (1994). S.J. Su et al., Chem. Mater. 13, 4787 (2001). C.Y. Yang et al., Synth. Met. 53, 293 (1993). E.V. Strounina et al., Synth. Met. 106, 129 (1999). W. Li et al., Adv. Func. Mater. 15, 1793 (2005). Y.P. Loom et al., Macromolecules 39, 5604 (2006). H. Goto, Macromol. Chem. Phys. 207, 1087 (2006).

Furthermore, it is known that the helical direction of chiral PANI changes due to a change in polymerization temperature in the electrochemical polymerization process (Non-Patent Document 6). Recently, research has been conducted on changes induced by chemical doping in the optical activity of substituted PANI containing a component having optical activity (Non-patent Document 7).
AG MacDiarmid et al., Synth. Met. 65, 103 (1994). SJ Su et al., Chem. Mater. 13, 4787 (2001). CY Yang et al., Synth. Met. 53, 293 (1993). EV Strounina et al., Synth. Met. 106, 129 (1999). W. Li et al., Adv. Func. Mater. 15, 1793 (2005). YP Loom et al., Macromolecules 39, 5604 (2006). H. Goto, Macromol. Chem. Phys. 207, 1087 (2006).

  However, although polyaniline having chiral optical property is attracting attention as an application to electrochromic (EC) materials, it has been possible to adjust the change in the chiral optical property of polyaniline by electrochemical doping. However, it has not been realized. That is, the actual situation is that control of optical activity is not realized.

  Moreover, the electrochemical polymerization reaction of polyaniline is attracting attention from the simplicity and rationality of its operation, but in the conventional electrolytic synthesis of polyaniline, a core oligomer is required first, and a commercial product, etc. There is a problem that it is difficult to directly use a polyaniline monomer which is easily available as

  Therefore, the present invention eliminates such conventional problems, and without using an oligomer, the aniline monomer is used as a starting material to control optical activity, for example, circular deflection dichroism actively with an external electric field. To provide a new electrolytic synthesis method of optically active polyaniline capable of adjusting (CD) and optical rotation angle, to provide a new optically active polyaniline obtained by this method, and an electrochromic (EC) material using the same Is an issue.

  The electrolytic synthesis method of the present invention for solving the above problems is characterized by the following.

First, an optically active molecule-doped polyaniline thin film is manufactured by performing repeated oxidative electrolytic polymerization in which aniline monomer is used as a raw material in the presence of optically active molecule camphorsulfonic acid (CSA). .

  Second: Electropolymerization is performed using cyclic voltammetry.

  Third: In any of the above methods, an acid polymerization is carried out in the presence of an acid to produce a polyaniline thin film that exhibits optically active electrochromic (EC) characteristics.

Fourth : Acid is sulfuric acid.

  And in this invention, the following is provided by said new electrolytic synthesis method.

  That is, it is an optically active polyaniline whose optical activity is adjusted by a redox process, and a polyaniline thin film that exhibits optically active electrochromic (EC) characteristics. Further, it is an optically active electrochromic (EC) material having these as a part of its configuration, and an electrochromic device using the same.

  According to the present invention in which the repeated oxidative electropolymerization as described above, that is, the electropolymerization as a repetition of the oxidation / reduction process, in other words, the electropolymerization by potential sweep, an oligomer is required as in the prior art. Therefore, it is possible to electrolyze optically active polyaniline using aniline monomer as a starting material. By this electrosynthesis, it is possible to control optical activity, in particular, actively control circular dichroism (CD) and optical rotation angle with an external electric field. An optically active polyaniline is provided. That is, a new optically active conductive polymer capable of controlling the optical rotation angle and brightness at high speed from an easily available aniline monomer is provided.

  For example, as specific examples, aniline is polymerized by oxidative electrochemical polymerization in water containing camphorsulfonic acid, and polyaniline containing (+)-CSA or (-)-CSA (PANI-(+)-CSA and PANI, respectively). -(-)-CSA). The polyaniline thin film thus prepared exhibits strong and tunable optical activity based on electrochemical reduction / oxidation in 0.1 M aqueous sulfuric acid. The circular dichroism (CD) as well as the optical rotation angle of this polymer can be tuned by appropriately adjusting the externally applied potential in the form of light modulation.

  Optical modulation elements using Faraday rotation and Kerr rotation are now applied to optoelectronic media and communication optical devices. With the optically active polyaniline of the present invention, a new organic light modulation element based on EC characteristics having optical activity can be created.

  Embodiments of the present invention will be described below.

  The starting material (raw material) in the method for electrolytic synthesis of the optically active polyaniline of the present invention is an aniline monomer, and this includes those having various substituents allowed on the benzene ring of aniline. And these may be one kind or two kinds or more.

As the optically active molecule, camphorsulfonic acid (CSA) which is an optically active molecule having a sulfonic acid substituent is used.

  In the present invention, using the above aniline monomer, repeated oxidative electropolymerization is carried out in the presence of these optically active molecules to produce a polyaniline thin film doped with optically active molecules. Here, “repetitive oxidative electrolytic polymerization” in the present invention means a polymerization reaction in which the process of electrolytic oxidation is repeated. In other words, it is electrolytic oxidation polymerization by the potential sweep as described above.

  In the present invention, the above repetitive oxidative electrochemical polymerization is carried out in the presence of an acid, for example, sulfuric acid as a representative example. This acid regulates electrochemical doping and de-doping. Or it may be said that double doping is realized.

  Such repeated oxidative electropolymerization of the present invention can be carried out using a medium in which the aniline monomer is dissolved. Such solvents include water or solvents as a mixture of water and organic solvents, such as alcohols, THF, aqueous media as mixtures with other hydrophilic or polar organic solvents, and polar organics. A solvent is mentioned. Of these, water is preferably used as a solvent.

  The repetitive oxidative electrolytic polymerization of the present invention as described above is made possible by, for example, cyclic voltammetry (CV), a method of applying a DC voltage, or the like. And it can be suitably implemented by using cyclic voltammetry (CV), which has good film formability and is excellent in producing a homogeneous film. As such a system and apparatus for electrochemical polymerization, well-known ones including the electrode configuration can be applied.

  For example, FIG. 1 shows an outline of an apparatus for electrolytic synthesis of CV. Electrolytic synthesis is carried out by introducing an electrolytic solution containing an aniline monomer into an electrolytic cell having a working electrode on which the produced polymer is deposited, a counter electrode, and a reference electrode, and energizing it.

  In the case of electrolytic synthesis of CV using camphorsulfonic acid (CSA) and sulfuric acid, for example, the following condition ranges are generally considered.

CSA: 0.1-5M (mol)
Sulfuric acid: 0.01-1M (mol)
Sulfuric acid / CSA (molar ratio): 0.01 to 1.0
Aniline: 0.01-3M (mol)
Aniline / CSA (molar ratio): 0.1-5.0
Liquid temperature: 0-50 ° C
Voltage: -1.22V to 1.22V
Current: Arbitrary When the voltage is swept, aniline consumes current in accordance with polymerization, but the current is usually small, for example, 10 mA / cm or less.

  The EC (electrochromic) characteristics can be observed by changing to the electrolytic solution using an organic solvent containing an aqueous solution of sulfuric acid or an electrolyte containing no aniline monomer and CSA in the apparatus of FIG.

  For example, when the optically active polyaniline of the present invention is used as an EC element, it is preferable that the optically active polyaniline is brought into contact with a sulfuric acid aqueous solution. Means called an electric gel is known. For example, as shown in FIG. 2, sulfuric acid or tetrabutylammonium perchlorate, tetrabutylammonium fluoride, lithium pentafluoroarsenate is added to the gel. A supporting salt such as id and salt is dissolved, and this is sandwiched with conductive glass such as ITO glass together with a polymer layer of optically active polyaniline, and the bipolar method (electrode system consisting only of an anode and a cathode without using a reference electrode) ), An EC device capable of optical rotation can be obtained by switching the potential between 0 and 1.3V.

  Therefore, a more detailed description will be given below along the embodiments. Of course, the present invention is not limited by the following explanation.

  Oxidative electrochemical polymerization of aniline (monomer) was carried out in water containing 0.1 M aniline in the presence of 0.5 M (+)-or (-)-CSA. The electrochemical polymerization process was performed using three electrolytic cells. The components of this cell are a glass working electrode coated with transparent indium-tin oxide (ITO), an ITO counter electrode, and a saturated calomel electrode (SCE) reference electrode. PANI-CSA was deposited on ITO glass by repeated oxidative polymerization using cyclic voltammetry over a voltage range from 0V to 1.1V relative to SCE. An increase in current occurred at 0.47 V, indicating the peak monomer oxidation potential. During the repeated scan, this value shifted toward the anode side (0.50 V in the fifth scan). After the fifth scan, the polymer-coated electrode is dried under reduced pressure, followed by washing the thin film with water and acetone and placing it in a monomer-free 0.1 M aqueous sulfuric acid solution to characterize the spectroelectrochemical features. Examined. For the polymers thus obtained, PANI-(+)-CSA and PANI-(-)-CSA, a combination of cyclic voltammetry and ultraviolet / visible absorption analysis, or circular dichroism (CD) spectroscopy. Characteristic analysis was performed by the method, and their electrical activity and optical properties were clarified.

Revealing the redox behavior of both PANI-(+)-CSA and PANI-(-)-CSA indicated that these polymers have the same basic chemical structure. FIG. 3 shows the change in CD intensity at 465 nm that occurred during the electrochemical polymerization process of aniline in the presence of (+)-CSA (solid line) and (−)-CSA (dotted line). This corresponds to the absorption band in the π-π ^* transition of the main chain from the scan to the fifth scan. A repetitive triangular wave applied voltage generated by cyclic voltammetry at the electrode forms a polymer thin film on the ITO substrate, and this process causes a change in CD intensity.

  No CD signal was observed at the first scan, but the intensity increased slightly with the second scan. A strong CD signal at 460 nm was obtained by 5 scans, which corresponds to the 437 nm absorption band seen in the polymer on ITO [see FIG. 5 (C)]. The thickness of the thin film increases due to repeated scanning, and therefore the intensity of the CD spectrum increases with the number of scans. This CD intensity decreased during the oxidative process of each cycle (potential = 0V to 1.1V). This is probably due to the fact that the length of the polymer main chain actually increased during the oxidative process and at the same time the planar quinoid nature of the main chain appeared. This planar structure reduces the amount of one-handed helical twist and consequently suppresses the optical activity of the polymer under 1.1V conditions in the polymerization process. On the other hand, the CD intensity of the polymer is strengthened during the reduction process (potential = 1.1 V to 0 V), because the quinoid structure is converted into a benzenoid structure and the polymer does not grow. This phenomenon is also observed in in situ CD spectroscopic analysis during the monomer-free electrochemical polymer doping-de-doping process (described later). Polymerization proceeds with repeated concavo-convex CD cycles, increasing the total CD intensity of the polymer.

FIG. 4 shows a cyclic voltammogram (CV) of monomer-free polyaniline-(−)-camphor sulfonic acid [PANI-(−)-CSA] under the condition of a scan rate of 10 mV · S ⁻² . Is. CV is measured in 0.1 M sulfuric acid aqueous solution.

  In FIG. 4, the monomer-free polymer exhibits a clear and quasi-reversible redox process at oxidation potentials of 0.45 V and 0.73 V, which is associated with the formation of polarons and bipolarons by sulfuric acid, respectively. In addition, as shown in FIG. 4, reduction potentials of 0.63 V and 0.34 V were observed. Cyclic voltammogram (CV) shows the electrochemical doping-de-doping of PANI with sulfuric acid, but no features related to CSA desorption on PANI were observed.

  In order to investigate the optical properties of PANI-(+)-CSA and PANI-(−)-CSA by absorbance and CD spectrum, the polymer thin film on ITO was transferred into the cuvette and subjected to spectroelectrochemical analysis. In 0.1 M sulfuric acid aqueous solution, as shown in FIG. 5, a series of in situ CD absorption spectra were measured under conditions in which various voltages were applied in the range of 0.2 V to 0.7 V with respect to SCE.

As can be seen from the results of the spectroelectrochemical analysis shown in FIG. 5 (C), the π-π * transition of the PANI main chain at 440 nm decreases during electrochemical doping (increase in applied voltage) in the presence of sulfuric acid. On the other hand, the doping band (> 700 nm) increases. At the same time, the CD intensity of the polymer changes with electrochemical doping, and this is shown in FIGS. 5 (A) and 5 (B). PANI-(+)-CSA and PANI-(-)-CSA show complementary mirror-image cotton effects in the π-π ^* transition region of this 0.2V neutral state (dedoped form) backbone However, this indicates that the two polymers are comparable but have opposite chirality. In the oxidized state (doped state), the CD spectrum of the polymer showed a decrease in intensity. The possibility that a complementary mirror image relationship between PANI-(+)-CSA and PANI-(-)-CSA has occurred due to the use of CSA as a chiral dopant is due to the fact that CSA cotton This is because the effect is observed only at wavelengths in the ultraviolet region.

  Both PANI-CSAs switch between a light greenish yellow reduced form (dedoped with sulfuric acid) and a dark blue oxidized form (doped with sulfuric acid). It may be considered that the initial polyaniline is half-doped with CSA after polymerization. For example, PANI-(−)-CSA under an applied voltage of 0.2 V with respect to SCE is electrochemically dedoped, but still shows a doping band on the long wavelength side. This broad absorption band is also observed after hundreds of doping-de-doping processes. Here, CSA is bonded to the N-position of polyaniline by static interaction even after undergoing an electrochemical reduction process, but not all nitrogen atoms of polyaniline are occupied by CSA. Absent. In the main chain, further doping with sulfuric acid occurs resulting in a change in chirality. In other words, polyaniline half-doped with CSA can be further subjected to acid doping with sulfuric acid. As a result of this electrochemical double doping process, a spectral change occurs.

  Optical switching of electrically active conducting polymers has been developed and used in polymer EC devices. Therefore, when the CD intensity of the PANI-CSA during the voltage scanning in the range of 0V to 0.9V is seen, a reversible and symmetrical change occurs as shown in FIG. This electrochemical redox-induced change seen in CD can be well explained if it is due to the main chain being electrochemically doped / dedoped with sulfuric acid. This result indicates that the polymer exhibits reversible optically active electrochromism.

  The CD intensity under the condition of 460 nm is lowest under an applied voltage of 0.9 V with respect to SCE (doping state), both polymers show a cotton effect, PANI-(+)-CSA is negative, PANI -(-)-CSA was positive. A reduced state occurs at an applied voltage of 0 V with respect to SCE, which subsequently increases the CD intensity under 460 nm conditions. Therefore, the CD intensity can be reversibly changed by adjusting the redox process.

  FIG. 7 shows optical rotatory dispersion (ORD) spectra of PANI-(+)-CSA and PANI-(−)-CSA under various applied voltage conditions. These ORD spectra are obtained by performing a Kramers-Kronig (KK) conversion of the CD spectra of PANI-(+)-CSA and PANI-(−)-CSA. Reduction (de-doping) after oxidation (doping) resulted in optical rotation signals of 428 nm and 482 nm.

  By applying a reducing potential, these peaks return to the original intensity observed in the reduced state. This indicates that the polymer has electro-optical activity, and the optical rotation can be adjusted by an electrochemical process. By properly adjusting the externally applied voltage, the optical rotation angle of the polymer can be adjusted in the ultraviolet / visible region. This property is equivalent to the functionality of Kerr devices and Faraday rotators. The optical activity is adjusted by the electrochemical doping-de-doping process. The optical rotation adjustment observed in this polymer is due to changes in the electronic state that occur as a result of this process.

It is the schematic which illustrated the apparatus structure for the electropolymerization by cyclic voltammetry (CV). It is the schematic which showed the structural example of EC element. It is the figure which showed the CD intensity change at 465 nm produced in the middle of the electrochemical polymerization process of aniline in the presence of (+)-CSA (solid line) and (-)-CSA (dotted line). Aniline monomer (0.1M), (+)-camphorsulfonic acid (0.5M) or (-)-camphorsulfonic acid (0.5M), SCE (reference electrode), ITO counter electrode and working electrode were used. A chiral optical polymer was deposited on the working electrode. It is a cyclic voltammogram (CV) of monomer-free polyaniline-(−)-camphorsulfonic acid [PANI-(−)-CSA]. Scan rate: 10 mV · s ⁻² . The CV of PANI-(−)-CSA was measured in a 0.1 M aqueous sulfuric acid solution. In-situ CDs of PANI-(+)-CSA (A) and PANI-(-)-CSA (B) produced on an ITO-coated glass substrate under various applied voltages to SCE It is an absorption spectrum figure. These spectra were measured in a 0.1 M aqueous sulfuric acid solution. Monomer-free PANI-(+)-CSA (blue line) and PANI- (produced on an ITO-coated glass substrate when an applied voltage of 0 V to 0.9 V was applied to SCE in 0.1 M sulfuric acid aqueous solution. It is the figure which showed the repetitive change of CD intensity monitored at 460 nm about-)-CSA (red line). . The applied voltage of the triangular wave was generated using cyclic voltammetry. It is an in-situ ORD spectrum of PANI-(+)-CSA (A) and PANI-(-)-CSA (B) generated on an ITO-coated glass substrate when various applied voltages are applied. The ORD spectrum was calculated by converting the CD spectrum into Kramers-Kronig (KK).

Claims (6)

An optically active molecule-doped polyaniline thin film is produced by performing repeated oxidative electrolytic polymerization in which aniline monomer is used as a raw material in the presence of the optically active molecule camphorsulfonic acid (CSA). An electrolytic synthesis method of optically active polyaniline.   2. The method for electrolytic synthesis of optically active polyaniline according to claim 1, wherein the electrolytic polymerization is carried out using cyclic voltammetry.   3. The method of electrosynthesis of optically active polyaniline according to claim 1 or 2, wherein a polyaniline thin film exhibiting optically active electrochromic (EC) characteristics is produced by performing electropolymerization in the presence of an acid. The method for electrolytic synthesis of optically active polyaniline according to claim 3, wherein the acid is sulfuric acid. An optically active polyaniline thin film synthesized by the method according to any one of claims 1 to 4 and having optical activity adjusted by a redox process and exhibiting optically active electrochromic (EC) characteristics is at least a part of the structure. An optically active electrochromic (EC) material characterized in that an optical rotation angle can be controlled by an external electric field. An electrochromic device using the optically active electrochromic (EC) material according to claim 5.

Images