Improved synthesis and chromophoric properties of tetra-β-(2- octanyloxy)substituted nickel phthalocyanine

Article abstract of DOI:10.14233/ajchem.2014.15946

In order to further apprehend chromophoric properties of phthalcyanine materials, a lipophilic tetra-β-(2-octanyloxy)-substituted nickel phthalocyanine was synthesized with a yield of 78 % by a facile method without nitrogen protection and long-term heating performance. The synthetic compound was characterized by mass spectra, ¹H NMR, UV-visible, IR and elemental analysis, which were consistent with the proposed molecular structure. The compound not only behaved excellent solubility in many organic solvents, but also exhibited different chromophoric properties in various types of solvents, e.g., blue in isooctane and green in tetrahydrofuran. More interestingly, the chromophoric properties could be largely modulated by employed solvent, solution concentration and environment temperature.

Full text of DOI:10.14233/ajchem.2014.15946

Asian Journal of Chemistry; Vol. 26, No. 8 (2014), 2351-2356
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.15946
Improved Synthesis and Chromophoric Properties of
Tetra-β-(2-octanyloxy)substituted Nickel Phthalocyanine
1
1
2
1
1
FANGDI CONG , HAIFENG WANG , JIANXIN LI , LINGLING LI , QIANYUN YAN ,
XINXIN CHU , YANYAN MENG , KEZHI XING1,* and XIGUANG DU
2
2
2,*
1Tianjin Key Laboratory of Aqua-ecology and Aquaculture, Department of Basic Science, Tianjin Agricultural University, Tianjin 300384,
P.R. China
2Faculty of Chemistry, Northeast Normal University, Changchun 130024, P.R. China
*Corresponding authors: E-mail: tn_aqua_lab@aliyun.com; xgdum@aliyun.com
Received: 21 June 2013;
Accepted: 14 October 2013;
Published online: 15 April 2014;
AJC-15024
In order to further apprehend chromophoric properties of phthalcyanine materials, a lipophilic tetra-β-(2-octanyloxy)-substituted nickel
phthalocyanine was synthesized with a yield of 78 % by a facile method without nitrogen protection and long-term heating performance.
The synthetic compound was characterized by mass spectra, 1H NMR, UV-visible, IR and elemental analysis, which were consistent with
the proposed molecular structure. The compound not only behaved excellent solubility in many organic solvents, but also exhibited
different chromophoric properties in various types of solvents, e.g., blue in isooctane and green in tetrahydrofuran. More interestingly, the
chromophoric properties could be largely modulated by employed solvent, solution concentration and environment temperature.
Keywords: Phthalocyanine, Synthesis, Chromophoric property, Modulation.
solution concentration and environment temperature being
important10-15. However, this does not suggest that these
external factors can be ignored, but implies that some potential
consequences have not been adequately revealed from the
corresponding phthalocyanine compounds. For further
apprehending chromophoric properties of phthalocyanine
molecules, here a lipophilic tetra-β-(2-octanyloxy)-substituted
nickel phthalocyanine (ONPc) was synthesized by a facile
method and its chromophoric properties were modulated by
the aforesaid external factors. It was found that ONPc chromo-
phore could sensitively respond to the alteration of employed
solvent, solution concentration and environment temperature.
INTRODUCTION
Phthalocyanine (Pc) compounds are blue or green
chromophores widely applied in many forefront areas such as
functional films1,2, solar cells3,4 and biological probes5,6, etc.
All these applications are attributed to their uniquely large
and flat π-conjugation systems localized over an arrangement
of alternated carbon and nitrogen atoms7. Thus studying the
nature of π system and attempting to modulate π system have
been extensively and intensively investigated8. Typical
examples are the preparation of asymmetrical phthalocya-
nines9, sub-phthalocyanines10, super-phthalocyanines11,
aggregative phthalocyanines12 and various substituted phthalo-
cyanines13. Among these phthalocyanine compounds, the
substituted phthalocyanine derivatives are paid more attentions
because it is easy for them to be synthesized and they usually
EXPERIMENTAL
DMSO was pre-dried over BaO and distilled under reduced
pressure. All other reagents and solvents are commercial
available and used without further purification. The synthesis,
characterization and property study of ONPc were carried out
according to follow procedure and method, respectivly.
General procedure: Synthesis of 4-(2-octanyloxy)-
phthalonitrile 3. 10.39 g 4-Nitrophthalonitrile 1 (60 mmol) and
7.81 g 2-octanol 2 (60 mmol) were added to 100 mL anhydrous
DMSO at room temperature. The reaction mixture was stirred
and 3.6 g LiOH (150 mmol) was interfused over a 2 h period,
and the mixture was then stirred and monitored by TLC. After
behave excellent solubility in water or organic solvents14,15
.
To date, a number of substituted metal and metal-free phthalo-
cyanines have been synthesized so as to modify phthalocyanine
rings and find novel physicochemical properties11-14. But most
of the interests are centralized on how new substituents situated
around molecular periphery and diverse metals located in the
center of phthalocyanine ring impact on the π systems and
therefore modulate the chromophoric properties of phthalo-
cyanine compounds, few are mentioned of employed solvent,

2352 Cong et al.
Asian J. Chem.
1 day, the mixture was then poured into 300 mL of 10 % NaCl
solution and extracted with 100 mL chloroform twice. The
combined organic layer was washed by 100 mL water and
dried with Na2SO4. The product was collected by removing
solvent and further purified by flash column chromatography
with chloroform as the mobile phase to afford light yellow
and sticky liquid 4-(2-octanyloxy)phthalonitrile 3: 12.46 g,
Namely, the thick solution was first prepared, and then the
suitable quantity of thick solution was diluted into the required
concentration for analysis on a UV-visible 1800 Spectropho-
tometer.
The solid ONPc film employed in UV-visible analysis
was obtained by immersing a piece of clear quartz slice (10 ×
10 × 0.2 mm) in a 10 mL solution (8 × 10-5 mol L-1, in isooctane)
in a 50 mL beaker, and enveloping the beaker with filter paper
and then setting it for 3 days in air. The UV-visible analysis at
different temperature was mainly recurred to an equipped low-
constant-temperature bath using water as the heating and
cooling media. Cycled water can pass the colormetric stand
through the insulating hoses to make the sample solution in
quartz flow-cell (10 mm path length) maintain the same tempe-
rature as water.Although water temperature is indicated by an
electronic meter furnished in this spectrophotometer, a thermo-
meter is still put into water to show correct water temperature.
Before measurements, the solutions in the quartz cell sealed
tightly with a quartz cover were pretreated for 10 min in the
isothermal water.
1
yield: 81 %; b.p. > 200 °C; H NMR (500 MHz, CDCl3): δ
7.69 (d, 1H, ArH), 7.22 (s, 1H, ArH), 7.14 (d, 1H, ArH), 4.45
(m, 1H, OCH), 1.75 (m, 2H, CH2), 1.62 (m, 3H, CH3), 1.42
(m, 2H, CH2), 1.28-1.35 (m, 6H, CH2CH2CH2), 0.88 (m, 3H,
CH3); MS (CHCl3): m/z calcd for [M + Na+]: 279.3, found:
279.6 (an isotopic cluster peak) [M + Na+]; IR (KBr, νmax, cm-1):
2231 vs (C=N), 1253 vs (C-O-C); UV-visible (CHCl3): λmax
=
264, 302, 310 nm.Anal. Calcd for C16H12N2O (256.3): C 74.97,
H 7.86, N 10.93, Found: C 74.93, H 7.63, N 10.85.
Synthesis of tetra-β-(2-octanyloxy)-substituted nickel
phthalocyanine (ONPc): 4.10 g Phthalonitrile derivative 3
(16.0 mmol), 0.95 g NiCl2·6H2O (4.0 mmol), 10 g urea and
0.05 g (NH4)2MoO4 were mixed well and added in a 100 mL
beaker. The beaker was covered with a watch glass and heated
at 180 °C for 2 h in a heat-collection-type heater (DF-101S).
After cooling, the resultant blue solid was ground and then
washed with methanol by Soxhlet extraction to remove
unreacted 3 and other remnants. In the end, the collected solid
was purified by flash column chromatography with chloro-
form as the mobile phase to give pure blue solid ONPc: 3.39
g, Yield: 78 %; 1H NMR (500 MHz, CDCl3): δ 8.09-6.05 (m,
broad, 12H, ArH), 4.77-4.93 (m, broad, 4H, 4OCH), 2.14-
1.04 (m, broad, 64H, 4CH3(CH2)5 and 4CH3); MS (CHCl3):
RESULTS AND DISCUSSION
The common synthesis of lipophilic metal phthalocyanines
was carried out by heating substituted phthalonitriles and
inorganic salt at 135 °C for more than 12 h in presence of
DBU as catalyst in a suitable organic solvent and under
nitrogen atmosphere16. Though the reaction temperature was
comparatively low, the long reaction time and nitrogen
protection did not benefit performance, and also the final yield
usually was not over 60 %. In order to facilitate synthesis, the
substrate-melting synthetic method generally employed in
preparation of hydrophilic substituted metal phthalocyanines
was imported17 and accordingly a facile protocol for synthesis
of lipophilic ONPc was designed as in Scheme-I. By this
means, the substituted phthalonitriles 3 and nickel salt were
melted at 180 °C for 2 h in the presence of (NH4)2MoO4 as
catalyst in melted urea. After purified by column chromato-
graphy, the ONPc yield was about 78 %. Comparing with the
routine way of lipophilic phthalocyanines synthesized in
solution16, here the synthetic method not only gave a high yield
more than 70 % but also was more facile due to no nitrogen
protection and long-term heating performance.
m/z calcd for [M]: 1082.6, found: 1082.7 [M]; IR (KBr, νmax
,
cm-1): 1235 vs (C-O-C); Anal. Calcd for C64H80N8O4Ni: C
70.91, H 7.44, N 10.34, Found: C 70.87, H 7.47, N 10.26.
1
Detection method: H NMR spectra were recorded on
an INOVA-500 spectrometer. IR spectra were measured on a
Thermo FT-IR-200 spectrometer. UV-visible spectra were
taken on a Shimadzu UV-visible-1800 spectrophotometer. MS
spectra were obtained on a LDI-1700-TOF mass spectrometer.
Elemental analyses were performed on a Perkin-Elmer 2400
Elemental Analyzer.
UV-visible analysis of ONPc: The solution of ONPc in
various solvents was prepared by weighing and diluting methods.
CN
O
O
O2N
CN
N
Ni
N
NC
CN
1
N
N
N
N
N
Urea, (NH4)2MOO4
180 °C
N
DMSO, LiOH
+
r.t.
OH
O
O
O
2
3
ONPc
Scheme-I: Synthesis of ONPc

Vol. 26, No. 8 (2014)
Synthesis and Chromophoric Properties of Tetra-β-(2-octanyloxy)substituted Nickel Phthalocyanine 2353
Tetra-β-(2-octanyloxy)-substituted nickel phthalocyanine
was characterized by mass spectra, 1H NMR, UV-visible, IR
and elemental analysis, which were consistent with the proposed
structure in Scheme-I. In the mass spectrum, the peak of singly
charged molecular ion was obvious and moreover a weak peak
of dimer could be distinguished, which meant that phthalocyanine
molecules were inclined to aggregate (Fig. 1). The 1H NMR
spectrum was strongly impacted by paramagnetism of the
center Ni(II) in a square planar environment17, which resulted
in that ONPc displayed three broad bands in 1H NMR spectra:
δ 8.09-6.05 (12H ArH), 4.77-4.93 (4H CH), 2.14-1.04 (64H
CH2 and CH3). The IR absorption at 1235 cm-1 (C-O-C) meant
the characteristic vibration of chemical bond linking 2-octany-
loxy group to phthalocyanine ring. The UV-visible spectra and
chromophoric properties of ONPc were discussed.
2-ocatanyloxy groups allowed it to be dissolved in those organic
molecules with enough size and/or suitable polarity based on
the similarity and intermiscibility principle. The fine solubility
implied that solvents could sufficiently conquer the aggregation
among phthalocyanine rings and dispersed them well. The
more interesting thing was that ONPc molecules behaved very
unlike chromophoric properties in various types of solvents,
e.g., being blue in isooctane and green in THF (Fig. 2 solutions
in two bottles). The phenomena could be analyzed based on
the UV-visible spectra of ONPc in two solvents (Fig. 2). In THF,
ONPc like those usual substituted metal phthalocyanines
displayed a standard UV-visible spectrum with a narrow Q band
at 676 nm, which meant that phthalocyanine molecules had
been dispersed into molecular monomers16. In isooctane, it
gave an abnormally broad Q band at 668 nm, and a broader and
stronger shoulder peak at 609 nm.All these were the evidences
that some phthalocyanine molecules had stacked by H-aggre-
gation pattern, namely face-to-face fashion19. H-aggregation
usually occurred among hydrophilic phthalocyanine molecules
due to the high hydrophobicity of phthalocyanine rings in
water, and those lipophilic phthalocyanines were seldom found
having this aggregation in organic solvents16. The H-aggre-
gation among lipophilic ONPc molecules in isooctane might
be comprehended by the interaction between solute and solvent
molecules. In solution, there were two molecular interactions
related to ONPc dissolution. One was the interaction between
solvent and solute molecules, favoring dissolution. Another
one was the stacking among ONPc flat π systems, helping H-
aggregation. In THF, the solvent molecules interacted on not
only the long alkyl chain but also the oxygen of substituents
as well as the center Ni(II), which was enough to overcome
the intermolecular π stacking force and disperse ONPc into
molecular monomers. Comparing with THF, isooctane
molecules mainly pulled the long alkyl chain of 2-octanyoxyl
groups, which does not adequately prevented the π stacking,
Monomer
1959.6
Dimer
2164.8
1988.5
1900
2000
2100
2200
Mass (Charge)
1050
1100
Mass (Charge)
1150
676 nm
1.5
Fig. 1. TOF mass spectra of ONPc: m/z, 1082.7 for monomer; 2164.8 for
dimer
The synthetic ONPc have four 2-octanyloxy groups around
macromolecular ring and thereby it can be dissolved in many
organic solvents, but the solubility is different in various types
of solvents (Table-1). It was hard dispersed by small molecule
solvents, e.g, methanol and acetone, or by high polar solvents,
e.g, DMF and DMSO. In ethanol and propanol, ONPc dissolved
slowly and slightly. In some bulky or suitable polar molecules,
the phthalocyanine compound behaved excellent solubility.
The soluble diversity was attributed to the difference of affinity
between solvent and phthalocyanine molecules18. In terms of
ONPc structure, the long alkyl chain and weak polarity of
1.0
in isooctane
8 ×10-5 mol L
in THF
-1
0.5
0.0
609 nm
-5
c (1×10 mol L-1):
in isooctane;
in THF
400
500
Wavelength (nm)
600
700
Fig. 2. Colours (up) and UV-visible spectra (down) of ONPc in isooctane
and THF
TABLE-1
SOLUBILITY OF ONPC IN VARIOUS ORGANIC SOLVENTS
Easy
Solubility
Solvents
Hard
Slight
Blue
Green solution
Chloroform, THF, paraffin,
aromatic hydrocarbons
Methanol, acetone, Ethanol, propanol
DMF, DMSO
Butanol, petroleum
ether, isooctane
Octanol, ethyl acetate,
ethyl ether, triethylamine

2354 Cong et al.
Asian J. Chem.
2.0
1.5
1.0
0.5
0.0
and left a few ONPc molecules to aggregate slightly in iso-
octane. The results were that the Q band appeared hypochromic
effect at 668 nm and the shoulder peak presented strong
hyperchromic effect at 609 nm. Thus the solution was blue
instead of green as in THF. This showed that ONPc chromo-
phore could be remarkably modulated by suitable solvents.
Although paraffin like isooctane was also mainly consisted
of alkyl hydrocarbons, ONPc was green in paraffin and had a
narrow Q band at 675 nm (Fig. 3 a). This should result from
the strong interaction between bulky paraffin molecules and
2-octanyloxy groups around phthalocyanine rings, for widely
known that the bulkier the molecule is, the stronger interaction
it gives. The similar situation could be met in the other types
of solvents, e.g., 1-butanol and 1-octanol. ONPc dissolved
slowly in 1-butanol and gave a broad Q band as in isooctane,
but dissolved well in 1-octanol and presented a slightly nice
Q band at 676 nm (Fig. 3 b).
675 nm
669 nm
671 nm
678 nm
drops
c
: 1× ·
10-5mol L-1
0
5
10
20
40
60
c: (× ·
10-6mol L-1)
in chloroform
in ethyl ether
in THF
10.0
5.00
2.50
1.25
0.63
(a)
(c)
600
700
Wavelength (nm)
600
700
Wavelength (nm)
10-5 mol L-1
c: 3
×
·
in isooctane with
0-60 drops of THF
(b)
300
400
500
600
700
Wavelength (nm)
Fig. 4. UV-visible spectra of ONPc in organic solvents with various polarities
slightly even if isooctane was mixed into cinnamene. The
mixed solvent of cinnamene and isooctane (2:1, v:v) only cause
Q band with a slightly hypochromic effect and a 2 nm blue-
shift from 679 to 677 nm. The mixed solvent of cinnamene
and isooctane (1:2, v:v) induced Q band with an obviously
hypochromic effect and a 5 nm blue-shift from 679 to 674
nm, but the Q band still was normal profile (Fig. 5a). Whereas
a few drops of cinnamene were mixed into isooctane, then
hyperchromic effect appeared obviously at 668 nm (Fig. 5b).
The aforesaid phenomena showed that cinnamene greatly
interacted with ONPc molecules and dispersed them well.
Comparing with isooctane, cinnamene had a π conjugation
benzene ring and hence the hydrocarbon not only pulled 2-
octanyloxy groups but also attracted the large π system of
ONPc by π-π interaction similar to Pc-Pc stacking19. It was
the two affinities that dispersed ONPc well in cinnamene.
1.2
675 nm
676 nm
c
: 1.0× ·
10-5mol L-1
c
: 1.0× ·
10-5mol L-1
in isooctane
in paraffine
0.9
0.6
0.3
0.0
in 1-butanol
in 1-octanol
668 nm
671 nm
(a)
600
700
Wavelength (nm)
(b)
400
500
600
700
Wavelength (nm)
Fig. 3. UV-visible spectra of ONPc in size-different organic molecules
The solvent polarity also gave obvious impact on the
ONPc chromophore. Ethyl ether had elemental compositions
similar to THF, but it was endowed with weak polarity for the
better molecular symmetry. The result was that ethyl ether
could not disperse ONPc well and only offered it with a broad
Q absorption band at 669 nm (Fig. 4a). Contrarily, chloroform
with suitable polarity in despite of being little molecule could
dissolve ONPc very well and present it with a narrow Q band
at 678 nm. And the Q band did not distort following concen-
tration alteration (Fig. 4b). But the more high polarity was not
helpful for employed solvents, e.g., DMF and DOSO, to
disperse ONPc on account of disobeying the similarity and
intermiscibility principle (Table-1). Now that the suitable
polarity was another favorable factor for solvent to dissolve
ONPc, then ONPc chromophore might be modulated by altering
solvent polarity via mixing one into another solvent. This was
agreed with the fact that THF, gradually mixed into solution
of ONPc in isooctane, induced hyperchromic effect, Q band
narrowing and a red shift from 668 nm to 671 nm (Fig. 4c).
Unlike isooctane, aromatic hydrocarbons were very
favorable in dispersing ONPc (Table-1) and provided it with a
narrow Q band (Fig. 5). In cinnamene, ONPc appeared a
narrow Q band at 679 nm and the absorption was impacted
679 nm
670 nm
c
: 1.0× ·
10-5mol L-1
in isooctane with 0-9
drops of cinnamene
677 nm
c
: 1.0
×
10-5mol
·
L-1
1.5
1.0
0.5
0.0
674 nm
drops
in solvent
(isooctane
:cinnamene,
0
1
2
3
4
5
6
7
8
9
V:V)
2:1
1:2
0:1
(b)
600
700
Wavelength (nm)
(a)
400
500
600
700
800
Wavelength (nm)
Fig. 5. UV-visible spectra of ONPc in cinnamene, isooctane and mixed solvent
The fact that ONPc dissolved well but preferred aggrega-
tion in isooctane revealed that the space between two adjacent
phthalocyanine molecules was not enough to prevent inter-
molecular aggregation. Well then diluting solution might pull
them apart from one another and help to lessen aggregation.
Therefore the solution of ONPc in isooctane was diluted

Vol. 26, No. 8 (2014)
Synthesis and Chromophoric Properties of Tetra-β-(2-octanyloxy)substituted Nickel Phthalocyanine 2355
TABLE-2
PHYSICAL PARAMETERS OF ONPC IN ISOOCTANE
Parameters
Corresponding data
x = 5
4.0
x = 6
2.5
x = 7
3.1
x = 8
3.9
54
ca (× 10-x mol L-1)
8.0
1.8
2.3
2.0
3.2
3.1
1.0
4.3
3.5
5.0
6.0
3.9
1.3
11
6.3
15
1.6
25
7.8
30
2.0
70
15
Qc
Sd
2.3
2.7
8.2
20
εb (× 104 L mol-1 cm)
4.2
4.6
4.8
5.4
5.8
7.7
13
a Concentration of ONPc in isooctane, b Molar extinction coefficient, c Q band around 667 nm, d Shoulder peak around 609 nm
0.9
0.6
0.3
0.0
gradually by two folds once and it was found that dilution
caused the shoulder peak at 609 nm decrease relative to the Q
band at 667 nm (Fig. 6a), which meant that aggregation was
gradually weaken. Accordingly the Q band had a 39-fold
increase in molar extinction coefficient (ε) from 1.8 to 70 ×
104 L mol-1 cm and the shoulder peak only had a 6.5 fold
increase in ε from 2.3 to 15 × 104 L mol-1 cm (Table-2). When
the concentration decreased down to 6.3 × 10-7 mol L-1, the Q
band had already turned into a normal profile and gave a red
shift from 667 to 669 nm (Fig. 6b). These changes illuminated
that H-aggregation in dilute solution of ONPc in isooctane
became difficult due to lengthening phthalocyanine-inter-
molecular space. Certainly ONPc should be inclined to aggregate
greatly in solid, which could be concluded by the exceptionally
broad Q band of solid ONPc film (Fig. 6c).
675 nm
×
10-5mol/L
669 nm
c: 1.0
in paraffine
c: 1.0×
10-5mol/L
in isooctane
25
0
50
℃
℃
℃
25
0
℃
℃
℃
50
(b)
600
700
Wavelength(nm)
(a)
400
500
600
700
800
Wavelength (nm)
Fig. 7. UV-visible spectra of ONPc in isooctane and paraffine at different
temperatures
c
(mol·L-1):
8.0
×
10-5,
4.0
×
10-5,
2.0×
10-5,
1.0
6.3
3.9
×
×
×
10-5,
10-7,
10-8,
5.0
×
×
×
10-6,
10-7,
10-8
2.5
1.6
×
×
10-6,
10-7,
1.3
7.8
×
×
10-6,
10-8,
Conclusion
3.1
2.0
A facile method was imported to synthesize lipophilic
ONPc by modifying the strategy employed in preparation of
hydrophilic phthalocyanine compounds. The method not only
could improve resultant yield up to 78 % but also largely cut
reaction time down to 2 h, and also needed not nitrogen protec-
tion. ONPc behaved excellent solubility in various organic
solvents, but showed greatly different chromophoric properties
in them. In small or weakly polar molecules, it exhibited blue
due to intermolecular H-aggregation. In those bulky, suitable
polar or aromatic molecules, it displayed green for phthalo-
cyanine molecules dispersed well. After diluted, ONPc in iso-
octane appeared obviously hyperchromic effect at Q band for
large phthalocyanine-intermolecular space weakening H-
aggregation. In addition, higher temperature also induced
hyperchromic effect of Q band for energetic phthalocyanine
molecules effectively resisting intermolecular stacking.
2
1
0
669 nm
609 nm
609 nm
667 nm
(c)
solid film of ONPc on a
quartz slice (10 10 0.2 mm)
(a)
×
×
600
700
Wavelength (nm)
(b)
400
600
Wavelength (nm)
800
Fig. 6. UV-visible spectra of ONPc in isooctane and solid film
Based on molecular thermodynamics, high temperature
caused liquid molecules move more intensively to overcome
intermolecular interaction20. In terms of ONPc molecules, the
intermolecular stacking among them in isooctane should be
influenced by temperature and accordingly its chromophoric
properties also should be altered. It was found that the Q band
of ONPc in isooctane exhibited obviously hyperchromic effect
at 50 °C and contrarily appeared hypochromic effect at 0 °C,
relative to the absorbance at 25 °C (Fig. 7a). The temperature-
dependent chromophoric properties were also observed in the
solutions of ONPc in other solvents, e.g., paraffin (Fig. 7b). It
was obvious that the higher temperature could availably
activate ONPc molecules into energetic molecules to resist
intermolecular stacking and induce the hyperchromic effect
of Q band.
ACKNOWLEDGEMENTS
The authors thank the National Natural Science
Foundation of China (20530115) and the 41st Postdoctoral
Science Foundation of China, for financial support.
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