JP2003036896A - Photo energy-to-electrical energy transformation series using ito electrode chemically modified with porhyrin- fullerene-combined molecule - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo energy-to-electrical energy transformation series, which remarkably improves the quantum efficiency upon generating photocurrents. SOLUTION: The photo energy-to-electrical energy transformation series includes a single molecule film, which is formed by self-organizing at least one compound selected among a compound group represented by the general formula (A) on the electrode surface of an indium-tin oxide(ITO) via a covalent bond symbolized by Bin. (Bin. Stands for O3 Si-, carboxylic acid ester, or phosphoric acid ester. Each of X<1> -X<3> stands for a group selected among single bond compounds -N-H-CO-,-CO-NH-,-Ph-,-O-, or -CO-O-. n stands for a natural numbers among 1 to 20. Ar stands for a phenyl group, which may include a substituent of a heavy molecular weight. M stands for 2H (hydrogen) or Zn (zinc). A fullerene derivative is selected among formulas (a) and (b), where the part consisting of fullerene is C60 to C90 ).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light transmissive semiconductor electrode, ITO (indium-tin-oxide).
n-Oxide) Electrode donor (sometimes called donor) -acceptor (sometimes called acceptor) structure, specifically, a compound having a porphyrin-fullerene structure in the same molecule is self-assembled. Self-Assembled Monolayer
s = SAM) to provide a highly efficient light energy / electric energy conversion system.

[0002]

2. Description of the Related Art Plants and certain photosynthetic bacteria have a system that functions to replace solar energy with chemical energy. It was known from the biochemical and spectroscopic analysis data that many photoreceptor molecules, like an antenna, form an aggregate in this system in order to efficiently collect dilute photons. This system is called the antenna system. In photosynthesis, organic pigments such as chlorophyll and carotenoids are arranged around the reaction center protein for energy transfer. Then, the light energy trapped by the antenna complex is collected by the chlorophyll dimer (called a special pair) located in the reaction center complex, and the charge separation reaction is performed. When the electronic interaction between the electron donor and the electron acceptor is large, the electron transfer rate depends on the change in the free energy of electron transfer (-ΔG) and the rearrangement energy (λ) associated with the electron transfer (of the chemical bond of electron transfer). Energy of change and interaction with nearby molecules such as solvent), but as the interaction becomes smaller, the electron transfer rate becomes exponentially slower depending on the distance.

Recently, attempts have been actively made to construct an efficient antenna system based on the X-ray structure determination based on the X-ray crystallographic analysis of the light-harvesting complex in the ecosystem. By constructing the antenna system, it is possible to efficiently transfer the energy collected here to the reaction center protein that performs charge separation at high speed,
It is possible to absorb sunlight more efficiently and use the energy.

The antenna complex in nature is formed by self-assembly, where the protein assists in the formation of the self-assembly complex. In such research, a method of forming an artificially organized molecular assembly, particularly a monomolecular film has been studied. As a method therefor, a Langmuir-Blodgett film (so-called LB film) or a lipid film is used. However, the method for forming a monomolecular film lacks uniformity (defects such as pinholes are generated), and the monomolecular film formed on the substrate is Since the molecules that constitute the film are physically attached to the surface of the substrate, there is a disadvantage that the stability of the film is poor. Under such circumstances, since it was found that alkanethiol formed a self-assembled monolayer on the gold surface, the principle of this monolayer formation, that is, the self-assembly function was used (coadsorption) monolayer. Techniques for forming molecular films have been studied. Further progressing further, in order to obtain a monolayer having functionality, a monomolecule formed by combining the group exhibiting the functionality and the group exhibiting the self-assembly function, and formed by self-assembly. A compound has been introduced into which a group that stably fixes the membrane to the electrode surface has been designed, and the compound has been self-assembled into monolayers with various functions. This has led to the development of research (Hiroshi Imahori, et al., J. Phys. Chem.
B 2000, 104, 1253-1260). The present inventor has also proposed an antenna system composite in which the above antenna system is further improved (Japanese Patent Application No. 2000-120511, Hiroshi Imahori et. A.
l., J. Am. Chem. Soc. 2001, 123, 100-110).

Under these circumstances, the inventors of the present invention returned to the basics in order to make a new development of the above-mentioned technique, and the quantum efficiency of photocurrent of the electrode constituent material and the self-assembled film formed on the electrode. A method of forming a self-assembled film (hereinafter, also referred to as SAM) on the gold (Au) electrode and the ITO electrode in order to confirm the relationship with (to suppress the deactivation of the photoexcited dye by the electrode). Porphyrin monomolecular films were prepared by using the films, and the photocurrent characteristics of each film were measured using a system containing triethanolamine (sacrificial reagent). As a result, compared to porphyrin SAM on the gold plate, porphyrin SA on ITO
When M was used, it was revealed that the anode photocurrent flows with a photocurrent quantum efficiency of 280 times, and it was revealed that ITO is superior to gold as an electrode material (Hiroko Yamada et. al., Chem. Commun. 2000, 1921-
1922). Although coupling structure for coupling the electrode material and the photoelectric current conversion system was not studied systematically about how it affects the photocurrent conversion efficiency, "ITO" an ITO electrode surface in the present invention O ₃ Si- It is expected that the use of the material treated with (CH ₂ ) ₃ —NH ₂ (FIG. 1) also has some technical meaning in improving the photocurrent conversion efficiency.

[0006]

Therefore, the object of the present invention is to further advance the basic researches by the present inventors,
It is to provide a light energy / electric energy conversion system that is more practical. In order to solve the above problems, the present inventors have found that a binary compound having a donor-acceptor in the same molecule on an ITO electrode, particularly a porphyrin (P) -fullerene (P: metal-free or Zn-ized) binary compound. Formation of self-assembled monolayer of system compounds, and further O ₃ Si-
An attempt was made to form a self-assembled monolayer of the binary compound through the bonding structure of A self-assembled monolayer of the binary compound is used as a working electrode, a platinum wire is used as a counter electrode, and Ag / A
Using a gCl (saturated KCl) electrode as a reference electrode, an aqueous solution containing 0.1 mol Na ₂ SO ₄ as an electrolyte, oxygen (O ₂ ) as an electron acceptor or hexyl viologen (H
V ²⁺ ) is used as an electrolytic solution, and a photovoltaic system is constructed by these, and the photocurrent of the self-assembled monolayer is measured by irradiating monochromatic light from an Xe lamp to measure the photocurrent. As a result of investigating chemical properties, it was confirmed that a quantum efficiency of photocurrent generation of 10 times or 30 times as high as that of a compound having no fullerene portion was obtained, and it was found that the above problems can be solved.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to indium
On the surface of the tin oxide (ITO) electrode, at least one selected from the group of compounds represented by the general formula (A), B
in. A light energy / electric energy conversion system characterized in that a monomolecular film is formed by self-organization through a covalent bond represented by. Preferably, the light energy / electric energy conversion system is characterized in that the light energy / electric energy conversion system is characterized in that it is bonded in the form 1 and self-assembled to form a single film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail. A. The features of the present invention will be described with reference to the drawings. The outline of the photovoltaic system of the present invention can be represented as shown in FIG.
That is, the light energy (hv) supplied from the outside is porphyrin (metal free when M = 2H, M = Z).
In the case of n, it is absorbed by the zinc porphyrin) part, and the electron first moves from the excited porphyrin to the fullerene,
Further, oxygen (O ₂ ) which functions as an electron acceptor in the electrolyte solution
Alternatively, transfer to hexyl viologen (HV ²⁺ ). These reduced electron acceptors diffuse in the solution and transfer the electrons to the platinum electrode which is the counter electrode. On the other hand, electrons are supplied from the ITO electrode to the porphyrin radical cation generated by electron transfer. As a result, the cathode current flows in the circuit due to the light irradiation on the modified electrode.

B. The construction method of the light energy / electric energy conversion system of the present invention. Synthesis of compounds of formula B.

[0010]

[Chemical 4]

(Wherein P is a metal-free porphyrin ring) is a compound of formula C

[0012]

[Chemical 5]

(M is 2H) 4-methoxycarbonylaniline and 4-methoxycarbonylaniline
(4,4'-Dimethyl-2,6-dioxacyclohexyl) aniline [4- (4,4'-dimethyl-2,6-dioxacyclohexy
l) aniline] and cross-condensation, followed by hydrolysis with acid and alkali.

The compound of formula D (where P is a metal-free porphyrin ring) can be obtained by reacting the compound of formula B with pentafluorophenol.

[0015]

[Chemical 6]

Then, the compound of the above D is cycloadded with C ₆₀ fullerene in the presence of N-methylglycine to give a formula E having a porphyrin-fullerene structure (wherein P is a metal-free porphyrin ring). .) Binary compounds are obtained.

[0017]

[Chemical 7]

3. The compound of E is used as the IT shown in FIG.
Represented by the above-mentioned form 1 by reacting with an O electrode,
An aspect system of the light energy / electric energy conversion system of the present invention can be constructed.

[0019]

EXAMPLES Example 1A, Porphyrin-Fullerene C ₆₀ Binary Compound Used to Form Self-Assembled Membrane Preparation of Formula E Compound 1, Formula C Porphyrin Compound Dissolved in 6 mL CH ₂ Cl ₂ To this, 4-pyrrolidinopyridine (4-pyrrolidin
Add opyridine: 3.3 mg, 0.2 mmol) and pentafluorophenol (37 mg, 0.022 mmol). The solution is cooled to 0 ° C. and N, N′-dicyclohexylcarbodiimide (4.5 mg, 0.022 mmol) is added under nitrogen atmosphere. Then slowly reach room temperature and stir the solution for 18 h. After removing the solvent, the residue was purified by silica gel column chromatography (solvent CHCl ₃ ) to obtain the desired compound of the above formula D in a yield of 60% (16 mg, 0.012 mmol). Physical Properties of Compound of Formula D; Melting Point> 300
° C, ¹ H-NMR (270 MHz, CDCl ₃ ) d = 10.01 (s, 1H), 8.93
(d, J = 5 Hz, 4H), 8.78 (d, J = 5 Hz, 4H) 8.3 (m,
13H), 8.09 (m, 4H), 8.01 (s, 1H), 7.98 (s, 4H), 7.8
3 (s, 2H), 1.53 (s, 36H), -2.70 (s, 2H) mass spectrometry: FAB (fast atom bombardment method), 13
15 (M + H ⁺ )

80 mg of the compound of D, C ₆₀ fullerene (220 mg, 0.305 mmol) and N-methylglycine (272 mg, 3.01 mmol) are dissolved in 400 mL of dry toluene and the solution is refluxed overnight.
The organic solvent was removed under reduced pressure and the residue was toluene-CHCl.
Purification by silica gel chromatography using ₃ solutions gave the above binary compound E containing porphyrin-C ₆₀ fullerene in 83% yield (104 mg, 0.050 mmol). Physical properties of compound E: melting point> 300 ° C., ¹ H-NMR (270 MHz, CDCl ₃ ) δ = 8.9
1 (m, 4H), 8.78 (m, 4H), 8.49 (s, 1H), 8.40 (d, J
= 8 Hz, 4H), 8.30 (d, J = 8 Hz, 4H), 8.26 (s, 4
H), 8.06 (s, 4H), 8.02 (d, J = 8 Hz, 2H), 7.94 (d,
J = 8 Hz, 2H), 7.82 (s, 2H), 7.78 (s, 1H), 4.79
(d, J = 9 Hz, 1H), 4.67 (s, 1H), 4.02 (d, J = 9 Hz,
2H), 2.77 (s, 3H), 1.55 (s, 36H), -2.77 (s, 2H), mass spectrum: (FAB) 2063 (M + H +).

B, formation of light energy / electric energy conversion system 1, ITO of 190-200 nm thickness on transparent glass slide surface
ITO electrode formed with (Evers, Inc. (J
apan)) surface trimethoxysilyl propylamine _{(((MeO) 3 Si (} CH 2) 3 NH 2) (10% v / v) and placed in a toluene solution were dissolved isopropylamine (2% v / v) Then, it is treated under reflux for 20 hours to prepare an aminopropylsilylated ITO electrode (FIG. 1) that binds to the surface with a siloxy bond 2. The porphyrin (2H) -of the formula E is used as the aminopropylsilylated ITO electrode. It was placed in a toluene solution in which a binary compound of C ₆₀ fullerene was dissolved and treated under reflux for 20 hours to obtain 1a / ITO whose ITO surface was modified with a binary compound of porphyrin-C ₆₀ fullerene.

Example 2 Z was added to the porphyrin ring portion of the 1a / ITO prepared above.
Porphyrin (Zn) -in which zinc was inserted into a porphyrin ring by placing it in a CHCl ₃ solution in which zinc acetate [Zn (OAc) ₂ ] was dissolved in order to insert n and treating it under reflux for 6 hours under an argon atmosphere. C ₆₀ fullerene binary compounds modified electrode 1
b / ITO was obtained. .

Comparative Examples 1 and 2 Instead of 1a / ITO and 1b / ITO modified with the binary compounds of Examples 1 and 2, the univalent C ₆₀ fullerene-containing linking group was removed, in other words, only porphyrin was used. 2a / ITO (containing a metal-free porphyrin ring) and 2b / ITO (containing a porphyrin ring metallized with Zn) modified with a containing compound were prepared.

The modified ITO electrodes of Examples 1 and 2 above,
The adsorption amount (Γ) of the self-assembling compound on the surface of the modified ITO electrodes of Comparative Examples 1 and 2 was determined from the anode peak of porphyrin by electrochemical measurement, and summarized in Table 1. ^{1a / ITO (2.5 × 10 -10} molcm -2) and ^{2a / ITO (1.8 × 10 -10} mol cm -2) is analogous porphyrin SAM on the ITO surface (2.4 × 1
0 ^-10 mol cm ^-2 ).

Photocurrent was measured with an ITO / 1a / HV ²⁺ / Pt battery system as described in "0006" above. When light having a wavelength λ = 430 ± 5 nm and an intensity of 500 μWcm ⁻² was used and the working electrode potential was set to −0.2 V, light irradiation was performed, and a cathode current was observed. As the working electrode potential was changed in the positive direction, the photocurrent became smaller, and when the working electrode potential was +0.8 V, the photocurrent became zero. Similar measurements were performed on ITO / 1b, 2a or 2b / HV ²⁺ / Pt battery systems. The quantum yield results, which represent the ratio of the number of electrons flowed to the number of photons absorbed by the compound on ITO, are summarized in Table 1. From these results, the C _{60 of} the present invention
It can be seen that the photocurrent generation characteristics of the binary system containing fullerenes (acceptor moieties) were significantly improved compared to the reference system containing porphyrin alone.

1a, 1b, 2a, or 2b / ITO
The fluorescence lifetime of the porphyrin site of was investigated by measuring the fluorescence lifetime of the ITO surface using the picosecond single-photon counting method and excitation light of 453 nm, and is summarized in Table 1. Observation of fluorescence corresponds to fluorescence at the porphyrin site, 655n
m (1a and 2a / ITO) or 605nm (1b
And 2b / ITO). The average fluorescence lifetime of 2a / ITO (3.2 nanoseconds) is 25 times the average fluorescence lifetime of 2b / ITO (0.14 nanoseconds).
(0.12 nanoseconds) was 5 times that of 1b / ITO (0.031 nanoseconds). The value of the average fluorescence lifetime is
It corresponds to the quantum yield of photocurrent. 2a / ITO has an average fluorescence lifetime (3.2 nanoseconds) of mercapto group gold (A
u) It is 80 times as long as the fluorescence lifetime (40 picoseconds) of the compound having only the corresponding porphyrin site self-assembled on the surface, and when the ITO electrode is used, quenching of the porphyrin excited state by the gold electrode can be suppressed. confirmed.

[0027]

[Table 1]

From the above results, the use of ITO as the electrode constituent material and the use of the binary compound as the self-assembled monomolecular film forming material in the present invention
It is clear that the quantum efficiency of photocurrent generation could be significantly improved.

[0029]

As described above, the construction of a light energy / electric energy conversion system in which the quantum efficiency of photocurrent generation is remarkably improved by the present invention is aimed at the realization of a practical system improved from such a system. It has an excellent effect of giving a big suggestion of.

[Brief description of drawings]

FIG. 1 is an embodiment of a bonding group of ITO constituting a light energy / electric energy conversion system of the present invention

FIG. 2 Outline of mechanism of light energy / electric energy conversion system of the present invention

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4C050 PA02                 4H048 AA01 AA03 AB78 VA32 VA66                       VB40                 5H032 AA06 AS19 BB04 BB07 CC11                       EE07 EE16 EE20

Claims (2)

[Claims] 1. At least one selected from the group of compounds represented by general formula (A) on the surface of an indium-tin oxide (ITO) electrode is treated with Bin. A light energy / electric energy conversion system characterized in that a monomolecular film is formed by self-assembly via a covalent bond represented by. [Chemical 1] (However, Bin. Is selected from O ₃ Si—, a carboxylic acid ester or a phosphoric acid ester. X ¹ , X ² and X
³ is a single bond, -NH-CO-, -CO-N, respectively.
A group independently selected from the group consisting of H-, -Ph-, -O-, or -CO-O-, n is an integer of 1 to 20, Ar
Is a phenyl group which may have a bulky substituent, and M is 2
The H or Zn, fullerene derivative is selected from the formula (a) or the formula (b). Fullerene part is C ₆₀ , C ₇₀ ,
C ₇₆ , C ₇₈ , C ₈₀ , C ₈₂ , C ₈₄ , C ₈₆ , C ₈₈ , and C ₉₀ [in formulas (a) and (b), these fullerenes are represented by C ₆₀ . ]. [Chemical 2] 2. The light according to claim 1, wherein the ITO electrode and the compound selected from the compounds of the general formula A are combined in the form 1 and self-assembled to form a single film. Energy / electric energy conversion system. [Chemical 3] (Here, Ar is a 3,5-di (t-butyl) -phenyl group, M is Zn or 2H, and the fullerene is a C ₆₀ fullerene in which R 2 of the formula (a) is CH _3. )