Synthesis of alkylthio substituted pyridoporphyrazines and their photophysicochemical properties

Article abstract of DOI:10.1142/S1088424617500626

Phthalocyanine and their related compounds are utilized as various applications, such as photosensitizing agents for photodynamic therapy of cancer. In this study, zinc bis(thiodidecylbenzo)-bis(pyrido)porphyrazines, especially zinc bis(1,4-didecylthioben

Full text of DOI:10.1142/S1088424617500626

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2017; 21: 1–7
DOI: 10.1142/S1088424617500626
Published at http://www.worldscinet.com/jpp/
Synthesis of alkylthio substituted pyridoporphyrazines
and their photophysicochemical properties
Keiichi Sakamoto*a,b◊, Shouta Watabiki , SatoruYoshino and Tomoe Komoriya
b
a
a
a
Department of Sustainable Engineering, College of Industrial Technology, Nihon University,
1
-2-1 Izumi-cho, Narashino-shi, Chiba-ken 275-8575, Japan
b
Academic Major of Applied Molecular Chemistry, Graduate School of Industrial Technology, Nihon University,
1
-2-1 Izumi-cho, Narashino-shi, Chiba-ken 275-8575, Japan
Received 12 September 2017
Accepted 19 October 2017
ABSTRACT: Phthalocyanine and their related compounds are utilized as various applications, such as
photosensitizing agents for photodynamic therapy of cancer. In this study, zinc bis(thiodidecylbenzo)-
bis(pyrido)porphyrazines, especially zinc bis(1,4-didecylthiobenzo)-bis(3,4-pyrido)porphyrazine and
zinc bis(1,4-didecylthiobenzo)-bis(2,3-pyrido)porphyrazine were synthesized. Quaternation of the
pyridine nitrogen in these provides an amphiphilic property. Photoexcited triplet lifetime of synthesized
and quaternized zinc bis(1,4-didecylthiobenzo)-bis(3,4-pyrido)porphyrazine and zinc bis(1,4-didecyl-
thiobenzo)-bis(2,3-pyrido)porphyrazine were reported using laser-flash photolysis and singlet oxygen
quantum yields by the 1,3-diphenylisobenzofurne method.
KEYWORDS: pyridoporphyrazine, quaternation, laser-flash photolysis, triplet lifetime, PTDF method.
of phthalocyanines and their related compounds can be
INTRODUCTION
utilized for both phototherapy and photovoltaic cells.
Phthalocyanines and their related compounds possess
Phthalocyanines and their related compounds are
similar molecular structures as porphyrins.They are known
particularly known to have potential as photosensitizers of
to be used as important colorants since their discovery, and
photodynamic therapy of cancer (PDT) [2, 4–8]. Phthalo-
have attracted attention as functional materials for various
cyanines and their related compounds used for PDT are
applications such as catalysts, laser light absorbers in data
required to have long life-time triplet states and show
storage systems, electron-charge carriers in photocopiers,
strong absorption of far red light between 600 and 800 nm,
photoconductors in chemical sensors, photo-antenna
values of wavelengths which have a greater penetration of
devices in photosynthesis, photovoltaic cells and photo-
sensitizers [1–3]. For these the applications, the absorp-
tion maximum of phthalocyanines and their related
compounds must be moved to the near-infrared region
tissue and satisfactory photosensitization of singlet oxygen
[2]. In general, it is known that phthalocyanines and their
related compounds having no-substituents are insoluble
in common organic solvents. Insolubility of unsubstituted
phthalocyanines and their related compounds present greater
problems for use as photosensitizers in PDT. The short-
comingofphthalocyaninesandtheirrelatedcompoundscan
be overcome by introduction of substituents such as alkyl
or aryl groups onto the ring system of the phthalocyanine.
Alkyl or aryl substituted phthalocyanines and their related
compounds become a lipophilic property [9, 10].
At present, photosensitizers for PDT in medical
institutions have been using hematoporphyrins, which
possess a few weak points such as shorter absorption
maxima around 500 nm, lower metabolization rates and
[1–3]. When this occurs, the photosensitization properties
◊SPP full member in good standing
Correspondence to: KeiichiSakamoto, email: sakamoto.keiichi@
*
nihon-u.ac.jp. tel: +81 47-474-2554, fax: +81 47-474-9759.
This is an open access article published by World Scientific
Publishing and distributed under the terms of the Creative
Commons Attribution (CC BY) 4.0 License, which permits
use, distribution and reproduction in any medium, provided the
original author(s) and source are credited.
Copyright © 2017 The Author(s)

2
K. SAKAMOTO ET AL.
a side effect of dermatitis solaris. In contrast, phthalo-
cyanines and their related compounds exhibit suitable
properties for PDT photosensitizers and they show no
cytotoxity when no light is irradiated [2].
The strongest absorption maxima of phthalocyanines
and their related compounds in visible region called the
Q band can be moved by bathochromic effect to introduce
an electron-donating substituent at a non-peripheral (1, 4,
(KBr) pellets and a Perkin-Elmer Spectrum 65 FT-IR
spectrometer by an attenuated total reflection (ATR)
method. UV-vis spectra were measured on a Shimazdu
UV-2400PC spectrometer. Each sample was prepared at
-5
1.0 × 10 M in chloroform (CHCl ) or N,N-dimethyl-
3
formamide (DMF). Fluorescent spectra were recorded at
-
5
1.0 × 10 M in CHCl on a Nihon Bunko Jasco FP-6600
3
1
spectrofluorometer. The proton magnetic resonance ( H
8
, 11, 15, 18, 22, 25) position. For PDT photosensitizers,
NMR) spectra were measured on a Bruker Advance 400s
and a Bruker Advance III 500 in dimethyl sulfoxide
(DMSO)-d or CHCl -d using tetramethylsilane (TMS)
the absorption maxima of phthalocyanines and their
related compounds are best when moved to the near-
infrared region [2, 9].
6
3
as the internal standard. Elemental analysis was carried
out using a Perkin-Elmer 2400CHN instrument. Mass
(MS) spectra were taken with a Nihon Denshi Joel
JMS-AX500 mass spectrometer. Melting points were
measured with a Stanford research system MPA 100
optimelt automated system. The molecular orbital
calculation was achieved in order to obtain the allowed
highest occupied molecular orbital (HOMO) — lowest
unoccupied molecular orbital (LUMO) energy level with
MOPAC 2016. Photoexcited triplet lifetime was observed
using Laser-flash photolysis (Tokyo Instruments) at 1.5 ×
As phthalocyanine-related compounds, zinc bis-
(didecylthiobenzo)-bis(pyrido)porphyrazines have been
synthesized by cross cyclotetramerization from 3,6-
didecylthiophthalonitrile and 3,4-dicyanopyridine or
2,3-dicyanopyridine for 1:1 mol ratio.The phthalocyanine
related compounds containing a pyridine ring in place
of one or more of benzenoid rings are interesting com-
pounds because quaternation of pyridine nitrogen is
expected to confer solubility in an aqueous media [2, 11].
Furthermore, the authors have reported that the length of
triplet lifetime alkylbenzopyridoporphyrazines increased
with the number of pyridine rings in the molecule [2].
Moreover, Shinokubo and co-workers reported that the
ultraviolet-visible (UV-Vis) spectra of N-heterocyclic
compounds shifted to longer wavelengths [12].
Zinc bis(1,4-didecylbenzo)-bis(2,3-pyrido)porphyra-
zines exhibited solubility in organic solvents [9, 13] and
was expected to show a tumor affinity. Then, quaternation
of the pyridine nitrogen in zinc bis(thiodidecylbenzo)-
bis(pyrido)porphyrazines were conferred solubility in an
aqueous media. Thus, the quaternation of metal bis(1,4-
didecylbenzo)-bis(2,3-pyrido)porphyrazines provided an
amphiphilic property [9, 13].
-
5
10 MinCHCl .Singletoxygenquantumyields(F )were
3
D
estimated by DPBF method using zinc phthalocyanine
as standard material for FD = 0.67 [5]. Compounds 5
and 6 containing DPBF as a singlet oxygen quencher in
1.7 mL of 3 × 10 M DMF solution was irradiated at
635 nm Laser (2 mW) for 10 s, 6 times.
Std
-5
Materials
All chemicals were purchased from Aldrich, Tokyo
Chemical Industry or Wako Chemicals. They were used
as received without further purification. For chromato-
graphic separation, silica gel was used (60, particle
size 0.063–0.200 nm, 7734-grade; Merck). Thin-layer
chromatography (TLC) was performed using Merck 60
F254 silica gel.
Non-peripheral thio-substituted metal phthalocyanines
were synthesized [1–3, 13, 14]. They displayed Q band peaks
between 780 and 860 nm. The Q band of thio-substituted zinc
phthalocyanines appeared at around 800 nm [1–3, 13, 14].
Currently, asymmetric phthalocyanines are synthe-
sized in order to achieve a shift of the absorption maxima
towards the near-infrared region [15–17].
Synthesis of phthalocyanine-related compounds
and their intermediates
The synthetic route to zinc bis(1,4-thiodidecylbenzo)-
bis(3,4-pyrido)porphyrazine (5) and zinc bis(1,4-thiodi-
decylbenzo)-bis(2,3-pyrido)porphyrazine (6) is shown in
Scheme 1. Target compounds 5 and 6 were synthesized
by cross cyclotetramerization between 3,6-bis(decylthio)
phthalonitrile (2), which was prepared using phthalonitrile-
We report herein synthesis of zinc bis(1,4-didecyl-
thiobenzo)-bis(3,4-pyrido)porphyrazine (5) and zinc bis-
(1,4-didecylthiolbenzo)-bis(2,3-pyrido)porphyrazine (6).
We also report their photophysicochemical properties
obtained from photoexcited triplet lifetimes using laser-
flash photolysis and singlet oxygen quantum yields by
the 1,3-diphenylisobezofurane (DPBF) method.
3,6-ditrifluoromethanesulfate (1), and 3,4-dicyanopyridine
(3) or 2,3-dicyanopyridine (4).
Preparation of phthalonitrile-3,6-ditrifluorometh-
anesulfate (1). Compound 1 was synthesized in accor-
dance with our previous report [3]. The crude product
was recrystallized from dichloromethane to afford 1
EXPERIMENTAL
(
0
6.35 g, 50%) as colorless needles. Found: C, 28.32%; H,
Equipment
.48%; N, 6.59%. Calcd. for C H F N S O : C, 28.31%;
1
0
2
6
2
2
6
Infrared (IR) spectra were recorded on a Shimadzu
IR-8400A spectrometer using potassium bromide
H, 0.48%; F, 26.87%; N, 6.60%; O, 22.63%; S, 15.12%.
IR (ATR): cm 3115 (vC-H), 2550 (vC-N), 1601 (vC-C), 1472
-1
Copyright © 2017 The Author(s)
J. Porphyrins Phthalocyanines 2017; 21: 2–7

SYNTHESIS OF ALKYLTHIO SUBSTITUTED PYRIDOPORPHYRAZINES AND THEIR PHOTOPHYSICOCHEMICAL
3
CF3
C10H21
O
S
O
S
O
O
S
O
C10H21
S
S
OH
OH
F3C
O
CF3
O
N
C10H21 SH
CN
CN
O
O
CN
CN
CN
N
Zn
N
C10H21
S
N
N
N
Py, CH2Cl2
K2CO3, DMSO
R.T., 24 h
CN
ZnCl2
N
N
O
S
S
-
78 to R.T, 24 h
N
DBU, 1-PeOH
S
C10H21
O
C10H21
CF3
160°C, 7 h
N
1
2
S
C10H21
5
COOH
COOH
COOC2H5
COOC2H5
COONH2
CN
CN
N
N
N
N
C10H21
S
COONH2
3
N
Zn
N
N
C10H21
S
N
N
N
COOH
COOH
N
COOC2H5
COOC2H5
N
COONH2
COONH2
N
CN
CN
ZnCl2
N
N
N
N
S
C10H21
DBU, 1-PeOH
N
4
1
60°C, 7 h
S
C10H21
6
Scheme 1. Synthetic pathway of zinc bis(1,4-didecylthiobenzo)-bis(pyrido)porphyrazines
(
vC-C), 1439 (vC-C), 1134 (vS=O). 1H NMR (500 MHz,
6, mixtures 2 and 4 for 1 (0.24 g, 0.6 mmol):1 (0.08 g,
0.6 mmol) mol ratio, respectively, were dissolved in
pentanol (1-PeOH) (10 mL) and zinc chloride (ZnCl2)
(0.10 g) was added. The mixture was refluxed for 3 h in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as
a catalyst.After cooling, the reaction mixture was dissolved
in toluene (50 mL) and the solution filtered. The solvent
was removed by evaporation. The products were separated
and purified by silica gel column chromatography.
DMSO-d ): d, ppm 8.44 (s, 2H). MS (FAB): m/z found
3
6
96, calcd. 396.26.
Preparation of 3,4-dicyanopyridine (3) and 2,3-dicya-
nopyridine (4). Compounds 3 and 4 were prepared from
pyridine-3,4-dicarboxylic acid (cinchomeronic acid) and
pyridine-2,3-dicarboxylic acid (quinolinic acid), respec-
tively by esterification, amidation and dehydration [2].
Product 3 was purified by chromatography over silica
gel, (1.97 g, 17%), m.p. 81°C. Found: C, 65.12%; H,
Compound 5 was a bluish green solid (0.51 g, 25%).
Found: C, 65.59%; H, 7.63%; N, 11.26%. Calcd. for
C H N S Z : C, 65.58%; H, 7.62%; N, 11.25%; S,
2
2
.34%; N, 32.56%. Calcd. for C H N : C, 65.11%; H,
7 3 3
-
1
.34%; N, 32.55%. IR (KBr): cm 3090 (nC-H), 2240
68
94 10
4
n
-1
(
7
nC-N), 1600 (nC-C), 1550 (nC-C), 1470 (nC-C), 1220 (dC-H),
10.30%; Zn, 5.25%. IR (KBr): cm 3030 (nC-H), 2990
(nC-H), 2930 (nC-H), 1600 (nC-C), 1510 (nC-C), 1490
(nC-C), 690 (n ). H NMR (500 MHz, DMSO-d ): d, ppm
1
50 (dC-H). H NMR (400 MHz, DMSO-d ): d, ppm 9.09
6
1
(
1
s, 1H), 7.75 (s, 1H), 7.26 (s, 1H). MS (FAB): m/z found
C-s
6
29, calcd. 129.13.
Product 4 was purified by chromatography over silica
9.03–7.35 (m, 10H), 4.52–0.82 (m, 40H). MS (FAB): m/z
found 1245, calcd. 1245.41.
gel, m.p. 85°C. Found: C, 65.11%; H, 2.33%; N, 32.56%.
Compound 6 was a bluish green solid (0.50 g, 25%).
Found: C, 65.51%; H, 7.59%; N, 11.22%. Calcd. for
C H N S Zn: C, 65.58%; H, 7.62%; N, 11.25%;
Calcd. for C H N : C, 65.11%; H, 2.34%; N, 32.55%. IR
7
3
3
-
1
(
KBr): cm 3090 (nC-H), 2240 (nC-N), 1600 (nC-C), 1550
68
94 10 4
1
-1
(
nC-C), 1470 (nC-C), 1220 (dC-H), 750 (dC-H). H NMR (400
S, 10.30%; Zn, 5.25%. IR (KBr): cm 3030 (nC-H),
2990 (nC-H), 2930 (nC-H), 1600 (nC-C), 1510 (nC-C), 1490
MHz, DMSO-d ): d, ppm 8.92 (s, 1H), 8.91 (s, 1H), 8.33
6
1
(
s, 1H). MS (FAB): m/z found 129, calcd. 129.13.
(nC-C), 690 (n ). H NMR (500 MHz, DMSO-d ): d, ppm
C-s
6
Preparation of zinc bis(1,4-didecylthiobenzo)-bis-
9.10–7.31 (m, 10H), 4.50–0.75 (m, 40H). MS (FAB): m/z
(pyrido)porphyrazines (5) and (6). Phthalocyanine related
found 1245, calcd. 1245.41.
compounds, zinc bis(1,4-didecylthiobenzo)-bis(3,4-pyrido)-
porphyrazine 5 and zinc bis(1,4-didecylthiobenzo)-
bis(2,3-pyrido)porphyrazine 6 were prepared by cross
cyclotetramerization of intermediate 2, with 3 or 4. In
the experimental procedure for 5, mixtures 2 and 3 for
Quaternization of phthalocyanine related
compounds (7) and (8)
Phthalocyanine-relatedcompounds5and6werequater-
1
(0.24 g, 0.6 mmol):1 (0.08 g, 0.6 mmol) mol ratio, for
nized with pyridine nitrogen in using dimethyl sulfate
Copyright © 2017 The Author(s)
J. Porphyrins Phthalocyanines 2017; 21: 3–7

4
K. SAKAMOTO ET AL.
C10H21
S
2+
C10H21
S
CH3
N
N
N
N
Zn
N
C10H21
S
C10H21
S
N
N
N
N
N
N
N
N
Zn
N
N
Dimethyl sulfate,DMF
53°C, 2h
N
N
N
2SO42-
S
C10H21
S
C10H21
1
N
N
H3C
S
S
C10H21
5
C10H21
7
C10H21
S
2+
C10H21
S
N
N
N
C10H21
S
N
N
N
N
C10H21
S
CH3
N
N
N
N
N
N
Zn
N
N
Dimethyl sulfate,DMF
153°C, 2h
2SO 2-
N
N
Zn
N
4
S
C10H21
N
H3C
S
C10H21
N
S
S
C10H21
6
C10H21
8
Scheme 2. Synthesis of quaternized zinc bis(didecylthiobenzo)-bis(pyrido)porphyrazines
to obtain compounds 7 and 8, respectively. The quater-
nization route is shown in Scheme 2. A typical quater-
nization procedure is as follows: compounds 5 or 6
RESULTS AND DISCUSSION
Synthesis
(
1
0.18 g, 0.15 mmol) were reacted with DMSO (0.2 g,
/55 mmol) in DMF (5 mL) at 153°C for 2 h. After
reaction, the reaction mixture was dissolved in acetone
20 mL), cooled to room temperature and the solution
Synthetic routes of the target compounds 5 and 6, and
their intermediates 1–4 are summarized in Scheme 1.
The target compound zinc bis(didecylthiobenzo)-
bis(pyrido)porphyrazines were synthesized by cross
cyclotetramerization between their intermediates 3,6-
bis(decylthio)phthalonitrile (2) and 3,4-dicyanopyri-
dine (3) or 2,3-dicyanopyridine (4). Intermediate 2 was
synthesized from phthalonitrile-3,6-ditrifluorometh-
anesulfate (1) and decanethiol. Intermediate 1 was
synthesized from 2,3-dicyanohydroquinone and trifluoro-
methanesulfonic anhydride for 24 h in accordance
with a description from the literature [3]. The other
intermediates 3 and 4 were synthesized from pyridine-
3,4-dicarboxylic acid (cinchomeronic acid) and pyridine-
2,3-dicarboxylic acid (quinolinic acid), respectively, via
their diethyl ether and diamide. The intermediates 1 to 4
(
filtered. The solvent was removed. The products were
purified by TLC (eluent: tetrahydrofuran–toluene, 8:2).
Each product was recovered by being scraped from
the TLC plate, dissolved in pyridine (py), the solution
filtered, and the solvent removed. (a) Compound 7
prepared from 5: dark blue solid (yield 30%). Found: C,
6
5.93%; H, 8.01%; N, 11.11%. Calcd for C H N S Zn:
70 100 10 4
C, 65.91%; H, 7.92%; N, 10.98%, S, 10.05%; Zn, 5.18%.
-
1
IR (KBr): cm 3030 (nC-H), 2990 (nC-H), 2930 (nC-H), 1600
1
(
nC-C), 1510 (nC-C), 1490 (nC-C), 690 (n ). H NMR (500
C-s
MHz, DMSO-d ): d, ppm 9.03–7.35 (m, 10H), 4.52–0.82
m, 40H), 1.05–0.80 (m, 6H). MS (FAB): m/z found
6
(
1275, calcd. 1275.49. (b) Compound 8 prepared from 6:
1
dark blue solid (yield 25%) Found: C, 65.89%; H, 7.94%;
N, 10.86%. Calcd for C H N S Zn: C, 65.91%; H,
were analyzed using IR, H NMR and MS spectra and
elemental analysis. Their analytical data showed good
agreement with the proposed structure.
7
0
100 10 4
7
.92%; N, 10.98%, S, 10.05%; Zn, 5.18%. IR (KBr):
-
1
cm 3030 (nC-H), 2990 (nC-H), 2930 (nC-H), 1600 (nC-C),
The target compounds zinc bis(1,4-didecylthiobenzo)-
bis(3,4-pyrido)porphyrazine (5) and zinc bis(1,4-
didecylthiobenzo)-bis(2,3-pyrido)porphyrazine (6) were
synthesized respectively from 3 and 4 with 2 and ZnCl2
in the presence of DBU as a catalyst by refluxing in
1
1
510 (nC-C), 1490 (nC-C), 690 (n ). H NMR (500 MHz,
C-s
DMSO-d ): d, ppm 9.10–7.31 (m, 10H), 4.50–0.75 (m,
6
40H). 1.08–0.75 (m, 6H). MS (FAB): m/z found 1276,
calcd. 1275.49.
Copyright © 2017 The Author(s)
J. Porphyrins Phthalocyanines 2017; 21: 4–7

SYNTHESIS OF ALKYLTHIO SUBSTITUTED PYRIDOPORPHYRAZINES AND THEIR PHOTOPHYSICOCHEMICAL
5
1
-PeOH. The products were isolated using column
The strongest absorption of phthalocyanines is
detected in the visible region between the 650 and
690 nm, Q band, and in UV between 320 and 370 nm,
called the Soret band. A typical value for the extinction
coefficient (e) of the Q band is around 10 cm mol .
The Q band is attributed to the allowed HOMO–LUMO,
p-p* transition of the phthalocyanine ring. The log e for
the Q band of 5 and 6 is estimated to be around 5.
In our previous study, the Q bands of unsubstituted
zinc phthalocyanine and zinc 1,4,8,11,15,18,22,25-
octakis(didecylocytobenzo)phthalocyanine showed at
650 (see Table 1) and 792 nm [3]. With regard to
UV-Vis spectra, the Q band of compound 5 shows 676
nm, which is shifted by 26 nm to longer wavelengths in
comparison to unsubstituted zinc phthalocyanine, while
in the case of compound 6, the Q band shows 646 nm,
then no bathochromic effect is observed. The Q band
shift of compound 5 depends upon the change in the
electron distribution in the phthalocyanine ring caused
by thioalkyl groups and nitrogen atoms in pyridine rings.
Whereas in the case of compound 6, it is thought that the
position of nitrogen atoms in pyridine rings counteracts
the bathochromic effect of thiodidecyl groups.
chromatography on silica gel with CHCl and py as
eluent. The target compounds 5 and 6 were analyzed
using elemental analysis, IR, H NMR and MS spectra.
The analytical data showed good agreement with the
proposed structures.
In general, phthalocyanines and their related
compounds can be prepared from cyclotetramerization
of the appropriate phthalic acid derivatives such as
the anhydride, amide or dinitrile. Undoubtedly, the
obtained phthalocyanines and their related compounds
were composed of only one constituent, while on the
other hand, it is thought that target compounds zinc
bis(didecylthiobenzo)-bis(pyrido)porphyrazines 5 and
3
1
5
2
-1
6
, synthesized from mixed raw materials by cross
cyclotetramerization, were prepared as a mixture of
products which have different number of pyridine rings
in the molecule. The authors previously reported that
alkylbenzopyridoporphyrazine synthesized from mixed
raw materials has desired molecular structure for its main
constituents [11].
As reported earlier, it was expected that the zinc
bis(didecylthiobenzo)-bis(pyrido)porphyrazines 5 and
6
prepared by cross cyclotetramerization of mixed
The shapes and maximum wavelength (lmax) of
UV-Vis spectra correspond to almost the same excitation
materials would have the proposed molecular structure
in accordance with the stoichiometric coefficient. As
the synthesized 5 and 6 were purified by TLC (eluent:
toluene), each product had only one constituent. These
results mean that the 5 and 6 have a proposed structure
in accordance with the stoichiometric ratio. Of course,
each compound is a mixture of five regioisomers which
possess two pyridine rings and two non-peripheral
substituted benzenoid rings at different locations in the
molecules as previously reported [11]. In Scheme 1,
typical molecular structures of 5 and 6 are described.
maxima (l ). Then fluorescence maxima (Fmax) of 5 and
ex
6 appeared 741 and 702 nm, respectively. The difference
between lmax or l and F showed to be approximately
ex
max
60 nm in the case of 5 and 6. Fluorescence is reflected as
aromatic double-bonded with a high degree of resonance
stability. The same as Fmax signifies dependence on the
p electron environment. In the case of phthalocyanines,
the Stokes shift overlaps with the wavelength at which
fluorescence occurs, since the structure of the molecule
changes little between the grand and excited electronic
states due to the rigid structure [13]. In the case of
target compounds 5 and 6, the molecular transformation
depends upon their structures between electron transitions
because their constitutions exhibit flexibility as a result
of thioalkyl substituents in its molecule.
Photochemical property
The fluorescence spectrum of a compound is generally
known to be the mirror image of its UV-Vis spectrum.
The difference between absorption maxima of UV-Vis
or excitation spectra and peak of fluorescence spectra is
known as the Stokes shift.
Photophysical property
UV-Vis, excitation and fluorescence spectral data of
compounds 5, 6 and reference compounds are shown in
Table 1.
Fluorescence peaks and transient decays were
-5
observed upon pulsed excitation (355 nm) in 1.5 × 10 M
CHCl solution. The transient absorption was reasonably
3
Table 1. UV-Vis, excitation and fluorescence spectral data of target compounds 5 and 6
Compound
Q Band
Excitation Fluorescence
Stokes shift
7
41
Log e
5.154
5.186
5.551
lex/nm
650
Fmax/nm
669
DStokes/nm
Zinc phthalocyanine
702
676
646
19
65
56
5
6
676
741
646
702
1
,4,8,11,15,18,23,35-Octakis(didecylthio-
7
83
4.2
Ref. 3
benzo)phthalocyanine
Copyright © 2017 The Author(s)
J. Porphyrins Phthalocyanines 2017; 21: 5–7

6
K. SAKAMOTO ET AL.
Table 2. Photophysical parameters of target compounds
5
and 6
Compound
Triplet lifetime /ms
FD
Zinc phthalocyanine
0.4
1.2
1.2
0.64
0.43
0.43
5
6
assigned to the triplet state. The strongest fluorescence
was quenched by oxygen for laser flash excitation of
5
60nm.Asimilardecaycurvewasobtainedforcompound
6. Transient absorptions were reasonably assigned to the
triplet state. The strongest fluorescence was quenched by
oxygen for the laser-flash excitation of 560 nm.
The photoexcited triplet state lifetimes of 5 and 6
are shown in Table 2. The photoexcited triplet state
Fig. 1. A typical spectrum for the determination of singlet
oxygen quantum yield of compound 5 in DMF using DPBF as
a singlet oxygen quencher
lifetime of 5 and 6 were estimation to be around 1.2 ms.
of compounds (5 and 6) and zinc phthalocyanine was
the standard, respectively. Symbols Iabs and Iabs are
compounds (5 and 6) and zinc phthalocyanine.
1
Photooxidation progresses via singlet oxygen ( O ) in the
Std
2
presence of phthalocyanines and their related compounds
as a photosensitizer [2]. Phthalocyanines and their related
UV-Vis spectra for determination of F compound 5
D
compounds include compounds 5 and 6 in the excited
using DPBF shown in Fig. 1. Absorption bands appeared
at 416 and 676 nm for DPBF and the Q band of compound
3
triplet state react with ground triplet state oxygen ( O ).
2
Non-transition metal phthalocyanines, especially
aluminium and zinc, are excellent photosensitizers for
5
4
, respectively. The intensity of the DPBF peaks at
16 nm decreased with increasing elapsed time, while
the type II mechanism because they exhibit high triplet
no change was observed for the Q band of 5 at 676 nm
during FD measurements. The DPBF absorbance at
416 nm was decreased in proportion to the elapsed time.
The relationship is shown in the inset in Fig. 1. The FD
of compound 5 was estimated to be 0.43, which had a
lower value than the standard zinc phthalocyanine (0.64,
1
lifetimes and give high quantum yields for O formation
2
1
[
2, 3, 9, 13]. The O reacts with a substrate to produce
2
oxide in accordance with the type II mechanism [2].
The photochemistry of target compounds 5 and 6 results
in the same process of the above-mentioned type II
mechanism shown in Equations 1–3.
Table 2). The F value is considered to be sufficient to
D
utilize as a photosensitizer for PDT [5, 8]. A similar
hv
observation was obtained for compound 6.
Compound 5 and 6  → Singlet state of 5 and 6
(1)
Intersystem crossing

Quaternization of compounds 5 and 6
 → Triplet state of 5 and 6
Compounds 5 and 6 were reacted with a quaternizing
agent such as dimethyl sulfate in DMF as solvent at
153°C for 2 h (Scheme 2). Yields of quaternized zinc
bis(1,4-didecylthiobenzo)-bis(3,4-pyrido)porphyrazines
3
1
Triplet state of 5 and 6 + O → Compound5 and 6 + O
2
2
(
(3)
2)
1
O + substrate → substrate oxide
2
(7) and quaternized zinc bis(1,4-didecylthiobenzo)-
bis(2,3-pyrido)porphyrazines (8) were 30 and 25%,
respectively. The quaternized compounds 7 and 8 were
analyzed using IR and H NMR spectra. Their analytical
The F were estimated using Equation 4, in which F
D
D
indicates the potential of the photosensitizer in applications
where singlet oxygen is required in a type II mechanism.
The values of FD were determined in air with zinc
phthalocyanine as the standard material, and DPBF was
used as chemical quencher for singlet oxygen. An efficacy
of singlet oxygen quenching is monitored by decrease of
DPBF peak intensity at 416 nm on UV-Vis spectra.
1
data showed good agreement with the proposed structure.
Acknowledgements
We thank our students, Mr. Yuma Sakaguchi and Miss
Yumiko Igarashi for their experimental assistance.
Std
abs
RI
Std
Φ∆ = Φ∆
(4)
Std
R I
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abs
Std
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D
Std
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Copyright © 2017 The Author(s)
J. Porphyrins Phthalocyanines 2017; 21: 6–7

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J. Porphyrins Phthalocyanines 2017; 21: 7–7