Synthesis and catalytic performance of a soluble asymmetric zinc phthalocyanine

Article abstract of DOI:10.1080/00958972.2019.1578878

The soluble asymmetric phthalocyanine (Pc) (ZnPc-OH) was synthesized and used as a photosensitizer to degrade water pollutants. The catalytic ability of zinc Pc was proved by degrading Rhodamine B. In addition, ZnPc-OH, which has good solubility, can be u

Full text of DOI:10.1080/00958972.2019.1578878

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis and catalytic performance of a soluble
asymmetric zinc phthalocyanine
Shanlei Guo, Dongni Li, Bo Gao, Yanhui Li, Haotian Zhang, Yanwei Li & Qian
Duan
To cite this article: Shanlei Guo, Dongni Li, Bo Gao, Yanhui Li, Haotian Zhang, Yanwei Li & Qian
Duan (2019): Synthesis and catalytic performance of a soluble asymmetric zinc phthalocyanine,
Journal of Coordination Chemistry, DOI: 10.1080/00958972.2019.1578878
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Synthesis and catalytic performance of a soluble asymmetric zinc
phthalocyanine
SHANLEI GUO#†, DONGNI LI#†‡, BO GAO*†§, YANHUI LI†, HAOTIAN ZHANG†, YANWEI LI†
and QIAN DUAN*†§
†
School of Materials Science and Engineering, Changchun University of Science and Technology,
989 Weixing Road, Changchun 130022, China
Department of Blood Transplantation, China–Japan Union Hospital of Jilin University, Jilin University,
26 Xiantai Street, Changchun, 130033, China
7
‡
1
§
Engineering Research Center of Optoelectronic Functional Materials, Ministry of Education,
Changchun 130022, China
The soluble asymmetric phthalocyanine (ZnPc-OH) was synthesized and used as a
photosensitizer to degrade water pollutants. The catalytic ability of zinc phthalocyanine was
proved by degrading Rhodamine B (RhB). In addition, ZnPc-OH, which has good solubility, can
also be used in photodynamic therapy.
Keywords: Zinc phthalocyanine; Photosensitizer; Soluble; Asymmetric; Catalytic
Graphical abstract
1
. Introduction
Photosensitizers (PS), which were used in fields such as photodynamic therapy (PDT) [1-4] and
catalysis [5, 6], have attracted much attention. Metal complexes can be applied in many fields
*
#
Corresponding authors. Email: gaobo@ciac.ac.cn (B. Gao); qianduan88@hotmail.com (Q. Duan)
These authors contributed equally to this work and should be considered as co-first authors.
1

because of their special properties [7-16]. Metal porphyrin and metal phthalocyanine derivatives
are the major types of photosensitizers. Phthalocyanine (Pc) is best as second generation of
photosensitizers which has been applied as nonlinear optical [17], sensor [18], PDT [19-23] and
catalytic [24-27]. However, the solubility of Pc limits its applications [28].
We are making efforts to develop new Pc derivatives to solve its solubility problem. In
order to solve the solubility purification problem, we modified the precursor of Pc by increasing
its carbon chain. In the design of the Pc structure, we considered the derivatives using a structure
that only left a single reaction site. The introduction of terminal hydroxyl groups led to increase
of polarity of molecule, thus increasing its solubility in water. This asymmetrical structure of Pc
has rarely been reported in comparison with symmetric ones. This study describes the
preparation of a soluble asymmetric Pc and studies its ability to degrade RhB.
2
2
. Experimental
.1. Materials and instrumentation
Dimethyl formamide (DMF) and dichloromethane (DCM) were dried over calcium hydride
before use. THF was refluxed with sodium chips under N before use. All other chemical
2
1
reagents were analytic grade and used without purification. H NMR spectra were recorded on a
Bruker Avance 500 MHz spectrometer using DMSO-d as solvent at ambient temperature.
6
FT-NIR measurements were performed as KBr pellets on a Shimadzu-8400S IR spectrometer.
UV-Vis spectra of the samples were recorded over different irradiation time intervals using a
Thermo Scientific Evolution 220 spectrophotometer.
2
.2. Synthesis of 4-decyloxy phthalonitrile
4
-Hydroxyphthalonitrile (1.15 g, 8.0 mmol), 1-bromodecane (1.94 g, 8.8 mmol) and K CO
2
3
(
4.14 g, 30 mmol) were added to a flask charged with DMF (20 mL) under nitrogen, and the
mixture was stirred at 90 °C for 3 h. After cooling to room temperature, the product was
resolved in DCM and washed by H O, drying over anhydrous MgSO . After DCM was
2
4
removed by rotary evaporation, the crude product was purified by column chromatography
SiO . The product was 1.59 g. Yield: 70.0%. Anal. Calcd. for C H2 N O (Mr = 284.4): C,
2
18
4
2
-
1
7
6.02; H, 8.51; N, 9.85. Found: C, 76.50; H, 8.17; N, 9.89. FT-NIR (KBr, cm ): 2230 (νC≡N),
1
1
600, 1460 (νAr-C-C-). H NMR (500ꢀMHz, DMSO-d ), δ ppm: 8.04 (d, J = 8.8 Hz, 1H,
6
2

Ar-H), 7.76 (d, J = 2.6 Hz, 1H, Ar-H), 7.45 (dd, J = 8.8 Hz, J = 2.6 Hz, 1H, Ar-H), 4.13 (t,
J = 6.6 Hz, 2H, -OCH -), 1.72 (p, J = 7.0 Hz, 2H, -CH -), 1.32 (m, 14H, -CH -), 0.85 (t, J =
2
2
2
1
3
6
1
1
.9 Hz, 3H, -CH ) (figure S1). C NMR (125 MHz, DMSO-d ): 162.62, 135.56, 119.91,
3 6
19.71, 117.76, 116.16, 115.72, 107.31, 69.71, 32.25, 29.87, 29.67, 29.61, 29.11, 26.18, 23.05,
4.50.
2
2
2
.3. Synthesis of 4-[2-(2-bromoethoxy-pyran)] phthalonitrile
-(2-Bromoethoxy)-pyran was synthetized according to the literature [29]. A mixture of
-(2-bromoethoxy)-pyran (2.0 g, 9.6 mmol), 4-hydroxyphthalonitrile (1.325 g, 9.2 mmol) and
K CO (4.14 g, 30.0 mmol) in DMF (50 mL) was stirred at 60 ℃ for 8 h. Then the product
2
3
was cooled to room temperature adding DCM (50 mL) and washed by water. After removing
DCM, the product was purified by chromatography, finally getting 0.8 g white solid. Yield:
-
1
3
0.0%. FT-NIR (KBr, cm ): 2224 (νC≡N), 1600, 1560, 1460 (νAr-C-C), 1260, 1120
1
(
νC-O-C). H NMR (500ꢀMHz, DMSO-d ), δ ppm: 8.05 (d, J = 8.8 Hz, 1H, Ar-H), 7.82 (d,
6
J = 8.8 Hz, 1H, Ar-H), 7.50 (dd, J = 8.9 Hz, J = 2.7 Hz, 1H, Ar-H), 4.65 (t, J = 3.5 Hz, 1H,
-
CH-), 4.33 (m, 2H, -CH -), 3.93, 3.45 (m, 2H, -CH -), 3.75 (m, 2H, -CH -), 1.46-1.65 (m,
2 2 2
6
H, -CH -) (figure S2).
2
2
.4. Synthesis of 3-ethoxyhydroxy-9(10),16(17),23(24)-tris decyloxy phthalocyanine zinc(II)
(
ZnPc-OH)
-Decyloxy phthalonitrile (568 mg, 2.0 mmol) and 4-[2-(2-bromoethoxy-pyran)]
phthalonitrile (182 mg, 0.67 mmol) in the presence of Zn(CH CO ) (240 mg, 1.10 mmol),
4
3
2 2
1
-pentanol (10 mL) and 0.75 mL DBU were refluxed for 48 h under nitrogen. Methanol
50 mL) was added after the reaction completed. The residue was treated with
p-toluenesulfonic acid (0.30 g, 1.70 mmol) in a mixture of methanol and dichloromethane
10 mL, 1:2 v/v) to remove the tetrahydropyran protecting group. The solvent was removed
(
(
by rotary evaporation and the residue was washed with methanol. The crude product was
purified, getting asymmetrical phthalocyanine 72.41 mg. Yield: 10%. Anal. Calcd. for
C H N O Zn (%): C, 69.45; H, 7.29; N, 10.12. Found: C, 69.30; H, 7.32; N, 10.24. HRMS
6
4
80
8
5
-
1
(
m/z): calcd for C H N O Zn: 1104.55; Found: 1104.50 [M + H]+. FT-NIR (KBr, cm ):
64 80 8 5
1
3
404 (νOH), 2953 (νCH ), 2853 (νCH ), 1605 (νC=C), 1341 (νC-N). H NMR (500ꢀMHz,
3 2
3

DMSO-d ), δ ppm: 9.06 (4H, Ar-H), 8.68 (4H, Ar-H), 7.69 (4H, Ar-H), 5.19 (1H, -OH), 4.27
6
(
10H, -OCH -), 1.31-2.04 (48H, -CH -), 0.91 (9H, -CH ).
2
2
3
3
3
. Results and discussion
.1. Preparation and characterization
The soluble asymmetric phthalocyanine (ZnPc-OH) (figure 1) was prepared by separating the
synthesized products of 4-decyloxy phthalonitrile and 4-[2-(2-bromoethoxy-pyran)]
phthalonitrile by column chromatography. As shown in figure 2, 4-decyloxy phthalonitrile was
synthesized from reaction of 4-hydroxyphthalonitrile and 1-bromodecane in DMF with K CO at
2
3
9
0 C under a nitrogen atmosphere for 6 h. The crude product was purified by column
1
chromatography. The H NMR spectrum of 4-decyloxy phthalonitrile is shown in figure S1.
Proton peaks at 8.04 ppm, 7.76 ppm and 7.45 ppm were assigned to the phenyl protons, and
4
.13 ppm, 1.72 ppm, 1.32 ppm corresponded to the peaks of methylene groups at different
positions. The methyl peak was at 0.85 ppm. The result above proved that the 4-decyloxy
phthalonitrile was synthesized. 2-(2-Bromoethoxy)-pyran was synthetized according to the
literature [29] and then transformed to 4-[2-(2-bromoethoxy-pyran)] phthalonitrile by reacting
with 4-hydroxyphthalonitrile in the presence of K CO with DMF as solvent at room temperature
2
3
1
for 9 h. The H NMR spectrum of 4-[2-(2-bromoethoxy-pyran)] phthalonitrile is shown in
figure S2. The peaks of phenyl protons were at 8.05 ppm, 7.82 ppm and 7.50 ppm. The peaks of
1
methylene groups at different positions were clearly identified in the H NMR spectrum,
indicating that 4-[2-(2-bromoethoxy-pyran)] phthalonitrile was synthesized.
To synthesize ZnPC-OH we used statistical methods; 4-[2-(2-bromoethoxy-pyran)]
phthalonitrile and 4-decyloxy phthalonitrile were fed at a ratio of 1:3 with DBU as a catalyst in
1
-pentanol solution with Zn(CH CO ) under N at 150 C for 48 h. After that the protecting
3
2 2
2
1
group was removed and the crude product separated and purified. The H NMR spectrum of
ZnPc-OH is shown in figure 3 and the IR spectra of ZnPc-OH and precursor are shown in
figure 4. As shown in figure 3, the proton peaks at 9.06 ppm, 8.68 ppm and 7.69 ppm were
assigned to phthalocyanine ring protons. The peak at 0.91 ppm was assigned to the protons of
-1
methyl group. It can be clearly seen that the band at 2230 cm (νC≡N) disappeared and the other
peaks were consistent with the precursors from figure 4c. The results indicated that ZnPc-OH
4

was synthesized. The Q band of ZnPc-OH was at 685 nm (figure 5). All the results proved that
we synthesized the soluble asymmetric phthalocyanine.
3
.2. Degradation of Rhodamine B
RhB threatens health as an organic dye contaminant that is carcinogenic to humans. Recently,
degradation of RhB has received attention [30-33]. RhB has a characteristic absorption at
5
54 nm and is often chosen as a representative hazardous organic dye to research the
photocatalytic activity of catalysts under visible light [34]. The degradation ability of
photosensitizers could be reflected by the degradation of RhB. H O is usually used to enhance
2
2
organic pollutant degradation in photocatalytic reaction. In order to determine the effects of H O ,
2
2
we test the photocatalytic efficiency of blank (only RhB), H O , ZnPc-OH and ZnPc-OH/H O ,
2
2
2
2
respectively. If only ZnPc-OH or H O is added into the system, the photocatalytic efficiency of
2
2
RhB under visible light irradiation for 180 min reaches 45% and 69%, respectively (figure 6).
However, it is clear from figure 7 that 85% of RhB was degraded during 180 min with
ZnPc-OH/H O , indicating that ZnPC-OH/H O has ability for degradation.
2
2
2
2
The mechanism of H O decomposition was proposed according to references [35, 36].
2
2
H O decomposition produces hydroxyl radicals (HO•). The Pc could turn oxygen into singlet
2
2
-
1
oxygen ( O ) [37] and superoxide radical anions (•O ) [22] under light. It has been widely
2
2
-
acknowledged that •O2 and •OH are the major factors for photocatalytic oxidation [30].
According to the literature [38], the schematic diagram of the mechanism for RhB degradation is
shown in figure 8.
4
. Conclusion
Modification of the precursor was used to improve the solubility of phthalocyanine. A soluble
asymmetric phthalocyanine was synthesized by statistical methods and verified to have good
solubility in DMF and dichloromethane. The degradation of RhB showed that ZnPc-OH could be
used in catalysis and has good degradation. The solubility of ZnPc-OH makes it easy to modify
to use in PDT and catalysis. The ZnPc-OH is a potential photosensitizer.
5

Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 21204082);
Jilin Province Science and Technology Development Program (No. 20180101189JC). Youth
Scientific Research Fund of the Science and Technology Department, Jilin Province, China
(
No. 20160520132JH); Foundation of Department of Education of Jilin Province (Nos. 2016363
and JJKH20170606KJ); China Postdoctoral Science Foundation (Nos. 2016M601356 and
014M561268); Youth Science Foundation of Changchun University of Science and Technology
No. XQNJJ201506).
2
(
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Figure 1. Chemical structure of soluble asymmetric phthalocyanine (ZnPc-OH).
9

Figure 2. The synthesis of soluble asymmetric phthalocyanine (ZnPc-OH).
1
0

1
Figure 3. H NMR spectrum of ZnPc-OH in DMSO-d at room temperature.
6
1
1

Figure 4. IR spectrum of 4-decyloxy phthalonitrile (a), 4-[2-(2-bromoethoxy-pyran)]
phthalonitrile (b) and ZnPc-OH (c).
1
2

Figure 5. UV-vis spectrum of ZnPc-OH.
1
3

Figure 6. The UV-vis absorbance spectra changes of RhB upon visible light irradiation: (a) only
RhB, (b) ZnPc-OH, (c) H O .
2
2
1
4

Figure 7. (a) Comparison of the decay rate of RhB (black) alone and in the presence of H O
2
2
(
red), ZnPc-OH (blue) and ZnPc-OH/H O (green) under visible light irradiation in water at
2 2
room temperature. (b) The UV-vis absorbance spectra of RhB upon visible light irradiation in the
presence of ZnPc-OH/H O in water at room temperature.
2
2
1
5

Figure 8. The mechanism for degradation of RhB in the presence of radicals.
1
6