JP2883348B2 - Porphyrin metal complex - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel porphyrin metal complex or an alkali metal salt thereof.

[Prior art] Conventionally, as a porphyrin metal complex, for example, protohemin (iron-porphyrin) or copper-protoporphyrin is commercially available.

Protohemin has the formula: Wherein copper-protoporphyrin has the formula: It has the structure shown by.

When the protohemin or copper-protoporphyrin is used, for example, as an electrode modifier having an electron transfer function, it is developed as a monomolecular film on a gas-water interface, and is accumulated on a metal substrate under a constant film pressure; So-called Langmuir
It is preferable to use a film having a regularity controlled at a molecular level, such as a Langmuir-Blodgett (LB) film, but an LB film cannot be obtained as it is.

The present invention has been made in view of such a conventional situation, and has developed a novel porphyrin derivative that can be used as an LB film and thereby can be preferably used as an electrode modifier having an electron transfer function. It was done for the purpose of doing.

[Means for Solving the Problems] The present invention provides a compound represented by the general formula (I): General formula (II): Or the general formula (III): (Where M is Fe or Ru, X, Y and Z are each M
And can have the structure of (I), (II) or (III) depending on the type and valence of M, and each of them is a halogen atom, CO, —OCOCH ₃ , pyridine,
Imidazole, P (OR) ₃ or PR ₃ (R is a lower alkyl group of C ₁ -C ₄₎ indicates, X and Y may be the same or different, m and n each integers of from 5 to 20 Indicates that
m and n may be the same or different), or a porphyrin metal complex or an alkali metal salt thereof.

[Action] The porphyrin metal complex according to the present invention employs the LB method because m, n, M, X, Y and Z in the above general formulas (I) to (III) are selected within a specific range. Thus, a porphyrin metal complex can be stably formed as a thin film on an electrode, and a modified electrode can be obtained.

Further, by appropriately selecting X, Y, and Z for the Ru-porphyrin complex or the Fe-porphyrin complex, the redox potential can be changed within a certain range. Further, in the case of Ru-porphyrin complex, X, Y,
By appropriately selecting Z, the valence of Ru can be controlled between divalent and trivalent.

As described above, since the redox potential and the redox state can be selected in various combinations, a highly functional electron transfer functional LB film-modified electrode can be produced by using a porphyrin metal complex or an alkali metal salt thereof.

[Example] The porphyrin metal complex of the present invention has the general formula (I): General formula (II): Or the general formula (III): Has a structure represented by

M in the general formulas (I) to (III) is Fe or Ru;
Since M is Fe or Ru, the acid value reduction reaction between divalent and trivalent occurs stably.

X, Y and Z in the general formulas (I) to (III) each represent a halogen atom (a chlorine atom or a bromine atom), CO, -OCOC
H ₃ , pyridine, imidazole, P (OR) ₃ or PR ₃ (R is C
A lower alkyl group) of ₁ -C _4. When X, Y, or Z is not one of these atoms and groups, the stability of the divalent or trivalent state is low, and deterioration is likely to occur. Note that X and Y may be the same or different.

M and n in the general formulas (I) to (III) are each 5
-20, preferably an integer of 5-15. When m and n are less than 5, the compounds represented by the general formulas (I) to (III) become insufficient in hydrophobicity, so that a monomolecular film preferable for forming an LB film cannot be formed. , 20
On the contrary, if the ratio exceeds the above, the hydrophobicity of the compounds represented by the general formulas (I) to (III) becomes too strong, so that a monomolecular film preferable for forming an LB film cannot be formed. Note that m and n may be the same or different.

The alkali metal salt of the porphyrin metal complex of the present invention,
An alkali metal salt of the compound represented by any one of the above general formulas (I) to (III). Examples of the alkali metal include Na and K. In the alkali metal salt of the porphyrin metal complex of the present invention, one of the carboxyl groups in the general formulas (I) to (III) may be a salt, or two may be salts. It is to be noted that the number of salts is not important, and the hydrophobic portion is essential for forming the monomolecular film necessary for forming the LB film on the compounds represented by the general formulas (I) to (III). It is important whether or not the hydrophilic portion and the hydrophilic portion can be provided in a well-balanced manner.

Among the porphyrin metal complexes of the present invention as described above,
Specific examples of the compound represented by the general formula (I) include, for example, (Wherein Iz represents imidazole), (Where Py represents pyridine), Specific examples of the compound represented by the general formula (II) include, for example, Specific examples of the compound represented by the general formula (III) include, for example, And so on.

The -OC ₁₃ H ₂₇ groups Specific examples of the porphyrin metal complex, and the like of a preferable embodiment that instead of -C _{8 to 20} H _{seventeen to forty-one} group.

For example, porphyrin metal complex A stable LB film is produced when using
When an LB film is formed and used as a conductive substrate modifier, the redox potential is about +300 mV (VS. Ag / AgCl).

Next, the method for producing the porphyrin metal complex or the alkali metal salt thereof of the present invention will be described.

The first method for producing the porphyrin metal complex of the present invention is a method for producing the porphyrin metal complex by the following steps (A) to (D).

In the step (A), the formula (IV): 7,12-diethenyl-3,8,13,17-tetramethyl-2,18-bis (methoxycarbonylethyl) -21H, 23 represented by
H- and Porifin general _{formula: C n H 2n + 1 -OH} (n is 5-20) reacted with the one or more aliphatic alcohols represented by the general formula (V): The hematoporphyrin derivative represented by is produced.

When the aliphatic alcohol is allowed to act on the compound represented by the formula (IV), for example, the compound represented by the formula (IV) is dissolved in methylene chloride (CH ₂ Cl ₂ ), and 30% HBr / AcOH
, And the solvent is distilled off after the reaction to obtain a hydrogen bromide adduct. The hematoporphyrin derivative represented by the general formula (V) is produced by, for example, adding 1 to 3 mol of an aliphatic alcohol to 1 mol of the hydrogen bromide and refluxing the mixture.

At this time, methylene chloride is usually used as a solvent so that the final concentration is about 5 to 30%. Further, as the reaction temperature, a temperature that can be generally refluxed can be adopted.

After the reaction, for example, by purifying by chromatography using a column filled with alumina,
The hematoporphyrin derivative represented by the general formula (V) is obtained in a yield of about 30% with respect to the compound represented by the formula (IV).

Then, the obtained hematoporphyrin derivative is dissolved in, for example, benzene, and then reacted with ruthenium carbonyl (Ru ₃ (CO) ₁₂ ) to obtain, for example, a compound of the general formula (VI): Is produced (Step (B)).

The concentration of the solution of the hematoporphyrin derivative represented by the general formula (V) is usually about 0.5 to 2%. About 1.5 to 2 mol of ruthenium carbonyl is added to 1 mol of the hematoporphyrin derivative to this solution, and the mixture is refluxed under an inert gas atmosphere to produce a porphyrin complex represented by the general formula (VI).

After the reaction, for example, by purifying by chromatography using a column filled with alumina,
For example, a Ru-porphyrin complex represented by the general formula (VI) can be obtained at a yield of about 45 to 50% based on the hematoporphyrin derivative represented by the general formula (V).

Further, by dissolving the Ru-porphyrin complex or the like in, for example, dichloroethane and reacting with trimethoxyphosphine (P (OCH ₃ ) ₃ ), pyridine or the like,
For example, general formula (VII): The Ru-porphyrin complex ((when using P (OCH ₃ ) ₃ )) or the like is produced (Step (C)), and when pyridine or the like is used, the amount of the solvent is increased by increasing the amount used. It can be done without using it.

The concentration of the solution such as the Ru-porphyrin complex represented by the general formula (VI) is usually about 2%. Said Ru
In the reaction between the porphyrin complex (VI) and trimethoxyphosphine, it is preferable to monitor the progress of the reaction while measuring the absorption spectrum while stirring the mixture with the stirrer and dropping the latter in small portions. Further, as the reaction temperature, room temperature can be usually employed.

After the reaction, the porphyrin complex represented by the general formula (VII) is purified by, for example, chromatography using a column packed with alumina or the like so that the porphyrin complex represented by the general formula (VII) is about 50 to 75%. In a yield of

This Ru-porphyrin complex or the like is subjected to a general ester hydrolysis method (Step (D)) using an acid such as hydrochloric acid as a catalyst by the following formula: And a porphyrin metal complex represented by

When the alkali metal salt of the porphyrin metal complex is obtained, it can be obtained, for example, by contacting with an aqueous solution of an alkali metal hydroxide.

Conversely, when an alkali metal hydroxide is used as the hydrolysis catalyst, the alkali metal salt of the porphyrin metal complex of the present invention can be obtained. The porphyrin metal complex of the present invention can be obtained by adding an acid such as hydrochloric acid to the solution of the alkali metal salt or the like and performing solvent extraction or the like.

For example, when a compound represented by the general formula (VII) is produced from a compound represented by the general formula (VI), for example, a compound such as pyridine, trimethyl phosphate or trimethyl phosphite is used together with a compound serving as a ligand to form an alkali metal hydroxide. When an aqueous solution or the like is present, the ester can be hydrolyzed at the same time.

In the above description, purification was performed in each step,
These are not always necessary and may be omitted as appropriate.

The second method for producing the porphyrin metal complex of the present invention is (A)
This is a method for producing by the following steps (E) to (G) using the hematoporphyrin derivative obtained in the step.

First, the hematoporphyrin derivative represented by the general formula (V) obtained in the step (A) is dissolved in a solvent such as methylene chloride or pyridine, and a ferrous salt such as ferrous acetate is allowed to act on the solution. Formula (VIII): To produce the Fe-porphyrin complex represented by (E)
Process).

Furthermore, this Fe-porphyrin complex can be
And reacted with pyridine to give a compound of the general formula (IX): Is produced (in the case of using pyridine (Py)), etc. (Step (F)).

By subjecting the Fe-porphyrin complex or the like to ester hydrolysis (step (G)), for example, a compound represented by the general formula (X): And a Fe-porphyrin metal complex represented by

When the alkali metal salt of the porphyrin metal complex is obtained, for example, first, the hematoporphyrin derivative represented by the general formula (V) obtained in the step (A) is dissolved in pyridine, and then, for example, sodium hydroxide is allowed to act. General formula (XI): To obtain a sodium salt of a hematoporphyrin derivative. Then, the reaction may be carried out in the same manner as in the steps (E) and (F).

 Next, the present invention will be described based on examples.

Example 1 [7,12-bis (1- (oxyoctadecyl) ethyl)-
Synthesis of 3,8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -21H, 23H-porphine] 7,12-diethenyl-3,8,13,17-tetramethyl-2 , 18
2 g of bis (methoxycarbonylethyl) 21H, 23H-porphine was dissolved in 30 ml of methylene chloride, 25 ml of a 30% hydrogen bromide-acetic acid solution was added thereto, and the mixture was stirred overnight. Then, the solvent was distilled off under reduced pressure. A hydrogen bromide adduct was obtained. Next, a solution of 5 g of 1-octadecanol dissolved in 30 ml of methylene chloride was added thereto, and the mixture was refluxed for 3 hours. After cooling, 200 ml of methylene chloride was added for dilution, washed with 500 ml of water six times, and dried over anhydrous sodium sulfate. The residue obtained by distilling off the solvent from this methylene chloride solution was used to remove unnecessary components using a column packed with 500 g of alumina (activity II to III) using methylene chloride as a developing solvent. The solvent was distilled off from the red solution to obtain 1.1 g (yield: 29.1%) of a dark red-purple oily substance (the target substance).

The results of electronic spectrum analysis, infrared absorption spectrum analysis, and nuclear magnetic resonance spectrum analysis of the obtained oil are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 399, 506.2, 540.4, 567.6, 622 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 3300, 2910, 2850, 1739, 1100 Nuclear magnetic resonance spectrum analysis Results (δ ppm, CDCl ₃ ) 10.51 (S, 2H), 10.12 (S, 2H), 6.12 (dd, 2H),
4.45 (m, 4H), 3.67 (br S, 18H), 3.30 (m, 4
H), 2.29 (dd, 6H), 1.79 (m, 4H), 1.59-1.03
(M, 64H), 0.88 (br, t, 6H), -3.73 (br S, 2
H) [7,12-bis (1- (oxyoctadecyl) ethyl)-
Synthesis of 3,8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) -21H, 23H-porphine disodium salt] [7,12-bis (1-oxyoctadecyl) ethyl obtained) -580 mg of -3,8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -21H, 23H-porphine
Was dissolved in 50 ml of pyridine, 2 ml of an aqueous solution containing 80 mg of sodium hydroxide was added, and the mixture was refluxed for 2 hours. After the reaction solution was allowed to cool, the residue was dried under reduced pressure, and the residue was dissolved by adding 50 ml of water. The crystals precipitated by adding acetic acid were collected, washed with water and dried, and dried to obtain 550 mg (yield 97.3%) of dark purple crystals. (Object)

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 400, 507, 541, 567, 622 Infrared absorption spectrum analysis results (cm ⁻¹ , KBr) 3350, 2910, 2850, 1560, 1440, 1100 [μ− Synthesis of disodium iron (III) oxobis-7,12-bis (1- (oxyoctadecyl) ethyl) -3,8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) porphinato The obtained 7,12-bis (1- (oxyoctadecyl) ethyl) -3,8,13,17-tetramethyl-2,18-bis (2-
(Carboxyethyl) -21H, 23H-porphine disodium salt (400 mg) was dissolved in methylene chloride (30 ml). Then
A ferrous acetate solution prepared by previously suspending 400 mg of reduced iron in 20 ml of acetic acid and refluxing in a nitrogen stream for 3 hours was added, and the mixture was kept at 50 ° C. for 30 minutes under a nitrogen stream.
After cooling, the reaction solution was washed three times with a saturated saline solution and dried over anhydrous sodium sulfate. The residue obtained after distilling off the solvent from this solution was applied to a column packed with 100 g of silica gel, and methylene chloride / methanol = 10/1 as a developing solvent.
Unnecessary components were removed using a mixed solvent (volume ratio) to obtain a dark red solution. The obtained solution was recrystallized to give 140 mg (yield 3
3.7%) of dark brown crystals (the desired product).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 399, 560, 593 Infrared absorption spectrum analysis results (cm ⁻¹ , KBr) 3400, 2910, 2850, 1560, 1438, 1100 [7,12-bis ( 1- (oxyoctadecyl) ethyl)-
Synthesis of 3,8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) -porphinatoiron (III) monochloride] The obtained μ-oxobis-7,12-bis (1- (oxy Octadecyl) ethyl) -3,8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) -porphinatoiron (III) disodium salt (140 mg) was dissolved in benzene (50 ml), and then dissolved in 10% hydrogen chloride aqueous solution. Washed twice with 50 ml. Thereafter, it was washed with water, dried over anhydrous sodium sulfate, and then the solvent was distilled off to obtain 120 mg (yield: 84.5%) of dark brown crystals (the desired product).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis result (▲ λ ^nm _max ▼, CHCl ₃ ) 377.5, 507, 535.4, 637.5 Infrared absorption spectrum analysis result (cm ⁻¹ , KBr) 2910, 2850, 1705, 1100 Example 2 [7,12-bis (1- (oxytridecyl) ethyl) -3,
Synthesis of 8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -21H, 23H-porphine] 7,12-diethenyl-3,8,13,17-tetramethyl-2,18
5 g of -bis (methoxycarbonylethyl) -21H, 23H-porphine is dissolved in 100 ml of methylene chloride, treated with a hydrogen bromide-acetic acid solution in the same manner as in Example 1, and then a methylene chloride solution containing 16 g of 1-tridecanol is added. In addition, the mixture was treated in the same manner to obtain 3.1 g (yield: 36.7%) of a dark red-purple oily substance (the target substance).

The results of electronic spectrum analysis, infrared absorption spectrum analysis, and nuclear magnetic resonance spectrum analysis of the obtained oil are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 399, 505, 540, 567, 622 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 3300, 2910, 2850, 1740, 1100 Nuclear magnetic resonance spectrum analysis Result (δppm, CDCl ₃ ) 10.48 (s, 2H), 9.93 (s, 1H), 9.91 (s, 1H),
6.03 (dd, 2H), 4.80 (m, 4H), 3.58 (brS, 18H),
3.24 (m, 4H), 2.24 (dd, 6H), 1.91 to 0.98 (m, 48
H), 0.82 (brt, 6H), -3.70 (brS, 2H) [7,12-bis (1- (oxytridecyl) ethyl) -3,
Synthesis of 8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -porphinatoruthenium (II) carbonyl] The obtained 7,12-bis (1- (oxytridecyl) ethyl) 2 g of -3,8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -21H, 23H-porphine is dissolved in 200 ml of benzene, and 2 g of ruthenium carbonyl (Ru ₃ (CO) ₁₂ ) is dissolved. Was added and refluxed in an argon gas atmosphere for 40 hours. After completion of the reaction, the residue obtained by distilling off the solvent was removed using a column packed with 200 g of alumina, using a mixed solvent of methylene chloride / methanol = 100/1 (volume ratio) as a developing solvent to remove unnecessary components. The solvent was distilled off from the obtained red-orange solution to obtain 1.1 g (yield: 48.7%) of dark red-orange crystals (the target substance).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 398.6, 519.8, 550.6 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 2910, 2850, 1930, 1739, 1720, 1100 [7,12-bis ( 1- (oxytridecyl) ethyl) -3,
Synthesis of 8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) -porphinatoruthenium (II) pyridine carbonyl] 7,12-bis (1- (oxytridecyl) ethyl obtained ) -3,8,13,17-Tetramethyl-2,18-bis (2-methoxycarbonylethyl) polyfinatruthenium (I
I) 200 mg of carbonyl was dissolved in 10 ml of pyridine, 1 ml of an aqueous solution containing 40 mg of sodium hydroxide was added, and the mixture was refluxed for 2 hours. After allowing to cool, the solvent was distilled off. The obtained residue was dissolved by adding 40 ml of water, and extracted three times with 50 ml of benzene. The benzene layer was washed twice with 100 ml of a 0.1N aqueous hydrochloric acid solution, then with 100 ml of water and 100 ml of saturated saline, and then dried over anhydrous sodium sulfate. After that, the solvent was distilled off and 180 mg (9
1.8%) of dark red crystals (the desired product).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 392.6, 507.4, 540 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 2910, 2850, 1940, 1705, 1100 [7,12-bis (1- (Oxytridecyl) ethyl) -3,
Synthesis of 8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -porphinatoruthenium (II) trimethyl phosphite] 7,12-bis (1- (oxytridecyl) ethyl ) -3,
Dissolve 150 mg of 8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -polyfinatoruthenium (II) pyridine carbonyl in 10 ml of benzene,
g of trimethyl phosphite (P (OMe) ₃ ) was added and the mixture was refluxed for 2 hours, then the solvent was distilled off.
Was removed using methylene chloride as a developing solvent, and the solvent was distilled off from the obtained dark red solution to obtain 130 mg (70.6%) of dark red crystals (the desired product).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 402.5, 526 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 2960, 2920, 2850, 1740, 1060, 1030 [7,12-bis (1- (Oxytridecyl) ethyl) -3,
Synthesis of 8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) porphinatoruthenium (II) trimethyl phosphite] The obtained 7,12-bis (1- (oxytridecyl) Ethyl) -3,8,13,17-tetramethyl-2,18-bis (2-methoxycarbonylethyl) -polyfinatoruthenium (II) 130 mg of trimethyl phosphite was dissolved in pyridine. -Similar to the synthesis of bis (1- (oxytridecyl) ethyl) -3,8,13,17-tetramethyl-2,18-bis (2-carboxyethyl) -polyfinatoruthenium (II) pyridine carbonyl The mixture was treated with an aqueous sodium hydroxide solution. After completion of the reaction, the solvent was distilled off, and water 30
After adding 3 ml with benzene, extract the benzene layer with water.
After washing twice with 100 ml, it was dried with anhydrous sodium sulfate. After that, the solvent was distilled off to obtain 120 mg (94.5%) of dark red crystals (the desired product).

The results of electronic spectrum analysis and infrared absorption spectrum analysis of the obtained crystal are shown below.

Electronic spectrum analysis results (▲ λ ^nm _max ▼, CHCl ₃ ) 405.6, 524.8 Infrared absorption spectrum analysis results (cm ^-1 , KBr) 3420, 2950sh, 2930, 2850, 1735, 1060, 1035 Reference example [Cyclic voltan Evaluation of electron transfer function by measurement] Sodium perchlorate was dissolved in a phosphate buffer (pH 7.0, 20 mM) to a concentration of 100 mM, and argon was passed to remove oxygen to prepare an electrolytic solution. .

On the other hand, a modified electrode was prepared in which a Ru-porphyrin complex (having the structure shown in the following formula) was provided on a gold electrode as an LB film (accumulated in six layers) by the LB method.

Using the electrolytic solution and the modified electrode, cyclic voltammetry was performed using a potentiostat. The results are shown in FIG.

As shown in FIG. 1, a redox peak corresponding to a divalent / trivalent oxidation-reduction reaction of Ru was observed. This result indicates that the Ru-porphyrin complex-modified electrode has an electron transfer function.

In FIG. 1, the vertical axis represents the current value, and the horizontal axis represents the current value.
The set potential based on the Ag / AgCl reference electrode is shown.

Ru-porphyrin complexes can be replaced with others, such as A similar result can be obtained when switching back.

[Effects of the Invention] As described above, according to the present invention, a novel porphyrin metal complex or an alkali thereof, which can be used as an LB film, and thereby can be preferably used as an electrode modifier having an electron transfer function A metal salt may be provided.

[Brief description of the drawings]

FIG. 1 shows an example of the porphyrin metal complex of the present invention, Ru.
FIG. 3 is a characteristic diagram showing a cyclic voltammogram of an LB film-modified electrode (base electrode is Au) manufactured using a porphyrin complex.

Continuation of front page (56) References JP-A-63-104987 (JP, A) JP-A-62-205081 (JP, A) Can. J. Chem. 62 (1984) p. 1238-p. 1245 (58) Field surveyed (Int. Cl. ⁶ , DB name) CA (STN) CAOLD (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] (1) (Wherein M represents Fe or Ru, X, Y and Z are each a ligand for M, and have a structure of (I), (II) or (III) depending on the type and valence of M It can be respectively a halogen atom, CO, -OCOCH _3, pyridine,
Imidazole, P (OR) ₃ or PR ₃ (R is a lower alkyl group of C ₁ -C ₄₎ indicates, X and Y may be the same or different, m and n each integers of from 5 to 20 Indicates that
m and n may be the same or different), or a porphyrin metal complex or an alkali metal salt thereof.