Metalloporphyrins in Polymeric Matrices, Micelles, and Vesicles, IV. Photochemical and Peroxide...

950 J.-H. Fuhrhop, A.-B. Kerkhoff; and S . Besecke

Liebigs Ann. Chem. 1982, 950-959

Metalloporphyrins in Polymeric Matrices, Micelles, and Vesicles, IV ')

Photochemical and Peroxide Oxidations of Magnesium Octa- ethylporphyrinate in the Presence of Polymeric and Monomeric Imidazole Derivatives

Jiirgen-Hinrich Fuhrhop *, Alois-Rernhard Kerkhoff, and Siegmund Resecke

lnstitut fur Organische Chemie der Freien Universitat Berlin, 'Takustr. 3 . D-1000 Berlin 33

Received October 13, 1981

Magnesium octaethylporphyrin (MgOEP) in foils of polystyrene was oxygenated quantitatively by visible light and oxygen to yield the corresponding formylbilinate. In poly[l -phenylethylene- co-1-(l-imidazolyl)ethylene] (95 : 5 or 78: 22 mol '70) the quantitative formation of MgOEP cation radical was observed. The photooxygenation was fully suppressed in this copolymer. This is explained with a physical quenching of singlet oxygen by imidazole. - Oxidation of MgOEP with benzoyl peroxide in the presence ol' imidazole yields either octaethyl-5-imidazolylporphyrin or 10-benzoyloxy-octaethyl-5,15-diimidazolylporphyrin and other highly substituted porphyrins. The latter produces only one absorption band (h,,, = 560 nm) in the visible range and yields isoporphyrins (Xma = 900 nm) in a reversible reaction with an excess of benzoyl peroxide. The same reaction with the imidazole-containing copolymer leads to a covalent binding of MgOEP. The reversible formation of an isoporphyrin is observed with molecular oxygen.

Metalloporphyrine in polymeren Matrizen, Mizellen und Vesikeln, IV I). - Photochemische und Peroxid-Oxidationen von Magnesium-octaethylporphyrinat in Gegenwart von polymeren und monomeren Imidazol-Derivaten Magnesium-octaethylporphyrin (MgOEP) wurde in Polystyrolfolien mit sichtbarem Licht und Sauerstoff quantitativ zum entsprechenden Formylbilinat oxigeniert. In Poly[l-phenylethylen-co- I-(1-imidazolyl)ethylen] (95 : 5 oder 78: 22 mol-%) wurde hingegen die quantitative Bildung von MgOEP-Kationradikal beobachtet. Die Photooxigenierung war in diescm Poiymeren vollstandig unterdruckt, was auf eine physikalische Loschung von Singulettsauerstoff durch das lmidazol zu- ruckgefuhrt wird. - Oxidation von MgOEP mit Benzoylperoxid in Gegenwart von Imidazol fuhrt entweder zu Octaethyl-5-imidazolylporphyrin oder zu 10-Benzoyloxy-octaethyl-5,15-di- iniidazolylporphyrin und anderen hochsubstituierten Porphyrinen, die jeweils nur eine Absorp- tionsbande im Sichtbaren (hmaX = 560 nm) aufweisen. Diese Produkte ergeben mit iiberschussi- gem Benzoylperoxid in reversibler Reaktion Isoporphyrine (Xmm = 900 nm). Wendet man die gleiche Reaktion in Gegenwart des irnidazolhaltigen Copolymeren an, so wird MgOEP kovalent eingebaut. Man beobachtet eine reversible Isoporphyrinbildung mit molekularem Sauerstoff.

-___.___

Chlorophyll a in the photoreactive centre of higher plants is oxidized to give rt-cation radicals by sun light and weak oxidants. This reaction is fundamental to light-induced charge separation in nature2). It is fully reversible with weak reductants. On the other

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Metalloporphyrins in Polymeric Matrices, Micelles, and Vesicles, I V 95 1

hand it is known, that magnesium porphyrins such as chlorophyll are easily photooxy- genized in the presence of molecular oxygen to give f~rmylb i l ina tes~*~) . This irreversible degradation reaction must be prevented in leafs in order to keep the photocatalytic centre active. Often p-carotene and ubiquinones have been made responsible for this protective t a ~ k ~ - ~ ) . It has, however, also been shown that mutants of green algae lacking in carotene can be quite active in photosynthesis7). Since chlorophylls are adsorbed to proteins in the photosynthetic apparatus, one may think of several other protection mechanisms. We report here on photooxidation reactions of magnesium octaethylporphyrinate in solid polystyrene matrices with and without copolymerized I-vinylimidazole. In polystyrene irreversible photooxygenation was observed, whereas in the presence of imidazole ligands this reaction was completely inhibited and reversible radical formation occurred. It is also shown that oxidation of magnesium por- phyrinates with peroxides leads to an irreversible reaction between imidazole units of the polymeric matrix and the methine bridges of the porphyrin.

Photochemical Reactions Magnesium octaethylporphyrin (MgOEP, la ) in a solid foil of polystyrene (mol. wt.

= 2oooO) was irradiated with visible light. Its red color changed to brownish green (kmm = 830 nm; Fig. 1). This was stable for several months. It resembles closely t o the spectrum of magnesium octaethylbilinate 2a in benzene3). After dissolving the irradiated polymer in chloroform the magnesium could be replaced by zinc, and again the electronic spectra were identical with authentic zinc formylbilinate 2b. No ESR signal was observed in the solid polymer.

ld

le

I f

la-f

-H -H

- N g M -H -H -ti M g -H -H 2 H

- 0 - C O a -H -H -H 2 H

- N Z N - 0 - C O O - N g -H 2 H

- N T other substituents unknown Mg

-0-co-4-9 -NZ~ -H Zn

‘-‘Lopolymer

2a: M = Mg 2b: M = Zn

Liebigs Ann. Chem. 1982

952 J.-H. Fuhrhop, A.-B. KerkhofS, and S. Besecke

The visible spectra of MgOEP (1 a) in solid foils of copolymers 3 of styrene and 5- or 22-mol percent of vinylimidazole deviated from the spectra which were observed in polystyrene. In polystyrene foils a ratio of the visible absorption bands p/a of 1.22 was found (Fig. 3 ) . This is similar to the corresponding ratio of 1.15 in the 22-Yo vinylimidazole copolymer but quite different from the p/a ratio of 1.43 in the 5-% vinylimidazole copolymer (Fig. 2). We relate the p/a = 1.2 ratios to four- or six-coordinated magnesium potphyrinates, whereas the p/ol = 1.4 ratio points to a five- coordinated magnesium complex.

Irradiation of MgOEP (la) in the copolymers under the same conditions as in polystyrene gave no photooxygenation of MgOEP but quantitative conversion to its cation radical. This was shown by the electronic spectra (Fig. 2), ESR spectra and by the quantitative re-reduction of the radical to MgOEP by triethylamine.

I I I 1 - 900 800 70 0 600 500 h"n1

Fig. 1. Electronic spectra of MgOEP ( l a ) in a foil of polystyrene before (-) and after ( - - - ) irradiation with visible light

700 600 500 X Ioml Fig. 2. Electronic spectra of MgOEP ( l a ) in a foil of copolymer 3b before (-) and after

( - - -) irradiation with visible light


Metalloporphyrins in Polymeric Matrices, Micelles, and Vesicles, IV 953

The oxidation rate in the 5-% vinylimidazole copolymer 3 b was comparable to the rate of the photooxygenation in polystyrene ( f , , 2 = 20 min). In the 22-Vo vinylimidazole copolymer the rate was much slower ( t , , , = 2h). Quantum yields of the photoreactions were not determined, but a rough estimate can be obtained from the quantum yield of the MgOEP photooxygenation in benzene solution (@ = 2 . and a comparison of reaction rates. The photooxygenation in polystyrene and the one- electron photooxidation in the 5-% vinylimidazole copolymer would occur with a quantum yield of @ = whereas in the copolymer 3d it drops to a value of @ =

In copolymers containing 0.1% or 1% of vinylimidazole MgOEP was photo- oxygenized to 2a, but some radical was also detected by ESR spectroscopy.

Mole fraction of imidazde in the copolymers

3

0.01 0.05 0,lO 0,22

1 3 a b E d

In benzene solutions the following photochemical reactions of 1 a were observed: (i) In the presence of polystyrene photooxygenation occurred at the same rate as in

its absence (t,,, = 10 min). (ii) In the presence of copolymers 3b or 3d or of I-methylimidazole no reaction was

observed. In acetonitrile solution (see discussion) no photoreaction of l a occurred neither in the absence nor in the presence of I-methylimidazole.

Fluorescence spectra of l a in benzene were identical in the presence or absence of polystyrene or I-methylimidazole or poly[l-phenylethylene-co-1-(1-imidazoly1)ethyl- enels 3.

Peroxide Oxidation Benzoyl peroxide oxidation of 1 a in benzene solution in the presence of polystyrene

gave the 5-benzoyloxyporphyrin l c , but no reaction with the polystyrene. The porphyrins could be extracted quantitatively from the benzene solution with a mixture of aqueous sulfuric acid and methanol. In the presence of copolymer 3d, however, only 70% of the porphyrin could be extracted. The rest was bound to the non-extractable polymer. The electronic spectrum of the polymer-bound porphyrin showed a broad absorption at 560 nm. This band disappeared slowly in the presence of air and a new broad absorption band at 930 nm was observed. Reduction with triethylamine led back to the 560-nm product.

In order to evaluate the spectroscopic observation on the polymeric porphyrin product, we repeated the experiments with monomeric imidazole in chloroform solution. Oxidation of l a in the presence of monomeric imidazole with benzoyl peroxide


954 J.-H. Fuhrhop, A. -B. Kerkhoff, and S . Besecke

yielded the highly substituted porphyrin Id, which was characterized by 'H NMR and mass spectra. It also produced one broad absorption band at 560 nm in the visible range. In the presence of a n excess of benzoyl peroxide it was converted into products absorbing around 900 nm (Fig. 3) which were unstable and could not be isolated in pure form. An extremely weak ESR signal indicated a small percentage of a radical. Immediate reduction with triethylamine gave the starting material in almost quantitative yield. The non-polymeric product, however, did not react with molecular oxygen.

E

Fig. 3. Electronic spectra of I d in CH,CI, (-), 30 min after the addition of benzoyl peroxide ( - - -) and immediately after re-reduction with triethylarnine (. . . . . . .)

Discussion Three types of oxidation reactions of magnesium octaethylporphyrinate l a have

been observed and will be briefly commented: (i) Photooxidation in solid polystyrene leads to the addition of oxygen to the

porphyrin periphery and ring opening to formylbilinate 2a. No difference between solution and solid phase chemistry is observed.

(ii) In poly[l-phenylethylene-co-(1-imidazolyl)ethylene] 3d a n electron is removed from the magnesium porphyrinate to yield the cation radical. The magnesium-bound imidazole base8s9) acts as efficient physical quencher of singlet oxygenlO.'l), but the reversible photooxidation is still possible. We assume that the electron migrates to oxygen molecules, which are close enough to the porphyrin to allow electron transfer from the excited porphyrin state, but also far enough to prevent fast recombination of charges (ca. 1 - 3 nm)12) (cf. Figure 4). - In benzene solution containing imidazole

Liebigs Ann. Chern. 1982


derivatives no photooxidation is observed, because the recombination of charges is not hindered.

Fig. 4. Hypothetic structure of a ternary MgOEP-copolymer-oxygen complex which allows the photochemical one-electron transfer from MgOEP (1 a) to molecular oxygen

(iii) Chemical oxidation with benzoyl peroxide in the presence of copolymer 3d leads to a binding between the polymeric imidazole and the porphyrin's methine bridges. The polymer-bound porphyrin reacts with oxygen. A monomeric model compound does not give this reaction.

Since the x-cation radical of l a does not react with copolymer 3d (see above), we suggest that benzoyloxygenated or thallated isoporphyrins are formed from porphyrin and benzoyloxy radicals as first Substituted isoporphyrins or phlorins may undergo nucleophilic substitution reactions16-18) and their oxidation potential is quite I O W ~ ~ ' ~ ) allowing further radical addition reactions at other methine bridges.

oxidation - l c 6 H N z N C,H5C03H R N s N oxidation - - Id, l e

The 900-nm oxidation products provide evidence for the formation of isoporphyrins. They are long-lived when the planarity of the porphyrin base is disturbed by several large substituents on the methine bridges. This is in accordance with the reported stabil- ity of isoporphyrins from tetraphenylporphyrin16). The reducibility of the isoporphyrins with weak reductants demonstrates the lability of the C - 0 bond at the sp3- hybridized bridge carbon atom. Therefore, the proposed nucleophilic substitution should easily occur. The exact nature of the isoporphyrin formed from molecular oxygen and 1 a in solid poly[ I-phenylethylene-co-1-(I-imidazolyl)ethylene]s remains unknown, since model compound Id did not give this reaction, nor could a peroxy radical be observed in the ESR spectrum.

This work was supported by the Deutsche Forschungsgemeinschafr and the Fonds der Chemi- schen Indusirie.


956 J.-H. Fuhrhop, A.-B. Kerkhoffi and S. Beserke

Experimental

The 'H NMR spectra were recorded on a Varian XI, 100 spectrometer in CDCI, and are reported in 6-values. IR spectra were obtained with Perkin-Elmer models 521 or 580 B in KBr. Mass spectra (MS) were measured on AEI spectrometers MS 30 or MS 9. ESR spectra were obtained using a Bruker B-ER 414 spectrometer. Electronic spectra were taken with zpectrophotometers Zeiss DMR 21 or Beckman DK 2 A. Fluorescence mcasurernents were performed with a Perkin-Elmer spectrophotometer MPF 44 B. Irradiation studies were carried out at room temp. using an Osram 1000-W halogen movie lamp or a 300-W movie lamp Osram G 176. Microanalyses were performed by I . Beetz, Kronach, or by the Mikrolabor des Instituts fur Organische Chemie der Freien Universitat Berlin. Thin layer chromatography (TLC) was carried out on 1-mm coated plates (100 x 20 cm) of silica gel without indicator (Woelm). Column chromatography was performed with silica gel for dry column chromatography without indicator (W oelm).

.Maynesium 2,3,7,8,12,13,17,18-oc1uerh.vlporphyrinate (1 a) and polyrl-phenyleih.vlene-co-I- (irrriduzolyl)eihylene]s 3 a - d were prepared as described previously8.9). Polystyrene (mol. wt. = 20000) was purchased from Carl Roth.

2,3,7,8,12,13,1 7,18-Ortuelhyl-5-(l-imiduzolyl)porphyrin (1 b): 167 mg (0.3 mmol) of 1 a and 467 mg (7.0 mmol) of imidazole were dissolved in 60 ml of CHCI,. 80 mg (0.26 mmol) of benzoyl peroxide, containing 20% of water, were added and the solution was stirred for 1 h a t room temp. 100 ml of 4% hydrochloric acid in water were added. The organic phase turned to a purplish green color, the aqueous phase was green. The aqueous phase was extracted three times with 50 ml of chloroform. The organic phases were combined, washed to neutrality with several portions of distilled water and dried with calcium chloride. The solvent was removed and the residue chromatographed on silica gel for dry column chromatography (withoul indicator, Woelm) with chloroform. Effluents: (i) 1 a (10%); (ii) 5-benzoyloxy-2,3,7,8.12,13,17,18-0cta- ethylporphyrin ( lc) (20%); (iii) 1 b (61 070).

1 b: MS: m/e = 600 ( M i , loo%), 534 ( M + - imidazolyl, 13%), 300 (M2+, 6%). - ' H NMR (CDCl,): 6 = 1.38 (I; 6 H , 2CH3), 1.83-2.00(m; 18H, 6CH3), 2.68(q; 4 H , 2CH,), 3.96-4.25 (m; 12H. 6 CH,), 7.61, 7.94, 8.94 [s; 1 C H (imidazole), each], 10.05 (s; 1 H. 1 CH), 10.25 (s; 2H, 2 CH). - IR (KBr): 1735, 1600 cm-'. - Electronic spectrum (CH2C12): A,, (E) = 628 (2800). 574 (5500), 540 (7600), SO6 (12900), 403 nm (143000).

C,,H,8N,. H 2 0 (618.8) Calc. C. 75.70 H 8.15 N 13.58 Exp. C 75.79 H 7.93 N 14.34

Zinc complex of l b : Electronic spectrum (CH,CI,): A,,, (E) = 580 (17700), 543 (16600). 410 nm (275000).

5-Benzoyloxy-2,3,7,8,12,13,17,I8-ortuerhylporphyrin (Ic): 100 mg (0.19 mmol) of I a and 100 g of polystyrene (mol. wt. = 20000) were dissolved in 30 ml of benzene and 200 mg (0.7 nimol) of mortarized benzoyl peroxide were added. After 12 min the color had changed from red to green and the reaction mixture was transferred into 350 ml of methanol. A few crystals of sodium chloride were added. The precipitated polystyrene was filtered off and redissolved in benzene. This solution was only slightly red. With conc. hydrochloric acid all the porphyrin could be extracted. Thc benzene phase contained all the polystyrene which remained as a colorless solid after removal of the solvent. The white polystyrene could also be obtained from the benzene solution by several precipitations with methanol-sodium chloride. l a (20'70) and 1 c (40%) were isolated from thc combined methanolic and aqueous phases. The spectroscopic data of I c werc identical to thosc reported by Bonnelr et al. 13).



IO-Benzoyloxy-2,3,7,8,12,13,17, Id-octaethyl-5, Ili-bis(l-irnidazolyl)porphyrin (1 d): 200 mg (0.36 mmol) of l a and 1.2 g (18 mmol) of imidazole were dissolved in 50 ml of dichloromethane and mixed with 300 mg (1.0 mmol) of benzoyl peroxide. The color changed from red to violet. After 5 min the solution was diluted with 200 ml of dichloromethane and washed with 300 ml of 0.1% hydrochloric acid to remove the imidazole. Thereafter 250 ml of 0.3% hydrochloric acid were added. The color changed to green. Demetalation occurred and some porphyrin went into the aqueous phase. This was extracted with 20 ml of dichloromethane. Another extraction with 0.2% hydrochloric acid followed. The combined organic phases were neutralized by washing with water. The color changed again to red. The solution was dried with sodium sulfate and the solvent removed in oacuo. The product was chromatographed twice by preparative TLC [silica gel, Woelm, without indicator; CHC13/CH30H (97.5 : 2.5)] and yielded brown crystals from chloroform/methanol. Yield 70 mg (25%) Id . - Electronic spectrum (CH2C12): h,, ( E ) = 636 (2800), 589 (8300), 542 (7900). 515 (21500), 416 nm (23oooO).

C4,H5,N8O2. H 2 0 (804.9) Calc. C 73.1 H 7.0 N 13.9 Exp. C 73.1 H 7.3 N 15.0

Zinc complex I f of Id: Electronic spectrum (CH,C13: h,, (E) = 587 (13400), 556 (23500), 423 nm (300000). - MS: m/e = 786 (M+, 5 I%), 666 (M+ - C6H,CO0 + H, 100%), 600 (M' - C6H&OO - C,H,N, + 2H, 38%). - 'H NMR (CDCI,): 6 = 0.84 (t; 6H, 2 CH3), 0.92 (ti 6H, 2 CH,), 1.64 (ti 6H, 2 CH,), 1.82 (t; 6H, 2 CH,), 2.38 (9; 4H, 2 CH,), 2.62 (9; 4H, 2 CH3,3.85 (4; 4H, 2 CH3,4.01 (9; 4H, 2 CH3,7.60 [s; 2H, CH (imidazole)], 7.85 [t; 3H, CH (phenyl)], 8.00 [s; 2H, CH (imidazole)], 8.48 [s; 2H, CH (imidazole)], 8.72 (m; 2H, CH (phenyl)], 9.91 [s; 1 H, CH (porphyrin)].

The structure of I d follows from the 2: 2: 2:2 patterns produced by the eight ethyl groups. Only the imidazole substituents give a large downfield shift of the corresponding protons and they must be symmetrically oriented to cause the observed pattern. The less symmetrical 15-benzoyl- 5,lO-diimidazolyl isomer would be expected to yield a more complex pattern of sixteen separated signals one for each of the methyl and methylene groups.

Adduct 1 e of magnesium 2,3,7.8,12.13,17,1d-octaethylporphorinate ( 1 a) with the copolymer of22% of I-oinylimidazole and 78% of styrene: 100 mg (0.18 mmol) of l a and 1.06 g of the copolymer were oxidized with benzoyl peroxide as described above. The polymer precipitated from methanol after addition of sodium chloride, was dark violet. The violet methanol solution was decanted and the residue redissolved in benzene. This benzene solution was again added dropwise to methanol (200 ml) and precipitated with sodium chloride. The residue was redissolved and reprecipitated until the methanol remained completely colorless. This was usually the case after five reprecipitations. The precipitate then was still dark purplish green and contained about 25 mg of covalently bound l a . It could be demetalated with conc. hydrochloric acid, but it would not be extracted from a benzene or chloroform sulution. - The residue was finally redissolved in chloroform. On a TLC silicagel plate it did migrate with chloroform/methanol (1 : 1 ) where the monomeric product Id ran at the solvent front. The yield of the polymer was approximately 1 g (ca. 92%). - Electronic spectrum: 28.4 mg l e in 25 ml chloroform produced the following spectrum: h,,, (optical density): 590 inflexion (0.48), 561 ( O M ) , 428 nm (12.1). With the assumptions, that the polystyrene had been recovered quantitatively and &561 = 2oooO a covalent attachment of about 25 mg of l a can be estimated.

mmol) of l a and 30 mg of polystyrene or poly[l-phenylethylene-co-l-(l-imidazolyl)ethylene] were dissolved in 2.5 ml of benzene or dichloromethane in a quartz cuvette. Most of the solvent was removed in a nitrogen stream. The cuvette was then turned into a horizontal position. The viscous polymer solution distributed evenly on the cuvettes window and was further dried in a weak stream of


Preparation of polymer foils and irradiation: Approximately 0.1 mg (1.8 .

958 J.-H. Fuhrhop, A.-B. Kerkhoff, and S. Besecke

nitrogen. A thin (0.05 -0.1 mm) and homogeneous film remained. - A 1000-W movie lamp at a distance of 30 cm served as light source. Lamp and cuvette were cooled with a fan and a hair dryer. The optical spectra of the foil were continously run. The quantitative conversion of l a in a copolymer containing 22% 1-vinylimidazole to its cation radical took 90 min; tl,* was 35 rnin. The photo-oxygenation in pure polystyrene was complete after 15 min. In a copolymer containing 1% of I-vinylimidazole the decomposition of l a took 30 min. A strong band at 830 nm (compound 2a) was observed, but some radical was also present.

Irradiation of 1 a in benzene solutions containing polystyrene or 1-methylimidazole or copoly- mer3d: Ca. 0.1 mg (1.8 . mmol) of l a and 50 mg of polystyrene were dissolved in 5 ml of benzene and irradiated with a 300-W movie lamp from a distance of 25 cm. After 20 rnin all of 1 a was converted into the formylbilinate 2a. With 4 mg (4.9. l o w 2 mmol) of 1-methylimidazole instead of polystyrene no reaction of l a was observed after 20 min. The same was true if the benzene solution contained 50 mg of the poly[l-phenylethylene-co-l -(l-imidazo1yl)ethylene) (3c). The fluorescence spectrum of a benzene solution of 1 a was identical to the spectra obtained after addition of polystyrene or I-methylimidazole of poly[l-phenylethylene-co-1-(1-imidazoly1)- ethylene] (hmm = 591 and 644 nm).

Peroxidation of zinc I0-benzoyloxy-2,3,7,8,12,13,17,18-octaethyl-5,1.5-bis(~-imidazo/y~porphyrinate (If): Ca. 0.1 nig (1.2 . mrnol) of 1 f were dissolved in 3 ml of dichloromethane. - Electronic spectrum (CH2C12): h,,, (E) = 587 sh (13500), 556 (23500), 423 nm (300000). - 2 mg of solid benzoyl peroxide were added. After 30 s the absorption band at 556 nm had diminished to half of its initial value and a new broad absorption band at 900 nm was observed. After 30 min this new band had reached its maximum height (see. Fig. 3). -- Electronic spectrum (CH,C13: h,,,, (E) = 900 (16600). 435 nm (54000). The band at 556 nm had disappeared. - After addition of a few drops of triethylamine a spectrum, which was similar to the initial spectrum, was measured. - Electronic spectrum (CH,Cl2): h,,, (E) = 565 (18800), 435 nm (312000).

Oxygenation of1 e: 5 mg of l e (the copolymer contained 22% 1-vinylimidazole) were dissolved in 5 ml of chloroform. - Eleclronic spectrum (CHCI,) h,, (optical density) = 561 (0.88), 428 nm (12.1). - The solution was left for ca. 12 h. Its color changed from purplish green to greenish brown. A broad absorption band with a maximum at 930 nm was observed. A few drops of triethylamine were added and the starting material (hmm = 560, 424 nm) was immediately recovered.

1 ) Part 111: see referenceg). 2, 2a) J.-H. Fuhrhop, Angew. Chem. 86, 363 (1974); Angew. Chem., lnt. Ed. Engl. 13, 321

(1974). - 2b) J.-H. Fuhrhop, Angew. Chem. 88, 704 (1976); Angew. Chem., Int. Ed. Engl. 15, 648 (1976).

3) J.-H. Fuhrhop, P. K . W. Wasser, J . Subramanian, and U. Schrader, Liebigs Ann. Chem. 1974, 1450.

4, J.-H. Fuhrhop and D. Mauzerall, Photochem. Photobiol. 13, 453 (1971). 5 , T. G. Truscott, E. J . Land, and A . Sykes, Photochem. Photobiol. 17, 43 (1973). 6 ) P. Koka and P. S. Song, Photochem. Photobiol. 28, 509 (1978). 'J D. W. Reed and R. K . Clayton, Biochem. Biophys. Res. Commun. 30, 47 (1968). 8, K. M. Smith (ed.), Porphyrins and Metalloporphyrins, chapters 5 and 6, Elsevier, Amsterdam

y, J.-H. Fuhrhop, S . Besecke, W. Voigt, J. Ernsf, and J. Subramanian, Makromol. Chern. 178,

In) T. Imura, T. Furutsuka, and K . Kawabe, Photochem. Photobiol. 22, 129 (1975). I * ) I . B. C. Matheson, R. D. Etheridge, N. R. Kratowich, and J. Lee, Photochern. Photobiol. 21,

1975.

1621 (1977).

165 (1975).



j2) D. Mauzerall and F. T. Hong in ref.8), p. 107ff. 13) R. Bonnett, M . J. Dimsdale, and G. F. Stephenson, J. Chem. SOC. C 1969, 534. 14) S. Besecke, B. Evans, C. H . Barnett, K . M. Smith, and J.-H. Fuhrhop, Angew. Chem. 88,616

(1976); Angew. Chem., Int. Ed. Engl. 15, 551 (1976). G. H. Barnett, B. Evans, K . M. Smith, S. Besecke, and I . -H. Fuhrhop, Tetrahedron Lett. 1976, 4009.

16) D. Dolphin, R . H . Felton, D. C. Borg, and J. Fajer, J . Am. Chem. SOC. 92, 143 (1970). 17) D. Dolphin, Z . MuUiani, K . Rousseau, D. C. Borg, J. Fajer, and R. Felton, Ann. N. Y . Acad.

Sci. 206, 177 (1973). R. E . Woodward, Ind. Chim. Belge 1962, 1293.

1 9 ) J.-H. Fuhrhop and J . Subramanian, Philos. Trans. R . SOC. London, Ser. B 213, 335 (1976).

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