Synthesis and separation of the constitutional isomers of 1(4),8(11),15(18),22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]-phthalocyaninato zinc(II) complexes

Article abstract of DOI:10.1016/j.dyepig.2013.01.016

Cyclic tetramerization of 3-[(methyloxycarbonyl)phenoxy]phthalonitrile (1a-1c) in the presence of Zn(OAc)₂·2H₂O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by transesterification in refluxing n-pentanol afforded 1(4),8(11),15(18),22(25)- tetrakis[(pentyloxycarbonyl)phenoxy]phthalocyaninato zinc(II) complexes (2a-2c) as a mixture of four constitutional isomers. Simple silica-gel column chromatography leads to the successful separation of pure isomers with the C_4h and D_2h symmetry together with a section containing the C_2v and C_s isomers, which have been characterized with a wide range of spectroscopic methods including MALDI-TOF mass, electronic absorption, ¹H NMR, and 2D COSY spectroscopy. Synthesis yields in combination with the NMR spectroscopic results reveal that the distribution of the four isomers in the final product for 2a-2c does not strictly follow that expected according to statistical calculation with the ratio of C _4h:C_2v:C_s:D_2h = 1:2:4:1, indicating the effect of steric hindrance of substituents on the formation of various constitutional isomers.

Full text of DOI:10.1016/j.dyepig.2013.01.016

Dyes and Pigments 97 (2013) 469e474
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and separation of the constitutional isomers of 1(4),8(11),15(18),
22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]-phthalocyaninato zinc(II)
complexes
*
Ming Bai , Yan Zhang, Rui Song, Senjian Han, Peihong Wan, Chongxi Zhang
Marine College, Shandong University at Weihai, Weihai 264209, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cyclic tetramerization of 3-[(methyloxycarbonyl)phenoxy]phthalonitrile (1ae1c) in the presence of
Zn(OAc)2$2H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by transesterification in reflux-
ing n-pentanol afforded 1(4),8(11),15(18),22(25)-tetrakis[(pentyloxycarbonyl)phenoxy]phthalocyaninato
zinc(II) complexes (2ae2c) as a mixture of four constitutional isomers. Simple silica-gel column chro-
matography leads to the successful separation of pure isomers with the C4h and D2h symmetry together
with a section containing the C2v and Cs isomers, which have been characterized with a wide range of
spectroscopic methods including MALDI-TOF mass, electronic absorption, 1H NMR, and 2D COSY spec-
troscopy. Synthesis yields in combination with the NMR spectroscopic results reveal that the distribution
of the four isomers in the final product for 2ae2c does not strictly follow that expected according to
statistical calculation with the ratio of C4h:C2v:Cs:D2h ¼ 1:2:4:1, indicating the effect of steric hindrance of
substituents on the formation of various constitutional isomers.
Received 22 October 2012
Received in revised form
17 January 2013
Accepted 19 January 2013
Available online 29 January 2013
Keywords:
Phthalocyanines
Low symmetry
Constitutional isomers
Silica-gel column chromatography
NMR
Ó 2013 Elsevier Ltd. All rights reserved.
Distribution
1. Introduction
chromatography was still rarely reported, to the best of our
knowledge. In 2004, the C4h and C2v isomers of phthalocyaninato
Phthalocyanines as versatile functional dyes have got a wide
range of applications in the fields of organic semiconductors,
nonlinear optical and optical limiting materials, chemosensors,
organic photovoltaics, catalysis, and photosensitisers for photo-
dynamic therapy [1e7]. Their physichemical, electrochemical, and
spectroscopic properties, and intermolecular interactions can be
modulated by rational modification of the metal center and the
substituents of phthalocyanines. In line with this idea, lowering the
molecular symmetry of phthalocyanine derivatives through suit-
able modification on the peripheral substituents and/or the nature
metal complexes of Zn and Pb were prepared from cyclic tetra-
merization of 3-(2,4-dimethyl-3-pentyloxy)phthalonitrile and
separated by column chromatography on silica gel [10a], while the
other two isomers with D2h and Cs symmetry were not detected. In
a similar manner, a trace amount of D2h isomer was isolated from
the mixture of four constitutional isomers of tetrahexyl phthalo-
cyaninato vanadium(IV) oxide complex [10b]. Very recently, three
of the four constitutional isomers with the C4h, Cs, and C2v sym-
metry (except the D2h one) for the triazolo-fused azaph-
thalocyanine synthesized from 3-substituted 8-(diethylamino)-
[1,2,4]triazolo[4,3-a]-pyrazine-5,6-dicarbonitrile were successfully
isolated [10c]. However, it should be mentioned that the C4h isomer
of phthalocyanine derivatives with bulky substituents at the
1,8,15,22-positions usually could be obtained and isolated by con-
trolling the reaction at relatively low temperature condition [11,12].
In the presented paper, a series of 1(4),8(11),15(18),22(25)-tet-
rakis[(pentyloxycarbonyl)phenoxy]phthalocyaninato zinc(II) com-
plexes 2ae2c, which are a mixture of four constitutional isomers,
were synthesized by the cyclic tetramerization of 3-[(methylox-
ycarbonyl)phenoxy]phthalonitrile (1ae1c) and the trans-
esterification of substituents in the presence of Zn(OAc)2$2H2O and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-pentanol.
of the
p-conjugation system has been attracting increasing
research interests [8]. Among the low symmetry phthalocyanines,
isolation of constitutional isomers arising from cyclic tetrameriza-
tion of one unsymmetrical precursor such as 3-subsituted-phtha-
lonitrile has been common but extremely difficult. However, quite
a few constitutional isomers of corresponding low symmetry
phthalocyanine compounds have been successfully isolated by
means of HPLC technique or TLC method [9]. Separation of con-
stitutional isomers depending on simple silica-gel column
* Corresponding author.
E-mail address: ming_bai@sdu.edu.cn (M. Bai).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.01.016

470
M. Bai et al. / Dyes and Pigments 97 (2013) 469e474
Scheme 1. Synthesis of constitutional isomers of complexes 2ae2c.
Most importantly, the constitutional isomers with the C4h and D2h
symmetry together with a mixture containing the C2v and Cs iso-
mers have been successfully separated by simple silica-gel column
chromatography.
2.2.2. 3-(3-Methoxycarbonylphenoxy)phthalonitrile (1b)
Yield: 76%. 1H NMR (CDCl3)
d
7.973(d, 1H, J ¼ 7.6 Hz, ArH),
7.745(dd, 1H, J ¼ 2.0 Hz, J ¼ 1.6 Hz, ArH), 7.600(dd, 1H, J ¼ 8.0 Hz,
J ¼ 8.0 Hz, ArH), 7.548(dd, 1H, J ¼ 8.0 Hz, J ¼ 8.0 Hz, ArH), 7.506(d,
1H, J ¼ 7.6 Hz, ArH), 7.330(dd, 1H, J ¼ 8.0 Hz, J ¼ 2.4 Hz, ArH),
7.096(d, 1H, J ¼ 8.8 Hz, ArH), 3.927(s, 6H, eCOOCH3). 13C NMR
2. Experimental section
(CDCl3)
d 165.67, 160.16, 154.04, 134.82, 132.73, 130.71, 127.65,
127.09, 124.74, 121.04, 121.00, 117.31, 115.02, 112.54, 106.46, 52.46.
2.1. General remarks
2.2.3. 3-[3,5-Bis(methoxycarbonyl)phenoxy] phthalonitrile (1c)
n-Pentanol and dimethylformamide (DMF) were distilled from
sodium and anhydrous MgSO4, respectively. Column chromatog-
raphy was carried out on a silica-gel column (Qingdao Haiyang,
200e300 mesh) with the indicated eluents. All of the other re-
agents and solvents were used as received.
Yield: 75%. 1H NMR (CDCl3)
d 8.583(s, 1H, ArH), 7.940e7.944(m,
2H, ArH), 7.639(dd, 1H, J ¼ 8.4 Hz, J ¼ 8.2 Hz, ArH), 7.554(d, 1H,
J ¼ 8.0 Hz, ArH), 7.124(d, 1H, J ¼ 8.4 Hz, ArH), 3.958(s, 6H, e
COOCH3). 13C NMR (CDCl3)
d 165.10, 159.70, 154.57, 134.85, 133.36,
128.26, 128.02, 125.17, 121.42, 117.94, 114.94, 112.32, 107.38, 52.91.
1H NMR spectra were recorded on a Bruker DPX 400 spec-
trometer (1H: 400 MHz) in CDCl3 solution unless otherwise stated.
Spectra were referenced internally using the residual solvent res-
2.3. Synthesis of phthalocyanines (2ae2c)
onances (
d
¼ 7.26 for 1H NMR) relative to SiMe4
(
d
¼ 0 ppm). 13
C
A mixture of phthalonitrile 1 (0.1 mmol), Zn(OAc)2$2H2O
(110 mg, 0.05 mmol), and DBU (0.5 g) in n-pentanol (15 mL) was
heated at 140 ꢀC overnight under a slow stream of nitrogen. After
cooling, the solvent was removed in vacuo. The residue was puri-
fied by silica-gel column chromatography using CH2Cl2 containing
MeOH as eluent. Three fractions were collected.
NMR spectra were referenced internally by using the solvent res-
onances (
d
¼ 77.0 ppm for CDCl3). Electronic absorption spectra
were recorded on a Hitachi U-4100 spectrophotometer. MALDI-TOF
mass spectra were taken on a Bruker BIFLEX III ultrahigh resolution
Fourier transform ion cyclotron resonance (FT-ICR) mass spec-
trometer with R-cyano-4-hydroxycinnamic acid as a matrix.
2.3.1. Phthalocyanine 2a
2.2. Synthesis of 3-substituted-phthalonitriles (1ae1c)
Mobile phase: CH2Cl2 containing MeOH from 0.3% to 1.5% (V/V).
C4h isomer: 1H NMR (CDCl3)
d
8.850(d, 4H, J ¼ 7.6 Hz, PcHa),
A mixture of 3-nitrophthalonitrile (1.72 g, 0.01 mol), methyl
hydroxybenzoate (0.01 mol), and potassium carbonate (13.90 g,
0.1 mol) in DMF (80 mL) was heated at 80 ꢀC overnight. Then the
reaction mixture was poured into ice water. After filtration, the
solid product was purified by silica-gel chromatography using
CH2Cl2 as eluent to give a white solid product.
Table 1
Yields of isolated isomers and mass spectroscopic data for compound 2ae2c.a
Compound
Isomer
Total yield (%)
23.2
Yield (%)
Mþ (m/z)
2a
C4h
6.0
15.6
1.6
1400.119
1400.892
1400.992
C2v & Cs
D2h
2.2.1. 3-(2-Methoxycarbonylphenoxy)phthalonitrile (1a)
2b
C4h
C2v & Cs
D2h
74.3
37.5
13.8
49.5
10.9
1400.521
1400.454
1400.343
Yield: 80%, 1H NMR (CDCl3)
d
8.069(dd, 1H, J ¼ 7.6 Hz, J ¼ 1.6 Hz,
ArH), 7.655(ddd, 1H, J ¼ 7.6 Hz, J ¼ 7.6 Hz, J ¼ 1.6 Hz, ArH), 7.513(dd,
1H, J ¼ 8.4 Hz, J ¼ 8.2 Hz, ArH), 7.425(dd, 1H, J ¼ 7.6 Hz, J ¼ 7.6 Hz,
ArH), 7.427(d, 1H, J ¼ 7.6 Hz, ArH), 7.198(d, 1H, J ¼ 8.4 Hz, ArH),
6.854(d, 1H, J ¼ 8.4 Hz, ArH), 3.781(s, 3H, eCOOCH3). 13C NMR
2c
C4h
C2v & Cs
D2h
10.4
22.4
4.7
1858.491
1858.250
1858.263
a
Calculated values for ZnC80H72N8O12 (2a and 2b) [Mþ] 1400.456;
(CDCl3)
d 164.67, 161.59, 152.57, 134.70, 134.35, 132.92, 126.92,
126.69, 124.09, 123.51, 119.22, 117.30, 115.32, 112.84, 105.53, 52.56.
ZnC104H112N8O20 (2c) [Mþ] 1857.732.

M. Bai et al. / Dyes and Pigments 97 (2013) 469e474
471
Fig. 1. 1H NMR spectra of C4h (in CDCl3), Cs & C2v, and D2h isomers of compound 2c (in CDCl3 with a drop of pyridine[D5]).
8.221(dd, 4H, J ¼ 7.6 Hz, J ¼ 1.6 Hz, ArH), 7.955(dd, 4H, J ¼ 7.6 Hz,
2.3.2. Phthalocyanine 2b
Mobile phase: CH2Cl2 containing MeOH from 0.1% to 0.5% (V/V).
C4h isomer: 1H NMR (CDCl3 with a drop of pyridine[D5])
8.769(d,
J ¼ 7.6 Hz, PcHb), 7.610(d, 4H, J ¼ 7.6 Hz, PcHb), 7.282(ddd, 4H,
J ¼ 8.0 Hz, J ¼ 7.6 Hz, J ¼ 6.2 Hz, J ¼ 1.2 Hz, ArH), 7.193(d, 4H,
J ¼ 7.6 Hz, ArH), 7.178(d, 4H, J ¼ 7.6 Hz, ArH), 4.301(t, 8H, J ¼ 6.8 Hz,
eCOOCH2e), 1.471e1.542(m, 8H, eCH2e), 1.130e1.206(m, 8H, e
CH2e), 0.848e0.941(m, 8H, eCH2e), 0.434(t, 12H, J ¼ 7.2 Hz, e
CH3). D2h isomer: 1H NMR (CDCl3 with a drop of pyridine[D5])
d
4H, J ¼ 7.6 Hz, PcHa), 8.211(br s, 4H, ArH), 7.923(dd, 4H, J ¼ 7.6 Hz,
J ¼ 7.6 Hz, PcHb), 7.799(d, 4H, J ¼ 7.6 Hz, ArH), 7.637(d, 4H, J ¼ 7.6 Hz,
PcHb), 7.524e7.550(ddd, 4H, J ¼ 8.0 Hz, J ¼ 2.6 Hz, J ¼ 2.4 Hz, ArH),
7.412(dd, 4H, J ¼ 8.0 Hz, J ¼ 8.0 Hz, ArH), 4.261(t, 8H, J ¼ 6.8 Hz,
COOCH2e), 1.654e1.724(m, 8H, eCH2e), 1.226e1.372(m, 16H, e
CH2e), 0.807(t, 12H, J ¼ 7.2 Hz, eCH3). D2h isomer: 1H NMR
d
9.100(d, 4H, J ¼ 6.8 Hz, PcHa), 7.897(dd, 4H, J ¼ 8.0 Hz, J ¼ 7.6 Hz,
PcHb), 7.806(d, 4H, J ¼ 7.6 Hz, ArH), 7.355(dd, 4H, J ¼ 8.0 Hz,
J ¼ 5.2 Hz ArH), 7.333(d, 4H, J ¼ 7.2 Hz, ArH), 7.141e7.160(m, 4H,
ArH; 4H, J ¼ 7.6 Hz, PcHb), 3.813(t, 8H, J ¼ 6.2 Hz, eCOOCH2e),
0.974(br s, 8H, eCH2e), 0.739(br s, 8H, eCH2e), 0.533(br s, 8H, e
CH2e), 0.197(br s, 12H, eCH3).
(CDCl3 with a drop of pyridine[D5]) d 8.972(br s, 4H, PcHa), 8.039(s,
4H, ArH), 7.847(dd, 4H, J ¼ 7.6 Hz, PcHb), 7.813(d, 4H, J ¼ 7.6 Hz,
ArH), 7.463(d, 4H, J ¼ 7.6 Hz, ArH), 7.327(dd, 4H, J ¼ 8.0 Hz,
J ¼ 7.6 Hz, ArH), 7.169(br s, 4H, PcHb), 4.329(t, 8H, J ¼ 6.6 Hz, e
COOCH2e), 1.726e1.795(m, 8H, eCH2e), 1.279e1.441(m, 16H, e
CH2e), 0.848(t, 12H, J ¼ 7.2 Hz, eCH3).
Table 2
Chemical shifts of protons on phthalocyanines 2ae2c rings.a
2.3.3. Phthalocyanine 2c
Compound
Isomer
Ha
Hb
Hb
2
1
Mobile phase: CH2Cl2 containing MeOH from 0.1% to 0.5% (V/V).
2a
C4h
C2v & Cs
8.850 (4)
7.955 (4)
8.091[Cs]
7.891[C2v
7.955[C2v
7.756[Cs]
7.610 (4)
7.661[Cs]
7.178[C2v
7.606[C2v
7.076[Cs]
C4h isomer: 1H NMR (CDCl3 with a drop of pyridine[D5])
d 8.523(d,
9.351 (1.42) [Cs]
9.151 (0.58) [C2v
8.883 (0.58) [C2v
8.678 (0.71) & 8.652
(0.71) [Cs]
]
]
]
]
]
]
D2h
9.110 (4)
7.897 (4)
7.923 (4)
7.151 (4)
7.637 (4)
2b
C4h
8.769 (4)
C2v & Cs
8.982 (2) [C2v & Cs]
8.604 (0.73) [C2v
8.579 (0.73) [Cs]
8.105 (0.54) [Cs]
8.972 (4)
]
D2h
7.847 (4)
7.843 (4)
7.169 (4)
7.635 (4)
2c
C4h
8.523 (4)
C2v & Cs
8.974 (2) [C2v & Cs]
8.654 (0.65) [C2v
8.570 (1.35) [Cs]
9.136 (4)
]
D2h
7.855 (4)
7.181 (4)
a
The integration values given in parentheses. The assignment of the isomers
mixture given in bracket.
Fig. 2. Definition of “free Ha” and “shelding Ha”.

472
M. Bai et al. / Dyes and Pigments 97 (2013) 469e474
Fig. 3. 1H NMR spectrum (
d
6.9e9.5 ppm) of Cs & C2v mixture of compound 2a in CDCl3 with a drop of pyridine[D5].
4H, J ¼ 6.8 Hz, PcHa), 8.286(s, 4H, ArH), 8.097(s, 8H, ArH), 7.843(dd,
4H, J ¼ 7.6 Hz, J ¼ 7.2 Hz, PcHb), 7.635(d, 4H, J ¼ 7.6 Hz, PcHb),
4.168(t, 16H, J ¼ 6.6 Hz, COOCH2e), 1.622e1.673(m, 16H, eCH2e),
1.278e1.286(br m, 32H, eCH2e), 0.812(t, 24H, J ¼ 6.8 Hz, eCH3).
C4h symmetry for 2c only in CDCl3. The nature of the C4h and D2h
isomers of 2ae2c can be easily distinguished by their NMR spectra,
Fig. 1 and S2e11 (Supplementary material) and Table 2. Fig. 1 dis-
plays the 1H NMR spectra of the single C4h and D2h as well as the
mixed C2v and Cs isomers of compound 2c. The spectrum of C4h
isomer shows a doublet at 8.523 ppm, an overlapping doublet of
doublets at 7.843 ppm, and a doublet at 7.635 ppm, which are
D2h isomer: 1H NMR (CDCl3 with a drop of pyridine[D5])
d 9.136(br
s, 4H, PcHa), 8.417(s, 4H, ArH), 8.191(s, 8H, ArH), 7.855(br s, 4H,
PcHb), 7.181(br s, 4H, PcHb), 4.311(t, 16H, J ¼ 5.8 Hz, COOCH2e),
1.719e1.753(m, 16H, eCH2e), 1.263e1.407(m, 32H, eCH2e),
0.815(t, 24H, J ¼ 7.2 Hz, eCH3).
assigned to the three protons of Ha, Hb1, and Hb at the phthalo-
2
cyanine ring, respectively. Compared with the chemical shift of
protons in the spectrum of C4h isomer, the peak of Ha (free Ha) for
D2h isomer shifts to low field at 9.153 ppm owing to no shielding
effect of substituent arising from the benzene ring of opposite side
3. Results and discussion
(Fig. 2), while the peak of Hb for D2h shifts to high field at
7.201 ppm because it suffers bigger shielding from the pentylox-
ycarbonylphenoxy group of adjacent position, which is excluded to
2
As shown in Scheme 1, 3-substitued phthalonitriles (1ae1c) was
afforded by treating 3-nitrophthalonitrile with methyl hydrox-
ybenzoate
(methyl
2-hydroxybenzoate,
methyl
3-
closer position of Hb by the other pentyloxycarbonylphenoxy
2
hydroxybenzoate, and methyl 3,5-dihydroxybenzoate) and K2CO3
in DMF. Cyclisation of 1ae1c followed by transesterification in the
presence of DBU and Zn(OAc)2$2H2O in refluxing n-pentanol led to
the formation of 1(4),8(11),15(18),22(25)-tetrakis[(pentylox-
ycarbonyl)phenoxy]phthalocyaninato zinc(II) complexes 2ae2c as
a mixture of four constitutional isomers [7a]. The C4h and D2h iso-
mers of all the three phthalocyanine compounds could be sepa-
rated by simple silica-gel column chromatography in the first and
third fraction respectively, while the C2v and Cs isomers were col-
lected as a mixture in the second fraction. As summarized in Table 1,
the phthalocyanine 2b was obtained with the highest yield among
the series of three compounds due to the relatively less steric
hindrance arising from only one alkyloxycarbonyl group attached
at the meta-position of the phenoxyl moieties in comparison with
the same alkyloxycarbonyl group attached at the ortho-position for
2a and two alkyloxycarbonyl groups for 2c. Due to the same reason,
the distribution of the constitutional isomers obtained from 2b
shows the most consistency (C4h:C2v & Cs:D2h ¼ 1:3.6:0.8) with the
statistical expected yields (C4h:C2v & Cs:D2h ¼ 1:6:1).
group at a face-to-face position. Meanwhile, the interaction of two
substituents in the D2h isomer also make the chemical shifts of
phenoxy protons (H1, H2) and aliphatic protons (H3 to H7) move to
high field to some extent in comparison with those peaks related to
the C4h isomer.
Interestingly, although C2v and Cs isomers cannot be separated by
column chromatography, their ratio in the product can be estimated
The phthalocyanine compounds including the mixed isomers
with C2v and Cs symmetry have been characterized by MALDI-TOF
mass and electronic absorption spectroscopy in addition to ele-
mental analysis. The MALDI-TOF mass spectra of these compounds
clearly showed intense signals of molecular ions (M)þ (Table 1). The
isotopic pattern closely resembled the simulated one as exempli-
fied by the spectrum of C4h isomer of 2a, Fig. S1 (Supplementary
material).
1H NMR and 2D COSY spectra of all the single isomers were
recorded in CDCl3 with a drop of pyridine[D5] except the one with
Fig. 4. Electronic absorption spectra of C4h (full) and D2h (dotted) isomers of com-
pound 2a in THF. Spectra were normalized to the same absorption at Q-band.

M. Bai et al. / Dyes and Pigments 97 (2013) 469e474
473
Table 3
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the distribution of C2v and Cs isomers in this mixture, which is
almost in consistent with the statistical expected yield (1:2). For the
compounds 2b and 2c, the signals of the free Ha for the C2v and Cs
isomers are overlapped, but the shielding H0a can be used to reveal
their distribution in the mixture (1:1.74 for 2b, 1:2.08 for 2c, Table 2
and Fig. 1 and Figs. S14e16 (Supplementary material).
The electronic absorption spectra of the C4h and D2h isomers of
2ae2c have been recorded in THF. As can be seen in Fig. 4, S17, and
S18 (Supplementary material), Table 3, both isomers of these
compounds show typical electronic absorption spectra of the
phthalocyaninato metal complexes [1a]. The absorption spectra of
C4h isomers show a Soret band at 341e348 nm, an intense and
sharp Q band at 681e687 nm, and a vibronic band at 615e620 nm,
while the spectra of D2h isomers exhibit a 10 nm red-shift in the Q-
band and 5e7 nm in the vibronic band probably due to the non-
planarity of the macrocycle in these sterically stressed isomers
[10c].
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We have prepared a series of 1(4),8(11),15(18),22(25)-tetrakis
[(pentyloxycarbonyl)phenoxy]phthalocyaninato zinc(II) complexes
as a mixture of four constitutional isomers. Their C4h and D2h iso-
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The yields in combination with the NMR spectroscopic results
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Financial support from the Natural Science Foundation of China
(Grant No. 21001069) and the Independent Innovation Foundation
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Appendix A. Supplementary data
Supplementary data related to this article can be found in the
online version at http://dx.doi.org/10.1016/j.dyepig.2013.01.016.

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