Synthesis and photosensitizing properties of porphycene with imidazolium tag

Article abstract of DOI:10.1142/S1088424612500551

Porphycene having an imidazolium cation tag was synthesized and characterized by elemental analysis, UV-vis, NMR and ESI-mass spectroscopies. This porphycene derivative easily dissolves in various ionic liquids and produces singlet oxygen under irradiation by visible light (λ < 460 nm). The photophysical parameters of the porphycene in ionic liquids were determined and the values were compared to those in acetonitrile. Photosensitizing reactions using this new porphycene for the oxidation of 1,5-dihydroxynaphthalene in ionic liquids were investigated and found to form 5-hydroxy-1,4-naphthoquinone. The recycled use of the porphycene was efficiently achieved in N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([TMPA][TFSA]) and N-methyl-N-propyl-piperidinium bis(trifluoromethanesulfonyl) amide ([P13][TFSA]).

Full text of DOI:10.1142/S1088424612500551

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 530–536
DOI: 10.1142/S1088424612500551
Published at http://www.worldscinet.com/jpp/
Synthesis and photosensitizing properties of porphycene
with imidazolium tag
Hisashi Shimakoshia, Kenichi Sasakia, Yusuke Isekia andYoshio Hisaeda*a,b◊
a Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Fukuoka
819-0395, Japan
b International Research Center for Molecular Systems (IRCMS), Kyushu University, Fukuoka 819-0395, Japan
Dedicated to Professor Emanuel Vogel in memoriam
Received 3 October 2011
Accepted 8 February 2012
ABSTRACT: Porphycene having an imidazolium cation tag was synthesized and characterized by
elemental analysis, UV-vis, NMR and ESI-mass spectroscopies. This porphycene derivative easily
dissolves in various ionic liquids and produces singlet oxygen under irradiation by visible light (l ≥
460 nm). The photophysical parameters of the porphycene in ionic liquids were determined and the
values were compared to those in acetonitrile. Photosensitizing reactions using this new porphycene
for the oxidation of 1,5-dihydroxynaphthalene in ionic liquids were investigated and found to form
5-hydroxy-1,4-naphthoquinone. The recycled use of the porphycene was efficiently achieved in N,N,N-
trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([TMPA][TFSA]) and N-methyl-N-
propylpiperidinium bis(trifluoromethanesulfonyl)amide ([P13][TFSA]).
KEYWORDS: porphycene, ionic liquid, singlet oxygen, imidazolium tag, recycled catalysis.
in an interesting electronic structure of the porphycene
INTRODUCTION
[7–13]. For example, porphycene shows a more intense
Natural tetrapyrrole macrocycles, such as porphyrin,
absorption than porphyrin in the red spectral region due
corrin, and chlorophyll, are attractive compounds in
to its lower molecular symmetry. Therefore, utilizations
the bio- and organic chemistry fields because of their
of porphycenes as a visible light photosensitizer and
important role in biological processes and unique
photocatalyst have been established by many groups
structure [1]. The main features of these macrocycles
[14–23]. Among the photochemical properties of the
are visible light absorption, conjugated structure and
porphycene, singlet oxygen generation with visible light
they coordinate to a variety of metals. To expand these
sensitization has been well studied in photodynamic
unique properties of the tetrapyrrole macrocycles,
therapy and photo-oxidation reactions. To develop this
the preparation of new porphyrin analogs has been
unique property of the porphycene, the combined use of
developed over the years [2–5]. Among the porphyrin
the porphycene with an ionic liquid was achieved in this
analogs, porphycene, a structural isomer of porphyrin,
study. Immobilization of a catalyst on various supports
was first synthesized by Vogel and co-workers in 1986
is a desirable approach for the establishment of “Green
[6]. This porphyrin isomer exhibits geometries of the N4
Chemistry” since the catalyst is easily separated from
core, which deviates from the ideal square shape of the
the reaction medium and reused [24]. Ionic liquids have
porphyrin core, and this unique structural property results
various advantages as a reaction medium because of
the their low melting point, negligible vapor pressure,
non-flammability and good solubility for many organic
SPP full member in good standing
compounds [25–29]. Furthermore, ionic liquids allow for
*Correspondence to: Yoshio Hisaeda, email: yhisatcm@
simple work-up procedures and straightforward isolation
protocols for products from the catalytic reaction since
mail.cstm.kyushu-u.ac.jp, tel: +81 92-802-2826, fax: +81 92-
802-2827
Copyright © 2012 World Scientific Publishing Company

SYNTHESIS AND PHOTOSENSITIZING PROPERTIES OF PORPHYCENE WITH IMIDAZOLIUM TAG
531
ionic liquids are not miscible with a number of organic
LCMS-IT-TOF in acetonitrile. The GC-mass spectra
were obtained using a Shimadzu GC-QP5050A equipped
with a J&W Scientific DB-1 column (length 30 m; ID
0.25 mm, film 0.25 mm).
solvents. The reaction can be carried out in an ionic
liquid and the product is isolated by extraction using an
organic solvent. Therefore, dissolving and retaining the
porphycene photosensitizer in an ionic liquid and the
recycled use of the solution is a promising approach in
this field. In this study, new porphycene photosensitizer
having an imidazolium cation tag was synthesized
in order to enhance the ionic liquid solubility, and its
photophysical properties and photosensitizing reaction in
ionic liquids were investigated.
Photophysical measurements
The Ff values of the porphycene were measured
using an absolute photoluminescence quantum
efficiency measurement system (Hamamatsu C9920-02)
incorporating an integrating sphere. To measure the Ff,
degassed solutions of the porphycene were prepared and
the concentration was adjusted so that the absorbance
of the solution at 337 nm would be less than 0.1. The
excitation was performed at 337 nm.
EXPERIMENTAL
The tS was determined by time-correlated single
photon counting using a HORIBA FluoroCube. A
light-emitting diode (LED) at 370 nm was used for
the excitation. The fluorescence lifetimes (tS) were
determined by curve fitting using a microcomputer. The
concentration was adjusted so that the absorbance of the
solution at 337 nm would be less than 0.1.
Reagents and apparatus
All solvents and chemicals used in the syntheses
were of reagent grade, and were used without further
purification.
2,7,12,17-tetra-n-propyl
porphycene
(H2TPrPc) and 2,7,12,17-tetra-n-propyl porphycene-3-
sulfonyl chloride (1) were synthesized as described in the
literature [6, 22]. The ionic liquids, N,N,N-trimethyl-N-
propylammonium bis(trifluoromethanesulfonyl)amide
([TMPA][TFSA]), 1-butyl-3-methyl imidazolium bis-
(trifluoromethanesulfonyl)amide ([bmim][TFSA]), and
N-methyl-N-propylpiperidinium bis(trifluoromethanesul-
fonyl)amide ([PP13][TFSA]) (Chart 1) were purchased
from Kanto Chemical Co., Inc., and dried under reduced
pressure for 1 day before use. Toluene and acetonitrile
were of spectroscopic grade (Kishida Chemical, Japan).
1,5-dihydroxynaphthalene was purchased from Nacalai-
tesque (Japan) and used as received.
The transient absorbance spectra were obtained using
a laser flash photolysis system (Unisoku TSP-1000M).
To measure the transient absorbance spectra, degassed
solutions of the porphycenes in [TMPA][TFSA] or [bmim]-
[TFSA] or acetonitrile were prepared in a glove box and the
concentration was adjusted so that the absorbance of the
solution at 532 nm would be less than 0.1. A Xe arc lamp
was employed as the source of the probe light to follow the
spectral changes. For the laser flash photolysis, a sample
was excited with 5 ns pulses (532 nm) from a Q-switched
Nd:YAG laser (Surelite I, Continuum). The time course
of the absorbance decay was analyzed by single-phase
kinetics to determine the lifetimes of the triplet state
(tT). The rate constant for the oxygen quenching (kq) was
determined from a Stern–Volmer analysis of the triplet
lifetime in degassed, air- and oxygen-saturated solutions.
The measurements for both the air- and oxygen-saturated
solutions were performed under similar conditions. The
concentration of oxygen in the acetonitrile solution in air
(0.0019 M-1) and dioxygen (0.0091 M-1) was obtained from
published oxygen solubility data [30]. The concentration
of oxygen in the [bmim][TFSA] solution in air (0.000423
M-1) and dioxygen (0.0020 M-1) were estimated from
Henry’s constant [31]. Due to the lack of a Henry’s constant
for [TMPA][TFSA] in the literature, the values were used
of that for a similar structure of an ionic liquid, N-methyl-
N,N,N-tributylammonium bis(trifluoromethanesulfonyl)-
amide, in air (0.00049 M-1) and dioxygen (0.00237
M-1) [31]. For the singlet oxygen phosphorescence
measurements, an air-saturated toluene solution containing
the sample in a quartz cell (optical path length 10 mm) was
excited at 600 nm using a HORIBA JOBIN YUON FL3-
21 at room temperature. Each FD value (3) was determined
from the slope of the plot with intensities at 1270 nm vs.
3 based on H2TPrPc as the standard (FD = 0.36) [32, 33].
The 1H, 13C and 2-D COSY NMR spectra were
recorded by a Bruker Avance 500 spectrometer installed
at the Center ofAdvanced InstrumentalAnalysis, Kyushu
University, and the chemical shifts (in ppm) were
referenced relative to the residual protic solvent peak. The
UV-vis absorption spectra were measured by a Hitachi
U-3300 spectrophotometer. The fluorescence (FL) spectra
were measured by a Hitachi F-4500 spectrophotometer
at room temperature. The IR spectra were measured by
a JASCO FT-IR 460 plus KH spectrophotometer using
KBr discs. The MALDI-TOF mass spectra were obtained
using a Bruker autoflex II with dithranol as the matrix.
The ESI-mass spectra were obtained using a Shimadzu
N+
N
N+
N+
N-
O
S
O
S
O
S
O
S
O
O
S
O
O
N-
N-
S
O
CF3
CF3
CF3
CF3
CF3
CF3
O
O
O
[bmim][TFSA]
[TMPA][TFSA]
[PP13][TFSA]
Chart 1.
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 531–536

532
H. SHIMAKOSHI ET AL.
Synthesis of imidazolium cation tag porphycene
108.89, 112.15, 113.02, 115.36 (methine CH), 122.05,
123.36, 123.55, 124.81, 125.64, 130.33, 131.30, 131.52,
133.20, 135.78, 137.64, 139.95, 140.74, 143.42, 144.02,
145.03, 150.14, 152.02, 154.16 (pyr and Im).
Bromopropylamido porphycene (2). One mL
of dry triethylamine (TEA) was added to a stirred
mixture of
a solution of 2,7,12,17-tetra-n-propyl
porphycene-3-sulfonyl chloride (1) (27 mg, 0.046
mmol) and 3-bromopropylamine hydrobromide (200
mg, 0.91 mmol) in dry THF (20 mL) over 5 min at
room temperature. The mixture was stirred for 2 h at
room temperature. The solution was evaporated under
reduced pressure and then chromatographed on silica
gel (Silica Gel 60N, spherical, neutral; column size:
f = 5 × 30 cm) using dichloromethane as the eluent.
Recrystallization from dichloromethane/n-hexane (1:1)
gave the blue compound 2 (25 mg, 79%). UV-vis and
FL (CH2Cl2): lmax, nm 375, 387, 575, 620, 656; lflu, nm
(excitation at 370 nm) 662, 722. MS (MALDI): m/z
calcd. for C35H44N5Br1O2S1, 677.2. Found 678.3 [M +
H]. Anal. calcd. for C35H44N5Br1O2S1: C, 61.94; H, 6.53;
General procedure of the photoreaction
A typical example of the photoreaction catalyzed
by a sensitizer is shown below. A 5 mL [TMPA]-
[TFSA] solution of porphycene (3) (1.0 × 10-6 M) and
1,5-dihydroxynaphthalene (3.5 × 10-3 M) was stirred in
air under irradiation of a 500 W tungsten-lamp through
a cut-off filter (TOSHIBA Y-46, ≥460 nm) for 3 h. The
progress of the reaction was monitored by absorption
at 427 nm, typical for the product, 5-hydroxy-1,4-
naphthoquinone (Juglone) [34]. After the photoreaction,
the product was extracted by dipropyl ether and the
resulting ionic liquid layer containing 3 was used for the
1
recycling reaction. Juglone: H NMR (CDCl3, 293 K):
1
N, 10.32. Found C, 61.80; H, 6.62; N, 10.05. H NMR
d, ppm 6.94 (s, 2H), 7.27 (dd, 1H), 7.60–7.65 (m, 2H),
11.90 (s, 1H, OH). GC-MS (EI): m/z 174 [M]+. A mixture
of dipropyl ether:n-hexane (2:1 v/v) and toluene:diethyl
ether:n-hexane (2:2:1, v/v/v) were used for extracting the
solvent in case of the [PP13][TFSA] and [bmim][TFSA]
reaction media, respectively.
(CDCl3): d, ppm 1.36–1.40 (m, 12H, -CH3), 1.69 (t,
3H, -CH2CH2CH2Br), 2.30–2.41 (m, 8H, b-CH2-), 2.97
(q, 2H, -CH2CH2CH2Br), 3.02 (t, 2H, -CH2CH2CH2Br),
3.89–4.36 (tx4, 8H, a-CH2-), 5.43 (t, 1H, NH), 9.11
(s, 1H, pyrrole), 9.28 (s, 1H, pyrrole), 9.56 (d, 1H,
methine), 9.61 (d, 1H, methine), 9.70 (d, 1H, methine),
9.83 (d, 1H, methine), 10.19 (s, 1H, pyrrole).
Determination of rate constant for oxidation of
1,5-dihydroxynaphthalene by 3
N-methyl 3-imidazolium-1-propylamido por-
phycene (3). To a solution of 2 (35 mg, 0.052 mmol) in
30 mL of ethanol was added 1-methylimidazole (144 mg,
1.81 mmol) under nitrogen, and solution was refluxed
for 48 h. Ammonium hexafluorophosphate (85 mg, 0.52
mmol) was then added to the solution and stirred at room
temperature. The solution was evaporated under reduced
pressure and then chromatographed on silica gel (Silica
Gel 60N, spherical, neutral; column size: f = 5 × 30 cm)
using dichloromethane/methanol (9:1) as the eluent.
Recrystallization from acetonitrile/dichloromethane
(1:1) gave the blue compound 3 (32 mg, 73%). UV-vis
and FL ([bmim][TFSA]): lmax, nm (e) 373 (95400), 384
(86100), 571 (33600), 615 (23100), 651 (37500); lflu,
nm (excitation at 371 nm) 655, 715. HR MS (ESI): m/z
calcd. for C39H50N7Br1O2S1, 680.3747. Found 680.3744
[M–PF6]. Anal. calcd. for C39H50N7F6O2P1S1: C, 56.72;
H, 6.10; N, 11.87. Found C, 56.58; H, 5.96; N, 11.82. 1H
NMR (CD3CN): d, ppm 1.29–1.40 (m, 12H, -CH3), 1.65
(t, 3H, -CH2CH2CH2-Im), 2.24–2.45 (m, 8H, b-CH2-),
2.89 (t, 2H, -CH2CH2CH2-Im), 3.05 (s, 3H, Im-CH3),
3.72 (t, 2H, -CH2CH2CH2-Im), 3.82–4.30 (tx4, 8H,
a-CH2-), 6.33 (t, 1H, NH), 6.55 (s, 1H, Im-H), 6.65
(s, 1H, Im-H), 7.35 (s, 1H, Im-H), 9.06 (s, 1H, pyrrole),
9.26 (s, 1H, pyrrole), 9.53 (d, 1H, methine), 9.57 (d, 1H,
methine), 9.75 (d, 1H, methine), 9.86 (d, 1H, methine),
10.18 (s, 1H, pyrrole). 13C NMR (CD3CN): d, ppm
14.03, 14.11, 14.22, 14.71 (-CH2CH2CH3), 25.04, 25.24,
25.84, 28.52 (-CH2CH2CH3), 29.38, 29.48, 30.05, 30.37
(-CH2CH2CH3), 29.41 (-NHCH2CH2CH2-Im), 35.60
(Im-CH3), 39.63 (-NHCH2-), 46.78 (-CH2CH2CH2-Im),
Using the change in the absorption at 427 nm, the rate
constant (k) for the 1,5-dihydroxynaphthalene oxidation
was determined using the following equation at 25
1 °C, where k is the rate constant, A427 is the absorption
at 427 nm, A∞ is the final absorption at 427 nm, t is the
irradiation time and C is a constant. The temperature was
directly determined using a thermometer on the surface
of the reaction cuvette during the UV light irradiation.
ln (A427 - A∞) = -kt + C
RESULTS AND DISCUSSION
Synthesis and optical properties of imidazolium
cation tag porphycene (3)
The
parent
porphycene,
2,7,12,17-tetra-n-
propylporphycene (H2TPrPc), is slightly soluble in ionic
liquids, such as the imidazolium or ammonium-type
ionic liquids (e.g. < 1 × 10-4 M in [bmim][TFSA]). To
enhance the solubility of porphyne in an ionic liquid,
the imidazolium cation tag was covalently attached to
the porphycene. The porphycene derivative having an
imidazolium cation tag was synthesized from H2TPrPc
as shown in Scheme 1 and was identified by elemental
analysis, UV-vis, fluorescence, NMR and high resolution
(HR)-mass spectra. The imidazolium cation tag
porphycene is soluble in a variety of ionic liquids and
hard to extract in any kind of organic solvent. This is a
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 532–536

SYNTHESIS AND PHOTOSENSITIZING PROPERTIES OF PORPHYCENE WITH IMIDAZOLIUM TAG
533
SO2Cl
HSO3Cl
N
H
N
N
N
H
N
N
H
H
N
in CH2Cl2
N
1
H2TPrPc
N
Br
N
HN
HN
O
O
S
S
O
N
N
O
(1)
Br(CH2)3NH2 HBr /TEA
in dryTHF
(2) NH4PF6
in EtOH
N
H
N
N
N
N
H
N
H
H
N
N
-
PF6
2
3
Scheme 1.
significant advantage for a catalyst used in a recycling
reaction as already described. The UV-vis absorption
and the fluorescence spectra of 3 in [TMPA][TFSA] are
shown in Figs 1a and 1b, respectively. The absorption
and fluorescence peaks of the solutions from the spectra
are listed in Table 1. The Q-type absorption bands are
red-shifted compared to those of H2TPrPc due to the
sulfonamido substitution on the porphycene ring [19, 22]
and its color changed to blue from purple of the parent
H2TPrPc. The UV-vis spectra of 3 were almost similar
in [TMPA][TFSA], [bmin][TFSA] and acetonitrile. The
fluorescence maximum in 3 was shifted to 655 nm and
the fluorescence intensity decreased compared to that
of H2TPrPc with the Ff value 0.20 (in H2TPrPc, lflu
=
641 nm, Ff = 0.36 in toluene) [32, 33]. These spectral
features were due to the sulfonamido substitution on the
porphycene ring, while the imidazolium tag provided no
significant change in the UV-vis and fluorescence spectra.
Photophysical properties of imidazolium cation tag
porphycene (3)
The lifetimes of the singlet state (ts) and the triplet state
(tT) were measured under degassed conditions in several
solvents, and the tT values were also measured under
air and oxygen to determine (kp + knr) and kq from the
Stern–Volmer analysis where kp is the phosphorescence
rate constant, knr is the rate constant of the nonradiative
decay, and kq is the rate constant of oxygen quenching.
The fluorescence rate constants (kf) are readily calculated
using the measured values, Ff and ts, as eqn. kf = Ff / ts
[18].Thesedeterminedphotophysicalparametersfor3are
Fig. 1. (a) UV-vis absorption spectrum of 3 in [TMPA][TFSA],
(b) fluorescence spectrum of 3 in [TMPA][TFSA] at the
excitation wavelength of 371 nm
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 533–536

534
H. SHIMAKOSHI ET AL.
Table 1. UV-vis absorption and fluorescence maxima for 3 in several
solvents
intensities of the 1270-nm emission by
3 were compared in acetonitrile and the
ionic liquids, and the intensities were
almost similar in these solvents except for
[bmin][TFSA] as shown in Fig. 2. Thus,
the singlet oxygen should be generated
in the ionic liquids, and we tried to use
the imidazolium cation tag porphycene as
a photosensitizer in the ionic liquids. To
investigate the photocatalytic activity of
the porphycene, the photo-oxygenation of
the 1,5-dihydroxynaphthalene was carried
out under visible light irradiation (l ≥
460 nm). As expected, the photoreaction
effectively proceeded and the oxygenated
product, 5-hydroxy-1,4-naphthoquinone
(Juglone), was quantitatively obtained
in the ionic liquids as shown in
Fig. 3, and the turnover number of the
porphycene photosensitizer was 3500.
From the UV-vis spectral changes of
the solutions, the rate constant for the
1,5-dihydroxynaphthalene oxidation was
determined to be k = 2.33 × 10-2 s-1 and
1.47 × 10-2 s-1 in acetonitrile and [TMPA]-
[TFSA], respectively. The efficiency in
Solvent
labs, nm
lflu, nma
Viscosity, cP
[TMPA][TFSA]
[bmim][TFSA]
CH3CN
373, 384, 571, 615, 651
373, 384, 570, 615, 651
371, 383, 570, 615, 651
367, 379, 559, 597, 629
655,716
658, 720
657,718
635, 688
72b
52c
0.345
0.345
CH3CNd
aExcitation at 371 nm. bViscosity value (cP) was obtained from Kanto
Chemical Co., Inc. cData from Ref. 36. dData for H2TPrPc.
Table 2. Photophysical parameters of 3 in several solventsa
Solvent
Ffb ts, nsc tt, usd kf /107s-1 kp + knr/104 s-1 kq/109 M-1,S-1
[TMPA][TFSA] 0.20 7.8
[bmim][TFSA] 0.20 8.0
825
660
142
2.6
2.5
2.6
0.12
0.16
0.58
3.3
4.2
3.4
CH3CN
0.18 7.0
aFluorescence quantum yield (Ff), lifetime of the singlet (ts), lifetime of the
triplet (tT), the fluorescence rate constant (kf), the phosphorescence rate
constant (kp), the rate constant for nonradiative decay (knr), the oxygen
quenching rate constant (kq). bExcitation at 337 nm. cExcitation at 370 nm.
dExcitation at 532 nm.
the ionic liquid was lower than that in acetonitrile. The
low efficiency in the ionic liquid is probably caused by
the low oxygen solubility in the ionic liquid and its high
viscosity: [TMPA][TFSA], 72 cP; acetonitrile, 0.345 cP
at 298 K [35, 36]. The advantage of the ionic liquid in the
photoreaction is the recycled use of the solution retaining
the porphycene. After extraction of the product from the
ionic liquid layer by an organic solvent, the imidazolium
tag porphycene stably remained in the ionic liquid. The
reaction proceeded with almost the same efficiency in the
3rd run, and the porphycene in the ionic liquid did not
summarized in Table 2. The fluorescence quantum yields
and lifetimes of the singlet state slightly increased in an
ionic liquid compared to those observed in acetonitrile,
whereas the lifetimes of the triplet state under degassed
conditions were quite different in the ionic liquids and
acetonitrile of tt = 825 ms, 660 ms and 142 ms in [TMPA]-
[TFSA], [bmim][TFSA] and acetonitrile, respectively.
The significant increase in the tt value in [TMPA][TFSA]
and [bmim][TFSA] were explained by the increase in the
medium viscosity (71 cP at 298 K for [TMPA][TFSA],
52 cP at 298 K for [bmim][TFSA]). Restriction of the
intramolecular motion in a viscous medium should lead
to a decrease in the nonradiative decay process with the
relatively small kp + knr value to be kp + knr = 0.12 × 104 s-1,
0.16 × 104 s-1 and 0.58 × 104 s-1 in [TMPA][TFSA],
[bmim][TFSA] and acetonitrile (0.345 cP at 298 K),
respectively.
Photocatalysis of imidazolium cation tag porphycene
with singlet oxygen generation (3)
The quantum yield of the singlet oxygen generation
(FD) for 3 was determined by the phosphorescence at
1270 nm in an air-saturated toluene solution. The values
were determined by comparing the emission intensity of
the standard H2TPrPc (FD = 0.36) of 0.28 [32, 33]. Though
similar emissions were observed in the ionic liquids,
[bmim][TFSA] or [TMPA][TFSA] or [PP13][TFSA], we
could not determine the exact quantum yields in these
ionic liquids because of nostandard values (reference
photosensitizers) in the ionic liquids. Alternatively, the
Fig. 2. Phosphorescence spectra of singlet oxygen sensitized by
3 (4.7 × 10-6 M) in air-saturated solutions at room temperature
with excitation at 600 nm
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 534–536

SYNTHESIS AND PHOTOSENSITIZING PROPERTIES OF PORPHYCENE WITH IMIDAZOLIUM TAG
535
(JSPS). We thank Prof. N. Nakashima and Prof. T.
Fujigaya, Kyushu University, for helping to measure
the photoluminescence spectra. We also thank Dr. M.
Kanakubo, National Institute of Advanced Industrial
Science and Technology, for his helpful discussion.
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Fig. 3. Oxidation of 1,5-dihydroxynaphthalene in various ionic
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undergo any bleaching during the reaction. Interestingly,
the reaction was dependent on the type of ionic liquid,
and the quaternary ammonium-type ionic liquids,
[TMPA][TFSA] and [PP13][TFSA] had good results
as shown in Fig. 3. In contrast, the imidazolium cation-
type ionic liquid, [bmim][TFSA], showed a low yield
for the product of ca. 60%. The finding described here
is a guideline for using an ionic liquid as a photoreaction
medium.
CONCLUSION
Porphycene having an imidazolium cation tag was
synthesized, and the photophysical parameters of the
porphycene were determined in ionic liquids. The
imidazolium cation tag porphycene generated singlet
oxygen during visible light irradiation and shows a
photosensitizing activity for the oxidation of an organic
compound. The photooxidation reactions efficiently
proceeded in an ammonium-type ionic liquid with the
imidazolium cation tag porphycene and can be recycled
without any loss of activity.
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This study was partially supported by the Global
COE Program “Science for Future Molecular Systems,”
a Grant-in-Aid for Scientific Research on Priority Areas
(452) and Innovative Areas (2204) from the Ministry
of Education, Culture, Sports, Science and Technology
(MEXT) of Japan, and a Grant-in-Aid for Scientific
Research (C) (No. 23550125) and (A) (No. 21245016)
from the Japan Society for the Promotion of Science
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