Light harvesting and efficient energy transfer in dendritic systems: New strategy for functionalized near-infrared bf2-azadipyrromethenes

Article abstract of DOI:10.1002/asia.200800391

A series of dendritic systems, which are capable of funneling energy from the periphery to the core, have been synthesized. The photophysical properties of the dendrimers, generations 0-2, have been determined. The light-harvesting ability of these compou

Full text of DOI:10.1002/asia.200800391

DOI: 10.1002/asia.200800391
Light Harvesting and Efficient Energy Transfer in Dendritic Systems: New
Strategy for Functionalized Near-Infrared BF2-Azadipyrromethenes
Mingjian Yuan,[a, b] Xiaodong Yin,[a, b] Haiyan Zheng,[a, b] Canbin Ouyang,[a, b]
Zicheng Zuo,[a, b] Huibiao Liu,[a] and Yuliang Li*[a]
Abstract: A series of dendritic systems, which are capable of funneling energy
from the periphery to the core, have been synthesized. The photophysical proper-
ties of the dendrimers, generations 0–2, have been determined. The light-harvest-
ing ability of these compounds increases with increasing generation arising from
the increase in molar extinction coefficient. Selective excitation of the donor leads
to an efficient energy transfer (>90%) to the acceptor. The approach provides a
facile synthesis for modification of near-infrared BF2-Azadipyrromethene.
Keywords: chromophores
dendrimers · FRET · near-infrared ·
time-resolved spectroscopy
·
Introduction
The aza-dipyrromethene (Aza-Bodipy) was first reported
over 60 years ago[5] but remained unstudied until the pio-
neering work by OꢀShea and co-workers.[6] Recently, Aza-
Bodipy and related structural analogues have been reported
as a new class of chromophore with high absorption extinc-
tion coefficients (70000–80000mÀ1 cmÀ1) and fluorescence
quantum yields between 650–750 nm.[7] The photophysical
characteristics suggest that this structural class would be an
excellent platform for developing new NIR materials for nu-
merous applications. Recently, much attention has been de-
voted to improving the photophysical properties of Aza-
Bodipy. One major approach for optimizing the materials
structure and to increase the emission efficiencies of Aza-
Bodipy has recently emerged. This approach involves the
preparation of constrained systems,[8] which has thus far pro-
duced NIR systems with enhanced quantum yields[9] that
can be exploited for potential applications in photodynamic
therapy[10] and as fluorescent chemosensors.[11]
In recent years, there has been considerable interest in the
development of organic chromophores with spectral proper-
ties in the near-infrared (NIR) region as well as their appli-
cations in imaging in vitro and in vivo.[1] The advantages of
imaging in the NIR region (650–900 nm) are numerous, and
have been extensively discussed. Prominent among these ad-
vantages is the absence or significant reduction of back-
ground absorption, fluorescence, and light scattering.[2] Un-
fortunately, there are still many key problems encountered
from the synthesis of NIR chromophores, such as spectral
broadening, photobleaching, aggregation, photo-instability,
and low quantum yields.[3] The most widely used NIR chro-
mophores are the cyanines as well as a few other chromo-
phores that are commercially available.[4] As such, the devel-
opment of new NIR chromophores with high quantum
yields remains a challenge.
Dendrimers, which consist of peripheral units, a core, and
intervening branching units, are interesting scaffolds for
light-harvesting applications (Figure 1). The periphery of the
dendrimers functionalized with light-absorbing chromo-
phores may funnel energy to a lower energy acceptor at the
core. The increasing numbers of functionalities from the
core to the periphery promise excellent candidates for light-
harvesting antenna. The use of dendrimers for harvesting
light has been elegantly demonstrated by several groups.[12]
A new strategy promising simple and efficient modification
to enhance the quantum yields of Aza-Bodipy is very urgent
in both fundamental research and application. Recently, at-
tention has focused on framework modification. However,
[a] M. Yuan, X. Yin, H. Zheng, C. Ouyang, Z. Zuo, Dr. H. Liu,
Prof. Y. Li
Beijing National Laboratory for Molecular Science (BNLMS)
CAS Key Laboratory of Organic Solids
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (P.R. China)
Fax : (+86)10-82616576
E-mail: ylli@iccas.ac.cn
[b] M. Yuan, X. Yin, H. Zheng, C. Ouyang, Z. Zuo
Graduate School of Chinese Academy of Sciences,
Beijing 100190 (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200800391.
Chem. Asian J. 2009, 4, 707 – 713
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
707

FULL PAPERS
thesis of a BODIPY dye 4. The reaction of 4 with NaN3 in
polar aprotic solvents gave compound 5 in nearly quantita-
tive yields. Then, 5 reacted with N,N-dimethyl-4-aminoben-
zaldehyde and gave 6 in moderate yields.[15] The synthesis of
the dendritic structure began with compounds 11 (genera-
tion 1) and 15 (generation 2), which have previously been
reported.[26] To functionalize the dendrimers simply and effi-
ciently, “click chemistry” was introduced to the reaction. In
the presence of CuI, 6 reacted with 12 and 16 to yield
BODIPY functionalized dendrimers 13 and 17, respectively.
Then, we treated dendrimers 13 and 17 with NaN3 in DMF
resulting in the azido-functionalized dendrimers 14 and 18
in high yield. Finally, a second “click chemistry” was con-
ducted to yield the target light-harvesting systems. The
azido-functionalized dendrimers (14 and 18) and the alkyne-
functionalized Aza-Bodipy reacted together in the presence
of CuSO4 and sodium ascorbate at RT giving compounds 1,
2, and 3 in high yields. All new compounds were character-
Figure 1. Structure of the dendritic light-harvesting systems (G0-G2).
1
ized by H and 13C NMR spectroscopy, and mass spectrome-
try.
utilizing dendrimers as light-harvesting antennae based on
an Aza-Bodipy platform has never been reported.
The primary condition for energy transfer is the spectral
overlap between the donor emission and the acceptor ab-
sorption.[16] This overlap is clear in Figure 2, in which the
Here, we present a new approach in which the multi-
donor BODIPY chromophores are attached to a central
Aza-Bodipy acceptor by efficient CuI-catalyzed 1,3-dipolar
cycloaddition.[13,14] Appended antenna molecules transfer
their excited-state energy to the core by fluorescence reso-
nance energy transfer (FRET), and amplified emission is
observed. The system displays efficient FRET and signifi-
cant antenna effects on excitation with UV radiation.
Results and Discussion
Synthesis of the Aza-Bodipy core started with the diaryl
a,b-unsaturated ketone 7 (chalcone), which was prepared by
an aldol/dehydration reaction of the corresponding benzal-
dehyde and acetophenone derivatives (Scheme 1). Thus, Mi-
chael addition of nitromethane to the a,b-unsaturated
ketone, with diethylamine (DEA) as base, gave the 1,3-
diaryl-4-nitrobutanone 8 in quantitative yields. Condensa-
tion of 8 with ammonium acetate in ethanol under reflux for
24 h gave a moderate yield of azadipyrromethenes 9. Com-
plexation of azadipyrromethenes with BF3·OEt2 gave the
Aza-Bodipy 10 in high yields. The antenna section was syn-
thesized starting from 4-(3-bromopropoxy)benzaldehyde.
The aldehyde was then used in the usual manner in the syn-
Figure 2. Emission spectrum of donor 6 and the absorption spectrum of
10, both of them were measured in THF.
emission spectrum of 6 (with an excitation wavelength at
602 nm) and absorption spectrum of 10 are depicted. From
this figure, it can be seen that the overlap of the donor emis-
sion and the acceptor absorption is extremely large. The
large spectral overlap between the two interacting chromo-
phores indicates that the possibility of donor–acceptor
energy transfer should be high.
The UV/Vis absorption spectra of the dendritic series 1–3
in THF solution are shown in Figure 3a, and the absorption
maxima (lmax) and the extinction coefficient (e) are collected
in Table 1. As can be seen from the spectra, there are two
distinct absorption bands, one is in the region 550–650 nm
and the other is in the region 650–750 nm. The absorption in
the region 550–650 nm is assigned to the donor chromo-
phore.[17] The absorption maximum around 702 nm is attrib-
uted to the Aza-Bodipy chromophore. Comparison of the
Abstract in Chinese:
708
www.chemasianj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 707 – 713

Light Harvesting and Efficient Energy Transfer in Dendritic Systems
Scheme 1.
absorption spectra of the den-
drimers G0, G1, and G2 (1, 2,
3) shows that the molar extinc-
tion coefficient and the posi-
tion of the longer band re-
mained constant. The absorp-
tion in the region 550–650 nm
of these compounds increases
steadily with increasing gener-
ation. This is attributed to the
increasing number of the
donor units with increasing
generation. Also, it should be
noted that there is no spectral
broadening or spectral shift
Figure 3. a) Comparison of the absorption spectrum of compounds 1–3. The spectrum is normalized at the
longer-wavelength peak that corresponds to the core. Inset: Plot of the number of donors in the dendrimers
versus absorbance at 602 nm. b) UV/Vis spectra of donor 6, acceptor 10, and compound 1, recorded in THF
solution and normalized at 602 nm.
Chem. Asian J. 2009, 4, 707 – 713
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
709

Y. Li et al.
FULL PAPERS
Table 1. Values of lmax and e for the dendritic compounds in THF.
ence of the acceptor, relative to the donor emission in the
absence of the acceptor.[19] Donor BODIPY emission in 1 is
quenched by 93% relative to its emission in compound 4.
So, the study resulted in calculated FRET efficiencies of
93% from donor to acceptor. Similar studies using 2 and 3
resulted in calculated FRET efficiencies of 90% and 86%,
respectively.
lmax (abs)
[nm]
e
lmax (abs)
[nm]
e
Compd
A
]
[MÀ1 cmÀ1
ACHTUNGTERNNUNG ]
6
10
1
2
3
602
702
602
602
602
8.9ꢃ104
8.7ꢃ104
3.52ꢃ105
7.13ꢃ105
1.41ꢃ106
702
703
703
8.7ꢃ104
8.8ꢃ104
8.7ꢃ104
To further confirm the energy transfer from the BODIPY
antenna to the central Aza-Bodipy, a time-resolved fluores-
cence experiment was conducted. Time-resolved fluores-
cence measurements examine the fluorescence decay profile
at different wavelengths and can provide evidence of inter-
related processes, such as energy transfer. Fluorescence
decays for all compounds were carried out in THF solution
using the time-correlated single-photon-counting method.
The sample was excited at 602 nm, and the fluorescence
decay was monitored at the emission maximums: 650 nm for
the donor compound 6 and 735 nm for the acceptor com-
pound 10. In 1, 2, and 3, emission at 650 nm was also moni-
tored to determine the detection of the residue decay from
the donor dyes. The data were fitted using a reconvolution
method of the instrument response function (IRF) produc-
ing c2 fitting values of 1–1.5. The entire set of acquired data
from the fluorescence decay experiment is summarized in
Table 2.
with increasing generation. As shown in Figure 3b, the
steady-state absorption spectrum of compound 1 is quite
similar to the sum of the absorption spectra of the compo-
nent chromophores. Similar behavior is also observed for 2
and 3. This provides evidence for the lack of direct electron-
ic communication between the BODIPY antenna and the
Aza-Bodipy core in the electronic ground state.[18]
FRET between the donor and the acceptor was confirmed
using fluorescence measurements of 1, 2, 3, 6, and 10. Exci-
tation of the dendritic compounds 1, 2, and 3 at 602 nm (the
donor absorption maximum) resulted in an emission pre-
dominantly from the acceptor dye at about 735 nm. The
emission spectra shows almost complete quenching of the
donor emission at 650 nm when 1, 2, and 3 are excited at
602 nm. For example in Figure 4, when excited at 602 nm, 1
Table 2. Summarized quantum yields, fluorescence maxima (Flmax), and
fluorescence lifetimes in THF.
Flmax [nm] tS1 [ns] a1
tS2 [ns] a2
Flmax [nm] tS3 [ns]
F
1
2
3
6
650
650
650
650
–
0.27
0.31
0.33
–
0.903 3.10 0.072 735
1.94
1.76
1.98
–
0.21
0.38
0.66
0.55
0.16
0.925 3.13
0.898 3.15
3.31
0.056 735
0.092 735
–
10
–
–
735
1.62
tS1 and tS2 refer to short-lived and long-lived emission, respectively. a1
and a2 are the contributions of each component to the total fluorescence
intensity.
In compound 1, the emission at 650 nm, corresponding to
the donor BODIPY, exhibits a short component followed by
a long-lived decay. The Aza-Bodipy emission at 735 nm ex-
hibits a long-lived monoexponential decay. We assume that
the short component is caused by energy transfer from the
BODIPY antenna to the Aza-Bodipy core.[20] Thus, the
emission at 650 nm yields biexponential lifetimes of 0.27 ns
(tS1) and 3.10 ns (tS2), and then the emission at 735 nm has a
lifetime of 1.94 ns (tS3). These lifetimes closely match those
observed for the donor 6 (3.31 ns) and acceptor 10 (1.62 ns).
When time-resolved fluorescence data are used, the calcu-
lated FRET efficiency for 1 is 91.8%. Similar calculations
using the parameters extracted from our time-resolved data
were performed. We obtain FRET efficiencies of 90.6% and
90% for G1 and G2, respectively (see Supporting Informa-
tion). As can be seen from the calculated values, a discrep-
ancy exists between the energy-transfer efficiencies from
steady-state versus time-resolved data. These results show
that the energy transfer from the periphery to the core is
Figure 4. Enhanced core emission on excitation of the donor BODIPY
units in dendritic molecules 1, 2, and 3.
showed a ~1.3-fold (F=0.21) increase in acceptor emission,
relative to the direct excitation of acceptor at 702 nm (F=
0.16). This significant ꢂantenna effectꢀ indicates that energy-
transfer efficiency is extremely high in this molecule. As the
donor units increases with increasing generation, the ꢂanten-
na effectꢀ exhibits more clearly. On the other hand, 2 (gener-
ation 1) showed a ~2.4-fold (F=0.38) increase in acceptor
emission, relative to the direct excitation of the acceptor
and, 3 (generation 2) showed a larger increment of about
4.1-fold to produce a quantum yield about 0.66. Steady-state
photophysical measurements of 1, 2, 3, 6, and 10 in THF en-
abled the determination of the approximate FRET efficien-
cies. The donor to acceptor FRET efficiencies were calculat-
ed by comparing the integrated donor emission in the pres-
710
www.chemasianj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 707 – 713

Light Harvesting and Efficient Energy Transfer in Dendritic Systems
the only pathway.[21] The proposed FRET process is shown
in Figure 5. It is observed that with an increasing number of
donors, the coreꢀs fluorescence increases steadily.
phase was dried over Na2SO4. After concentration in vacuum, the residue
was purified by column chromatography (silica gel, CHCl3) to afford
orange needles (166 mg, 36%). 1H NMR (400 MHz, CDCl3): d=7.18 (d,
2H), 7.01 (d, 2H), 5.98 (s, 1H), 4.16 (t, 2H), 3.64 (t, 2H), 2.55 (s, 6H),
2.36 (m, 2H), 1.44 ppm (s, 6H); 13C NMR: d=159.4, 155.4, 143.3, 141.9,
131.9, 129.4, 127.4, 121.3, 115.3, 69.0, 65.6, 32.5, 30.0, 14.7 ppm; MS (EI):
m/z (%) calcd for C22H24BBrF2N2O: 460.1; found: 460.0; elemental analy-
sis: calcd (%) for C22H24BBrF2N2O: C 57.30, H 5.25, N 6.07; found:
C 57.48, H 5.01, N 6.38.
4,4-Difluoro-8-(4-(3-azidopropoxy))phenyl-1,3,5,7-tetramethyl-4-bora-
3a,4a-diaza-s-indacene (5): Dry DMF (3 mL) was added to a 10 mL-ca-
pacity flask containing compound 4 (230 mg, 0.5 mmol) and sodium azide
(65 mg, 1 mmol). The mixture was stirred at RT for 4 h before being
cooled. After the reaction was completed, the mixture was poured into
water (50 mL), then extracted with CHCl3 several times. The combined
organic phase was dried over Na2SO4, and the solvent was removed
under vacuum. The crude residue was purified by silica gel chromatogra-
phy with CH2Cl2 as eluant, to afford an orange-red solid (191 mg, 90%).
1H NMR (400 MHz, CDCl3): d=7.18 (d, 2H), 6.99 (d, 2H), 5.97 (s, 1H),
4.11 (t, 2H), 3.56 (t, 2H), 2.55 (s, 6H), 2.10 (m, 2H), 1.43 ppm (s, 6H);
13C NMR: d=159.4, 155.4, 143.3, 141.9, 131.9, 129.4, 127.4, 121.2, 115.2,
64.8, 48.3, 28.9, 14.7 ppm; MS (EI): m/z (%)calcd for C22H24BF2N5O:
423.3; found: 423.0; elemental analysis: calcd (%) for C22H24BF2N5O:
C 62.43, H 5.72, N 16.55; found: C 62.71, H 5.41, N 16.98.
3-{2’-(4’’-dimethylaminophenyl)ethenyl}-4,4’-difluoro-8-(4-(3-azidopro-
poxy))-phenyl-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene
(6):
Compound 5 (460 mg, 1.1 mmol) and dimethylaminobenzaldehyde
(180 mg, 1.2 mmol) were refluxed in a mixture of toluene (20 mL), piper-
idine (900 ml), glacial acetic acid (750 ml), and a small amount of Mg-
Figure 5. Proposed FRET process occurred in dendrimers 1, 2, 3, and
their quantum yields.
AHCTUNTGREGUN(NN ClO4)2. Any water formed during the reaction was removed azeotropi-
cally by heating overnight in a Dean–Stark apparatus. The solvent was
removed under vacuum, and the residue was purified by silica gel column
chromatography (CH2Cl2 to CH2Cl2/MeOH=100:1). The blue fraction
Conclusions
was collected to afford
a
purple solid (256 mg, 42%). 1H NMR
(400 MHz, CDCl3): d=7.51 (d, 2H), 7.48 (s, 1H), 7.23 (d, 1H), 7.18 (d,
2H), 7.00 (d, 2H), 6.59 (s, 1H), 5.96 (s, 1H), 4.11 (t, 2H), 3.56 (t, 2H),
3.00 (s, 6H), 2.59 (s, 3H), 2.10 (m, 2H), 1.47 (s, 3H), 1.43 ppm (s, 3H);
13C NMR: d=159.3, 154.8, 152.9, 151.2, 143.0, 140.9, 139.0, 137.8, 133.6,
131.7, 129.8, 129.3, 127.9, 124.8, 120.5, 117.7, 115.0, 114.6, 112.2, 64.8,
48.4, 40.3, 28.9, 15.0, 14.7, 14.6 ppm; MS (EI): m/z (%) calcd for
C31H33BF2N6O: 554.4; found: 554; elemental analysis: calcd (%) for
C31H33BF2N6O: C 67.15, H 6.00, N 15.16; found: C 67.42, H 6.03, N 14.94.
In conclusion, we have successfully demonstrated a new
strategy for modifying Aza-Bodipy. A series of dendritic
Bodipy antennae are efficiently attached to a central Aza-
Bodipy core by “click chemistry”. Selective excitation of the
donor leads to a highly efficient energy transfer (>90%) to
the acceptor, resulting in an enhanced acceptor emission.
The synthesis process is a facile approach for extending the
functionalization of the Aza-Bodipy to develop novel NIR
dyes for numerous applications in optical devices.
1,3-Di[4-(2-Propynyloxy) phenyl]propenone (7): A solution of 4-(2-pro-
pynyloxy)benzaldehyde (3.2 g, 20 mol) and 1-[4-(2-propynyloxy)phenyl]-
1-ethanone (3.48 g, 20 mol) in absolute methanol (20 mL) was prepared
either in a closed system or under nitrogen at RT. Catalytic amount of
solid sodium hydroxide was added and the mixture was vigorously stirred
at RT for 10 h. After the reaction was completed, the precipitate was fil-
tered, washed with cold ethanol and water, and dried under vacuum to
afford a white solid (5.7 g, 90%). 1H NMR (400 MHz, CDCl3): d=8.03
(d, 2H), 7.77 (d, 1H), 7.60 (d, 2H), 7.42 (d, 1H), 7.05 (d, 2H), 7.00 (d,
2H), 4.76 (d, 2H), 4.73 (d, 2H), 2.56 ppm (m, 2H); 13C NMR: d=188.9,
161.3, 159.6, 144.0, 132.3, 130.9, 130.3, 128.8, 120.2, 115.5, 114.9, 78.3,
18.1, 76.4, 76.2, 56.1 ppm; MS (EI): m/z (%) calcd for C21H16O3: 316.3;
found: 316.0; elemental analysis: calcd (%) for C21H16O3: C 79.73,
H 5.10; found: C 77.46, H 5.31.
Experimental Section
General
Unless otherwise stated, reagents were commercially obtained and used
without further purification. 4-(3-bromopropoxy)benzaldehyde, 4-(2-pro-
pynyloxy)benzaldehyde,[24]
1-[4-(2-propynyloxy)phenyl]-1-ethanone,[25]
3,5-bis(2-propynyloxy)benzoic acid, 3,5-bis
ACHTUNGTRENNUNG
ACHTUNGTRNE(NUNG 3,5-bis(2-propynyloxy)benzyl-
oxy)benzoic acid[26] were prepared according to literature.
Syntheses
3-[4-(2-Propynyloxy)phenyl]-4-nitro-1-[4-(2-propynyloxy)phenyl]-butan-
1-one (8): To the solution of 1,3-di[4-(2-propynyloxy) phenyl]-propenone
4,4-Difluoro-8-(4-(3-bromopropoxy))phenyl-1,3,5,7-tetramethyl-4-bora-
3a,4a-diaza-s-indacene (4): 4-(3-bromopropoxy)benzaldehyde (242 mg,
1 mmol) and 2,4-dimethylpyrrole (190.3 mg, 2 mmol) were dissolved in
CH2Cl2 (200 mL) under N2 atmosphere. One drop of trifluoroacetic acid
was added, and the light-red solution was stirred at room temperature
for 5 h. A solution of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (227 mg,
1 mmol) in anhydrous CH2Cl2 (25 mL) was added by syringe, and the re-
sulting mixture was stirred for 15 min followed by the addition of 4 mL
triethylamine and 4 mL BF3·Et2O. After stirring for another 30 min, the
reaction mixture was washed with water (4ꢃ50 mL), and the organic
7
(390 mg, 1.2 mmol) in methanol (30 mL) was added diethylamine
(6 mmol, 600 mL) and nitromethane (6 mmol, 400 mL). The mixture was
then heated under reflux for 24 h. The solution was cooled and evaporat-
ed to dryness under vacuum. The residue was purified by silica gel chro-
matography with CH2Cl2/petrol ether (1:1) as eluant to afford a yellow
powder (398 mg, 89%). 1H NMR (400 MHz, CDCl3): d=7.91 (d, 2H),
7.20 (d, 2H), 7.05 (d, 2H), 6.92 (d, 2H), 4.80 (m, 1H), 4.75 (d, 2H), 4.62
(d, 2H), 4.60 (m,1H), 4.17 (t, 1H), 3.40 (t, 2H), 2.55 (s, 1H), 2.51 ppm (s,
1H); 13C NMR: d=195.6, 161.8, 157.3, 144.0, 132.3, 130.9, 130.5, 130.3,
Chem. Asian J. 2009, 4, 707 – 713
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
711

Y. Li et al.
FULL PAPERS
128.8, 115.6, 115.0, 80.0, 78.6, 76.2, 75.9, 56.1, 41.5, 38.9 ppm; MS (EI):
m/z (%) calcd for C22H19NO5: 377.4; found: 377.
MeOH=30:1) as eluant, to afford
a
brown solid (127 mg, 90%).
1H NMR (400 MHz, CDCl3): d=7.60 (s, 2H), 7.47 (m, 6H), 7.32 (s, 2H),
7.21 (s, 1H), 7.11 (s, 2H), 7.09 (d, 4H), 6.91 (d, 4H), 6.78 (s, 1H), 6.65
(d, 4H), 6.55 (s, 2H), 5.93 (s, 2H), 4.57 (t, 4H), 4.46 (t, 2H), 3.98 (t, 4H),
3.56 (t, 2H), 2.99 (s, 12H), 2.56 (s, 6H), 2.16 (t, 4H), 1.42 (s, 6H),
1.33 ppm (s, 6H); 13C NMR: d=165.8, 159.5, 159.0, 154.8, 152.9, 151.2,
143.5, 142.9, 141.0, 138.9, 137.9, 133.5, 131.6, 129.8, 129.4, 127.9, 124.7,
123.5, 120.6, 117.8, 115.1, 114.4, 112.1, 108.9, 107.6, 64.4, 64.2, 62.3, 48.5,
47.4, 40.3, 30.0, 28.9, 15.0, 14.7, 14.6 ppm; MS (MALDI): m/z (%) calcd
for C77H79B2F4N15O6: 1407.6; found: 1407.8; elemental analysis: calcd
(%) for C77H79B2F4N15O6: C 65.68, H 5.65, N 14.92; found: C 65.42,
H 5.16, N 15.37.
A
ACHTUNGERTN{NUNG 3,5-di[4-(2-propynyl-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
2 mmol) in THF (1 mL) was placed in a 50 mL-capacity flask, then am-
monium acetate (12 g, 0.156 mol) was added. The mixture was dissolved
in ethanol (20 mL) and heated under reflux for 24 h. The reaction solu-
tion was cooled to RT, and the solvent was concentrated to 10 mL, and
filtered. The isolated solid was washed with large amount of methanol
for several times. The residue was dried under vacuum to afford a brown
solid (466 mg, 70%). 1H NMR (400 MHz, [D6]DMSO): d=8.32 (s, 1H),
8.06 (m, 8H), 7.53 (s, 2H), 7.25 (d, 4H), 7.12 (d, 4H), 4.96 (s, 4H), 4.91
(s, 4H), 3.66 (s, 2H), 3.61 ppm (s, 2H); 13C NMR: d=compound was too
2-Bromoethyl-3,5-bis
ACHTUNGTRENNUNG
a stirred solution of 3,5-bisAHCNUTGTRENNUNG
insoluble to record
C44H31N3O4: 665.7; found: 665.6; elemental analysis: calcd (%) for
C44H31N3O4: C 79.38, H 4.69, N 6.31; found: C 79.21, H 4.87, N 6.52.
a spectrum; MS (MALDI): m/z (%) calcd for
(550 mg, 1 mmol) and 2-bromoethanol (124 mg, 1 mmol) in anhydrous
CH2Cl2 (50 mL) cooled on an ice bath, was added 4-DMAP (25 mg,
0.2 mmol) and EDC·HCl (205 mg, 1.1 mmol), and the reaction mixture
was stirred for 10 h at RT. The solution was washed with a saturated solu-
tion of citric acid and H2O. The organic layer was dried over anhydrous
MgSO4 and the filtrate was reduced in vacuum. The residue was purified
by silica gel chromatography with CH2Cl2/petrol ether (1:2) as eluant to
BF2 chelate of {3,5-di[4-(2-propynyloxy)phenyl]-1H-pyrrol-2-yl} {3,5-di[4-
(2-propynyloxy)-phenyl]pyrrol-2-ylidene}amine
(10):
Compound 9
(666 mg, 1 mmol) was dissolved in dry CH2Cl2 (100 mL), treated with dii-
sopropylethylamine (1.2 mL, 7 mmol) and BF3·OEt2 (1 mL, 8 mmol), and
stirred at RT for 10 h. The mixture was washed with water, and the or-
ganic phase was dried over sodium sulfate and evaporated to dryness.
The residue was purified by silica gel chromatography with CH2Cl2/petrol
ether (1:1) as eluant to afford a brown solid (571 mg, 81%). 1H NMR
(400 MHz, CDCl3): d=8.05 (m, 8H), 7.07 (m, 8H), 6.95 (s, 2H), 4.78 (d,
4H), 4.76 (d, 4H), 2.59 (s, 2H), 2.56 ppm (s, 2H); 13C NMR
([D6]DMSO): d=160.2, 159.2, 157.7, 145.0, 142.5, 132.1, 131.2, 125.8,
124.7, 118.9, 115.8, 115.7 ppm; MS (MALDI): m/z (%) calcd for
C44H30BF2N3O4: 713.5; found: 713.5; elemental analysis: calcd (%) for
C44H30BF2N3O4: C 74.06, H 4.24, N 5.89; found: C 74.43, H 3.93, N 6.22.
1
afford a white solid (592 mg, 90%). H NMR (400 MHz, CDCl3): d=7.28
(s, 2H), 6.83 (s, 1H), 6.77 (m, 4H), 6.56 (m, 2H), 5.00 (s, 4H), 4.66 (d,
8H), 4.59 (t, 2H), 3.61 (t, 2H), 2.53 ppm (t, 4H); 13C NMR: d=165.8,
159.7, 159.0, 139.1, 131.7, 108.9, 107.0, 102.0, 78.5, 75.9, 70.1, 64.5,
28.9 ppm; MS (MALDI): m/z (%) calcd for C35H29BrO8: 656.1 [M+Na+];
found: 679.2; elemental analysis: calcd (%) for C35H29BrO8: C 63.93,
H 4.45; found: C 64.35, H 4.19,
17: A solution of 16 (65.6 mg, 0.1 mmol) and 6 (211 mg, 0.5 mmol) in
THF were stirred under N2 atmosphere. Then, a small amount of sodium
ascorbate and CuSO4 were added to the solution. The resulting solution
was stirred at RT for 10 h. After evaporation of the solvents, the crude
product was purified by silica gel chromatography (CH2Cl2 to CH2Cl2/
2-Bromoethyl-3,5-bis(2-propynyloxy)benzoate (12): To a stirred solution
of 3,5-bis(2-propynyloxy)benzoic acid (230 mg, 1 mmol) and 2-bromo-
ACHTUNGTRENNUNGethanol (124 mg, 1 mmol) in anhydrous CH2Cl2 (50 mL) cooled on an ice
MeOH=20:1) to afford
a
brown solid (130 mg, 90%). 1H NMR
(400 MHz, CDCl3): d=7.57 (s, 4H), 7.45 (m, 12H), 7.19 (s, 2H), 7.14 (s,
2H), 7.08 (d, 2H), 6.89 (d, 2H), 6.78 (s, 1H), 6.67 (m, 12H), 6.53 (s, 2H),
6.50 (s, 4H), 5.92 (s, 4H), 5.11 (s, 12H), 4.99 (s, 4H), 4.54 (m, 10H), 3.95
(t, 8H), 3.59 (t, 2H), 2.99 (s, 24H), 2.55 (s, 12H), 2.35 (t, 8H), 1.41 (s,
12H), 1.33 ppm (s, 12H); 13C NMR: d=165.7, 159.8, 159.0, 154.8, 152.9,
151.2, 143.8, 142.9, 140.9, 139.3, 138.9, 137.9, 133.5, 131.7, 129.8, 129.4,
127.9, 124.7, 123.5, 120.6, 117.8, 115.1, 114.3, 112.2, 108.8, 106.5, 101.7,
70.1, 64.5, 62.2, 47.3, 40.3, 29.8, 15.0, 14.7, 14.6 ppm; MS (MALDI): m/z
(%) calcd for C159H161B4BrF8N24O12: 2873.2 [M+Na+]; found: 2896.6; ele-
mental analysis: calcd (%) for C159H161B4BrF8N24O12: C 66.42, H 5.64,
N 11.69; found: C 65.89, H 5.26, N 12.14.
bath, was added 4-DMAP (25 mg, 0.2 mmol) and EDC·HCl (205 mg,
1.1 mmol), and the reaction was allowed to stir for 10 h at RT. The solu-
tion was washed with a saturated solution of citric acid and H2O. The or-
ganic layer was dried over anhydrous MgSO4, and the filtrate was re-
duced in a vacuum. The residue was purified by silica gel chromatogra-
phy with CH2Cl2/petrol ether (1:2) as eluant to afford a white solid
(290 mg, 87%). 1H NMR (400 MHz, CDCl3): d=7.30 (s, 2H), 6.81 (t,
1H), 4.70 (s, 4H), 4.59 (t, 2H), 3.62 (t, 2H), 2.56 ppm (t, 2H); 13C NMR:
d=165.5, 158.7, 131.7, 109.2, 107.8, 78.1, 76.3, 64.6, 56.3, 28.8 ppm; MS
(EI): m/z (%) calcd for C15H13BrO4: 337.2; found: 337.1; elemental analy-
sis: calcd (%) for C15H13BrO4: C 53.43, H 3.89; found: C 53.76, H 3.93.
18: Dry DMF (10 mL) was added to a 25 mL-capacity flask containing 17
(287 mg, 0.1 mmol) and sodium azide (32.5 mg, 0.5 mmol). The mixture
was stirred at RT for 4 h before being cooled. After the reaction was
completed, the mixture was poured into water (50 mL), then extracted
with CHCl3 several times. The combined organic phase was dried over
Na2SO4, and the solvent was removed under vacuum. The crude residue
was purified by silica gel chromatography with (CH2Cl2 to CH2Cl2/
13: A solution of 12 (33.7 mg, 0.1 mmol) and 6 (85 mg, 0.22 mmol) in
THF was stirred under N2 atmosphere. Then, a small amount of sodium
ascorbate and CuSO4 were added to the solution. The resulting solution
was then stirred at RT for 10 h. After evaporation of the solvents, the
crude product was then purified by silica gel chromatography (CH2Cl2 to
CH2Cl2/MeOH=30:1) to afford a brown solid (130 mg, 90%). 1H NMR
(400 MHz, CDCl3): d=7.61 (s, 2H), 7.49 (m, 6H), 7.32 (s, 2H), 7.22 (s,
1H), 7.14 (m, 5H), 6.92 (d, 4H), 6.86 (s, 1H), 6.75 (d, 4H), 6.56 (s, 2H),
5.95 (s, 2H), 5.19 (s, 4H), 4.60 (m, 6H), 4.0 ( t, 4H), 3.62 (t, 2H), 3.01 (s,
12H), 2.57 (s, 6H), 2.42 (t, 4H), 1.44 (s, 6H), 1.34 ppm (s, 6H);
13C NMR: d=165.6, 159.5, 159.0, 154.3, 153.1, 151.6, 143.5, 142.9, 141.1,
138.9, 137.4, 134.2, 132.1, 131.9, 129.9, 129.4, 128.0, 123.5, 120.6, 116.8,
115.0, 112.2, 108.9, 106.7, 64.6, 64.4, 62.4, 47.4, 40.4, 30.2, 28.9, 15.05,
14.7 ppm; MS (MALDI): m/z (%) calcd for C77H79B2BrF4N12O6: 1444.6;
found: 1444.8; elemental analysis: calcd (%) for C77H79B2BrF4N12O6:
C 63.96, H 5.51, N 11.62; found: C 63.62, H 5.13, N 11.22.
MeOH=20:1) as eluant, to afford
a brown solid (227 mg, 80%).
1H NMR (400 MHz, CDCl3): d=7.58 (s, 4H), 7.44 (m, 12H), 7.19 (s,
2H), 7.13 (s, 2H), 7.05 (d, 2H), 6.89 (d, 2H), 6.78 (s, 1H), 6.67 (m, 12H),
6.53 (s, 2H), 6.50 (s, 4H), 5.92 (s, 4H), 5.11 (s, 12H), 4.99 (s, 4H), 4.54
(m, 8H), 4.46 (t, 2H), 3.95 (t, 8H), 3.59 (t, 2H), 2.99 (s, 24H), 2.55 (s,
12H), 2.35 (t, 8H), 1.41 (s, 12H), 1.33 ppm (s, 12H); 13C NMR: d=165.7,
159.8, 159.3, 154.5, 152.9, 151.2, 143.6, 143.0, 141.1, 139.3, 139.1, 137.9,
133.5, 131.7, 129.6, 129.4, 128.2, 124.7, 123.5, 120.6, 117.8, 115.1, 114.3,
112.3, 108.7, 106.5, 101.7, 70.1, 64.7, 62.4, 47.1, 40.3, 29.8, 15.1, 14.6,
14.5 ppm; MS (MALDI): m/z (%) calcd for C159H161B4F8N27O12: 2836.2;
14: Dry DMF (10 mL) was added to a 25 mL-capacity flask containing 13
(145 mg, 0.1 mmol) and sodium azide (32.5 mg, 0.5 mmol). The mixture
was stirred at RT for 4 h before being cooled. After the reaction was
completed, the mixture was poured into water (50 mL), then extracted
with CHCl3 several times. The combined organic phase was dried over
Na2SO4, and the solvent was removed under vacuum. The crude residue
was purified by silica gel chromatography with (CH2Cl2 to CH2Cl2/
found: 2836.8; elemental analysis: calcd (%) for C159H161B4F8N27O12
C 67.30, H 5.72, N 13.33; found: C 66.88, H 5.31, N 13.08.
:
1: A solution of 10 (71.4 mg, 0.1 mmol) and 4 (277 mg, 0.5 mmol) in THF
were stirred under N2 atmosphere. Then, a small amount of sodium as-
corbate and CuSO4 were added to the solution. The resulting solution
was then stirred at RT for 2 h. After evaporation of the solvents, the
712
www.chemasianj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 707 – 713

Light Harvesting and Efficient Energy Transfer in Dendritic Systems
crude product was then purified by silica gel chromatography (CH2Cl2 to
CH2Cl2/MeOH=50:1) to afford a brown solid (249 mg, 85%). 1H NMR
(400 MHz, CDCl3): d=8.03 (t 8H), 7.65 (d, 4H), 7.44 (d, 12H), 7.13 (m,
20H), 6.88 (m, 12H), 6.63 (d, 8H), 6.48 (d, 4H), 5.93 (d, 4H), 5.24 (d,
8H), 4.59 (d, 8H), 3.97 (d, 8H), 2.99 (s, 24H), 2.55 (s, 12H), 1.40 ppm
(m, 24H); 13C NMR: d=168.3, 160.6, 159.5, 159.1, 157.7, 154.9, 152.9,
151.2, 145.3, 144.0, 143.8, 143.0, 142.6, 140.9, 138.9, 138.0, 133.6, 132.2,
131.7, 131.3, 131.0, 129.9, 129.4, 129.1, 128.0, 126.0, 124.9, 123.6, 120.6,
117.9, 115.1, 112.2, 64.5, 64.4, 62.2, 52.8, 47.4, 40.4, 30.0, 15.1, 14.7 ppm;
MS (MALDI): m/z (%) calcd for C168H162B5F10N27O8: 2931.3; found:
2932.5; elemental analysis: calcd (%) for C168H162B5F10N27O8: C 68.84,
H 5.57, N 12.9; found: C 68.48, H 5.13, N 13.42.
[4] a) M. Halik, H. Hartmann, Chem. Eur. J. 1999, 5, 2511; b) N. Nar-
ayanan, L. Strekowski, M. Lipowska, G. Patonay, J. Org. Chem.
1997, 62, 9387.
[5] a) M. A. T. Rogers, J. Chem. Soc. 1943, 596; b) E. B. Knott, J. Chem.
Soc. 1957, 1196.
[6] a) S. O. McDonnell, M. J. Hall, L. T. Allen, A. Byrne, W. M. Gal-
lagher, D. F. OꢀShea, J. Am. Chem. Soc. 2005, 127, 16360; b) M. J.
Hall, S. O. McDonnell, J. K. Killoran, D. F. OꢀShea, J. Org. Chem.
2005, 70, 5571.
[7] J. Killoran, L. Allen, J. F. Gallagher, W. M. Gallagher, D. F. OꢀShea,
Chem. Commun. 2002, 1862.
[8] a) W. Zhao, E. M. Carreira, Angew. Chem. 2005, 117, 1705; Angew.
Chem. Int. Ed. 2005, 44, 1677; <lit b>W. Zhao, E. M. Carreira,
Chem. Eur. J. 2006, 12, 7254.
[9] a) A. Loudet, R. Bandichhor, L. Wu, K. Burgess, Tetrahedron 2008,
64, 3642; b) A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891.
[10] A. Gorman, J. Killoran, C. OꢀShea, T. Kenna, W. Gallagher, D. F.
OꢀShea, J. Am. Chem. Soc. 2004, 126, 10619.
[11] A. Coskun, M. D. Yilmaz, E. U. Akkaya, Org. Lett. 2007, 9, 607.
[12] a) W. R. Dichtel, J. M. Serin, C. Edder, J. M. J. Frꢄchet, M. Watus-
zewski, L.-S. Tan, T. Y. Ohulchanskyy, P. N. Prasad, J. Am. Chem.
Soc. 2004, 126, 5380; b) D. W. Brousmiche, J. M. Serin, J. M. J. Frꢄ-
chet, P. N. Prasad, L.-S. Tan, J. Phys. Chem. B 2004, 108, 8592; c) A.
Adronov, S. L. Gilat, J. M. J. Frꢄchet, K. Ohta, F. V. R. Neuwahl,
G. R. Fleming, J. Am. Chem. Soc. 2000, 122, 1175; d) K. R. Justin
Thomas, A. L. Thompson, A. V. Sivakumar, C. J. Bardeen, S. Thayu-
manavan, J. Am. Chem. Soc. 2005, 127, 373; e) C. Devadoss, P. Bhar-
athi, J. S. Moore, J. Am. Chem. Soc. 1996, 118, 9635; f) Y. Kikuzawa,
T. Nagata, T. Tahara, K. Ishii, Chem. Asian J. 2006, 1, 516.
[13] a) H. C. Kolb, K. B. Sharpless, Drug. Discuss. Today. 2003, 8, 1128;
b) M. D. Yilmaz, O. A. Bozdemir, E. U. Akkaya, Org. Lett. 2006, 8,
2871.
[14] a) C. Ornelas, J. R. Aranzaes, L. Salmon, D. Astruc, Chem. Eur. J.
2008, 1, 50; b) E. Boisselier, C. Ornelas, I. Pianet, J. R. Aranzaes, D.
Astruc, Chem. Eur. J. 2008, 14, 5577; c) R. J. Thibault, K. Takizawa,
P. Lowenheilm, B. Helms, J. L. Mynar, J. M. J. Frꢄchet, C. J. Hawker,
J. Am. Chem. Soc. 2006, 128, 12084.
[15] A. Coskun, E. U. Akkaya, J. Am. Chem. Soc. 2005, 127, 10464.
[16] T. Fçster, Ann. Phys. 1948, 2, 55.
[17] K. Rurack, M. Kollmannsberger, J. Daub, Angew. Chem. 2001, 113,
396; Angew. Chem. Int. Ed. 2001, 40, 385; Angew. Chem. 2005, 117,
396.
[18] P. Bauer, H. Wietasch, S. M. Lindner, M. Thelakkat, Chem. Mater.
2007, 19, 88.
[19] J. M. Serin, D. W. Brousmiche, J. M. J. Frꢄchet, Chem. Commun.
2002, 2605.
[20] M. A. Oar, W. R. Dichtel, J. M. Serin, J. M. J. Frꢄchet, J. E. Rogers,
J. E. Slagle, P. A. Fleitz, L.-S. Tan, T. Y. Ohulchanskyy, P. N. Prasad,
Chem. Mater. 2006, 18, 3682.
2: A solution of 10 (7.14 mg, 0.01 mmol) and 14 (70 mg, 0.05 mmol) in
THF were stirred under N2 atmosphere. Then, a small amount of sodium
ascorbate and CuSO4 were added to the solution. The resulting solution
was stirred at RT for 5 h. After evaporation of the solvents, the crude
product was then purified by silica gel chromatography (CH2Cl2 to
CH2Cl2/MeOH=10:1) to afford a brown solid (51.4 mg, 81%). 1H NMR
(400 MHz, CDCl3): d=8.02 (t, 8H), 7.74 (d, 8H), 7.65 (m, 12H), 7.46 (m,
24H), 7.03 (m, 38H), 6.83 (m, 24H), 6.66 (d, 8H), 6.53 (d, 8H), 5.90 (d,
8H), 5.18 (d, 8H), 4.81 (t, 16H), 4.53 (m, 16H), 4.24 (t, 8H), 3.95 (m,
16H), 2.98 (s, 24H), 2.60 (s, 12H), 1.40 ppm (m, 24H); 13C NMR: d=
168.5, 165.2, 161.3, 160.8, 159.3, 156.8, 154.5, 153.7, 152.2, 150.1, 145.8,
145.0, 144.2, 143.4, 143.0, 141.8, 141.2, 139.8., 138.5, 135.7, 133.0, 132.2,
130.7, 131.3, 131.1, 130.5, 129.6, 129.0, 128.6, 126.4, 124.7, 124.1, 120.5,
118.3, 114.5, 111.0, 64.8, 64.6, 62.3, 50.5, 44.9, 38.8, 28.6, 15.0, 14.8 ppm;
MS (MALDI): m/z (%) calcd for C352H346B9F18N63O28: 6343.8 [M+Na+];
found: 6366.4; elemental analysis: calcd (%) for C352H346B9F18N63O28
C 66.62, H 5.50, N 13.9; found: C 66.87, H 5.24, N 13.61.
:
3: A solution of 10 (7.14 mg, 0.01 mmol) and 14 (142 mg, 0.05 mmol) in
THF were stirred under N2 atmosphere. Then, a small amount of sodium
ascorbate and CuSO4 were added to the solution. The resulting solution
was then stirred at RT for 10 h. After evaporation of the solvents, the
crude product was then purified by silica gel chromatography (CH2Cl2 to
CH2Cl2/MeOH=5:1) to afford
a
brown solid. 1H NMR (400 MHz,
CDCl3): d=8.08 (t, 8H), 7.75 (d, 8H), 7.61 (m, 24H), 7.42 (m, 48H), 7.05
(m, 76H), 6.88 (m, 48H), 6.52 (d, 8H), 6.32 (d, 16H), 5.90 (s, 16H), 5.21
(d, 8H), 4.93 (m, 32H), 4.55 (m, 32H), 4.32 (t, 8H), 4.15 (s, 16H), 3.92
(m, 32H), 3.55 (t, 8H), 2.98 (s, 24H), 2.55 (s, 12H), 1.35 ppm (d, 24H);
13C NMR: d=169.1, 165.4, 161.7, 158.6, 158.2, 156.7, 155.4, 154.3, 153.1,
152.7, 151.6, 149.2, 146.8, 146.5, 145.1, 144.7, 143.9, 143.6, 143.1, 142.8,
141.9, 140.6, 139.3, 138.7, 138.3, 135.9, 133.2, 132.6, 132.0, 131.6, 131.2,
130.4, 129.7, 129.0, 128.4, 127.6, 126.5, 125.1, 122.4, 118.6, 117.2, 116.7,
113.8, 112.7, 108.7, 67.5, 66.8, 63.6, 54.5, 48.4, 46.4, 32.2, 15.7, 15.2 ppm;
elemental analysis: calcd (%) for C680H674B17F34N111O52 (12058.5): C 67.7,
H 5.63, N 12.89; found: C 67.11, H 5.21, N 13.44.
[21] H. Oevering, J. W. Verhoeven, M. N. Paddon-Row, J. M. Warman,
Tetrahedron 1989, 45, 4751.
[22] M. Thelakkat, H. W. Schmidt, Adv. Mater. 1998, 10, 219.
[23] T. Jiu, Y. Li, H. Liu, J. Ye, X. Liu, L. Jiang, M. Yuan, J. Li, C. Li, S.
Wang, D. Zhu, Tetrahedron 2007, 63, 3168.
Acknowledgements
This work was supported by the National Natural Science Foundation of
China (20531060, 20721061, 20873155.) and the National Basic Research
973 Program of China (Grant No. 2007CB936401).
[24] E. Lee, C. Lee, J. Tae, H. Whang, K. Li, Tetrahedron Lett. 1993, 34,
2343.
[25] M. R. Detty, D. E. Higgs, M. I. Nelen, Org. Lett. 2003, 5, 349.
[26] M. Malkoch, R. Vestberg, N. Gupta, L. Mespouille, P. Dubois, A. F.
Mason, J. L. Hedrick, Q. Liao, C. W. Frank, K. Kingsbury, C. J.
Hawker, Chem. Commun. 2006, 2774.
[1] a) D. J. Stephens, V. J. Allan, Science 2003, 300, 82; b) M. Matsuoka,
Infrared Absorbing Dyes, Plenum, New York, 1990.
[2] a) V. Ntziachristos, J. Ripoll, R. Weissleder, Opt. Lett. 2002, 27, 333;
b) J. Sowell, L. Strekowski, G. Patonay, J. Biomed. Opt. 2002, 7, 571.
[3] a) A. Mishra, R. K. Behera, P. K. Behera, B. K. Mishra, G. B.
Behera, Chem. Rev. 2000, 100, 1973; b) M. Fabian, H. Nakazumi, M.
Matsuka, Chem. Rev. 1992, 92, 1197.
Received: October 10, 2008
Revised: December 19, 2008
Published online: February 18, 2009
Chem. Asian J. 2009, 4, 707 – 713
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
713