The synthesis and photophysical properties of zinc (II) phthalocyanine bearing poly(aryl benzyl ether) dendritic substituents

Article abstract of DOI:10.1016/j.dyepig.2010.01.016

Zinc (II) phthalocyanines carrying four poly(aryl benzyl ether) dendritic substituents with terminal cyano and carboxylic acid functionalities were synthesized and characterized using elemental analysis, ¹H NMR, IR, UV-vis and matrix-assisted l

Full text of DOI:10.1016/j.dyepig.2010.01.016

Dyes and Pigments 87 (2010) 10e16
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and photophysical properties of zinc (II) phthalocyanine bearing
poly(aryl benzyl ether) dendritic substituents
,
a
b
a
a
c
Yiru Peng a , Hong Zhang , Haoling Wu , Baoquan Huang , Li Gan , Zhe Chen
*
a College of Chemistry & Materials Science, Fujian Normal University, Fujian Provincial Key Laboratory of Polymer Materials, Fuzhou 350007, China
b Affiliated First Hospital of Fujian Medical University, Fuzhou 350003, China
c College of Chemistry & Chemical Engineering, Xiamen University, Xiamen 361005, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Zinc (II) phthalocyanines carrying four poly(aryl benzyl ether) dendritic substituents with terminal cyano
and carboxylic acid functionalities were synthesized and characterized using elemental analysis, 1H NMR,
IR, UVevis and matrix-assisted laser-desorption ionization time-of-flight spectra. Phthalocyanines with
terminal cyano groups were essentially non-aggregated in common organic solvents whilst the aqueous
aggregation tendency of those which contained terminal carboxylic acid groups decreased with
increasing size of the dendron. Photoinduced electron transfer in these compounds was investigated
using a fluorescence quenching method, employing both neutral and cationic quenchers. Upon excitation
of the dendritic subunits in DMSO, the cyano compounds underwent intermolecular energy transfer
from the excited dendritic subunits to the phthalocyanine core which acted as an energy trap.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 26 October 2009
Received in revised form
19 January 2010
Accepted 20 January 2010
Available online 1 February 2010
Keywords:
Phthalocyanine
Dendrimer
Poly(aryl benzyl ester)
Cyano terminal groups
Synthesis
Photophysical property
1. Introduction
stacking of phthalocyanines in aqueous media is particularly
strong; consequently, hydrophilic and non-aggregated phthalocy-
Phthalocyanines and related macrocyclic compounds have
found widespread application in various areas including liquid
crystals, non-linear optical devices, catalysts, chemical sensors,
data storage systems, electrochromic and photochromic materials
and second generation photosensitizers for photodynamic therapy
[1,2]. Numerous studies have been carried out to modify these
macrocyclic compounds with the goal of moderating their prop-
erties and optimizing their performance for advanced materials.
In the context of photodynamic therapy, it is desired that
phthalocyanines should not aggregate and have high solubility in
aqueous media [3]. Molecular aggregation, which is an intrinsic
anines are extremely rare despite their great potential application
in photodynamic therapy.
Recently, phthalocyanines and their metal complexes encapsu-
lated within the inner core of dendrimers that bear hydrophilic
surface groups have been prepared and their high aqueous solu-
bility, absence of aggregation and other interesting photophysical
properties have been reported [5e15]. However, reports concerning
this type of substituted phthalocyanine are relatively rare.
This paper concerns the synthesis and photophysical properties
of two novel series of zinc (II) phthalocyanines containing four poly
(aryl benzyl ether) dendritic substituents with terminal cyano and
carboxylic acid functionalities. Both photoinduced intermolecular
electronic transfer and energy transfer in these novel macromole-
cules are described.
characteristic of these large
p-conjugated compounds, markedly
shortens the phthalocyanine triplet state lifetime and reduces
fluorescence quantum yield, thereby leading to a decrease in
photodynamic therapy efficiency. Displaying high solubility in
aqueous media would be beneficial not only for transportation of
photosensitizers to malignant tissues by serum albumin but also
for selective accumulation in the connective tissue which surround
the tumor cells [4]. However, owing to hydrophobic interactions,
2. Experimental
All reactions were carried out under nitrogen atmosphere in
dried solvents. All chemicals were used as supplied by chemical
companies. n-Pentanol and 1,8-diazabicyclo-(5,4,0)-undec-7-ene
(DBU) were purchased from Aldrich. A PerkineElmer ATR Fourier
transform infrared spectrometer was used for IR data collection.
* Corresponding author. Tel.: þ86 591 8346 5225.
E-mail address: yirupeng@hotmail.com (Y. Peng).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.01.016

Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
11
1H NMR spectra were recorded with a Bruker 400 MHz FT-NMR
spectrometer. Matrix-assisted laser-desorption ionization time-of-
flight (MALDI-TOF) spectra were obtained on a Bruker bench TOF
mass spectrometer equipped with a standard UV-laser-desorption
source, using dithranol as matrix. UV/Vis spectra were recorded on
the PerkineElmer Lambda 9 UV/Vis/IR spectrometers. The Fluo-
rescence spectra were recorded on the FL900/FS920 steady-state
florescence spectrometers.
Found: C: 75.36, H: 4.74, N 6.64. IR/cmꢁ1: 3400, 2930, 2230, 1500,
1450, 1415, 1318, 1298, 1214, 1160, 1050, 822. 1H NMR (DMSO-d6,
400 MHz,
d/ppm): 7.84e7.85 (m, 8H, CNPheH), 7.62 (s, 8H,
CNPheH), 6.73 (s, 4H, Ar0eH), 6.65 (s, 2H, AreH), 6.58 (s, 2H,
Ar0eH), 6.49 (s, 2H, AreH), 5.21 (s, 8H, CNPhCH2), 5.01 (s, 4H,
CH2OH), 4.44 (s, 2H, CH2OH). ESI-MS (m/z), 844. Found: 867
[M þ Na]þ.
The scheme for synthesis of compounds (3)e(11) was listed in
Fig. 1.
2.4. Synthesis of compound (6)
Anhydrous potassium carbonate (0.62 g, 4.50 mmol) was added
to a mixture of 4-nitrophthalonitrile (0.52 g, 3.02 mmol) and (3)
(1.11 g, 3.00 mmol) in DMF (20 mL). The mixture was heated at
60 ꢀC with stirring overnight, and then poured into an ice-water
mixture (100 mL). The precipitate formed was filtered off and
purified by recrystallization using methanol (50 mL) as solvent to
give (6) as a white solid. Yield: 50%; mp: 222e224 ꢀC. Analysis
Calcd. for C31N4H20O3, C: 75.00, H: 4.23, N: 11.29. Found: C: 74.99,
H: 4.25, N: 11.32. IR/cmꢁ1: 3400e3300, 3090, 2910e2800, 2228,
1599, 1443, 1416, 1318, 1295, 1214, 1165, 1060, 1020, 822. 1H NMR
2.1. Synthesis of compound (3)
The mixture of 4-(bromomethyl) benzonitrile (1) (14.1 g,
72.0 mmol), 3,5-dihydroxybenzylalcohol (2) (4.9 g, 35.0 mmol),
K2CO3 (12.1 g, 87.0 mmol), and 18-crown-6 (1.85 g, 7.0 mmol) in
tetrahydrofuran (THF) (50 mL) was heated at reflux and stirred
vigorously under nitrogen for 24 h. The mixture was allowed to cool
and evaporated to dryness under reduced pressure. The residue
was dissolved in water and CHCl3 (100 mL) (1:1 (v/v)) and the
aqueous layer extracted with CHCl3 (30 mL) for three times. The
combined organic layers were then dried over MgSO4 and evapo-
rated to dryness. The crude product was recrystallized from
hexane/CH2Cl2 (50 mL) (2:3 (v/v)) to give (3) as white colourless
crystals. Yield: 89%; mp: 144e146 ꢀC; Analysis Calcd. for
C23N2H18O3, C: 74.58, H: 4.89, N: 7.55. Found: C: 74.59, H: 4.86, N:
7.57. IR/cmꢁ1: 3400, 2900e2800, 2230, 1600, 1442, 1414, 1317, 1296,
(DMSO-d6, 400 MHz,
d
/ppm): 8.06e8.08 (d, J ¼ 8 Hz, 1H, AreH), 7.
84e7.87 (t, 5H, CNPheH), 7.61e7.63 (d, J ¼ 8 Hz, 4H, CNPheH),
7.49e7.51 (d, J ¼ 8 Hz, 1H, AreH), 6.69 (s, 1H, AreH), 6.74 (s, 1H,
AreH), 5.20e5.22 (d, J ¼ 8 Hz, 4H, PhCH2O), 5.10 (s, 2H, PhCH2O).
ESI-MS (m/z), 496. Found: 519 [M þ Na]þ.
2.5. Synthesis of compound (7)
1213, 1150, 1073, 1020, 822. 1H NMR (CDCl3, 400 MHz,
d/ppm):
7.85e7.87 (m, 4H, CNPheH), 7.61e7.63 (d, J ¼ 8 Hz, 4H, CNPheH),
6.54 (s, 2H, AreH), 6.60 (s, 1H, AreH), 5.20 (s, 4H, CNPhCH2), 4.42
(s, 2H, CH2OH). ESI-MS (m/z): 370. Found: 393 [M þ Na]þ.
According to the above procedure, 4-nitrophthalonitrile
(340 mg, 2.02 mmol) was treated with (5) (2.0 g, 2.0 mmol) and
anhydrous potassium carbonate (0.62 g, 4.5 mmol) in DMF (10 mL)
to give (7) as a white solid. Yield: 60%. Analysis Calcd. for
C61N6H42O7, C: 75.28, H: 4.23, N: 8.66. Found: C: 75.39, H: 4.33, N:
8.65. IR/cmꢁ1: 3300, 2932, 2230, 1599, 1450, 1430, 1318, 1295, 1250,
2.2. Synthesis of compound (4)
Carbon tetrabromide (5 g, 15.0 mmol) and triphenylphosphine
(caution: stable; incompatible with oxidizing agents, acids; 3.7 g,
15.0 mmol) were added to a solution of (3) (15 g, 13.5 mmol) in the
minimum amount of THF (10 mL), and the reaction mixture was
stirred at room temperature under nitrogen. The reaction mixture
changed from a transparent solution to a white solution with
a precipitate forming over time. The aqueous layer was extracted
with CHCl3 (30 mL) for three times, and the CHCl3 extracts were
combined, dried and concentrated under reduced pressure. The
crude product was recrystallized from hexane/CH2Cl2 (100 mL) (3:7
(w/w)) to give (4) as white powder. Yield: 83%; Analysis Calcd. for
C23N2H17O2Br, C: 63.58, H: 3.79, N: 6.56. Found: C: 63.74, H: 3.93, N:
1160, 1060, 1020, 822. 1HNMR (DMSO-d6, 400 MHz,
d/ppm):
8.02e8.05 (d, J ¼ 12 Hz, 1H, CNPheH), 7. 83e7.85 (d, J ¼ 8 Hz, 9H,
(CN)2PheH), 7.59e7.61 (d, J ¼ 8 Hz, 8H, CNPheH), 7.47e7.50 (d,
J ¼ 12 Hz, 1H, (CN)2PheH), 6.71 (s, 4H, AreH), 6.69 (s, 3H, AreH),
6.65 (s, 1H, AreH), 5.20 (s, 0H, CNPhCH2O), 5.02 (s, 4H, PhCH2O).
ESI-MS (m/z), 971. Found: 994 [M þ Na]þ.
2.6. Synthesis of compound (8)
A mixture of (6) (0.2 g, 0.4 mmol) and Zn(OAc) ꢂ 2H2O (0.02 g,
0.10 mmol) in n-pentanol (10 mL) was heated at 130 ꢀC, and then
a few drops of DBU were added. The mixture was heated at 150 ꢀC
with stirring overnight. The volatiles were then removed under
reduced pressure to give a greenish blue solid, which was chro-
matographed twice with ethyl acetate/hexanes (9:1(v/v)) as eluent.
The crude product obtained was dissolved in a minimum amount of
THF to which MeOH (30 mL) and H2O (70 mL) were added to induce
precipitation. A greenish blue solid was obtained after filtration and
drying in vacuo. Yield: 60%; Analysis Calcd. for C124N16H80O12Zn: C:
6.47. IR/cmꢁ1: 3400, 2900e2800, 2230, 1600, 1443, 1416, 1318, 1295,
1
1214, 1150, 1073, 1020, 822. H NMR (DMSO-d6, 400 MHz,
d/ppm):
7.66e7.68 (d, J ¼ 8 Hz, 4H, CNPheH), 7.50e7.52 (d, J ¼ 8 Hz, 4H,
CNPheH), 6.61 (s,2H, AreH), 6.47 (s,1H, AreH), 5.00 (s,4H, CNPhCH2),
4.63 (s, 2H, CH2OH). ESI-MS (m/z), 433. Found: 457 [M þ Na]þ.
2.3. Synthesis of compound (5)
72.62, H: 3.90, N: 10.93. Found: C: 72.64, H: 3.89, N: 10.91. IR/cmꢁ1
3300, 2920, 2230, 1600, 1450, 1430, 1318, 1295, 1250, 1165, 1060,
1020, 822, 580. 1H NMR (DMSO-d6, 400 MHz,
/ppm): 7.67 (s, 4H,
:
The mixture of (4) (5 g, 11.1 mmol), 3,5-dihydroxybenzylalcohol
(2) (0.74 g, 5.0 mmol), K2CO3 (12.1 g, 87.0 mmol), and 18-crown-6
(0.29 g, 1.07 mmol) in acetone (50 mL) was heated at reflux and
stirred vigorously under nitrogen for 48 h. The mixture was
allowed to cool and evaporated to dryness under reduced pressure.
The residue was dissolved in water and CHCl3 (100 mL) (1:1 (v/v))
and the aqueous layer extracted with CHCl3 (30 mL) for three times.
The combined organic layers were then dried over MgSO4 and
evaporated to dryness. The crude product was recrystallized from
hexane/CH2Cl2 (100 mL) (2:3 (v/v)) to give (5) as a colourless glass.
Yield: 75%. Analysis Calcd. for C53N4H39O3: C: 75.58, H: 4.51, N: 6.62.
d
PceH), 7.63e7.65 (d, J ¼ 8 Hz, 16H, AreH), 7.47e7.49 (d, J ¼ 8 Hz,
16H, AreH), 7.24e7.25 (d, J ¼ 4 Hz, 4H, PceH), 7.16e7.17 (d, J ¼ 4 Hz,
4H, PceH), 6.57 (s, 8H, AreH), 6.50 (s, 4H, AreH), 5.05 (s, 24H,
PhCH2O). MS (MALDI-TOF) (m/z), 2049. Found: 2068 [M þ H3O]þ.
2.7. Synthesis of compound (9)
Using the above procedure, Zn(OAc) ꢂ 2H2O (0.02 g, 0.10 mmol)
was treated with (7) (0.39 g, 0.40 mmol) and DBU in n-pentanol

12
Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
Fig. 1. The scheme for synthesis of compounds (3)e(11).

Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
13
(15 mL) to give (9) as a dark green solid. The volatiles were then
removed under reduced pressure to give a greenish blue solid,
which was chromatographed twice with ethyl acetate/hexanes (9:1
(v/v)) as eluent. A greenish blue solid was obtained after filtration
and drying in vacuo. Yield: 80%; Analysis Calcd. for
C244N24H168O28Zn: C: 74.11, H: 4.18, N: 8.48. Found: C: 74.15, H:
4.25, N: 8.51. IR/cmꢁ1: 3300, 2920e2800, 2230, 1600, 1450, 1430,
carbonate, in acetone at reflux to give the first generation alcohol
(3) in 89% yield. Reaction of (3) with carbon tetrabromide/triphe-
nylphosphine regenerated the benzyl bromide site at the focal
point to give (4). Coupling of (4) to the monomer unit (2), through
reaction with potassium carbonate afforded the second generation
dendritic alcohol (5). Cyano groups were chosen as the terminal
functionalities because of their strong electron withdrawal ability
and their stability to the reaction conditions used for dendritic
growth with 3,5-dihydroxybenzyl alcohol as the monomer unit
[17]. In the above reactions including all the coupling reactions to
the monomer unit, no tri-O-alkylated or C-alkylated products were
observed [18]. Treatment of these dendritic alcohols with 4-nitro-
phthalonitrile in the presence of K2CO3 led to nucleophilic aromatic
substitution giving the corresponding dendritic phthalonitriles
(6)e(7) in good yields. Cyclization of these phthalonitriles (6)e(7)
with Zn(OAc) ꢂ 2H2O in the presence of a strong organic base (DBU)
in n-pentanol gave the corresponding dendritic zinc (II) phthalo-
cyanines (8)e(9) with cyano terminal groups as mixtures of
constitutional isomers. Upon treatment with NaOH in water,
compounds (8)e(9) were hydrolyzed to afford corresponding
water-soluble zinc (II) phthalocyanines (10)e(11) with carboxylic
acid terminal groups in almost quantitative yields.
Compounds (8)e(9) were highly soluble in most organic
solvents such as CHCl3, CH2Cl2, acetone, DMF and DMSO. With
a substantial number of hydrophilic moieties, compounds
(10)e(11) possessed good solubility in aqueous media.
The structures of compounds (3)e(11) were characterized by
a combination of methods including elemental analysis, 1H NMR,
IR, and UVevis, ESI-MS and MALDI-TOF mass spectrometry.
Intense singly charged molecular ions peaks were observed for
the MALDI-TOF spectra of all phthalocyanines (8)e(11) with
dithranol as the matrix.
1251, 1153, 1067, 822, 580. 1H NMR (DMSO-d6, 400 MHz,
d/ppm):
7.80e7.82 (d, J ¼ 8 Hz, 32H, CNPheH), 7.56e7.58 (d, J ¼ 8 Hz, 32H,
CNPheH), 7.38 (s, 4H, PceH), 7.29 (s, 4H, PceH), 7.19e7.21 (d,
J ¼ 8 Hz, 4H, PceH), 6.69 (s, 16H, AreH), 6.61 (s, 12H, AreH), 6.57 (s,
8H, AreH), 5.17 (s, 40H, PhCH2O), 4.99 (s, 16H, PhCH2O). MS
(MALDI-TOF) (m/z): 3949. Found: 3968 [M þ H3O]þ.
2.8. General procedure for hydrolysis of compounds (8)e(9)
to form compounds (10)e(11)
A mixture of compound (8) (400 mg) in 1 mol Lꢁ1 NaOH (30 mL)
was stirred at 100 ꢀC for 7 h, and then the precipitate formed in
1 mol Lꢁ1 HCl (100 mL) was filtered off. The resulting blue solid
contaminated with NaOH was dissolved in water (30 mL), and
several drops of 1 mol Lꢁ1 HCl were added until the pH reached
about 7. Ethanol (100 mL) was then added to precipitate the salt,
and the mixture was allowed to stand overnight. The correspond-
ing product (10) was collected by filtration and dried in vacuo. By
using the similar procedure, compound (9) was hydrolyzed to
obtain (11).
A mixture of compound (9) (780 mg) in 1 mol Lꢁ1 NaOH (30 mL)
was stirred at 100 ꢀC for 7 h, and then the precipitate formed in
1 mol Lꢁ1 HCl (100 mL) was filtered off. The resulting blue solid
contaminated with NaOH was dissolved in water (30 mL), and
several drops of 1 mol Lꢁ1 HCl were added until the pH reached
about 7. Ethanol (100 mL) was then added to precipitate the salt,
and the mixture was allowed to stand overnight. The corresponding
product (11) was collected by filtration and dried in vacuo. The yield
of (10) was 82%, and that of (11) was 80%. For (10), Analysis Calcd. for
C124N8H88O28Zn: C: 70.02, H: 4.14, N: 5.27. Found: C: 70.01, H: 4.16,
N: 5.29. IR/cmꢁ1: 3300, 2930, 1690, 1600, 1450, 1430, 1318, 1295,
1250, 1153, 1067, 1020, 822, 580; 1H NMR (DMSO-d6, 400 MHz,
Dendritic phthalocyanines (8)e(11) gave similar IR spectra. After
dendritic phthalonitriles (6)e(7) having been converted into
corresponding zinc (II) phthalocyanines (8)e(9), the stretching
vibration absorption of the phthalocyanines at 1600e1610 and
1520e1530 cmꢁ1 appeared, indicating of the formation of phtha-
locyanines. Moreover, the vibrations at 2800e3000 and
1060e1165 cmꢁ1 belonging to the characteristic stretching vibra-
tion of the submethyls and CeOeC of the substituted dendritic
structure were also observed. Upon treatment with NaOH, the
terminal cyano functional groups in (8)e(9) underwent hydrolysis
yielding corresponding compounds (10)e(11). The intense stretch-
ing band at 2237 cmꢁ1 assigned to the cyano groups of (8)e(9)
disappeared, while two intense signals at 1600 and 1318 cmꢁ1
emerged which could be assigned to the vasy and vsym stretching for
the carboxylic acid groups in (10)e(11), indicating the hydrolysis
was essentially complete.
d/ppm): 7.90e7.92 (d, J ¼ 8 Hz, 16H, HOOCPheH), 7.50e7.52 (d,
J ¼ 8 Hz,16H, HOOCPheH), 7.18 (s, 4H, PceH), 7.04e7.06 (d, J ¼ 8 Hz,
4H, PceH), 6.92e6.93 (d, J ¼ 4 Hz, 4H, PceH), 6.71 (s, 4H, AreH),
6.55 (s, 4H, AreH), 5.23 (s, 4H, PhCH2O), 5.14 (s, 4H, PhCH2O), 5.08
(s, 4H, PhCH2O). MS (MALDI-TOF) (m/z), 2201. Found: 2203
[M þ 2]þ. For (11), Analysis Calcd. for C244N8H184O44Zn: C: 68.66, H:
4.24, N: 2.58. Found: C: 68.84, H: 4.33, N: 2.63. IR/cmꢁ1: 3300, 3040,
2930, 1700, 1600, 1450, 1400, 1250, 1160, 1053, 1020, 822, 580. 1H
NMR (DMSO-d6, 400 MHz,
d
/ppm): 7.94e7.96 (d, J ¼ 8 Hz, 32H,
HOOCPheH), 7.78e7.80 (s, 4H, PceH), 7.53e755 (d, J ¼ 8 Hz, 32H,
HOOCPheH), 7.31 (s, 4H, PceH), 7.11e7.14 (d, J ¼ 12 Hz, 4H, PceH),
6.73 (s, 16H, AreH), 6.72e6.71 (d, J ¼ 4 Hz, 12H, AreH), 6.66 (s, 8 H,
AreH), 5.18 (s, 32H, PhCH2O), 5.12 (s, 8H, PhCH2O), 5.12 (s, 8H,
PhCH2O). MS (MALDI-TOF) (m/z), 4253. Found: 4253 [M]þ.
Compounds (8)e(11) were found to be pure by 1H NMR with
both the dendritic substituents and phthalocyanine ring protons in
their respective aromatic and alkyl regions. The 1H NMR spectrum
of the second generation dendritic zinc (II) phthalocyanine (9)
presented a great deal of structural information. As a consequence
3. Results and discussion
Table 1
Photophysical properties of dendritic phthalocyanines (8)e(11).
3.1. Synthesis and characterization
a
Compounds
Q-band/nm (log
3
)
lem
ss (ns)
Vfb
(8)
(9)
(10)
(11)
685 (6.72)
687e693
704
678
5.06
3.62
0.45
0.44
0.86
0.71
The preparation of dendritic zinc (II) phthalocyanines
commenced with the synthesis of cyano-terminated dendritic
phenols. The cyano-terminated dendritic phenols (3) and (5) were
prepared by the convergent growth approach involving repetitive
sequential growth and activation steps [16]. Briefly, 4-(bromo-
methyl)benzonitrile (1) was coupled to the monomer unit, 3,5-
dihydroxybenzyl alcohol (2), in the presence of potassium
686 (6.27)
686 (5.99), 626c
5.37, 2.73d
0.49, 0.39d
684 (6.09), 626 (5.67)c
709
a
Excited at 610 nm.
b
c
Relative to ZnPc (Vf ¼ 0.32 in DMSO).
Due to aggregated species in water.
In water.
d

14
Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
a narrowed Q-band at 685 nm, suggesting that molecular aggre-
0.25
0.20
0.15
0.10
0.05
0.00
gation was not significant for this compound in this concentration
range. The absorption spectra of (9) were very similar to that of (8),
and the data were summarized in Table 1.
The absorption spectra of (10)e(11) in water are shown in Fig. 2,
and the photophysical data were also compiled in Table 1. The
spectrum of (10) showed a broad signal with a maximum at
626 nm, which could be attributed to a dimeric species [19] indi-
cating that (10) was highly aggregated in water even under dilute
conditions. The UVevis spectrum of (11) in aqueous solution
exhibited a broad band at 626 nm. But after sonication or being
heated to ca. 70 ꢀC, the spectrum changed remarkably, leading to
a
monomer like spectrum at 684 nm. The spectrum with
a maximum at 684 nm indicating that (11) was relatively free from
molecular aggregation under these conditions. The absorption
spectra of (10)e(11) in DMSO indicated that both compounds
existed mainly as a monomeric species.
300
400
500
600
700
800
wavelength(nm)
Fig. 2. UV/Vis spectra of (10) (2 ꢃ 10ꢁ5 mol Lꢁ1) (e e) and (11) (2 ꢃ 10ꢁ5 mol Lꢁ1) (d)
3.2. Photophysical properties
in water.
Upon excitation at 610 nm, compounds (8)e(9) showed fluores-
cence emission spectra at 687e693 and 704 nm in DMSO with
quantum yields of 0.45 and 0.44 (with relative to ZnPc in DMSO
Ff ¼ 0.32), respectively. The fluorescence emission spectra of water-
soluble phthalocyanines (10)e(11) in water were at 678 and 709 nm
with quantumyields of 0.86 and 0.71, respectively. The singlet excited
of the strong electron-withdrawing effect of the cyano groups, the
lowest shifted signals at 7.80e7.82 and 7.56e7.58 ppm were
assigned to exterior aromatic protons of the dendritic substitutions
with cyano terminal groups. Three sets of resonances were
observed at 7.38, 7.29 and 7.19e7.21 ppm integrating for four
protons each, making a total of 12 protons expected for the
phthalocyanine ring protons. The resonances at 6.69, 6.61 and
6.57 ppm were assigned to the signals of the interior aromatic
protons. The singlet at 5.17e4.99 ppm was due to the benzylic
methylene protons. Integration of the signals in the aromatic region
and comparison with other resonances in alkyl region allowed the
structure of (9) to be determined. Confirmation the structures for
the other phthalocyanines (8), (10) and (11) was similarly accom-
plished. The layers of the monomer units for the different genera-
tions were seen as additional peaks in the 1H NMR spectra slightly
shifted from one another.
lifetimes (ss) were determined by time-resolved experiments in
which the fluorescence decay profiles were found to fit to a mono-
s
s
exponential function [f(t) ¼ A þ B1 eꢁt/ 1 þ B2 eꢁt/ 2 þ B3 eꢁt/
3 þ B4 eꢁt/ 4]. These values were listed in Table 1. Having a larger
s
s
number of dendritic substituents, compounds (9) and (11) were
relatively non-aggregated in solvents, showed much stronger emis-
sion, and located at slightly red shifted position. These results showed
that the size of the dendrons had a significant influence on the
phthalocyanines photophysical properties. Fluorescence of phthalo-
cyanines was rarely seen in aqueous media [20]. To our knowledge,
the intense fluorescence observed for phthalocyanines (10) and (11)
in water without the aid of surfactants is virtually unprecedented.
Using anthraquinone as the quencher, the intensities of fluo-
rescence and the rate of fluorescence quenching of compounds
(8)e(9) were measured in DMSO. With increasing concentration of
The UVevis spectrum of (8) in DMSO exhibited a strong Q-band
at 685 nm in addition to the UV bands at 290 nm due to the
dendritic substituents. When the concentrations of (8) increased
from 2.0 ꢃ 10ꢁ7 to 2.2 ꢃ 10ꢁ5 mol dmꢁ3, (8) always exhibited
3.5
c
3.0
2.5
2.0
6
d
5
80000
a
b
12000
1.5
4
70000
1.0
0
3
10
20
30
[Q]
40
50
10000
2
60000
50000
40000
30000
20000
10000
0
1
0
10
20
30
[Q]
40
50
8000
6000
4000
2000
0
660 680 700 720 740 760 780 800
wavelength/nm
640 660 680 700 720 740 760 780 800
wavelength/nm
Fig. 3. Fluorescence spectra of (8) (a) and (9) (b) quenching by anthraquinone in DMSO. c(8),(9) ¼ 2.0 ꢃ 10ꢁ5 mol Lꢁ1 in all cases. canthraquinone ¼ (ꢃ10ꢁ5 mol Lꢁ1) from up to down: 0,
0.2, 0.5, 1, 7, 13, 50. Inset plots: SterneVolmer plots for the fluorescence quenching of (8) (c) and (9) (d) in DMSO.

Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
15
Table 2
c
0.8
Rate constants for quenching of the fluorescence of (8)e(9) in DMSO and (10)e(11)
in water.
Compounds Quencher
KSV ꢃ 103 (L molꢁ1
4.02
0.72
)
Kq ꢃ 1011 (L molꢁ1 sꢁ1
7.93
1.97
2.02
1.61
)
0.6
0.4
0.2
0.0
(8)
(9)
Anthraquinone
Anthraquinone
(10)
(11)
Methyl viologen 1.09
Methyl viologen 0.79
anthraquinone, the fluorescence intensities were reduced. The data
could be analyzed according to the SterneVolmer equation (Eq. (1))
[21], where I0 and I are the intensities of fluorescence in the absence
and presence of the quencher respectively, [Q] is the concentration
of the quencher, and KSV is the SterneVolmer quenching constant,
which is the product of the bimolecular quenching rate constant
(kq) and the lifetime of the fluorescing species in the absence of the
b
a
300
400
500
600
700
800
wavelength(nm)
quencher (ss).
Fig. 5. Fluorescence spectra of (8) (a), (9) (b) and second generation alcohol (c) when
they are excited at 290 nm.
I0=I ¼ 1 þ KSV½Qꢄ ¼ 1 þ kqsS½Qꢄ
(1)
Fig. 3 showed the SterneVolmer plots for (8)e(9) from which
the values of KSV and kq could be determined (Table 2). The results
showed that the value of KSV is greater for lower generation
dendrimers. This maybe due to the lower generation dendrimers
provided a less hindered environment enabling the quencher to
reach the vicinity of the phthalocyanine core. It could be concluded
that the fluorescence was more effectively quenched in lower
generation dendrimer compared with higher generation ones. As
the quenching constant for (9) is still comparatively large, it
appears that the four dendritic substituents are not bulky enough to
form a globular structure. Since the fluorescence lifetime of
anthraquinone is on the order of 10ꢁ8 s, the apparent quenching
coefficients kq for (8)e(9) are on the order of 1011 L molꢁ1 sꢁ1, about
1 order of magnitude higher than the normal value for dynamic
quenching (ca. 1010 L molꢁ1 sꢁ1 [22]). This may be related to the
large encounter distance associated with the dendritic molecules.
The fluorescence intensities of (10)e(11) in water was also
MV2þ. According to SterneVolmer quenching equation, the value of
KSV was also greater for lower generation dendrimer. Since the
fluorescence lifetime of MV2þ is of the order of 10ꢁ8 s, the apparent
quenching coefficient Kq for (10)e(11) are of the order of 1011
L
molꢁ1 ꢁ1, which is higher than the normal value for dynamic
s
quenching. This strongly suggested that the fluorescence quench-
ing of (10)e(11) by MV2þ was mainly through a static quenching
mechanism. Furthermore, addition of NaCl drastically diminished
the fluorescence quenching by MV2þ. These phenomena could be
explained that the local concentration of MV2þ adjacent to the
dendrimer surface decreased because of the competitive binding of
the sodium ions. This efficient quenching of phthalocyanine fluo-
rescence occurs via accumulation of MV2þ on the negatively
charged dendrimer surface. The fluorescence quenching results
suggested an electron transfer reaction between the zinc phthalo-
cyanine and MV2þ through the dendrimer framework.
examined by N,N-dimethyl-g,g
0-dipyridylium dichloride (methyl
Besides these photoinduced intermolecular electron transfer
processes, the photoinduced intramolecular energy transfer in
(8)e(9) was also examined. The second generation alcohol
exhibited absorption band at 290 nm in DMSO and an emission at
viologen, MV2þ) which acted as a cationic quencher (Fig. 4). The
fluorescence intensities of these water-soluble phthalocyanines
(10)e(11) were greatly quenched with an increasing amount of
c
14000
a
b
14000
d
12000
10000
8000
6000
4000
12000
10000
8000
6000
4000
2000
0
640 660 680 700 720 740 760 780 800
660
680
700
720
740
wavelength/nm
wavelength/nm
Fig. 4. Fluorescence spectra of (10) (a) and (11) (b) quenching by MV2þ in water. c(10),(11) ¼ 2.0 ꢃ 10ꢁ5 mol Lꢁ1 in all cases. cMV2þ ¼ (ꢃ10ꢁ5 mol Lꢁ1) from up to down: 0, 2, 5, 10, 25,
50. Inset plots: SterneVolmer plots for the fluorescence quenching of (10) (c) and (11) (d) in water by MV2þ
.

16
Y. Peng et al. / Dyes and Pigments 87 (2010) 10e16
Ministry of Health & United Fujian Provincial Health and Education
project for Tackling the Key Research, China.
400
300
200
100
0
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4. Conclusion
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subunits to the phthalocyanines which acts as an energy trap. These
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system can be developed based on dendritic phthalocyanine
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Acknowledgment
This study was supported by the National Natural Science
Foundation of China (No. 20604007), Natural Science Foundation
of Fujian (Nos. 2008J0078, 2007F30103, 2009J01020), Key Foun-
dation for Technology Department (No. 2007I0013) and Project
WKJ2008-2-61 supported by the Science Research Foundation of