Dendron-decorated cyanine dyes for optical limiting applications in the range of telecommunication wavelengths

Article abstract of DOI:10.1039/b822485d

Cyanine dyes decorated with 2,2-bis(methylol)propionic acid (bis-MPA) based dendrons up to third generation were synthesized. Dendrons were attached to the chromophore using a "click chemistry" reaction. Photophysical characterizations of these dyes show

Full text of DOI:10.1039/b822485d

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Dendron-decorated cyanine dyes for optical limiting applications
in the range of telecommunication wavelengths
Pierre-Antoine Bouit,a Robert Westlund,b Patrick Feneyrou,c Olivier Maury,a
b
b
a
¨
Michael Malkoch, Eva Malmstrom* and Chantal Andraud*
Received (in Montpellier, France) 15th December 2008, Accepted 16th March 2009
First published as an Advance Article on the web 7th April 2009
DOI: 10.1039/b822485d
Cyanine dyes decorated with 2,2-bis(methylol)propionic acid
(bis-MPA) based dendrons up to third generation were
synthesized. Dendrons were attached to the chromophore using
a ‘‘click chemistry’’ reaction. Photophysical characterizations of
these dyes show intense absorption and emission in the near-
infrared (NIR), while nonlinear transmission experiments of the
dendron-decorated chromophores indicate that properties in the
IR of the parent dyes are conserved. This synthetic approach is a
crucial preliminary step towards the preparation of solid func-
tional materials for optical limiting (OL) applications in the IR.
applied to porphyrins, polythiophenes and platinum
acetylides.6 In the meantime, ‘‘click chemistry’’ and especially
the copper-catalyzed 1,3-dipolar cycloaddition between
alkynes and azides (CuAAC) has gained growing interest in
the field of dendrimers synthesis and more generally in the field
of materials science.7
In this Letter, we present the synthesis of functionalized
cyanine dyes2a decorated with bis-MPA based dendrons linked
to the chromophore through a ‘‘click chemistry’’ reaction.
Their photophysical and nonlinear optical limiting properties
are described and compared to that of the parent cyanine dye.
The starting material for these syntheses is the chlorohepta-
methine Cy-1 (Scheme 1). The synthesis and optical properties
of this dye have already been reported.2a For this class of
compound, substitution of the meso-chlorine atom is a
powerful way to introduce various functional moieties.8
Following this strategy, Cy-2 featuring a meso-phenolate
group was synthesized by the reaction of Cy-1 with a solution
of sodium hydride and phenol in DMF at room temperature
(RT) (Scheme 1) and recovered with a 63% yield after
precipitation in n-pentane. This chromophore will be used as
a reference in order to compare the optical activity of the
dendronized molecules. The same reaction, carried out with
hydroxybenzyl alcohol, led to the formation of Cy-3
(72% yield)—an hydroxyl-functionalized cyanine that will be
used as the starting material for the preparation of dendro-
nized chromophores. It is worth noting that no protection of
the hydroxybenzyl moieties is required, which makes the
functionalization of the cyanine dye easier. In our hands,
further esterification between Cy-3 and dendrons possessing
a carboxylic acid at the focal point has been found to be
incomplete with residual by-products difficult to separate, and
consequently this first functionalization procedure has been
discarded.9 Therefore, a new synthetic approach involving
‘‘click chemistry’’ has been attempted. In order to introduce
the azide end-group precursor to ‘‘click chemistry’’ reactions,
Cy-3 was reacted with anhydride A10 and DMAP in dichloro-
methane (DCM) giving Cy-4. This latter compound was
further reacted with an excess of a polyester dendrons of
second (resp. third) generation possessing an alkyne at the
focal point D2 (resp. D3) in THF–water in the presence of
copper iodide and sodium ascorbate as the catalytic system
(Scheme 1). This method allowed the preparation of Cy-5 and
Cy-6 in acceptable (53% and 35%) yield, respectively. The
removal of the excess alkyne and of the catalysts was carried
out by filtration over silica and recrystallization from diethyl
With the development of laser based technologies, there is an
increasing need for devices able to protect detectors against
intense illumination. In this context, optical limiting (OL)
based on multiphotonic absorption of organic compounds
has been widely applied to perform protection in the visible
and NIR spectral range [400–1000 nm]1 and has been
recently extended to up to telecommunication wavelengths
[1300–1600 nm].2 For such an application, chromophores
featuring (i) a strong two-photon absorption (TPA) and
excited state absorption (ESA) properties, as well as (ii) high
solubility in organic solvents (around 100 g LÀ1) are required.
This latter requirement is certainly the reason why only a few
papers have reported real optical limiting experiments in the
IR, while numerous dipolar,3 quadrupolar4 porphyrin or
coordination complex5 based-chromophores have been
described for TPA application in this spectral range. Further-
more, it is important to design chromophores that are able to
avoid aggregation phenomenon in highly concentrated
solution and particularly in the solid state when doped in
polymer or sol–gel matrix, which represents the ultimate steps
toward the design of a real device. In order to tackle the
aggregation problem, some of us decorated the chromophores
with dendrons.6 The steric hindrance afforded by these bulky
substituents is known to enhance the solubility and prevent
aggregation and quenching of the excited states. In
this context, stable and transparent dendrons based on
2,2-bis(methylol)propionic acid (bis-MPA) are very attractive
for photonic applications. This strategy has been successfully
a
´
University of Lyon, Laboratoire de Chimie, UMR 5182 CNRS-Ecole
´
Normale Superieure de Lyon, 46 allee d’Italie, 69007, Lyon, France.
E-mail: chantal.andraud@ens-lyon.fr
´
b KTH Fibre and Polymer Technology, Royal Institue of Technology,
SE-100 44, Stockholm, Sweden
Thales Research & Technology France, route departementale 128,
91767, Palaiseau Cedex, France
c
´
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Scheme 1 Reagent and conditions: (i) DMF, RT, 6 h, (ii) DMAP, DCM, RT, 12 h (65%), (iii) CuSO4, sodium ascorbate, THF–water, 501C, 48 h.
1
ether. The purity of the product was confirmed by H NMR
spectroscopy and MALDI-TOF spectrometry (Fig. 1). This
convergent synthesis allows the easy synthesis of the
monodisperse dendronized chromophore and seems to be
extendable to the synthesis of dendronized chromophores of
higher generations.
All the compounds present the characteristic absorp-
tion spectra of cyanine dyes (Table 1) with an intense NIR
absorption (for example, lmax(Cy-6) = 778 nm and e =
170 000 L molÀ1 cmÀ1) and a shoulder at higher energy
(Fig. 2). Both dendron-decorated and reference Cy-2 dyes
present exactly the same maximal absorption wavelength
(lmax = 778 nm) with similar extinction coefficients. They
also feature the characteristic emission properties (Table 1) of
the cyanine compounds with emission maxima in the NIR
(for example, lem(Cy-6) = 800 nm, Fig. 2). As expected, the
maximal absorption and emission wavelengths of Cy-2–6
are slightly blue-shifted compared to the parent chloro-
heptamethine Cy-1.8a All these photophysical data show that
the typical linear optical properties of the cyanines are
conserved for the dendron-decorated dyes.
Fig. 1 MALDI-TOF spectrum of Cy-6.
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Table 1 Photophysical data in dichloromethane solution
max/L molÀ1 cmÀ1
lem/nm
ThOLa/J cmÀ2
b
Tmin (%)
Compound
lmax/nm
e
Cy-1c
Cy-2
Cy-5
Cy-6
794
778
778
778
350 000
190 000
210 000
170 000
817
802
803
800
0.4 Æ 0.2
0.4 Æ 0.2
0.4 Æ 0.2
—
70 Æ 5
70 Æ 5
70 Æ 5
—
a
ThOL is the OL threshold; this value is graphically determined as the intersection between the linear and the nonlinear part of the OL
b
curve. Tmin is the transmission reached for the maximal intensity of the laser (2.5 J cmÀ2). see ref. 2a.
c
Fig. 3 Nonlinear transmission curves at 1420 nm in DCM solution of
Cy-1 (n),Cy-2 (+) and Cy-5 (’) (c = 0.1 mol LÀ1
)
chromophores. Fig. 3 also shows that at this wavelength, the
dendronized chomophore Cy-5 and the reference Cy-2 possess
the same OL threshold (ThOL = 0.4 J cmÀ2) and the same
minimal transmission (Tmin = 70%). These results mean that
the presence of the dendrons do not affect the NLO properties
of the chromophore. For these solutions, the two-photon
induced ESA is believed to be the OL mechanism, as already
observed for similar cyanine dyes.2a It is also interesting to
note that comparable OL data are also obtained for the parent
dye Cy-1 (Fig. 3).2a This experiment illustrate that the modi-
fication on the meso-position of the chloroheptamethine is an
efficient strategy to introduce isolating functionalities on the
molecule, keeping its NLO properties.
Fig. 2 Absorption (top) and normalized emission (bottom) spectra of
Cy-2 (dash line), Cy-5 (grey) and Cy-6 (black) in DCM at room
temperature.
In conclusion, chromophores featuring different end-groups
(hydroxy, azide) linked to the meso-position of heptamethine
cyanine have been synthesized and bis-MPA based dendrons
have been linked to the chromophore using ‘‘click chemistry’’.
The general synthetic procedure seems to be suitable for the
synthesis of chromophores bearing higher generation
dendrons. The linear and nonlinear optical studies validate
this dendron strategy for cyanine based optical limiters.
Indeed, these dendron-decorated chromophores present
similar absorption and optical limiting properties as the parent
dyes. These NLO-active chromophores, by the introduction of
isolating sites minimizing aggregation and chromophore
interactions, open interesting possibilities for the design of
materials for solid state OL purposes.
In order to explore the NLO properties of these dyes,
nonlinear transmission experiments were also carried out. It
is worth noting that these NLO experiments require very high
solubility of the dyes. The dendron-decorated dye Cy-5
presents the typical behavior of optical limiters (Fig. 3): for
the operating wavelength, the highly concentrated solution
(0.1 mol LÀ1 in dichloromethane) is transparent at low laser
intensity and a decrease of the transmission (T) is observed at
higher energy. The OL threshold ThOL appeared for an
incident fluence of around 0.4 J cmÀ2 and the transmission
T
min reached for the maximal input energy is 70% (Fig. 3 and
´
The authors thank the DGA and the Ecole Doctorale de
Table 1). The relative dispersity of the experimental data allow
the graphical determination of ThOL to be given with a
precision of around 50%.2a It is worth noting that, in this
experiment, the minimal transmission value Tmin is limited by
the power of the laser and not by the NLO activity of the
Chimie de Lyon for a grant to P. A. B. and the Polymer
Factory Sweden AB for chemicals support. Dendrons D2 and
D3 were kindly provided by the Polymer Factory Sweden AB
(www.polymerfactory.com).
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(d, 3J = 8 Hz, 2H), 7.85 (d, 3J = 14 Hz, 2H). 13C NMR
(50.32 MHz, CDCl3): d 25.3, 27.5, 27.9, 28.1, 32.5, 42.6, 48.2,
49.2, 63.6, 100.4, 110.6, 114,3, 122.5, 123.1, 125.3, 126.5, 128.4,
128.8, 129.3, 129.4, 134.1, 137.2, 140.9, 142.6, 158.7, 165.3,
172.4. MS (ES): M+ = 779.5 (calcd for C55H59N2O2: 779.5).
Anal. calc. for: C45H59N2O2Br: C, 76.82, H, 6.92, N, 3.26,
Found: C, 76.30, H, 7.08, N, 2.96%.
Experimental
General
All reactions were routinely performed under argon. NMR
spectra (1H, 13C) were recorded at room temperature on a
BRUKER AC 200 operating at 200.13 MHz and 50.32 for 1H
and 13C, respectively and on a VARIAN Unity Plus operating
1
at 499.84 MHz for H NMR for variable-temperature experi-
Cy-4. Compound Cy-3 (210 mg, 0.24 mmol, 1 equiv.),
3-azidopropanoic anhydride (117 mg, 2 equiv.) and DMAP
(60 mg, 2 equiv.) were dissolved in DCM (5 mL). The solution
was stirred at room temperature overnight. Water (5 mL) was
then added, and the solution was stirred for 3 h. The layers
were separated and the organic layer was extracted with
aqueous Na2CO3 10% (3 Â 20 mL) then with a diluted
solution of aqueous hydrochloric acid (20 mL). The solution
was dried over magnesium sulfate and the solvents were
ments. Data are listed in parts per million (ppm) and are
reported relative to tetramethylsilane (1H, 13C), residual
solvent peaks being used as internal standard (CHCl3 1H:
7.26 ppm, 13C: 77.36 ppm). UV-visible spectra were recorded
on a Jasco V-550 spectrophotometer in diluted dichloro-
methane solution (ca. 10À5 mol LÀ1). The luminescence spec-
tra were measured using a Horiba–Jobin–Yvon Fluorolog-3s
spectrofluorimeter, equipped with a three-slit double-grating
excitation and emission monochromator with dispersions of
2.1 nm mmÀ1 (1200 grooves mmÀ1). Nonlinear transmission
experiments were carried out with 1420 nm as incident wave-
length using a ns-optical parametric oscillator pumped by a
frequency tripled Nd:YAG laser source; the complete experi-
mental set-up is described elsewhere.2a High resolution mass
spectrometry measurements and elemental analysis were
performed at the Service Central d’Analayse du CNRS
(Vernaison, France). Column chromatography was performed
on Merck Gerduran 60 (40–63 mm) silica. Compound Cy-1
was prepared according to a published procedure.2a
evaporated. The crude product was precipitated in
a
DCM–diethyl ether solution to afford a green solid (150 mg,
64%). 1H NMR (400 MHz, CDCl3): d 0.98 (s, 9H), 1.28
(m, 1H), 1.34 (s, 6H), 1.46 (s, 6H), 1.82 (q, J = 7 Hz, 2H),
3
2.0–2.1 (m, 2H), 2.35 (t, 2J = 7 Hz, 2H) 2.59 (dd, 3J = 2 Hz,
3
2J = 13 Hz, 2H), 3.26 (t, J = 7 Hz, 2H), 5.01 (s, 2H), 5.29
3
3
(m, 4H), 5.96 (d, J = 14 Hz, 2H), 6.91 (d, J = 8 Hz, 2H),
7.0–7.4 (m, 20H), 7.75 (d, 3J = 14 Hz, 2H). 13C NMR
(100 MHz, CDCl3): d 24.0, 25.1, 27.3, 27.7, 27.8, 30.9, 32.3,
42.4, 48.1, 48.8, 50.4, 51.6, 65.6, 100.8, 110.8, 114.7, 122.1,
122.8, 125.1, 126.5, 128.2, 128.8, 129.2, 130.0, 130.5, 134.1,
140.6, 141.7, 142.5, 159.3, 163.8, 171.9, 172.3. MS (MALDI-TOF):
M+ = 890.485 (calc. for C59H64N5O3: 890.500).
Syntheses
Cy-2. Phenol (40 mg, 0.43 mmol, 1.1 equiv.) was dissolved
in freshly distilled DMF (10 mL) under argon. NaH (19 mg,
1.2 equiv.) was added. The mixture was stirred at RT for
30 min and was added dropwise to a solution of Cy-1 (300 mg,
0.39 mmol, 1 equiv.) dissolved in DMF (10 mL). The solution
was stirred at RT for 8 h, then quenched with slow addition of
aqueous diluted solution of hydrochloric acid and DCM
(50 mL). The organic layer was washed with water (3 Â 25 mL),
brine (25 mL), dried with sodium sulfate and the solvents were
evaporated. The crude mixture was dissolved in the minimum
amount of DCM and precipitated in pentane to afford a green
solid (180 mg, 56%.). 1H NMR (200.13 MHz, CDCl3): d 0.99
Cy-5. (General procedure for triazole synthesis). Compound
Cy-4 (180 mg, 0.19 mmol, 1 equiv.) and the dendron D2
(103 mg, 1.1 equiv.) were dissolved in THF (10 mL). Sodium
ascorbate (115 mg, 3 equiv.), copper sulfate (145 mg, 3 equiv.)
and 5 drops of water were then added. The solution was stirred
48 h at 50 1C. The solution was the filtrated through a silica
plug (washed with DCM–methanol 9 : 1) and the solvents were
evaporated. The crude was dissolved in DCM (20 mL), and
the organic layer was extracted with diluted aqueous Na2CO3
(20 mL), water, and 10% HCl. After evaporation of the
solvents, the product was precipitated in DCM–diethyl ether
3
(9H, s), 1.31 (6H, s), 1.35 (s, 6H), 2.06 (dd, J = 13 Hz, 2J =
1
to afford a green solid (140 mg, 53%). H NMR (400 MHz,
13 Hz, 2H), 2.60 (dd, 3J = 2 Hz, 2J = 13 Hz, 2H), 5.32 (4H, s),
6.00 (d, 3J = 14 Hz, 2H), 7.2–7.5 (m, 23H), 7.80 (d, 3J =
14 Hz, 2H).13C NMR (50.32 MHz, CDCl3): d 25.3, 27.5, 27.8,
27.9, 32.5, 42.6, 48.2, 48.9, 100.9, 110.9, 114.6, 122.2, 122.7,
123.3, 125.2, 126.7, 128.3, 128.9, 129.3,130.4, 134.4, 140.8,
DMSO-d6): d 0.94 (s, 9H), 1.01 (s, 12H), 1.19 (s, 6H), 1.24
(s, 3H) 1.30 (s, 6H), 1,32 (s, 6H), 1.9–2.1 (m, 4H), 2.30 (t, 2J =
7 Hz, 2H), 2.66 (dd, 3J = 2 Hz, 2J = 13 Hz, 2H), 3.55 (d, 3J =
3
11 Hz, 4H), 3.91 (d, J = 11 Hz, 4H), 4.1–4.2 (m, 4H), 4.30
3
(t, J = 7 Hz, 2H), 4.99 (s, 2H), 5.12 (s, 2H), 5.35 (d, J =
142.1, 142.7, 159.6, 164.2, 172.1. MS (ESI+): MH+
=
2 Hz, 2H), 5.48 (d, J = 12 Hz, 2H), 6.19 (d, 3J = 14 Hz, 2H),
3
7.2–7.7 (m, 22H), 7.73 (d, J = 14 Hz, 2H), 8.06 (s, 1H). MS
749.4462 (calc. for C46H51N5O: 649.4471). Anal. calcd for:
C54H57N2O: C, 78.15, H, 6.92, N, 3.38, Found: C, 78.24, H,
7.02, N, 3.37%.
(MALDI-TOF): M+ = 1374.752 (calc. for C59H64N5O3:
1374.731).
Cy-3. Synthesis was carried out using the same procedure as
for Cy-2 but using 4-hydroxybenzyl alcohol instead of phenol
Cy-6. The product was synthesized according to the general
procedure for triazole synthesis from Cy-4 and the dendron
D3 in 35% yield. 1H NMR (400 MHz, DMSO-d6): d 0.97
1
leading to the formation of a green solid (810 mg, 72%). H
2
NMR (200.13 MHz, CDCl3): d 0.98 (s, 9H), 1.28 (m, 1H), 1.32
(s, 6H), 1.37 (s, 6H), 2.0–2.1 (m, 2H), 2.59 (dd, J = 2 Hz,
(s, 9H), 1–1.4 (m, 54H), 1.9–2.1 (m, 4H), 2.30 (t, J = 7 Hz,
3
3
2H), 2.66 (dd, J = 2 Hz, J = 13 Hz, 2H), 3.55 (d, J =
2
3
3
3
11 Hz, 8H), 3.96 (d, J = 11 Hz, 8H), 4.1–4.2 (m, 12H), 4.32
2J = 13 Hz, 2H), 4.65 (s, 2H), 5.21 (m, 4H), 5.89 (d, J =
3
14 Hz, 2H), 6.87 (d, J = 8 Hz, 1H), 7.0–7.4 (m, 18H), 7.45
(t, 3J = 7 Hz, 2H), 5.01 (s, 2H). 5.14 (s, 2H), 5.38 (d, J = 2 Hz,
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3
2H), 5.51 (d, J = 12 Hz, 2H). 6.22 (d, J = 14 Hz, 2H), 7.11
K. S. Kim, S. B. Noh, D. Kim and A. Osuka, Angew. Chem., Int.
Ed., 2006, 45, 3944–3947; (c) M. Drobizhev, Y. Stepanenko,
A. Rebane, C. J. Wilson, T. E. O. Screen and H. L. Anderson,
J. Am. Chem. Soc., 2006, 128, 12432–12433; (d) S. Mori, K. S. Kim,
Z. S. Yoon, S. B. Noh, D. Kim and A. Osuka, J. Am. Chem. Soc.,
2007, 129, 11344–11345; (e) J.-Y. Cho, S. Barlow, S. R. Marder,
J. Fu, L. A. Padilha, E. W. Van Stryland, D. J. Hagan and
M. Bishop, Opt. Lett., 2007, 32, 671–673; (f) Y. Tanaka,
S. Saito, S. Mori, N. Aratani, H. Shinokubo, N. Shibata,
Y. Higuchi, Z. S. Yoon, K. S. Kim, S. B. Noh, J. K. Park,
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(d, 3J = 8 Hz, 2H), 7.2–7.7 (m, 20H), 7.75 (d, 3J = 14 Hz, 2H),
8.10 (s, 1H). MS (MALDI-TOF): M+ = 1918.987 (calc. for
C59H64N5O3: 1918.983).
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