Photooxygenation of alkynylperylenes. Formation of dibenzo[jk,mn] phenanthrene-4,5-diones

Article abstract of DOI:10.1021/jo7016668

(Chemical Equation Presented) 3-(1-Alkynyl)perylenes undergo oxygenation when subjected to irradiation with visible light under aerated conditions. The structures of novel oxygenated products formed in this manner are assigned as regioisomeric dibenzo[jk,

Full text of DOI:10.1021/jo7016668

aromatic hydrocarbons, such as naphthacene,6 pentacene,7
benzo[a]anthracene,8 dibenzo[a,j]anthracene,9 dibenzo[a,o]p-
erylene,10 dibenzo[b,n]perylene,11 terrylene,12 tetrabenzo[a,c,l,n]-
pentacene,13 and diphenanthro[5,4,3-abcd:5′,4′,3′-jklm]perylene14
Photooxygenation of Alkynylperylenes. Formation
of Dibenzo[jk,mn]phenanthrene-4,5-diones
Hajime Maeda,*,† Yasuaki Nanai,† Kazuhiko Mizuno,†
Junya Chiba,*,‡ Sakiko Takeshima,‡ and Masahiko Inouye‡
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Department of Applied Chemistry, Graduate School of
Engineering, Osaka Prefecture UniVersity, 1-1 Gakuen-cho,
Naka-ku, Sakai, Osaka 599-8531, Japan, and Graduate School
of Pharmaceutical Sciences, UniVersity of Toyama,
Sugitani 2630, Toyama 930-0194, Japan
maeda-h@chem.osakafu-u.ac.jp; chiba@pha.u-toyama.ac.jp
ReceiVed July 30, 2007
3-(1-Alkynyl)perylenes undergo oxygenation when subjected
to irradiation with visible light under aerated conditions. The
structures of novel oxygenated products formed in this
manner are assigned as regioisomeric dibenzo[jk,mn]phenan-
threne-4,5-diones.
Photooxygenation of organic molecules has been used in
organic syntheses as a clean method to carry out oxygenation
reactions as well in the low-temperature synthesis of unstable
peroxides.1 Many synthetic and mechanistic studies have been
devoted to photooxygenations of alkenes, dienes, amines,
aromatic compounds, and heterocycles which are promoted by
photochemically generated singlet oxygen or electron-transfer
sensitization. As for the photooxygenation of aromatic com-
pounds, that of naphthalene1a-c,2 and anthracene1a-c,3 derivatives,
leading to the formation of endoperoxides and dione products,
has been extensively studied. Photooxygenation reactions
involving the benzene ring are limited to electron-donating-
substituted4 and structurally strained benzene (e.g., cyclophanes)
derivatives.5 Photooxygenation of more condensed polycyclic
(6) (a) Dufraisse, C.; Horclois, R. Bull. Soc. Chim. Fr. 1936, 1880-
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Fu, N. Y.; Chen, X. M.; Cai, Z. W.; Wong, H. N. C. Chem. Commun.
2005, 66-68. (d) Uno, H.; Yamashita, Y.; Kikuchi, M.; Watanabe, H.;
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1981-1983.
† Osaka Prefecture University.
‡ University of Toyama.
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10.1021/jo7016668 CCC: $37.00 © 2007 American Chemical Society
Published on Web 10/13/2007
8990
J. Org. Chem. 2007, 72, 8990-8993

SCHEME 1. Photooxygenation of DNA-like Fluorescent
Perylene Dimer Based on Alkynyl C-Nucleoside
derivatives has also been explored. Since more condensed
polyaromatic compounds have low triplet energies, they can
serve to sensitize singlet oxygen generation without the need
for external photosensitizers.
Photooxygenation of perylene, a versatile visible-light absorb-
ing fluorophore, has not been fully probed. To the best of our
knowledge, the sole reported study was carried out by Guillet
et al., where perylene was photooxygenated in water in the
presence of a water-soluble polymer photosensitizer.15 Impor-
tantly, photooxygenation reactions of substituted perylenes have
not been described.
Recently, we described the synthesis of DNA-like fluorescent
oligomers composed of alkynyl â-D-ribofuranosides bearing
pyrene, perylene, and anthracene fluorophores, and reported their
homo- and heteroexcimer emissions.16 During the course of that
study, we noticed that the alkynylperylene dimer 1a undergoes
facile photobleaching upon exposure to visible light. Below,
we report the novel photooxygenation reaction of alkynylp-
erylenes that is responsible for photobleaching and alert
photochemists that the fluorescence intensity of perylene is
easily decreased owing to this process.
FIGURE 1. Time-dependency of fluorescence spectra of 1a upon (a)
0-30 and (b) 30-201 h of photoirradiation.
contains a typical intramolecular excimer emission around 600
nm.16 In Figure 1 is shown the time-dependency of the
fluorescence spectrum of 1a in aerated water upon irradiation
with a desktop fluorescent lamp. Upon irradiation, the emission
due to the perylene excimer decreases concurrently with an
increase of monomer emission with an isoemissive point.
Monomer emission reaches a maximum after 30 h of irradiation
and then begins to decay. These observations indicate that at
first one of the two perylene fluorophores in 1a is converted to
a nonfluorescent moiety and then the other perylene group is
transformed to a nonfluorescent moiety. HPLC separation and
MALDI-TOF mass analysis of the crude mixture obtained after
24 h of irradiation of 1a indicates that products having molecular
weights that correspond to adducts of one and two molecules
of dioxygen are produced (Figure S3, Supporting Information).
Stimulated by this observation, we carried out the photore-
action of readily available alkynylperylenes and determined the
structures of the oxygenated products. A chloroform solution
of 3-(1-hexynyl)perylene 1b (10 mM, 200 mL) was irradiated
by using an incandescent lamp (300 W) with continuous stirring
and bubbling of dioxygen at room temperature for 24 h (Scheme
2). TLC analysis showed that components having higher
polarities (Rf 0.2, CHCl3) than the substrate were observed in
the crude photolysate. Silica gel column chromatography and
preparative HPLC led to isolation of a 1:1 regioisomeric mixture
of photooxygenated products as an orange solid in a 10% yield
(Table 1, run 2). One regioisomer was isolated by continuous
preparative HPLC.
When the photophysical properties of nucleosides bearing
fluorophores were investigated in aerated water, we became
aware of the instability of 1a when exposed to ambient indoor
lighting (Scheme 1). The fluorescence spectrum of pure 1a
(11) (a) Hewgill, F. R.; Stewart, J. M. J. Chem. Soc., Perkin Trans. 1
1988, 1305-1311. (b) Benshafrut, R.; Hoffman, R. E.; Rabinovitz, M.;
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2002, 58, 8875-8882.
(14) (a) Broene, R. D.; Diederich, F. Tetrahedron Lett. 1991, 32, 5227-
5230. (b) Sakai, K.; Nagashima, U.; Fujisawa, S.; Uchida, A.; Ohshima,
S.; Oonishi, I. Chem. Lett. 1993, 577-580. (c) Ohshima, S.; Uchida, A.;
Horiguchi, S.; Suzuki, A.; Fujisawa, S.; Oonishi, I. Bull. Chem. Soc. Jpn.
1994, 67, 924-928.
(15) (a) White, B.; Nowakowska, M.; Guillet, J. E. J. Photochem.
Photobiol. A: Chem. 1989, 50, 147-156. (b) Burke, N. A. D.; Templin,
M.; Guillet, J. E. J. Photochem. Photobiol. A: Chem. 1996, 100, 93-100.
See also refs 11b and: (c) Zinke, A.; Unterkreuter, E. Monatshefte 1919,
40, 405-410. (d) Nowakowska, M.; Guillet, J. E. Chem. Br. 1991, 27, 327-
330.
The structures of products were assigned as dibenzo[jk,mn]-
1
phenanthrene-4,5-diones 2b and 3b (Scheme 2) by using H
NMR, 1H-1H COSY, 13C NMR, ESI-MS, HRMS, and IR. The
1H-1H COSY spectrum of 2b is shown in Figure 2. As expected
1
from the structure of 2b, its 1D H NMR spectrum contains
(16) Chiba, J.; Takeshima, S.; Mishima, K.; Maeda, H.; Nanai, Y.;
Mizuno, K.; Inouye, M. Chem. Eur. J. 2007, 13, 8124-8130.
three pairs of doublets which are coupled to each other (H1-
J. Org. Chem, Vol. 72, No. 23, 2007 8991

and 1625 cm-1. Finally, MNa+ (385) and MH+ (363) fragments
SCHEME 2. Photooxygenation of Perylene Derivatives
are observed in ESI-MS of 2b.
Photoreaction of 3-(1-octynyl)perylene 1c under similar
conditions also proceeds in an analogous manner (run 4). The
absorption bands of perylene derivatives extend into the visible
region. For example, 1b in cyclohexane has maxima at 455 (ꢀ
) 4.71 × 104 mol-1 dm3 cm-1), 426 (ꢀ ) 3.47 × 104 mol-1
dm3 cm-1), and 403 nm (ꢀ ) 1.54 × 104 mol-1 dm3 cm-1).
Consequently, the irradiation by using an incandescent lamp or
a photoflood lamp is more effective for promoting photooxy-
genation than that by using a high-pressure mercury lamp (Table
1, run 3).
TABLE 1. Photooxygenation of Perylene Derivatives
To the best of our knowledge, the observations reported above
represent a rare case in which simple aromatic compounds
readily undergo photooxygenated in the absence of a singlet
oxygen generator or electron-transfer catalyst. Two possible
mechanisms for the novel photooxygenation reaction are shown
yields (%)
run sub-
no. strate
irradiation
time (h)
lamp
additive
none
2
3
1a
2c
3c
4c
5c
1a
1b
1b
1c
1d
desktop fluorescent
lamp (>400 nm)
incandescent
lamp (>400 nm)
high-pressure Hg
lamp (>280 nm)
photoflood lamp
(>400 nm)
201
24
24
72
48
b
b
none
none
none
5
0
5
0
1
in Scheme 3. One involves the generation of O2 by a route
that begins with the singlet excited state of alkynylperylene
(11*), formed by photoexcitation of 1. Intersystem crossing (ISC)
forms the excited triplet state (31*)17 and then energy transfer
from 31* to ground state dioxygen (3O2) takes place to generate
1O2.18 The second possible mechanism involves single electron
transfer via contact charge transfer (CT) complex19 formed from
1 and 3O2. The endoperoxides 4 and 5 produced through these
pathways undergo oxidative cleavage to give oxygenated
products 2 and 3.
6d,e
9d
Xe lamp, O-58 filter
(>580 nm)
methylene
blue
a In water. b Not determined. See Figure 1. c In CHCl3. d Mixture of 2
and 3. e Major isomer was 2c.
To gain insight into which of the above mechanisms operates
in the oxygenation process, reaction of 1O2 with 1b was
investigated. When photoreactions of 1b were carried out in
the presence of dyes, such as tetraphenylporphyrin, methylene
1
blue, and rose bengal, as O2 generators, product yields were
unchanged. Moreover, photooxygenation of 1b did not occur
1
in the presence of the O2 quencher 1,4-diazabicyclo[2.2.2]-
octane (DABCO) and 1b was recovered quantitatively. Photo-
reaction of 3-bromoperylene (1d) in the presence of methylene
blue, promoted by irradiation with a Xe lamp equipped with
O-58 filter (>580 nm, conditions under which only sensitizer
absorbs the light) gave 2d and 3d in moderate yields (Table 1,
run 5). This result is likely due to enhanced ISC rate caused by
a heavy atom effect. Absorption spectra, obtained on argon-
purged and dioxygen-purged solutions of 1b showed that a
several nanometer shift occurs in the case of dioxygen-purged
solution. To get information about the electron-transfer mech-
anism the effects of Mg(ClO4)2 as a promoter of charge
separation4e,f,20 and polar solvents such as acetonitrile were
investigated. In each case no changes in reaction yields were
noted. Under dark condition, the photooxygenated products were
(17) (a) Parker, C. A.; Joyce, T. A. Chem. Commun. 1966, 108-109.
(b) Nakabayashi, K.; Toki, S.; Takamuku, S. Chem. Lett. 1986, 1889-
1892.
FIGURE 2. 1H-1H COSY spectrum of 2b.
(18) McLean, A. J.; McGarvey, D. J.; Truscott, G.; Lambert, C. R.; Land,
E. J. J. Chem. Soc., Faraday Trans. 1990, 86, 3075-3080.
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1989, 62, 3863-3868. (c) Logunov, S. L.; Rodgers, M. A. J. J. Phys. Chem.
1993, 97, 5643-5648. (d) Kuriyama, Y.; Ogilby, P. R.; Mikkelsen, K. V.
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1058. (e) Maeda, H.; Miyamoto, H.; Mizuno, K. Chem. Lett. 2004, 33,
462-463.
H2, H4-H5, and H8-H9) and one doublet-triplet-doublet
sequence (H10-H11-H12). All signals observed in the COSY
spectrum agree with these coupling patterns. The structure of
3b was assigned by comparing the spectral data of the mixture
of regioisomers to that of 2b (Figures S7 and S8, Supporting
Information). The 1H NMR spectrum of 3b, containing a singlet
(H2, 6.95 ppm) and two triplets (H5 and H8, 7.80 and 7.86
ppm), is in accord with its structure. The 13C NMR spectrum
of 2b shows overlapped carbonyl signals at 187.4 ppm and its
IR spectrum contains two carbonyl stretching bands at 1657
8992 J. Org. Chem., Vol. 72, No. 23, 2007

SCHEME 3. Mechanism for the Photooxygenation
Progress of the reaction was monitored by fluorescence spectros-
copy (Figure 1).
not obtained. Photoreaction of perylene did not proceed under
the conditions used for reaction of 1a-d.
The above results suggest that the mechanism involving 1O2
is more likely for the photooxygenation reaction. The reason
for the large difference in efficiency of the reaction between
1a and 1b-d is likely due to the fact that photooxygenation
via a perylene excimer is faster than that via a perylene
monomer. However, due to the low solubility of perylene
derivatives in organic solvents and water, attachment of the two
perylene core onto a water-soluble chain (1a) or putting it into
a hydrophilic environment by mixing with a water-soluble
polymer15a,b is required to have a sufficient concentration of
the more reactive perylene excimer. In addition, the alkynyl
groups might contribute by increasing solubility and lowering
triplet energy.
Photooxygenation of 3-(1-Hexynyl)perylene (1b). A chloroform
solution of 3-(1-hexynyl)perylene 1b (10 mM, 200 mL) was
irradiated by using an incandescent lamp with continuous bubbling
of dioxygen for 24 h at room temperature. Components with higher
polarity than 1b were observed by TLC analysis (CHCl3, Rf 0.2).
Silica gel column chromatography and HPLC gave an orange solid
containing 2b and 3b in total 10% yield. One regioisomer (2b)
could be isolated by continuously cutting off the shoulder of the
peak in recycling preparative HPLC.
1
Data for 2b: H NMR (500 MHz, CDCl3) δ 1.02 (t, J ) 7.48
Hz, 3 H), 1.57 (sextet, J ) 7.55 Hz, 2 H), 1.72 (quint, J ) 7.48
Hz, 2 H), 2.60 (t, J ) 7.26 Hz, 2 H), 6.77 (d, J ) 9.83 Hz, 1 H),
6.81 (d, J ) 10.25 Hz, 1 H), 7.57 (d, J ) 9.83 Hz, 1 H), 7.68 (d,
J ) 7.26 Hz, 1 H), 7.74 (d, J ) 8.54 Hz, 1 H), 7.74 (t, J ) 8.55
Hz, 1 H), 8.15 (d, J ) 9.83 Hz, 1 H), 8.54 (d, J ) 8.97 Hz, 1 H),
8.59 (d, J ) 8.54 Hz, 1 H); 13C NMR (125 MHz, CDCl3) δ 13.9,
17.1, 19.8, 22.4, 78.2, 100.8, 124.7, 125.3, 125.6, 127.2, 127.3,
129.5, 129.96, 130.04, 130.4, 130.5, 130.59, 130.63, 130.8, 132.9,
134.8, 135.7, 138.8, 140.7, 187.4; IR (KBr) 1625 (CdO), 1657
(CdO), 2219 (CtC) cm-1; HRMS (ESI-TOF) calcd for C26H18-
NaO2 385.1205, found 385.1197.
In summary, we have observed an unprecedented photooxy-
genation reaction of alkynylperylenes. This is the first example
of photooxygenation of substituted perylenes. Recently, much
attention has been focused on the attachment of perylene
fluorophore to nucleosides.21 However, the results presented
above suggest that attention must be paid to the inevitable
oxygenation of the perylene fluorophore when it is present in
such biomolecules.
Acknowledgment. The present work is supported by the
Grant-in-Aid for Scientific Research (KAKENHI) in Priority
Area “Molecular Nano Dynamics” (17034056) from the Min-
istry of Education, Culture, Sports, Science and Technology of
Japan.
Experimental Section
Photooxygenation of 1a. A solution of 1a in MilliQ water (1 ×
10-5 M) in a 1 cm × 1 cm quartz cell was irradiated by using a
desktop fluorescent lamp without stirring at room temperature.
Supporting Information Available: Experimental details for
the syntheses and spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
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