Photophysical properties of pyridyloxy phthalocyanine encapsulated in nanoparticles

Article abstract of DOI:10.1080/00387010.2018.1461654

Two aluminum chloride phthalocyanines with pyridyloxy substitution at α/β positions were synthesized. Their structures were characterized by infrared spectroscopy, proton nuclear magnetic resonance as well as elemental analysis. Tetra-α(β)-(2-pyridyloxy)

Full text of DOI:10.1080/00387010.2018.1461654

Spectroscopy Letters
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Photophysical properties of pyridyloxy
phthalocyanine encapsulated in nanoparticles
Kuizhi Chen, Di Zeng, Ying Huang, Yawen Chen, Yide Huang, Shusen Xie, Yiru
Peng & Qing Ye
To cite this article: Kuizhi Chen, Di Zeng, Ying Huang, Yawen Chen, Yide Huang, Shusen Xie,
Yiru Peng & Qing Ye (2018): Photophysical properties of pyridyloxy phthalocyanine encapsulated in
nanoparticles, Spectroscopy Letters, DOI: 10.1080/00387010.2018.1461654
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SPECTROSCOPY LETTERS
https://doi.org/10.1080/00387010.2018.1461654
Photophysical properties of pyridyloxy phthalocyanine encapsulated
in nanoparticles
Kuizhi Chena, Di Zenga, Ying Huanga, Yawen Chenb, Yide Huangb, Shusen Xiec, Yiru Penga,c and Qing Yed
aFujian Provincial Key Laboratory of Polymer Materials, Fujian Provincial Key Laboratory of Advanced Oriented Chemical Engineering, Fujian
b
Normal University, Fuzhou, China; Provincial University Key Laboratory of Cellular Stress Response and Metabolic Regulation, College of Life
c
Sciences, Fujian Normal University, Fuzhou, China; Key Laboratory of Optoelectronic Science and Technology for Medicine of Ministry of
d
Education, Fujian Normal University, Fuzhou, China; Fujian Provincial Hospital, Fuzhou, China
ABSTRACT
ARTICLE HISTORY
Received 28 November 2017
Accepted 3 April 2018
Two aluminum chloride phthalocyanines with pyridyloxy substitution at α/b positions were
synthesized. Their structures were characterized by infrared spectroscopy, proton nuclear magnetic
resonance as well as elemental analysis. Tetra-α(b)-(2-pyridyloxy) aluminum chloride phthalocya-
nines were encapsulated into a diblock copolymer methoxy-poly(ethylene glycol)-block-poly(L-
lysine) through a cosolvent method. The morphologies and photophysical properties of phthalo-
cyanines encapsulated in nanoparticles were studied by transmission electron microscope, ultravio-
let-visible, and fluorescence spectroscopic methods. The photophysical properties of
phthalocyanines encapsulated into nanoparticles exhibited substitution positions dependence. The
phthalocyanines with substitution at α positions were found to be an excellent candidate for use
as photosensitizers for treatment of cancer by photodynamic therapy.
KEYWORDS
Aluminum chloride
phthalocyanine;
photophyscial properties;
poly(ethylene glycol)-block-
poly(L-lysine); polymeric
nanoparticles; pyridyloxy
Introduction
phthalocyanine with substitution at b positions, phthalocyanine
with substitution at α positions can reduce aggregation to
some extent. Metallophthalocyanines substituted at α and b
positions exhibit different photophysical properties (fluores-
cence quantum yields, triplet quantum yields, and lifetimes),
photochemical properties (singlet oxygen quantum yields and
photodegradation quantum yields), electrochemical properties
as well as photobiological properties.[4,6–13]
The other disadvantage of phthalocyanines for photo-
dynamic therapy is their limited accumulation at tumor
tissues. Nanoparticles show great promise in drug-delivery sys-
tems. There are some nanoparticles in clinical or pre-clinical
study, such as liposome, dendrimer, gold nanoparticle, lipid
nanoparticle, polymeric nanoparticle, and so on. Polymeric
nanoparticles are one of the excellent carrier systems for drug
delivery because of their ability to entrap or solubilize drugs in
their inner cores and deliver drugs to the tumors effectively.[14]
Besides, the use of polymeric nanoparticles can result in a
much better control over the release of drugs compared with
other nanoparticle systems.[15] Polymeric nanoparticles are
formed when amphiphilic block copolymers are dispersed in
aqueous solution above the critical micelle concentration.
Poly(ethylene glycol)-block-poly(L-lysine) copolymer has been
recognized as a novel gene delivery carrier.[16–18] Poly(ethylene
glycol), a hydrophilic block, can form a hydrated shell that
prolongs the circulation of nanoparticles in the bloodstream,
Phthalocyanines have been recognized as a promising second
generation photosensitizer for photodynamic therapy of can-
cers and other non-cancer diseases[1] due to their chemical
stability, strong absorption in the therapeutic window region
(600–900 nm), and high singlet oxygen generation ability.[2]
Many researches have been carried out to synthesize new
phthalocyanines to modulate their photophysical properties
for use in photodynamic therapy. However, one of the
disadvantages of phthalocyanines is their poor solubility in
solvents and their ease in forming aggregates, which decrease
their singlet oxygen quantum, in vitro and in vivo distribution
and bioavailability.[3] In order to overcome these problems, a
lot of novel phthalocyanines have been synthesized. The pyri-
dyloxy substitution has been reported to exhibit affinity with
biological cells and a possibility of forming water-soluble
derivatives by quaternization reaction.[4] Xie et al. reported
the photophysical properties of tetra-α(b)-(4-pyridyloxy)
zinc phthalocyanines[5], Wadzanai et al. reported the spectro-
scopic and photophysicochemical behavior of tetra-α(b)-(2-
pyridyloxy) cadmium phthalocyanines.[4] In this paper, two
aluminum chloride phthalocyanines with pyridyloxy substitu-
tion at α/b positions (tetra-α(b)-(2-pyridyloxy) aluminum
chloride phthalocyanines) were synthesized.
The substituted position on the phthalocyanines ring also
affects the aggregation of phthalocyanines. Compared with in the meantime it allows them to evade opsonization and
CONTACT Yiru Peng
yirupeng@fjnu.edu.cn
Fujian Provincial Key Laboratory of Polymer Materials, Fujian Normal University, Fuzhou, 350007, China;
Qing Ye
1158113213@qq.com Fujian Provincial Hospital, 134 East St, WuSi Lu ZhongYang ShangWu Qu, Gulou Qu, Fuzhou Shi, Fujian Sheng,
350001, China.
Supplemental data for this article can be accessed here.
ß 2018 Taylor & Francis

2
K. CHEN ET AL.
subsequent phagocytosis.[15] Polylysine is one of the most recorded on the Cary 50 UV-Vis spectrophotometer in the
attractive hydrophobic blocks for its biodegradable and bio- spectral range of 200–800 nm at room temperature.
compatible properties. In this paper, tetra-α(b)-(2-pyridyloxy) Fluorescence spectra were obtained on the FL900/FS920 steady-
aluminum chloride phthalocyanines were encapsulated into a state fluorescence spectrometers at room temperature. The
diblock copolymer methoxy-poly(ethylene glycol)-block-poly(L- fluorescence lifetimes were determined by time-resolved experi-
lysine) through a cosolvent method. The effects of substitution ments in which the fluorescence decay profiles were found to fit
positions on the photophyscial properties of phthalocyanines in to a mono-exponential function [f(t) ¼ A þ B1eꢀt/s1 þ B2eꢀt/s2].
N,N-dimethylformamide and polymeric nanoparticles were
reported for the first time.
The fluorescence quantum yields were reported relative to that
of unsubstituted zinc phthalocyanine (ZnPc) in dimethyl sulf-
oxide, as a standard (AF¼0.20).[19]
Ax ¼ AZnPc ꢁ ðFx=FZnPcÞ ꢁ ðAZnPc=AxÞ
(1)
Experimental
In Eq. [1], AZnPc and Ax are the respective absorbances of
unsubstituted ZnPc and the sample at excitation wave-
lengths. FZnPc and Fx are the integrated areas under the cor-
rected fluorescence spectra of ZnPc and the sample. Both
the samples and ZnPc were excited at the same wavelength.
Materials and equipment
3(4)-nitrophthalonitrile, 2-hydroxypyridine, anhydrous potas-
sium carbonate, potassium bromide (KBr), anhydrous alumi-
num chloride, methanol, N,N-dimethylformamide (DMF),
dimethyl sulfoxide (DMSO), and pyridine were purchased
from Shanghai Reagent Factory in China. 1,8-diazabicyclo-
[5,4,0]-undec-7-ene was purchased from Sigma-Aldrich
((Shanghai) Trading Co. Ltd. (China)). Diblock copolymer
methoxy-poly(ethylene glycol)-block-poly(L-lysine) was syn-
thesized and characterized by our group.[14]
Synthesis and characterization of tetra-α(b)-(2-
pyridyloxy) aluminum chloride phthalocyanines
The scheme for synthesis of tetra-α(b)-(2-pyridyloxy)
aluminum chloride phthalocyanines was listed in Fig. 1.
Infrared spectra (IR) were obtained on PerkinElmer IR
spectrometers. Proton nuclear magnetic resonance (1H-NMR)
data were measured on Varian UNITY-400 NMR spectrometer
Synthesis of 3-pyridyloxyphthalonitrile and
4-pyridyloxyphthalonitrile
using trimethylsilane as an internal standard. Mass spectra A mixture of 3-nitrophthalonitrile (4.5 g, 26 mmol), 2-
(MS) were recorded on a LCQ Deca XP Max mass spectrom- hydroxypyridine (3.5 g, 37 mmol), and anhydrous potassium
eter. Elemental data analyses were obtained from a Vario EL III carbonate (7.6 g, 50 mmol) in dimethyl sulfoxide (52 mL)
apparatus. Transmission electron microscope images were was heated at 85 ꢂC with stirring for 5 hr under nitrogen.
taken using JEM-1010 transmission electron microscope. The The reaction mixture was cooled to room temperature and
ultraviolet-visible electronic absorption (UV-Vis) spectra were poured into ice-water (300 mL) to give a yellow precipitate,
Figure 1. The scheme for synthesis of tetra-a(b)-(2-pyridyloxy) aluminum chloride phthalocyanines and the proton nuclear magnetic resonance chemical shift of
pyridine ring and the phthalocyanine ring.

SPECTROSCOPY LETTERS
3
which was collected by filtration and washed with water stirring, and the resulting solution was dialyzed against a large
volume of distilled water using a dialysis membrane (molecular
until pH ¼ 7 and dried in vacuum. The crude product was
weight cutoff: 3500) at room temperature for 72 hr. Similar
procedure was carried out to synthesize tetra-b-(2-pyridyloxy)
aluminum chloride phthalocyanines/methoxy-poly(ethylene
glycol)-block-poly(L-lysine) nanoparticles.
purified by re-crystallisation in methanol for four times to
give a yellow solid (50% yield). The elemental analysis calcd.
(Supplemental Table 1); IR spectra (Figure S1); 1HNMR
(Figure S2). ESI-MS (m/z): Calcd. 221; found 222[M þ H]þ.
According to the above procedure, a mixture of 4-
nitrophthalonitrile (4.5 g, 26 mmol), 2-hydroxypyridine (3.5 g,
37 mmol), and anhydrous potassium carbonate (7.6 g, 50 mmol)
in dimethyl sulfoxide (52 mL) was heated at 45 ꢂC with stirring
Results and discussion
Characterization of tetra-α(b)-(2-pyridyloxy) aluminum
for 48 hr under nitrogen to give a yellow solid (yield: 45%). chloride phthalocyanines
The elemental analysis calcd. (Supplemental Table 1); IR spec-
Both tetra-α-(2-pyridyloxy) aluminum chloride phthalocyan-
1
tra (Figure S1); HNMR (Figure S2). ESI-MS (m/z): Calcd. 221;
ine and tetra-b-(2-pyridyloxy) aluminum chloride phthalo-
cyanine were soluble in common organic solvents such as N,
N-dimethylformamide, dimethyl sulfoxide, methanol, and
pyridine. Their structures were characterized by elemental
found 222[M þ H]þ.
Synthesis of tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine
1
analysis, H-NMR, IR, and ESI-MS methods.
Intense singlet charged molecular ions peaks were observed
at m/z 912 in the ESI MS for tetra-α(b)-(2-pyridyloxy) alumi-
num chloride phthalocyanines.
A mixture of 3-pyridyloxyphthalonitrile (2.0 g, 9.0 mmol)
and anhydrous aluminum chloride (2.1 g, 15.7 mmol) was
heated at 130 ꢂC with stirring for 10 min, then 1,8-diazabicy-
clo-[5,4,0]-undec-7-ene (0.4 mL, 2.6 mmol) was added. The
resulting mixture was stirred for 7 hr at 220 ꢂC. The reaction
product was cooled to room temperature, dissolved in
methanol, and filtered under reduced pressure. The filtrate
was evaporated to give a blue solid, which was then chroma-
tographed on alumina column twice using methanol
(300 mL) as eluent. The green band was collected and
rotary-evaporated to give a dark green solid (yield: 62%).
The elemental analysis calcd. (Supplemental Table 1); IR
spectra (Figure S1); 1HNMR (Figure S2). ESI-MS (m/z):
Calcd. 911; found 912[M þ H]þ.
The IR absorption of tetra-α(b)-(2-pyridyloxy) aluminum
chloride phthalocyanines were very similar. After 3(4)-
pyridyloxyphthalonitriles having been converted into the cor-
responding aluminum chloride phthalocyanines, the intense
stretching band at 2235–2239cmꢀ1 assigned to the cyano
groups of 3(4)-pyridyloxyphthalonitriles disappeared, and the
vibration belonged to phthalocyanines at 1650–1660 and
1530–1580cmꢀ1 appeared, indicating of the formation of
phthalocyanines. Moreover, the vibrations of 1080–1140 cmꢀ1
belonging to the characteristic stretching vibration of C-O-C
were observed.
1
The H-NMR spectra of tetra-α(b)-(2-pyridyloxy) alumi-
num chloride phthalocyanines were obtained in DMSO-d6.
tetra-α(b)-(2-pyridyloxy) aluminum chloride phthalocyanines
were found to be pure by H-NMR with both phthalocyan-
Synthesis of tetra-b-(2-pyridyloxy) aluminum chloride
phthalocyanine
1
ine ring protons and the substituents protons in their
respective aromatic and pyridine regions. The 1H-NMR
spectra of tetra-α(b)-(2-pyridyloxy) aluminum chloride
phthalocyanines exhibited broad signals due to the slight
aggregation of tetra-α(b)-(2-pyridyloxy) aluminum chloride
phthalocyanines in DMSO-d6 and the existence of a mixture
of four positional isomers. Affected by the substitution posi-
tions (Fig. 1), the signals of protons on the phthalocyanine
ring were observed at 8.19, 7.71, and 7.68 ppm for tetra-α-
(2-pyridyloxy) aluminum chloride phthalocyanine, 9.14, 7.75,
and 6.64 ppm for tetra-b-(2-pyridyloxy) aluminum chloride
phthalocyanine; the signals of protons of the pyridine ring
were observed at 9.02, 8.42, 6.97, and 6.83 ppm for tetra-α-
(2-pyridyloxy) aluminum chloride phthalocyanine, 9.80, 8.43,
8.25, and 6.76 ppm for tetra-b-(2-pyridyloxy) aluminum
chloride phthalocyanine, respectively.
According to the above procedure for tetra-α-(2-pyridyloxy)
aluminum chloride phthalocyanine, 4-pyridyloxyphthaloni-
trile (2.0 g, 9.0 mmol) was treated with anhydrous aluminum
chloride (2.1 g, 15.7 mmol) and 1,8-diazabicyclo-[5,4,0]-
undec-7-ene (0.4 mL, 2.6 mmol) to give the product tetra-
b-(2-pyridyloxy) aluminum chloride phthalocyanine as a
blue green solid (yield: 52%). The elemental analysis calcd.
(Supplemental Table 1); IR spectra (Figure S1); 1HNMR
(Figure S2). ESI-MS (m/z): Calcd. 911; found 912[M þ H]þ.
Preparation of tetra-α(b)-(2-pyridyloxy) aluminum
chloride phthalocyanines/methoxy-poly(ethylene
glycol)-block-poly(L-lysine) nanoparticles
Stock solution of tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine was prepared in N,N-dimethylformamide at
10ꢀ4 mol/L. Methoxy-poly(ethylene glycol)-block-poly(L-lysine)
(10 mg) was added to tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine/N,N-dimethylformamide solution (10ꢀ4 M,
2 mL) with stirring. Then re-distilled water (8 mL) was added
slowly to the mixture of methoxy-poly(ethylene glycol)-block-
poly(L-lysine) and tetra-α-(2-pyridyloxy) aluminum chloride
Morphologies of tetra-α(b)-(2-pyridyloxy) aluminum
chloride phthalocyanines/methoxy-poly(ethylene glycol)-
block-poly(L-lysine) nanoparticles
Methoxy-poly(ethylene glycol)-block-poly(L-lysine) copolymers
phthalocyanine/N,N-dimethylformamide solution with constant were employed to load tetra-α(b)-(2-pyridyloxy) aluminum

4
K. CHEN ET AL.
chloride phthalocyanines to prepare tetra-α(b)-(2-pyridyloxy)
Whereas upon excitation at 610 nm, tetra-α-(2-pyridyloxy)
aluminum chloride phthalocyanines/methoxy-poly(ethylene aluminum chloride phthalocyanine and tetra-b-(2-pyridyloxy)
glycol)-block-poly(L-lysine) nanoparticles. The polymeric aluminum chloride phthalocyanine showed fluorescence
nanoparticles displayed average diameters of 50 nm for tetra-α- emission spectra at 713 and 699 nm in DMF, respectively
(2-pyridyloxy) aluminum chloride phthalocyanine/methoxy- (Fig. 4). Tetra-b-(2-pyridyloxy) aluminum chloride phthalo-
poly(ethylene glycol)-block-poly(L-lysine) and 70 nm for cyanine exhibited higher fluorescence signal and ca. 4 nm blue-
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine/
methoxy-poly(ethylene glycol)-block-poly(L-lysine) (Fig. 2).
Tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine/
methoxy-poly(ethylene glycol)-block -poly(L-lysine) were
entangled together, but tetra-b-(2-pyridyloxy) aluminum
chloride phthalocyanine/methoxy-poly(ethylene glycol)-block-
poly(L-lysine) had better dispersion. It may be because tetra-α-
(2-pyridyloxy) aluminum chloride phthalocyanine mainly
existed as a monomer and showed higher solubility in
nanoparticles, whereas tetra-b-(2-pyridyloxy) aluminum chlor-
ide phthalocyanine existed as aggregates and displayed
lower solubility.
shift than that of tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine. This can be explained by the probability of
emission from the singlet excited state to the ground state for
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine being
higher than that of tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine. The singlet excited state of tetra-α-(2-
pyridyloxy) aluminum chloride phthalocyanine underwent
electron spin conversion to the triplet excited state rather than
decaying back to the ground state by emitting fluorescence.[5]
The singlet excited lifetime values were found to be 4.22 ns for
tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine and
5.25 ns for tetra-b-(2-pyridyloxy) aluminum chloride phthalo-
cyanine. The fluorescence quantum yields values were found
to be 0.25 for tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine and 0.09 for tetra-b-(2-pyridyloxy) aluminum
chloride phthalocyanine.
UV-Vis spectra of tetra-α(b)-(2-pyridyloxy) aluminum
chloride phthalocyanines encapsulated in polymeric nanopar-
ticles exhibited substitution positions dependence (Fig. 5).
Compared with the corresponding free phthalocyanines, tetra-
α(b)-(2-pyridyloxy) aluminum chloride phthalocyanines encap-
sulated in polymeric nanoparticles exhibited higher intensity
and had blue-shift or bathochromic at the maximum absorp-
tion wavelength. The shift of Q bands of tetra-α(b)-(2-pyridy-
loxy) aluminum chloride phthalocyanines may be due to the
interaction of phthalocyanines and methoxy-poly(ethylene gly-
Photophysical properties of tetra-α(b)-(2-pyridyloxy)
aluminum chloride phthalocyanines and tetra-α(b)-(2-
pyridyloxy) aluminum chloride phthalocyanines/
methoxy-poly(ethylene glycol)-block-poly(L-lysine)
nanoparticles
UV-Vis spectra of tetra-α(b)-(2-pyridyloxy) aluminum chlor-
ide phthalocyanines exhibited B-bands at 355–338 nm, dimer
bands at 649–647nm, and strong narrow Q-bands at
682–684 nm in DMF (Fig. 3). Compared with the Q-bands of
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine,
tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine
exhibited 2 nm red-shift and its peak shape became broader.
Meanwhile, the dimer band at 645 nm was less obvious for col)-block-poly(L-lysine) nanoparticles. Tetra-α-(2-pyridyloxy)
tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine. aluminum chloride phthalocyanine encapsulated in polymeric
This might be due to higher steric hindrance of tetra-α-(2- nanoparticles remained in a monomeric state, while tetra-
pyridyloxy) aluminum chloride phthalocyanine with substitu- b-(2-pyridyloxy) aluminum chloride phthalocyanine tended to
tion at α positions, which had higher site isolation ability.[8]
form aggregates.
Figure 2. Transmission electron microscope images of tetra-a-(2-pyridyloxy) aluminum chloride phthalocyanines/methoxy-poly (ethylene glycol)-block-poly(L-lysine)
nanoparticles (a) and tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanines/methoxy-poly(ethylene glycol)-block-poly (L-lysine) nanoparticles (b). The
bar was 0.2 um.

SPECTROSCOPY LETTERS
5
The fluorescence spectra of tetra-α(b)-(2-pyridyloxy) alu- polymeric nanoparticles were almost the same, because the
minum chloride phthalocyanines encapsulated in polymeric aggregation behavior of tetra-b-(2-pyridyloxy) aluminum
chloride phthalocyanine remain unchanged in water and
polymeric nanoparticles.
nanoparticles also exhibited substitution positions depend-
ence (Fig. 6). Compared with the corresponding free phtha-
locyanines, tetra-α(b)-(2-pyridyloxy) aluminum chloride
phthalocyanines encapsulated in polymeric nanoparticles
exhibited a slight shift at the maximum fluorescence
emission, which might be due to the micro-environmental
changes from homogeneous to heterogeneous media.[14] The
micro-environment in polymeric nanoparticles can affect the
fluorescence spectrum of tetra-α-(2-pyridyloxy) aluminum
chloride phthalocyanine more obviously than that of
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine.
Tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine
encapsulated in polymeric nanoparticles exhibited a signifi-
cant fluorescence quenching, which might be due to the
aggregation of tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine encapsulated in polymeric nanoparticles.
Alternatively, the fluorescence signal of tetra-b-(2-pyridy-
loxy) aluminum chloride phthalocyanine in water and
Fluorescence decay curves of free tetra-α-(2-pyridyloxy)
aluminum chloride phthalocyanine and tetra-α-(2-pyridyloxy)
aluminum chloride phthalocyanine encapsulated in polymeric
nanoparticles are shown in Fig. 7. The fluorescence lifetime of
tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine
encapsulated in polymeric nanoparticles (7.64 ns) was longer
than that of free tetra-α-(2-pyridyloxy) aluminum chloride
phthalocyanine (4.22 ns). The internal molecular motion of
tetra-α-(2-pyridyloxy) aluminum chloride phthalocyanine
encapsulated in polymeric nanoparticles was restrained,
which resulted in the inhibition of non-radiative decay.[3]
Figure 5. The ultraviolet-visible electronic absorption spectra of a(b)-AlPc(PyO)4
and a(b)-AlPc(PyO)4/m in water. [a-AlPc(PyO)4]: 2 ꢁ 10ꢀ5 mol/L; [b-AlPc(PyO)4]:
2 ꢁ 10ꢀ5 mol/L. The spectra revealed that a-AlPc(PyO)4 encapsulated in
polymeric nanoparticles remained in a monomeric state, whereas tetra-b-(2-
pyridyloxy)
aluminum
chloride
phthalocyanine
tended
to
form
Figure 3. The ultraviolet-visible electronic absorption spectra of a(b)-AlPc(PyO)4
in DMF. [a-AlPc(PyO)4]: 2 ꢁ 10ꢀ5 mol/L; [b-AlPc(PyO)4]:2 ꢁ 10ꢀ5 mol/L. The
spectra revealed phthalocyanine with substitution at a positions can reduce
aggregation to some extent. a-AlPc(PyO)4—tetra-a-(2-pyridyloxy) aluminum
chloride phthalocyanine; b-AlPc(PyO)4—tetra-b-(2-pyridyloxy) aluminum
chloride phthalocyanine; DMF—N,N-dimethylformamide.
aggregates. a-AlPc(PyO)4—tetra-a-(2-pyridyloxy) aluminum chloride phthalo-
cyanine; b-AlPc(PyO)4—tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine;
a-AlPc(PyO)4/m—tetra-a-(2-pyridyloxy) aluminum chloride phthalocyanines/
methoxy -poly(ethylene glycol)-block-poly(L-lysine) nanoparticles; b-AlPc(PyO)4/
m—tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanines/methoxy -poly
(ethylene glycol)-block-poly(L-lysine) nanoparticles.
Figure 4. Fluorescence emission spectra (a) and fluorescence decay curves (b) of a(b)-AlPc(PyO)4 in DMF. [a-AlPc(PyO)4]: 2 ꢁ 10ꢀ5 mol/L; [b-AlPc(PyO)4]:2 ꢁ 10ꢀ5
mol/L. (a) the excitation wavelength was 610 nm; (b) the excitation wavelength was 350 nm. The spectra revealed that b-AlPc(PyO)4 exhibited higher fluorescence
signal and had longer singlet excited lifetime than those of a-AlPc(PyO)4. a-AlPc(PyO)4—tetra-a-(2-pyridyloxy) aluminum chloride phthalocyanine; b-AlPc(PyO)4—
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine; a-AlPc(PyO)4/m—tetra-a-(2-pyridyloxy) aluminum chloride phthalocyanines/methoxy -poly(ethylene
glycol)-block-poly(L-lysine) nanoparticles; b-AlPc(PyO)4/m—tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanines/methoxy -poly(ethylene glycol)-block-poly
(L-lysine) nanoparticles.

6
K. CHEN ET AL.
However, the fluorescence lifetime of tetra-b-(2-pyridyloxy) of tetra-α(b)-(2-pyridyloxy) aluminum chloride phthalocya-
aluminum chloride phthalocyanine encapsulated in polymeric nines encapsulated in polymeric nanoparticles exhibited
substitution positions dependence. Compared with the corre-
sponding free phthalocyanines, tetra-α-(2-pyridyloxy) alumi-
num chloride phthalocyanine encapsulated in polymeric
nanoparticles remained in a monomeric state and had longer
fluorescence lifetime, whereas tetra-b-(2-pyridyloxy) alumi-
num chloride phthalocyanine tended to form aggregates.
Therefore, phthalocyanines with substitution at α positions
were found to be excellent candidates for using as photosen-
sitizers for photodynamic therapy of cancer.
nanoparticles was too weak to be detected. That might be
because tetra-b-(2-pyridyloxy) aluminum chloride phthalo-
cyanine mainly existed in the form of aggregates in
polymeric nanoparticles, which led to massive non-radiative
energy transfer.
Conclusion
Two aluminum chloride phthalocyanines with pyridyloxy
substitution at α/b positions were synthesized and their
structures were characterized. The average diameters of
tetra-b-(2-pyridyloxy) aluminum chloride phthalocyanine/
methoxy-poly(ethylene glycol)-block-poly(L-lysine) (70 nm)
was larger than that of tetra-α-(2-pyridyloxy) aluminum
Funding
This research was supported by the National Key Basic Research
Program of China (973 project) [grant mumber 2015CB352006];
National Natural Science Foundation of China [grant number
61335011, 21274021]; Natural Science Foundation of Fujian [grant
number 2015J01040, 2014Y050] and Fujian Province Educational
Project A [grant number JA15124]; Scientific research innovation team
construction program of Fujian Normal University [grant number
IRTL 1702]; The college students’ innovative and entrepreneurial train-
ing program of Fujian province [grant number cxxl-2017151,
201710394074].
chloride
phthalocyanine/methoxy-poly(ethylene
glycol)-
block-poly(L-lysine) (50 nm). The photophysical properties
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