Photophysical and photocatalytic properties of β-sulfonatoporphycenes

Article abstract of DOI:10.1246/cl.2008.264

The photophysical properties and photooxidation ability of the β-sulfonatoporphycenes are reported. The photophysical parameters depend on the number of substitutions. The disulfonated porphycene 2 is expected to be a new photosensitizer due to its high catalytic activity and photostability. Copyright

Full text of DOI:10.1246/cl.2008.264

264
Chemistry Letters Vol.37, No.3 (2008)
Photophysical and Photocatalytic Properties of ꢀ-Sulfonatoporphycenes
Tatsushi Baba,1 Hisashi Shimakoshi,1 Ayataka Endo,2 Chihaya Adachi,2 and Yoshio Hisaedaꢀ1
1Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395
2Center for Future Chemistry, Kyushu University, Fukuoka 819-0395
(Received November 26, 2007; CL-071303; E-mail: yhisatcm@mbox.nc.kyushu-u.ac.jp)
Table 1. Photophysical parameters of sulfonated porphycenes
ꢁamax ꢁbfluorescence
The photophysical properties and photooxidation ability
of the ꢀ-sulfonatoporphycenes are reported. The photophysical
parameters depend on the number of substitutions. The disulfo-
nated porphycene 2 is expected to be a new photosensitizer due
to its high catalytic activity and photostability.
Compound Solvent
ꢂs/nsc ꢀdf ꢀeꢁ
/nm
/nm
1
2
2
3
3
CH3OD 643
CH3OD 653
648
657
657
—
8.38 0.33 0.29
3.94 0.17 0.25
1.61 0.10 0.10f
H2O
CH3OD 688
H2O 686
646
—
—
ꢁ0 0.01
Water-soluble porphyrins and their metal complexes have
attracted much attention because of their various uses as photo-
dynamic therapy photosensitizers,1 fluorescent tumor markers,2
and photooxidation catalysts3 in aqueous media. There are
also many reports concerning the photophysical properties4
and photooxidation abilities3 of water-soluble porphyrins.
On the other hand, porphycenes, the structural isomers of
porphyrins first synthesized by Vogel et al.,5 are considered to
be superior photosensitizers for singlet oxygen generation due
to their large absorption peaks in the visible region and suitable
photochemical attributes.6 In the previously submitted paper, we
reported the syntheses of water-soluble porphycenes containing
sulfonic acid groups.7 Here, we report the photophysical proper-
ties of sulfonated porphycenes and the photodegradation of
2,4,6-trichlorophenol (TCP), which is a major pollutant,8 using
disulfonated porphycene 2 as a photosensitizer.
The sulfonated porphycenes were synthesized by the direct
sulfonation7 or chlorosulfonation9 of 2,7,12,17-tetra-n-propyl-
porphycene (H2TPrPc) and followed by hydrolysis10 as shown
in Scheme 1. 2 and 3 exhibit a high water-solubility at pHs
between 0 and 14. The details of the photophysical properties
of the three sulfonatoporphycenes are discussed below. The
photophysical parameters of the sulfonated porphycenes are
summarized in Table 1.
—
ꢁ0 ꢁ0f
aMaximum of the lowest-energy absorption band. bMaximum of
the fluorescence. cLife time of the singlet state. ꢂs was measured
by a HORIBA FluoroCube. Two components of the fluores-
cence-decay kinetics were observed. The main component was
used to determine ꢂs. dQuantum yield of fluorescence. eQuantum
yield of singlet oxygen formation. ꢀꢁ was measured by a
f
HORIBA SPEX Fluorolog-NIR. Solv., D2O.
with the increasing number of sulfonic acid groups on the
pyrrole groups of H2TPrPc.
The absolute fluorescence quantum yields (ꢀf) of the sulfo-
nated porphycenes were based on photoluminescent measure-
ments using an integrating sphere. Compound 1 showed a strong
fluorescence maximum at 648 nm with the quantum yield ꢀf ¼
0:33 in air-saturated CH3OD, and compound 2 also showed a
fluorescence at 657 nm with the quantum yield ꢀf ¼ 0:17 in
CH3OD and ꢀf ¼ 0:10 in H2O at neutral pH. These values
are lower than that of H2TPrPc (ꢀf ¼ 0:36) in toluene,6a but
they are similar to that of the haematoporphyrin derivatives11
(ꢀf ¼ 0:09) used as tumor markers. Thus, these sulfonated por-
phycenes appear to be potential agents for tumor diagnosis.12
However, compound 3 does not show any fluorescence both in
CH3OD and in H2O. The ꢀf value of the sulfonatoporphycenes
decreased with an increase in the number of sulfonic acid
groups. It appears that the ꢀ-substitutions result in deformation
of the porphycene ring13 due to steric repulsion. The resulting
out-of-plane distortion of the porphycene macrocycle may
increase the rate constants of the non-radiative decay.14
Steady-state 1O2 phosphorescence detected at 1270 nm
was used to determine the quantum yield of the singlet oxygen
formation (ꢀꢁ) for the sulfonatoporphycenes in air-saturated
solutions. The ꢀꢁ values were determined from the phosphores-
cence intensity, which were compared to the intensity obtained
using heamatoporphyrin4 (ꢀꢁ ¼ 0:75 in CH3OD) and rose
bengal15 (ꢀꢁ ¼ 0:75 in D2O) as standards.
The electronic spectra of the sulfonatoporphycenes were
measured in CH3OD and in H2O. The Q-bands are red-shifted
-
-
-
-
-
SO
3
SO
3
SO
3
SO
3
SO
3
NH
N
NH
N
Route A
N
N
NH
N
NH
N
N
N
HN
HN
HN
HN
(a)
25% Fuming
sulfuric acid
-
-
-
SO
3
SO
3
O S
3
cis-2
trans-2
1
Yields
2
3
40%
NH
N
N
HN
57%
75%
60%
Route A
Route B
83%
H
TPrPc
(c) H O / Pyridine
2
2
SO Cl
2
SO Cl
2
SO Cl
2
(b)
Chlorosulfonic
acid
NH
NH
NH
N
N
N
The ꢀꢁ values decreased with the increasing number of
substitutions in a manner similar to the ꢀf values. The ꢀꢁ val-
ues were as follows: in CH3OD, ꢀꢁ ¼ 0:29, 0.25, and 0.01 for 1,
2, and 3, respectively: in D2O, ꢀꢁ ¼ 0:10 and 0 for 2 and 3. 2
was observed to have low ꢀꢁ and ꢀf values in water relative
to methanol. An increase in the solvent polarity results in an in-
crease of the non-radiative rate constants from the excited states,
therefore ꢀꢁ and ꢀf decrease as for aminoanthraquinones.16
N
N
N
HN
HN
HN
Route B
SO Cl
2
ClO S
2
4
cis-5
trans-5
5
Scheme 1. Synthesis of sulfonated porphycenes (a) direct
sulfonation of H2TPrPc, (b) chlorosulfonation of H2TPrPc,
(c) hydrolysis of chlorosulfonated porphycenes.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.3 (2008)
265
O
O
ing Technology Seeds (15-007) from the Japan Science and
Technology Agency (JST) and Global COE Program ‘‘Science
for Future Molecular Systems’’ from the Ministry of Education,
Culture, Sports, Science and Technology (MEXT) of Japan.
OH
0.8
1O 2
Cl
Cl
Cl
Cl
Cl-
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Cl
TCP
This paper is dedicated to the memory of Professor
Yoshihiro Matsumura.
References and Notes
1
a) R. K. Pandey, G. Zheng, in The Porphyrin Handbook, ed.
by K. M. Kadish, K. M. Smith, R. Guilard, Academic Press,
2000, Vol. 6, Chap. 43, pp. 157–230. b) S. Hirohara, M.
Obata, A. Saito, S. Ogata, C. Ohtsuki, S. Higashida, S. Ogura,
I. Okura, Y. Sugai, Y. Mikata, M. Tanihara, S. Yano,
Photochem. Photobiol. 2004, 80, 301. c) K. Hirakawa, S.
Kawanishi, T. Hirano, H. Segawa, J. Photochem. Photobiol.
B 2007, 87, 209.
250
300
350
Wavelength/nm
400
450
Figure 1. Electronic spectral changes observed during photo-
degradation of TCP in the presence of 2 in water at pH 10.
Table 2. Photodegradation of TCP in watera
Yields/%
Photo-
Conversion
/%
2
3
R. L. Lipson, E. J. Bales, A. M. Oleson, J. Natl. Cancer Inst.
1961, 26, 1.
R. Gerdes, D. Wohrle, W. Spiller, G. Schneider, G.
¨
Schnurpfeil, G. Schulz-Ekloff, J. Photochem. Photobiol., A
TONb
2,6-dichloro-
benzoquinone
sensitizer
Clꢃ
2
185
115
0
100
73
0
97
70
0
96
71
0
TPPS
none
1997, 111, 65.
C. Tanielian, C. Wolff, M. Esch, J. Phys. Chem. 1996, 100,
4
5
6
a[TCP] = 3:3 ꢂ 10ꢃ3 M, [sensitizer] = 7 ꢂ 10ꢃ6 M, under air
6555.
E. Vogel, M. Kocher, H. Schmickler, J. Lex, Angew. Chem.,
atmosphere with a 500-W tungsten lamp (ꢁ ꢄ 460 nm) at room
¨
Int. Ed. Engl. 1986, 25, 257.
b
temperature. Turnover number per 1 h.
a) S. Nonell, P. F. Aramendia, K. Heihoff, R. M. Negri, S. E.
Braslavsky, J. Phys. Chem. 1990, 94, 5879. b) J. C. Stockert,
M. Can˜ete, A. Juarranz, A. Villanueva, R. W. Horobin, J. I.
To confirm the catalytic activity of 2, the photodegradation
of 2,4,6-trichlorophenol8 (TCP, 3:3 ꢂ 10ꢃ3 M) was carried out
under irradiation with visible light (ꢁ ꢄ 460 nm). Figure 1
shows the spectral change observed during the photodegradation
of TCP using 2 as a sensitizer every one hours. The spectral
change shows decrease in the TCP absorption peak at 312 nm
and formation of 2,4-dichlorobenzoquinone at 273 nm.8 The
turnover number based on 2 is 1.5 times greater than that of
tetrakis(sulfonatophenyl)porphyrin (TPPS) as shown in Table 2,
though the ꢀꢁ value for 2 is lower than that for TPPS
(ꢀꢁ ¼ 0:51, in water).4 The high catalytic activity of 2 arises
from its high absorption in the visible region. A chlorine ion
was also detected as the product by the Fe(NO3)3 and Hg(SCN)2
method. An almost quantitative yield of the chlorine ion was
observed. Control experiments indicated that both light and 2
are essential for the degradation of TCP.
One of the important factors is the photostability of photo-
sensitizers. We found that 2 is more stable than TPPS during
photoirradiation. In order to compare the photostabilities of 2
and TPPS, photodecomposition experiments were carried out.
The air-saturated water solutions containing a sensitizer (4:5 ꢂ
10ꢃ6 M) were irradiated with visible light (ꢁ ꢄ 460 nm). The
irradiation of the samples leads to a decrease in the absorption
bands. After photoirradiation for 10 h, 51% of the TPPS had de-
composed. On the other hand, only 4% of 2 had decomposed.
The difference of the photostability is attributed to the structure
of the macrocycle.
´
Borrell, J. Teixido, S. Nonell, Curr. Med. Chem. 2007, 14,
997.
T. Baba, H. Shimakoshi, Y. Hisaeda, Tetahedron Lett. 2004,
45, 5973.
K. Ozoemena, N. Kuznetsova, T. Nyokong, J. Mol. Catal. A
2001, 176, 29.
N.-K. Mak, T.-W. Kok, R. N.-S. Wong, S.-W. Lam, Y.-K.
Lau, W.-N. Leung, N.-H. Cheung, D. P. Huang, L.-L. Yeung,
C. K. Chang, J. Biomed. Sci. 2003, 10, 418.
7
8
9
10 49 and 5 were obtained in 83% and 75% yields, respectively.
The hydrolysis of the chlorosulfonated porphycenes quantita-
tively proceeded.
4: UV-vis (in CH2Cl2): [ꢁmax/nm], 386, 577, 632, 669:
MALDI-TOF-MS (dithranol matrix, m=z) [M]þ 576.65. 5:
UV-vis (in CH2Cl2): [ꢁmax/nm], 386, 594, 644, 683:
MALDI-TOF-MS (dithranol matrix, m=z) [M]þ 674.77. The
ratio of isomers (cis-2 and trans-2) was determined by peak
1
integration of the H NMR spectrum. Route A: cis-2:trans-
2 = 1.8:1 Route B: cis-2:trans-2 = 2.5:1 Sample 2 synthe-
sized by the Route B method was used for these experiments.
11 G. J. Smith, Photochem. Photobiol. 1985, 41, 123.
12 M. Guardiano, R. Biolo, G. Jori, K. Schaffner, Cancer Lett.
1989, 44, 1.
13 T. Hayashi, Y. Nakashima, K. Ito, I. Aritome, A. Suzuki,
Y. Hisaeda, Org. Lett. 2003, 5, 2845.
In conclusion, the photophysical properties of the sulfonated
porphycenes were investigated and the photodegradation of TCP
using 2 was carried out. The photophysical parameters are de-
pendent on the number of sulfonic acid groups. 2 shows a higher
catalytic activity and photostability compared to TPPS.
14 S. Gentemann, C. J. Medforth, T. P. Forsyth, D. J. Nurco,
K. M. Smith, J. Fajer, D. Holten, J. Am. Chem. Soc. 1994,
116, 7363.
15 E. Gandin, Y. Lion, A. Van der Vorst, Photochem. Photobiol.
1983, 37, 271.
16 G. Jones, II, Z. Feng, W. R. Bergmark, J. Phys. Chem. 1994,
98, 4511.
This work was partially supported by Research for Promot-
Published on the web (Advance View) February 2, 2008; doi:10.1246/cl.2008.264