From graftable biphotonic chromophores to water-soluble organic nanodots for biophotonics: The importance of environmental effects

Article abstract of DOI:10.1002/chem.201202832

The photophysical and two-photon absorption (TPA) properties of biphotonic chromophores with one or two phenol pendant units were studied and compared with that of a model biphotonic quadrupolar chromophore. A water-soluble dendritic structure was then sy

Full text of DOI:10.1002/chem.201202832

DOI: 10.1002/chem.201202832
From Graftable Biphotonic Chromophores to Water-Soluble Organic
Nanodots for Biophotonics: The Importance of Environmental Effects
Cꢀdric Rouxel,[b] Marina Charlot,[b] Olivier Mongin,[b, d] Tathavarathy Rama Krishna,[c]
Anne-Marie Caminade,[c] Jean-Pierre Majoral,[c] and Mireille Blanchard-Desce*[a, b]
Abstract: The photophysical and two-
photon absorption (TPA) properties of
biphotonic chromophores with one or
two phenol pendant units were studied
and compared with that of a model bi-
photonic quadrupolar chromophore. A
water-soluble dendritic structure was
then synthesized by using the pendant
moieties as starting points for the con-
struction of dendritic branches. We
show that the polarity of the environ-
ment significantly modulates both the
fluorescence and the TPA responses of
the different chromophoric derivatives.
This extends to more subtle effects that
involve phenol pendant moieties that
were found to act as discrete solvating
units and to modify both the photophy-
sics and the TPA response of the chro-
mophore. This demonstrates the high
sensitivity of the TPA response of
quadrupolar derivatives to minute al-
terations in the environment. More-
over, the dendritic branches were
found to behave as a peculiar cybotac-
tic environment that was able to tune
the fluorescence and TPA response of
the inner chromophore by creating a
polar environment. This reveals a new
direction for exploiting such effects by
playing on the dendritic architecture
(e.g., the nature and shape of the build-
ing blocks, the geometry and position
of the chromophore) to modulate the
TPA responses.
Keywords: absorption
·
chromo-
phores · cross-coupling · dendrim-
ers · fluorescence
Introduction
(NIR) excitation wavelengths (thus leading to reduced scat-
tering) instead of UV/blue-visible one-photon excitation.
Multiphotonic excitation, however, requires the use of
short-pulse lasers as well as chromophores with reasonable
two-photon absorption (TPA) cross-sections. In particular,
chromophores with a much larger TPA cross-section (s2)
than endogenous chromophores (determined by Webb and
collaborators to be lower or much lower than 1 GM)[4] are
beneficial to ensure both selective and efficient photoexcita-
tion. However, the most popular chromophores and fluoro-
chromes used in biology do not show large TPA cross-sec-
tions.[5] This has triggered continuous efforts in the last
decade to engineer biphotonic chromophores with large
TPA cross-sections for various applications.[6] Water-soluble
chromophores that combine a large TPA cross-section in the
biological spectral window (700–1100 nm) as well as a large
fluorescence quantum yield (F), photostability, and reduced
toxicity are of particular interest for bioimaging and bio-
medical applications.
In this framework, we have developed a promising route
on the basis of the covalent embedding of a defined number
of lipophilic biphotonic chromophores within nontoxic and
biocompatible dendrimeric architectures. This route led to
soft “brilliant” all-organic nano-objects (organic nanodots,
or ONDs) that can overcome quantum dots in terms of both
one (eF) and two-photon brilliance (s2F) by several orders
of magnitude depending on the number of confined chromo-
phores.[7] Water-soluble monochromophoric organic nano-
dots in which core biphotonic chromophores are embedded
into the dendritic architecture were also developed. These
Multiphotonics has gained considerable popularity in recent
years in the biology community owing to the many advan-
tages it offers for bioimaging,[1] photodynamic therapy,[2] or
control and investigation of biological processes.[3] The use
of multiphotonics (i.e., two- or three-photon) excitation as
opposed to standard one-photon activation allows one to ad-
dress femtoliter volumes with 3D resolution while going
deeper into tissues by operating with red-near infrared
[a] Dr. M. Blanchard-Desce
Universitꢀ de Bordeaux
Institut des Sciences Molꢀculaires (UMR CNRS 5255)
351 Cours de la Libꢀration, 33405 Talence Cedex (France)
Fax : (+33)540006994
E-mail: m.blanchard-desce@ism.u-bordeaux1.fr
[b] Dr. C. Rouxel, Dr. M. Charlot, Dr. O. Mongin,
Dr. M. Blanchard-Desce
Chimie et Photonique Molꢀculaires, CNRS UMR 6510
Universitꢀ de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex (France)
[c] Dr. T. R. Krishna, Dr. A.-M. Caminade, Dr. J.-P. Majoral
Laboratoire de Chimie de Coordination, CNRS
205 route de Narbonne, BP 44099
31077 Toulouse Cedex 4 (France)
[d] Dr. O. Mongin
Institut des Sciences Chimiques de Rennes
CNRS UMR 6226, Universitꢀ de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202832.
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FULL PAPER
biocompatible ONDs are of particular interest as contrast
agent tracers for in vivo multiphotonic imaging.[8] These
proof of concept water-soluble monochromophoric ONDs
were built from a bis-acceptor quadrupolar biphotonic chro-
mophore with a TPA cross-section of 100 GM. To achieve a
larger TPA cross-section, we decided to shift to an analo-
gous bis-donor quadrupolar biphotonic chromophore, the
TPA cross-section of which has been shown to be signifi-
cantly larger.[7d,9] Following this aim, a symmetrically func-
tionalized quadrupolar chromophore with two phenol pend-
ant moieties (3) for incorporation into the core of the den-
dritic architecture was synthesized in parallel to its dissym-
metrical analogue (2) that bears only one phenol pendant
moiety, which was used as a decorating biphotonic chromo-
phore for the elaboration of superbrilliant nanodots.[7a,c] The
photophysical properties (including the TPA) of biphotonic
chomophore 3 were studied and compared with that of a
model lipophilic biphotonic chromophore 1, the photolumi-
nescence properties of which depend significantly on the en-
vironment, thus making it a sensitive probe in response to
its local environment. Water-soluble dendritic OND 4 was
then synthesized from chromophore 3. Its photophysical
properties were investigated and showed that chromophore
1 embedded in the dendritic shell experiences a polar envi-
ronment that strongly affects its photoluminescence proper-
ties. We hereafter describe in detail the synthesis and photo-
physical properties of the series of compounds and take
note of the variation from the model compound, the grafta-
ble chromophores, and finally the water-soluble OND. We
demonstrate that the environment significantly modulates
the TPA responses as shown by polarity-dependent meas-
urements conducted on the model chromophore. This ex-
tends to more subtle effects that involve appendices, cova-
lently linked to the chromophores, which act as discrete sol-
vating units with reduced mobility (and thus restricted reor-
ientation). This opens a new path for exploiting such effects
by playing on the dendritic architecture to modulate the
TPA responses.
Results and Discussion
Synthesis
Synthesis of model chromophore 1 and functionalized chro-
mophores 2 and 3: Fluorophores 1–3 were prepared by
means of Sonogashira cross-coupling reactions. Three differ-
ent synthetic pathways, direct or stepwise, were explored.
Along the first route (Scheme 1), diiodofluorene core 5a[10]
was treated with either trimethylsilylacetylene or 2-methyl-
3-butyn-2-ol under palladium(II)-catalyzed conditions to
afford 5b and 5c, respectively, the deprotection of which
gave bisACHTNUTRGNE(UNG alkyne) fluorene core 6. Double Sonogashira cou-
pling of 6 with one equivalent of both iodo derivatives 7[11]
and 8 simultaneously afforded fluorophores 1, 2, and 3 in a
single-step one-pot reaction. However, this attractive
method suffers from a major drawback: the purification is
very tedious and initially requires column chromatography
to separate three main fractions that contain 1, 2, and 3, re-
spectively. To reach the purity criteria required for fluores-
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M. Blanchard-Desce et al.
Scheme 1. a) Ethynyltrimethylsilane, [PdACTHNUGTRNEUNG(PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 16 h (88%); b) 2-methyl-3-butyn-2-ol, conditions as in (a), (87%);
c) NaOH, toluene/iPrOH, reflux, 30 min (63%); d) KOH (1m), THF/MeOH, 208C, 15 min (94%); e) [Pd
of 1, 6% of 2, 5% of 3).
ACHTNUGTERN(NUGN PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 15 h (4 %
cence measurements, each fraction had then to be purified
by medium-pressure liquid chromatography (MPLC) by
using 20–40 mm silica gel to separate the expected fluoro-
phores from numerous fluorescent byproducts, thus leading
to very low isolated yields of 4, 6, and 5%, respectively
(Scheme 1). A possible explanation for the presence of such
fluorescent impurities could be related to the oxidation of
[PdACTHUNGTERNU(NG PPh3)4] was used. This direct route could therefore not
be used for the gram-scale preparation of the target chromo-
phores.
A second route was then investigated for the synthesis of
dissymmetric fluorophore 2 on the basis of stepwise func-
tionalization of the fluorene bisACTHUNTGRNEUNG(alkyne) core (Scheme 2).
Dissymmetrization of core 5c was performed by deprotect-
ing one of two acetylene protective groups in 44% yield
(but the reaction kinetics were found to be somewhat diffi-
cult to control, thereby generating difficulties in reproduc-
tion). Sonogashira coupling of 9 with iodo derivative 7 led
to 10a in disappointing 37% yield, which could not be im-
bisACHTUNGTRENNUNG(alkyne) core 6, thereby resulting in diyne oligomers, the
terminal true acetylene functions of which could also react
with iodo derivatives 7 and 8. The use of copper-free condi-
tions and replacing palladium(II) by palladium(0) was un-
successful and led to an absence of reaction when
Scheme 2. a) NaOH, toluene/iPrOH, reflux (44%); b) [Pd
d) [Pd(PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 16 h (57%).
ACHTNUGTNERN(NUG PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 3.5 h (37%); c) KOH, toluene/iPrOH, reflux, 1 h (87%);
ACHTUNGTRENNUNG
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Water-Soluble Organic Nanodots
FULL PAPER
proved by varying catalysts, solvents, or concentrations.
Base-promoted deprotection of 10a afforded 10b in good
yield. Its cross-coupling with the second iodo derivative 8 fi-
tween 11a and 14a could be related to the presence of the
phenol function, compound 8 was esterified with acetyl
chloride. The cross-coupling of resulting compound 15a with
ethynyltrimethylsilane afforded 15b in a notably increased
81% yield. However, cleavage of the silyl protective group
gave 15c in a better but still unsatisfactory 45% yield
(Scheme 3).
If degradation during the purification is indeed the ex-
planation, 15c should not be isolated, but generated in situ
from 15b during the Sonogashira couplings. In a one-pot re-
action, 15b was therefore deprotected with tetra-n-butylam-
monium fluoride (TBAF), and the liberated alkyne was
treated with diiodo fluorene core 5a in the presence of pal-
ladium(II) and copper(I) in toluene/Et3N, thus leading to
dissymmetrized molecule 16. The concomitant formation of
the double coupling product was limited by using an excess
amount of the diiodo core (which could easily be recycled).
It should be noticed that, under the same conditions, cross-
coupling of 11a (or 12) with 5a did not proceed. In contrast,
compound 17 was obtained by reaction of 11a with 16 in a
satisfactory 75% yield. Saponification of acetate protective
groups of 17 with diluted
nally led to fluorophore
2 in moderate 57% yield
(Scheme 2). The major advantage of this second route is
that purifications are much easier than for the first route;
however, the overall yield of this four-step sequence (8%)
remained unsatisfactory.
The third route is based on the stepwise functionalization
of a diiodo fluorene core with two acetylenic moieties ob-
tained from the corresponding iodo derivatives 7 and 8
(Scheme 3 and 4). Building block 7[11] was treated with
either ethynyltrimethylsilane or 2-methyl-3-butyn-2-ol to
afford 11a[12] and 11b, respectively, and base-promoted de-
protection of the latter gave 12.[9c] On the other hand, iodo
derivative 8 (obtained from the Mitsunobu reaction between
13[13] and hydroquinone) was also treated with ethynyltrime-
thylsilane to afford 14a in mediocre 45% yield. Cleavage of
the trimethylsilyl group led to 14b in a very low isolated
yield (most probably due to degradation during the purifica-
tion). To check whether the large difference in yield be-
NaOH afforded fluorophore 2.
The overall yield of this three-
step sequence is 37%, which al-
lowed for gram-scale prepara-
tion of 2 (Scheme 4).
Symmetrical fluorophore
3
could be obtained similarly in a
two-step sequence from diodo
core 5a. Double Sonogashira
coupling of 5a with 15b (depro-
tected in situ with TBAF) led
efficiently to 18, the saponifica-
Scheme 3. a) Ethynyltrimethylsilane, [Pd
butyn-2-ol, conditions as in (a) (82%); c) NaOH, toluene/iPrOH, reflux, 1 h (87%); d) hydroquinone, diethyl
azodicarboxylate (DEAD), PPh3, THF, 208C, 16 h (51%); e) [Pd(PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 15 h
(45% of 14a, 81% of 15b); f) THF, TBAF, 208C, 15 min (12% of 14b, 45% of 15c); g) acetyl chloride,
DMAP, CH2Cl2/Et3N, 20 8C, 14 h (76%).
ACHTNUGNERT(NUGN PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 18 h (90%); b) 2-methyl-3-
tion of which afforded
3
(Scheme 5). However, the syn-
thesis of fluorophore 1 by reac-
tion between 5a and 11a or 12
failed under these conditions
and no coupling occurs. Among
attempts to increase reactivity,
the replacement of toluene with
THF was found to give 1 in fair
yield (Scheme 5).
AHCTUNGTRENNUNG
Synthesis of water-soluble or-
ganic dendrimer 4: Fluorophore
3, which bears two phenol
groups, was used as the core of
the water-soluble dendrimer 4.
The first reaction is the cou-
pling with hexachlorocyclotri-
phosphazene (N3P3Cl6), which
was used in
a large excess
amount to favor the monosub-
stitution reaction. Compound
19 was isolated in very good
Scheme 4. a) Compound 5a (3 equiv), 15b (1 equiv), TBAF, [PdACHTUNGTRENNUNG
(54%); b) TBAF, [Pd
15 min (91%).
ACHTUNGTRENNUNG
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16453

M. Blanchard-Desce et al.
Scheme 5. a) TBAF, [PdACHTUNGTRENNUNG(PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 16 h (76%); b) NaOH (0.5m), THF/EtOH, 208C, 25 min (98%); c) [PdAHCTUNGTREN(NGUN PPh3)2Cl2], CuI,
THF/Et3N, TBAF, 508C, 16 h (59%).
yield (93%). The nonsymmetric functionalization of N3P3Cl6
was demonstrated by the 31P NMR spectra in particular,
which display the presence of two signals, one of which re-
sembled a triplet at d=13.0 ppm, which corresponds to the
phosphorus atom that bears the chromophore, and the other
cence properties with large fluorescence quantum yields in
organic solvents. As illustrated in Figure 1, we observed that
the presence of phenol pendant moieties leads to a slight
but yet observable modification of absorption and emission
spectra, thus indicating that those end groups slightly
modify the environment. A slight blueshift of both absorp-
tion and emission spectra is observed with the addition of
pendant phenol moieties. In addition, a clear change of vi-
bronic structure is observed upon going from chromophore
1 to 3 with a relative rise of the 01 and 02 vibronic substruc-
ture with respect to that of the 00 one. This effect, which re-
veals an increase in reorganization energy,[16] indicates that
the alkyloxyphenol moieties act as discrete “solvating” mol-
ecules that contribute to solvent reorganization in the excit-
ed state. This is consistent with a regular increase of the
Stokes shift values with an increased number of appending
moieties (i.e., from 1 to 3).
The presence of pendant moieties also induces a slight
broadening of the absorption band (consistent with a lower
extinction coefficient at absorption maximum), which might
be attributed to an increase in inhomogeneous broadening
caused by the proximity of alkyloxyphenol moieties that are
connected by means of flexible spacers, thus generating a
distribution of conformations. We also observe that the
phenol moieties cause a decrease in the fluorescence quan-
tum yield as well as of the fluorescence lifetime. The shorter
radiative lifetime can be related to a slight increase in radia-
tive decay rate (in relation with the blueshifted emission
and the enhancement of oscillatory force[17]) and a marked
increase in the nonradiative decay rate. This marked in-
crease (by a factor larger than two for symmetrical chromo-
phore 3 relative to chromophore 1, which lacks the phenol
terminal moieties) suggests that phenol moieties are in-
volved in additional nonradiative decay channels. These
most probably involve hydrogen bonds with surrounding sol-
vent molecules that promote vibrational deactivation and
are therefore responsible for the decrease in fluorescence
quantum yield.
one of which resembled a doublet at d=22.4 ppm, which
2
corresponds to both PCl2 groups, with J
N
The growth of the branches was then carried out by using
our classical method of dendrimer synthesis.[14] The first step
of the growth is the nucleophilic substitution of Cl by 4-hy-
droxybenzaldehyde, which affords dendrimer 20, character-
ized by 31P NMR spectroscopy by the disappearance of the
doublet and triplet of 19 on behalf of a complex system at
d=7.2–7.9 ppm for 20. The second step of the growth is the
condensation reaction of the aldehydes of 20 with the phos-
phorhydrazide H2NN(Me)P(S)Cl2, which affords dendrimer
21. The completion of the reaction is characterized by the
total disappearance of the signals that correspond to the al-
dehydes in the 1H NMR spectra. The growth of the den-
drimer is pursued by repeating the first step (i.e., the substi-
tution reaction with 4-hydroxybenzaldehyde), thus leading
to dendrimer 22. The repetition of the second step (i.e., the
condensation with the phosphorhydrazide) affords dendrim-
er 23. All these reactions are quantitative, thus all the den-
drimers are isolated in excellent yields after workup.
To have a water-soluble dendrimer, the terminal groups
must bear charges. We chose to graft ammonium groups by
treating them with N,N-diethylethylenediamine.[15] The reac-
tion of the NH2 side with P(S)Cl2 terminal groups of the
dendrimer generates HCl, which is trapped by the NEt2
side, thereby affording water-soluble and multi-charged den-
drimer 4. The completion of the reaction is shown in the
31P NMR spectra by the disappearance of the singlet that
corresponded to P(S)Cl2 groups at d=62.8 ppm on behalf of
a
singlet at d=69.8 ppm, which corresponded to
P(S)(NHR)2 (Scheme 6).
ACHTUNGTRENNUNG
Photophysical properties
Absorption and fluorescence of chromophores 1–3: Structur-
al effects: The photophysical properties of chromophores 1–
3 are collected in Table 1. All chromophores strongly absorb
in the near-UV region and show attractive photolumines-
Influence of environment on the photophysical properties of
chromophores 1–3: The influence of environmental effects
was checked by investigating the absorption and emission
properties of chromophore 3 in solvents of varying polarities
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Water-Soluble Organic Nanodots
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Scheme 6. a) TBAF, [PdACHTUNGTRENNUNG(PPh3)2Cl2], CuI, toluene/Et3N, 40 8C, 16 h (76%); b) NaOH (0.5m), THF/EtOH, 208C, 25 min (98%); c) [PdAHCTUNGTREN(NGUN PPh3)2Cl2], CuI,
THF/Et3N, TBAF, 508C, 16 h (59%).
(Table 2). As shown in Figure 2, chromophore 3 absorption
spectra are only weakly affected by solvent polarity (except
for a high-polarity solvent like DMSO, which leads to a
slight redshift as well as a broadening of the absorption
band). In contrast, its emission is strongly dependent on sol-
vent polarity, which shifts from the violet to the blue-green
region upon going from low-polarity to high-polarity sol-
vents. As a consequence, chromophore 3 behaves like a sen-
sitive fluorescent probe toward its environment. A similar
behavior is observed for chromophores 1[18] and 2 (see the
Supporting Information). As shown in Figure 3, the solvato-
chromic behavior of each compound in solvents of medium
to high polarity can be fit with a Lippert–Mataga relation-
ship in which the Stokes shift values are linearly correlated
to the polarity/polarizability function of the solvent Df
[Eq. (1)]:[19]
nabsꢀnem ¼ 2Dm2Df=ðhca3Þ þ constant
ð1Þ
~
~
in which n˜abs (n˜em) is the wavenumber of the absorption (flu-
orescence) maximum, h is the Planck constant, c is the light
velocity, a is the radius of the solute spherical cavity, and
Df=(eꢀ1)/
(2e+1)ꢀ
E
(2n2+1), in which e is the dielec-
ACHTUNGTRENNUNG
Table 1. Photophysical data for compounds 1–3 in toluene.
F[e] t[f] [ns] kr[g] [109 sꢀ1
]
knr[g] [109 sꢀ1 t0[h] [ns] r[i]
]
abs [a]
max
em [d]
max
Compound
l
[nm]
e
[b] [mꢀ1 cmꢀ1
]
FWHM [cmꢀ1
]
f[c]
l
[nm] Stokes shift [cmꢀ1
]
1
2
3
388
386
381
85800
84900
83800
4190
4330
4640
1.4 422, 445
1.5 420, 444
1.6 418, 440
2080
2100
2320
0.87 0.74
0.83 0.67
0.77 0.55
1.18
1.24
1.40
0.17
0.25
0.42
0.85
0.81
0.71
0.18
0.18
0.18
[a] Experimental absorption maxima. [b] Molar extinction coefficient. [c] Oscillator strength. [d] Experimental emission maximum. [e] Fluorescence
quantum yield determined in chloroform relative to quinine in 0.5m H2SO4. [f] Experimental fluorescence lifetime. [g] Radiative (kr) and nonradiative
(knr) decay rates. [h] Radiative lifetime. [i] Fluorescence anisotropy.
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M. Blanchard-Desce et al.
Figure 3. Lippert–Mataga correlations for fluorophores 1–3.
Figure 1. Normalized absorption and emission spectra of chromophores
relation. This reveals that symmetry breakage occurs only in
medium- to high-polarity solvents, thanks to the stabilization
of the corresponding excited state provided by such sol-
vents.[20] This explains the higher radiative decay rate meas-
ured in toluene (relative to dibutyletheroxide) on account of
the extended delocalization in the emissive excited state
only in toluene.
1–3 in toluene.
The slopes values derived from the Lippert–Mataga rela-
tionship (i.e., 2Dm2/hca3, also termed specific shifts[21]), which
are directly related to the magnitude of the photoinduced
intramolecular charge transfer (Dm) and to the size of the
Onsager cavity (a), are collected in Table 3. To obtain infor-
mation on the size of the molecule, we used fluorescence
anisotropy (r) and lifetime (t) data in DMSO to calculate
the longitudinal rotational correlation time (q) by using the
Perrin equation [Eq. (2)]:[22]
Figure 2. Normalized absorption and emission spectra of chromophore 3
in solvents of different polarity.
Table 3. Solvatochromic and anisotropy data for chromophores 1–3.
Such behavior can be related to a symmetry
breakage that occurs in the excited state of the
quadrupolar donor–acceptor–donor (DAD) com-
pound, which leads to localization of the excitation
on a dipolar chromophoric subunit (donor–accept-
or, or DA).[19b] Hence the emission behavior is simi-
lar to that of push/pull chromophores and shows in-
tramolecular charge transfer (ICT) with an increase
Compound
Specific
shift[a]
r[b]
t[c]
q[d]
v[e]
l[f]
[ꢂ]
a[g]
[ꢂ]
Dm
[ns]
[ns]
[ꢂ3]
[D]
A
]
1
2
3
19.1
20.5
19.8
0.20
0.20
0.217 1.46
1.92
1.96
1.92
1.96
1.73
7900
8050
7100
12.4
12.4
11.9
6.2
6.2
6.0
20.9
21.9
20.2
[a] Slope derived from the linear dependence of the Stokes shift on the orientational
polarizability function Df. [b] Florescence anisotropy (in DMSO). [c] Fluorescence
in the dipole moment in the excited state. We note lifetime (in DMSO). [d] Longitudinal rotational correlation time (in DMSO). [e] Mo-
lecular rotor volume. [f] Molecular long axis derived from fluorescence anisotropy.
[g] Dipolar Onsager cavity radius
that the Stokes shift values in low-polarity solvent
(i.e., toluene) always stand out from the linear cor-
Table 2. Photophysical data of chromophore 3 in different solvents.
tf[d] [ns]
t0[e] [ns]
kr[f] [109 sꢀ1
]
]
abs [a]
max
em
max
[f]
knr [109 sꢀ1
Solvent
l
[nm]
emax [mꢀ1 cmꢀ1
]
l
[b] [nm]
Stokes shift [cmꢀ1
]
F[c]
toluene
Bu2O
AcOEt
THF
acetone
EtOH
CH3CN
DMSO
381
83800
82300
88800
83200
86000
84500
83300
86900
418, 440
413, 436
443
450
476
462
499
501
2300
2100
3600
3800
5200
4700
6100
5700
0.77
0.77
0.81
0.80
0.71
0.80
0.69
0.78
0.55
0.82
1.04
1.02
1.36
1.23
1.65
1.46
0.71
1.06
1.28
1.28
1.92
1.54
2.39
1.87
1.40
0.94
0.78
0.78
0.52
0.65
0.42
0.53
0.42
0.28
0.18
0.20
0.21
0.16
0.19
0.15
380
382
384
382
380
383
390
[a] Experimental absorption maxima. [b] Experimental emission maximum. [c] Fluorescence quantum yield determined relative to quinine in 0.5m
H2SO4. [d] Experimental fluorescence lifetime. [e] Radiative lifetime. [f] Radiative (kr) and nonradiative (knr) decay rates.
16456
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Chem. Eur. J. 2012, 18, 16450 – 16462

Water-Soluble Organic Nanodots
FULL PAPER
t
q ¼
(between that of acetonitrile and DMSO) in the core of the
dendritic structure relative to the bulk solution. This sug-
gests that DMSO molecules permeate the dendritic architec-
tures, thus leading to an effective polarity close to that of
DMSO. We also note that the fluorescence quantum yield is
reduced by about half in the dendritic architecture as com-
pared to the bulk solution. This indicates that competitive
nonradiative decay processes take place, which possibly in-
volve the dendritic backbone. On the other hand, the fluo-
rescence anisotropy markedly increases from chromophore
3 to dendritic chromophore 4 (thus almost reaching the limit
value) as expected on account of the larger size of com-
pound 4, which leads to much longer rotational correlation
time.
In contrast to DMSO, the emission characteristics of 4 in
water are strongly affected. The absorption band is clearly
broadened (in relation to inhomogeneous broadening) and
weakened, whereas the emission band is even more blue-
shifted, which is indicative of a less polar environment than
acetone (Figure 4). This indicates that water molecules have
ð2Þ
ð0:4=rÞ ꢀ 1
Assuming a prolate-type behavior,[22] the correlation time
(q) is directly related to the size of the chromophore (mo-
lecular rotor long axis l) according to Equation (3):
rffiffiffiffiffiffiffiffiffiffiffi
3kTq
4ph
3
ð3Þ
l ¼
in which h is the solvent viscosity.
From the long axis of the molecule derived from fluores-
cence anisotropy measurements (l), one can derive the
radius a of the Onsager cavity for the dipolar subunit.[23]
The derived data are gathered in Table 3. The presence of
the ethyloxyphenol appendages induces a slight reduction of
the Dm value in the case of symmetrical derivative 3 and a
slight increase in the case of asymmetrical derivative 2. This
confirms that the phenol pendant moieties influence the
photophysical properties of the core chromophore unit by
modifying its cybotactic environment, most probably by
means of dipole–dipole interactions that destabilize the
polar excited state in the case of chromophore 3 (in agree-
ment with blueshifted emission) but facilitates symmetry
breakage in the case of chromophore 2.
For all chromophores 1–3, we observed that the fluores-
cence quantum yields remain high in all solvents (0.7–0.8),
whereas the fluorescence lifetime increases with increasing
polarity. This peculiar behavior can be related to the parallel
and steady decrease in both radiative (as expected from the
redshifted emission) and nonradiative decay rates with in-
creasing polarity.
Absorption and fluorescence of water-soluble dendritic com-
pound 4: The photophysical properties of compound 4 were
first studied in DMSO, which was chosen owing to its ability
to dissolve both chromophore 3 and its water-soluble den-
dritic derivative 4 and thus allow direct comparison and as-
sessment of the effect of the dendritic architecture on the
photophysical properties of the embedded chromophore. As
observed in Table 4, the absorption band of the core chro-
mophore is slightly blueshifted owing to the overlap with
the red edge of the dendritic architectures absorption band
located in the UV region. We stress that selective one-
photon excitation of the inner chromophore is thus effective
only above 400 nm. The emission properties of chromophore
4 in DMSO are only slightly different from that of its parent
chromophore 3. The emission band is only slightly blueshift-
ed, which is indicative of a faintly less polar environment
Figure 4. Absorption and emission spectra of dendrimer 4 in DMSO and
water relative to those of isolated fluorophore 3 in DMSO.
much lower affinity for the dendritic structure core (owing
to the lipophilic nature of the branches) than DMSO, there-
by leading to a less polar environment for the core chromo-
phore. Strikingly, both the fluorescence quantum yield and
the anisotropy of dendritic derivative 4 were found to de-
crease dramatically. This suggests that these dendritic archi-
tectures tend to self-assemble in water, thus favoring fast
energy transfer between chromophores. The presence of
flexible linkers in molecule 3 as well as the elongated rod-
like shape and hydrophobic nature of the core chromophore
might facilitate the formation of aggregates of dendritic
compound 4 in water. Such behavior is consistent with the
double-exponential decay of fluorescence. Compared to the
results reported earlier for water-soluble dendritic architec-
tures built from a much more compact chromophoric core
that lacks flexible linkers,[8] these results indicate that the
core chromophore in compound 4 is not sufficiently isolated
from the external environment and that better (i.e., tighter)
Table 4. Fluorescence characteristics of dendritic compound 4.
abs [a]
max
em
max
Solvent
l
[nm]
l
[nm]
F
tf [ns]
r
4/DMSO
385
385
487
480
0.42
1.69 (80%)
0.33 (20%)
0.70 (70%)
2.39 (30%)
0.32
4/H2O
0.075
0.096
Chem. Eur. J. 2012, 18, 16450 – 16462
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16457

M. Blanchard-Desce et al.
shielding is needed to prevent self-aggregation and to fur-
ther enhance the fluorescence emission in water.
Two-photon absorption: Environmental and symmetry ef-
fects: To monitor environmental effects on TPA and com-
pare them with one-photon absorption, we first investigated
the two-photon properties of core chromophore 3 in sol-
vents of various polarities. The TPA spectra were deter-
mined in the NIR range (700–980 nm) by investigating their
two-photon excited fluorescence (TPEF) in various solu-
tions.[5] As noted from Figure 5, solvent polarity has much
Figure 6. Two-photon absorption spectra of dendrimer 4 in water relative
to 3 in acetonitrile and DMSO.
Figure 5. Two-photon absorption spectra of core fluorophore 3 in various
solvents.
Conclusion
more influence on TPA than on one-photon absorption (see
Table 1 and Figure 2) and a non-monotonous variation is ob-
tained. We observed a decrease in the TPA response upon
going from low-polarity (e.g., THF) to medium-polarity sol-
vent (e.g., acetone) followed by an increase in polar solvents
as well as redshift of the strongly two-photon-allowed ab-
sorption band (which lies at higher energy than that which
corresponds to the lowest one-photon-allowed excited state,
in relation with quadrupolar symmetry).[9c] As a result, the
TPA maximum is clearly seen in the 700–750 nm spectral
range only in the case of highly polar solvents such as
DMSO. This TPA redshift parallels the one-photon absorp-
tion redshift observed in DMSO.
The TPA properties of dendritic system 4 dissolved in
water were found to be between that of chromophore 3 in
DMSO and in acetonitrile (Figure 6). This confirms that the
dendritic shell provides a polar environment for the core
chromophore that affects its TPA response, as is the case for
fluorescence.
From the present study, we can deduce that not only bulk
polarity but also the presence of discrete solvating units
(such as ethyloxy phenol moieties) influences the fluores-
cence and TPA properties of prototypical quadrupolar bi-
photonic chromophores. As a result, the quadrupolar chro-
mophore embedded at the core of the dendritic structure
was found to be sensitive to the particular cybotactic envi-
ronment provided by the dendritic branches, which creates a
local setting that is favorable to TPA. This opens a new di-
rection for engineering the TPA response of biphotonic
chromophores by taking advantage of and tuning the den-
dritic environment. We are currently investigating this route.
We are also trying to provide better protection by the den-
dritic shell to prevent fluorescence quenching and ensure
high two-photon brightness in water.
Experimental Section
Interestingly, we observe a marked broadening, particular-
ly in the red-edge region, with the increase in the TPA band
that corresponded to the one-photon-allowed, two-photon-
forbidden excited state. This effect might be related to the
self-association of compound 4 in water, which promotes
symmetry breakage.
General synthetic methods: All air- or water-sensitive reactions were car-
ried out under dry argon. Solvents were generally dried and distilled
prior to use. Reactions were monitored by thin-layer chromatography on
Merck silica gel 60 F254 precoated aluminum sheets. For column chroma-
tography, Merck silica gel Si 60 (40–63 mm, 230–400 mesh or 63–200 mm,
70–230 mesh) was used. Melting points were determined using an Elec-
trothermal IA9300 digital melting-point instrument. For NMR spectro-
scopy, Bruker ARX 200 (1H: 200.13 MHz, 13C: 50.32 MHz) or Avance
AV 300 (1H: 300.13 MHz, 13C: 75.48 MHz) instruments were used with
16458
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Chem. Eur. J. 2012, 18, 16450 – 16462

Water-Soluble Organic Nanodots
FULL PAPER
1
CDCl3 solutions; H chemical shifts (d) are given in ppm relative to TMS
2H), 1.17 ppm (t, J=7.0 Hz, 3H); 13C NMR (50.32 MHz, CDCl3): d=
152.6, 149.6, 147.1, 137.7, 116.1, 115.5, 114.1, 76.5, 65.9, 49.6, 45.5,
12.0 ppm; HRMS (ES+): m/z calcd for C16H19INO2 [M+H]+: 384.0461;
found: 384.0459; elemental analysis calcd (%) for C16H18INO2 (383.23): C
50.15, H 4.73, N 3.65; found: C 50.36, H 4.85, N 3.65.
as internal standard, J values in Hz and 13C chemical shifts relative to the
central peak of CDCl3 at d=77.0 ppm. High- and low-resolution mass
spectra measurements were performed at the Centre Rꢀgional de Me-
sures Physiques de lꢃOuest (CRMPO, Rennes) using a Micromass MS/
MS ZABSpec time-of-flight (TOF) instrument with emitter–base–emitter
(EBE) TOF geometry. Liquid secondary ion mass spectrometry (LSIMS)
was carried out at 8 kV with Cs+ in m-nitrobenzyl alcohol (mNBA); ES+
(electrospray ionization, positive mode) at 4 kV; electron ionization (EI)
at 70 eV. Elemental analyses were performed at CRMPO. Compounds
5a,[10] 7,[11] 11b,[9c] 12,[9c] and 13[13] were synthesized according to the re-
spective literature procedures.
Compound 9: Solid NaOH (0.73 g) was added to a solution of 5c (4.02 g,
9.09 mmol) in toluene/iPrOH (6:1, 50 mL). The mixture was heated
under reflux conditions for 30 min. After cooling, NaOH was removed
by filtration, and the solvents were evaporated. The compounds were
separated by column chromatography (heptane/CH2Cl2 70:30 then 20:80)
to yield ) 6 (0.66 g, 22%) and 9 (1.54 g, 44%). Rf =0.33 (heptane/CH2Cl2
20:80); 1H NMR (200.13 MHz, CDCl3): d=7.61 (d, J=7.6 Hz, 2H), 7.47
(d, J=7.6 Hz, 1H), 7.45 (m, 1H), 7.40 (d, J=7.6 Hz, 1H), 7.38 (s, 1H),
3.15 (s, 1H), 2.04 (s, 1H), 1.94 (m, 4H), 1.65 (s, 6H), 1.07 (m, 4H), 0.66
(t, J=7.2 Hz, 6H), 0.52 ppm (m, 4H); 13C NMR (50.32 MHz, CDCl3):
d=150.92, 150.86, 141.0, 140.4, 131.2, 130.7, 126.4, 126.0, 121.5, 120.6,
119.9, 119.8, 94.0, 84.5, 82.9, 77.3, 65.7, 55.0, 40.1, 31.5, 25.7, 22.9,
Compound 5b: Air was removed from
5.66 mmol) in toluene/Et3N (5:1; 37.5 mL) by blowing argon for 20 min.
Then CuI (21.6 mg, 0.113 mmol), [Pd(PPh3)2Cl2] (79.6 mg, 0.113 mmol),
a
solution of 5a[10] (3.00 g,
AHCTUNGTRENNUNG
and trimethylsilylacetylene (2.4 mL, 1.67 g, 16.98 mmol) were added, and
the mixture was stirred at 408C for 16 h. After evaporation of the sol-
vents, the residue was purified by column chromatography (heptane/
CH2Cl2 90:10) to yield 5b (2.35 g, 88%). Rf =0.24 (heptane); 1H NMR
(200.13 MHz, CDCl3): d=7.64 (d, J=7.5 Hz, 2H), 7.48 (d, J=7.5 Hz,
2H), 7.46 (s, 2H), 1.98 (m, 4H), 1.08 (m, 4H), 0.69 (t, J=7.3 Hz, 6H),
0.55 (m, 4H), 0.33 ppm (s, 18H); 13C NMR (50.32 MHz, CDCl3): d=
150.9, 140.9, 131.3, 126.2, 121.8, 119.9, 106.1, 94.3, 55.2, 40.2, 25.8, 23.1,
13.7 ppm; HRMS (EI): m/z calcd for C28H32O [M+ ]: 384.2453; found:
C
384.2448; elemental analysis calcd (%) for C28H32O (384.56): C 87.45, H
8.39; found: C 87.02, H 8.51.
Compound 10a: Air was removed from
a solution of 9 (1.304 g,
3.39 mmol) and 7[11] (1.71 g, 4.41 mmol) in toluene/Et3N (5:1, 10.8 mL) by
blowing argon for 20 min. Then CuI (12.9 mg, 0.068 mmol) and [Pd-
AHCTUNGTRENN(GNU PPh3)2Cl2] (48 mg, 0.068 mmol) were added, and deaeration was contin-
13.8, 0.1 ppm; HRMS (EI): m/z calcd for C31H42Si2 [M+ ]: 470.2825;
found: 470.2848; elemental analysis calcd (%) for C31H42Si2 (470.85): C
79.08, H 8.99; found: C 78.88, H 9.12.
C
ued for 10 min. Thereafter the mixture was stirred at 408C for 3.5 h. The
solvents were removed under reduced pressure, and the crude product
was purified by column chromatography (heptane/CH2Cl2 75:25 then
30:70) to yield 10a (817 mg, 37%). Rf =0.37 (heptane/CH2Cl2 30:70);
1H NMR (200.13 MHz, CDCl3): d=7.61 (d, J=8.5 Hz, 1H), 7.60 (d, J=
8.5 Hz, 1H), 7.47 (d, J=8.5 Hz, 1H), 7.45 (m, 1H), 7.39 (d, J=8.5 Hz,
Compound 5c: Air was removed from
11.3 mmol) in toluene/Et3N (5:1, 40 mL) by blowing argon for 20 min.
Then CuI (86 mg, 0.45 mmol), [Pd(PPh3)2Cl2] (316 mg, 0.45 mmol), and
a
solution of 5a[10] (6.00 g,
AHCTUNGTRENNUNG
2-methyl-3-butyn-2-ol (2.84 g, 33.8 mmol) were added, and the mixture
was stirred at 408C for 16 h. After evaporation of the solvents, the resi-
due was purified by column chromatography (heptane/CH2Cl2 30:70 then
CH2Cl2) to yield 5c (4.37 g, 87%). Rf =0.29 (CH2Cl2/AcOEt 95:5);
1H NMR (200.13 MHz, CDCl3): d=7.60 (d, J=8.6 Hz, 2H), 7.40 (d, J=
8.6 Hz, 2H), 7.38 (s, 2H), 2.16 (s, 2H), 1.94 (m, 4H), 1.66 (s, 12H), 1.07
(m, 4H), 0.66 (t, J=7.3, 6H), 0.52 ppm (m, 4H); 13C NMR (50.32 MHz,
CDCl3): d=150.8, 140.5, 130.7, 126.0, 121.3, 119.8, 93.9, 82.9, 65.7, 55.0,
40.1, 31.5, 25.7, 23.0, 13.8 ppm; HRMS (EI): m/z calcd for C31H38O2 [M+
1H), 7.39 and 6.58 (AA’XX’, JACTHNURTGNEU(GN A,X)=9.1 Hz, 4H), 7.37 (m, 1H), 3.28
(m, 4H), 2.08 (s, 1H), 1.95 (m, 4H), 1.66 (s, 6H), 1.65–1.52 (m, 4H), 1.32
(m, 12H), 1.08 (m, 4H), 0.90 (m, 6H), 0.67 (t, J=7.2 Hz, 6H), 0.56 ppm
(m, 4H); 13C NMR (50.32 MHz, CDCl3): d=150.8 (2C), 147.9, 140.9,
139.6, 132.8, 130.7, 130.3, 125.9, 125.4, 123.0, 120.9, 119.8, 119.6, 111.1,
108.6, 93.7, 91.3, 88.0, 83.0, 65.6, 55.0, 50.9, 40.2, 31.6, 31.5, 27.1, 26.7,
25.8, 23.0, 22.6, 14.0, 13.8 ppm; HRMS (ES+): m/z calcd for C46H62NO
[M+H]+: 644.4831; found: 644.4832; elemental analysis calcd (%) for
C46H61NO (644.00): C 85.79, H 9.55, N 2.17; found: C 86.06, H 9.57, N
2.07.
C
]: 442.2872; found: 442.2859; elemental analysis calcd (%) for C31H38O2
(442.64): C 84.12, H 8.65; found: C 84.01, H 8.71.
Compound 6: Method A: Solid NaOH (303 mg, 7.73 mmol) was added to
a solution of 5c (3.322 g, 7.52 mmol) in toluene/isopropanol (3:1, 48 mL)
heated to reflux. The mixture was stirred under reflux for 30 min. After
cooling, NaOH was removed by filtration and the solvents were evapo-
rated. The crude product was purified by column chromatography (hep-
tane/CH2Cl2 90:10) to yield 6 (1.55 g, 63%). Method B: Aqueous KOH
(1m, 30 mL) was added to a solution of 5b (1.94 g, 4.12 mmol) in THF/
MeOH (3:1, 100 mL), and the mixture was stirred at 208C for 15 min.
After addition of water, extraction with CH2Cl2, and drying (MgSO4), the
solvents were removed under reduced pressure. The crude product was
purified by column chromatography (heptane/CH2Cl2 90:10) to yield 6
(1.26 g, 94%). Rf =0.34 (heptane/CH2Cl2 90:10); 1H NMR (200.13 MHz,
CDCl3): d=7.63 (d, J=8.6 Hz, 2H), 7.48 (d, J=8.6 Hz, 2H), 7.46 (s,
2H), 3.15 (s, 2H), 1.94 (m, 4H), 1.07 (m, 4H), 0.67 (t, J=7.2 Hz, 6H),
0.54 ppm (m, 4H); 13C NMR (50.32 MHz, CDCl3): d=151.0, 140.9, 131.2,
126.5, 120.8, 119.9, 84.5, 77.4, 55.1, 40.0, 25.8, 22.9, 13.7 ppm; HRMS
Compound 10b: Solid KOH (0.07 g) was added to a solution of 10a
(0.798 g, 1.24 mmol) in toluene/iPrOH (6:1, 8.75 mL). The mixture was
heated under reflux conditions for 1 h. After cooling, KOH was removed
by filtration and the solvents were evaporated. The crude product was
purified by column chromatography (heptane/CH2Cl2 90:10) to yield 10b
(0.632 g, 87%). Rf =0.19 (heptane/CH2Cl2 90:10); H NMR (200.13 MHz,
CDCl3): d=7.63 (d, J=8.5 Hz, 1H), 7.62 (d, J=8.5 Hz, 1H), 7.47 (d, J=
8.5 Hz, 2H), 7.46 (m, 2H), 7.39 and 6.58 (AA’XX’, JACTHNUGRTENUNG(A,X)=8.8 Hz, 4H),
3.28 (m, 4H), 3.14 (s, 1H), 1.96 (m, 4H), 1.60 (m, 4H), 1.32 (m, 12H),
1.08 (m, 4H), 0.90 (m, 6H), 0.67 (t, J=7.3 Hz, 6H), 0.57 ppm (m, 4H);
13C NMR (50.32 MHz, CDCl3): d=150.91, 150.85, 147.9, 141.4, 139.5,
132.8, 131.1, 130.3, 126.4, 125.5, 123.3, 120.3, 119.9, 119.6, 111.1, 108.6,
91.4, 88.0, 84.6, 77.1, 55.0, 50.9, 40.1, 31.7, 27.1, 26.8, 25.8, 23.0, 22.6, 14.0,
13.8 ppm; HRMS (ES+): m/z calcd for C43H56N [M+H]+: 586.4413;
found: 586.4411; elemental analysis calcd (%) for C43H55N (585.92): C
88.15, H 9.46, N 2.39; found: C 87.89, H 9.59, N 2.40.
1
(EI): m/z calcd for C25H26 [M+ ]: 326.2035; found: 326.2036; elemental
Compound 11a: Air was removed from
10.33 mmol) in toluene/Et3N (4:1, 75 mL) by blowing argon for 20 min.
Then CuI (59.4 mg, 0.306 mmol), [Pd(PPh3)2Cl2] (216 mg, 0.306 mmol),
a
solution of 7[11] (4.00 g,
C
analysis calcd (%) for C25H26 (326.48): C 91.97, H 8.03; found: C 92.17, H
8.07.
AHCTUNGTRENNUNG
Compound 8: A solution of diethyl azodicarboxylate (DEAD; 9.00 g,
51.7 mmol) in THF (40 mL) was added dropwise to a solution of 13[13]
(5.00 g, 17.2 mmol), hydroquinone (5.65 g, 51.3 mmol), and triphenyl-
phosphine (13.50 g, 51.5 mmol) in THF (110 mL). The mixture was stir-
red at 208C for 16 h, and the solvent was removed under reduced pres-
sure. The residue was purified by column chromatography (CH2Cl2) to
and ethynyltrimethylsilane (3.25 mL, 2.25 g, 15.5 mmol) were added, and
deaeration was continued for 5 min. Thereafter the mixture was stirred at
408C for 18 h. The solvents were removed under reduced pressure, and
the crude product was purified by column chromatography (heptane/
CH2Cl2 95:5 then 90:10) to yield 11a (3.317 g, 90%). Rf =0.50 (heptane/
CH2Cl2 90:10); 1H NMR (200.13 MHz, CDCl3): d=7.32 and 6.54
1
yield 8 (3.35 g, 51%). Rf =0.32 (CH2Cl2); H NMR (200.13 MHz, CDCl3):
(AA’XX’, JACTHNGUTRENNU(G A,X)=8.9 Hz, 4H), 3.29 (m, 4H), 1.60 (m, 4H), 1.32 (m,
d=7.44 and 6.50 (AA’XX’, J
N
12H), 0.90 (m, 6H), 0.25 ppm (s, 9H); 13C NMR (50.32 MHz, CDCl3):
1H), 4.03 (t, J=6.0 Hz, 2H), 3.65 (t, J=6.0 Hz, 2H), 3.43 (q, J=7.0 Hz,
d=148.6, 133.4, 111.4, 108.7, 107.2, 91.0, 51.3, 32.1, 27.5, 27.1, 23.1, 14.2,
Chem. Eur. J. 2012, 18, 16450 – 16462
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16459

M. Blanchard-Desce et al.
0.3 ppm; HRMS (EI): m/z calcd for C23H39NSi [M+ ]: 357.2852; found:
ACHUTGTNREN(NUG A,X)=8.5 Hz, 4H), 6.99 and 6.87 (AA’BB’, JACHUTNGTREN(NGUN A,B)=9.1 Hz, 4H), 4.11
C
357.2857.
(t, J=6.4 Hz, 2H), 3.75 (t, J=6.4 Hz, 2H), 3.50 (q, J=6.9 Hz, 2H), 3.28
(m, 4H), 2.27 (s, 3H), 1.97 (m, 4H), 1.59 (m, 4H), 1.32 (m, 12H), 1.22 (t,
J=6.9 Hz, 3H), 1.09 (m, 4H), 0.88 (m, 6H), 0.67 (t, J=7.2 Hz, 6H),
0.59 ppm (m, 4H). Aqueous NaOH (8.5 mL, 0.5m) was added to a solu-
tion of 17 (0.852 g, 0.965 mmol) in THF/EtOH (2:1, 54 mL). The mixture
was stirred at 208C for 15 min, then aqueous HCl (9 mL, 0.5m) was
added. After the addition of water, extraction with CH2Cl2, and drying
(MgSO4), the solvents were removed under reduced pressure. The crude
product was purified by column chromatography (heptane/CH2Cl2 20:80
then 10:90) to yield 2 (739 mg, 91%). Rf =0.31 (heptane/CH2Cl2 20:80);
1H NMR (200.13 MHz, CDCl3): d=7.62 (d, J=8.4 Hz, 2H), 7.47 (d, J=
Compound 15a: A solution of 8 (1.93 g, 5.04 mmol) and 4-dimethylami-
nopyridine (DMAP; 0.61 g, 0.50 mmol) in CH2Cl2 (95 mL) was cooled at
08C, then Et3N (1 mL) and CH3COCl (0.54 mL, 7.56 mmol) were added
dropwise. The mixture was stirred at 208C for 14 h. After addition of
water, extraction with CH2Cl2, and drying (Na2SO4), the solvent was re-
moved under reduced pressure. The residue was purified by column chro-
matography (heptane/CH2Cl2 50:50 then 40:60) to yield 15a (1.63 g,
76%). Rf =0.25 (heptane/CH2Cl2 50:50); 1H NMR (200.13 MHz, CDCl3):
d=7.47 and 6.52 (AA’XX’, J
ACHTUNGTRENN(UNG A,X)=9.0 Hz, 4H), 7.01 and 6.88 (AA’BB’,
JACHTUNGTRENNUNG(A,B)=9.1 Hz, 4H), 4.10 (t, J=6.0 Hz, 2H), 3.65 (t, J=6.0 Hz, 2H),
8.4 Hz, 2H), 7.45 (m, 2H), 7.43 and 6.72 (AA’XX’, J
ACHTUNGTREN(NUGN A,X)=9.1 Hz, 4H),
3.43 (q, J=7.0 Hz, 2H), 2.21 (s, 3H), 1.17 ppm (t, J=7.0 Hz, 3H);
13C NMR (50.32 MHz, CDCl3): d=169.8, 156.2, 147.0, 144.3, 137.8, 122.3,
115.0, 114.1, 76.5, 65.6, 49.5, 45.5, 21.1, 12.0 ppm.
7.39 and 6.58 (AA’XX’, J(A,X)=8.9 Hz, 4H), 6.76 (m, 4H), 4.58 (s, 1H),
AHCTUNGTRENNUNG
4.07 (t, J=6.1 Hz, 2H), 3.72 (t, J=6.1 Hz, 2H), 3.50 (q, J=6.9 Hz, 2H),
3.28 (m, 4H), 1.97 (m, 4H), 1.60 (m, 4H), 1.32 (m, 12H), 1.21 (t, J=
6.9 Hz, 3H), 1.09 (m, 4H), 0.90 (m, 6H), 0.67 (t, J=7.2 Hz, 6H),
0.59 ppm (m, 4H); 13C NMR (50.32 MHz, CDCl3): d=152.6, 151.0, 150.9,
149.9, 147.9, 147.4, 140.1, 139.9, 132.9, 132.8, 130.3, 125.5, 122.7, 122.5,
119.7, 119.6, 116.1, 115.5, 111.4, 111.2, 109.8, 108.7, 91.2, 90.8, 88.4, 88.2,
66.0, 55.0, 50.9, 49.6, 45.5, 40.2, 31.7, 27.1, 26.8, 25.8, 23.0, 22.6, 14.0, 13.8,
12.2 ppm; HRMS (ES+): m/z calcd for C59H73N2O2 [M+H]+: 841.5672;
found: 841.5660; elemental analysis calcd (%) for C59H72N2O2 (841.24): C
84.24, H 8.63, N 3.33; found: C 83.84, H 8.52, N 3.38.
Compound 15b: Air was removed from a solution of 15a (1.647 g,
3.87 mmol) in toluene/Et3N (4:1, 16 mL) by blowing argon for 20 min.
Then CuI (14.8 mg, 0.078 mmol), [PdACHTUNGRTNEUNG(PPh3)2Cl2] (54.4 mg, 0.078 mmol),
and ethynyltrimethylsilane (0.82 mL, 0.570 g, 5.805 mmol) were added,
and deaeration was continued for 5 min. Thereafter the mixture was stir-
red at 408C for 15 h. The solvents were removed under reduced pressure,
and the crude product was purified by column chromatography (heptane/
CH2Cl2 50:50 then 40:60) to yield 15b (1.246 g, 81%). Rf =0.28 (heptane/
CH2Cl2 60:40); 1H NMR (200.13 MHz, CDCl3): d=7.32 and 6.60
Compound 18: Air was removed from
a solution of 15b (0.232 g,
(AA’XX’, JACHTUNGTRENNUNG(A,X)=9.0 Hz, 4H), 6.98 and 6.84 (AA’BB’, JACHTUGNTREN(NUGN A,B)=9.1 Hz,
0.588 mmol) and 5a[10] (0.130 g, 0.245 mmol) in toluene/Et3N (4:1,
4H), 4.08 (t, J=6.0 Hz, 2H), 3.71 (t, J=6.0 Hz, 2H), 3.47 (q, J=7.0 Hz,
2H), 2.27 (s, 3H), 1.18 (t, J=7.0 Hz, 3H), 0.22 ppm (s, 9H); 13C NMR
(50.32 MHz, CDCl3): d=169.4, 156.0, 147.2, 144.1, 133.1, 122.1, 114.7,
111.0, 109.4, 106.4, 90.9, 65.5, 49.2, 45.3, 20.7, 11.9, 0.0 ppm; HRMS (EI):
3.8 mL) by blowing argon for 20 min. Then CuI (2.3 mg, 0.012 mmol),
[PdACTHUNTGRNEUGN(PPh3)2Cl2] (8.6 mg, 0.012 mmol), and TBAF (1m in THF, 0.6 mL,
0.6 mmol) were added, and deaeration was continued for 10 min. There-
after the mixture was stirred at 408C for 16 h. The solvents were removed
under reduced pressure, and the crude product was purified by column
chromatography (heptane/CH2Cl2 40:60, then 30:70) to yield 18 (0.169 g,
76%). Rf =0.58 (CH2Cl2); 1H NMR (200.13 MHz, CDCl3): d=7.63 (d,
J=7.8 Hz, 2H), 7.48 (d, J=7.8 Hz, 2H), 7.46 (m, 2H), 7.43 and 6.68
m/z calcd for C23H29NO3Si [M+ ]: 395.1917; found: 395.1924.
C
Compound 15c: TBAF (1m in THF, 0.97 mL, 0.97 mmol) was added to a
solution of 15b (219 mg, 0.962 mmol) in THF (10 mL), and the mixture
was stirred at 208C for 15 min. After addition of CaCl2, the solvent was
removed under reduced pressure, and the residue was purified by column
chromatography (heptane/CH2Cl2 30:70) to yield 15c (140 mg, 45%).
Rf =0.20 (heptane/CH2Cl2 30:70); 1H NMR (200.13 MHz, CDCl3): d=
(AA’XX’, JACTHUNRTGENNUG(A,X)=8.9 Hz, 8H), 6.99 and 6.88 (AA’BB’, JACHTUGNTREN(NUGN A,B)=9.1 Hz,
8H), 4.11 (t, J=6.0 Hz, 4H), 3.75 (t, J=6.0 Hz, 4H), 3.51 (q, J=7.0 Hz,
4H), 2.28 (s, 6H), 1.97 (m, 4H), 1.22 (t, J=7.0 Hz, 6H), 1.09 (m, 4H),
0.67 (t, J=7.3 Hz, 6H), 0.58 ppm (m, 4H); 13C NMR (50.32 MHz,
CDCl3): d=166.3, 156.3, 150.9, 147.3, 144.3, 140.1, 133.0, 130.3, 125.5,
122.5, 122.4, 119.7, 115.0, 111.3, 109.8, 90.7, 88.4, 65.7, 55.0, 49.5, 45.6,
40.3, 25.8, 23.0, 21.0, 13.9, 12.3 ppm; elemental analysis calcd (%) for
C61H64N2O6 (921.19): C 79.54, H 7.00, N 3.04; found: C 79.20, H 7.08, N
2.92.
7.37 and 6.64 (AA’XX’, J
ACHTUNGTRENUN(NG A,X)=8.8 Hz, 4H), 7.00 and 6.87 (AA’BB’, J-
ACHTUNGTRENNUNG
(q, J=7.0 Hz, 2H), 2.99 (s, 1H), 2.28 (s, 3H), 1.20 ppm (t, J=7.0 Hz,
3H); 13C NMR (50.32 MHz, CDCl3): d=169.7, 156.2, 147.6, 144.3, 133.4,
122.3, 114.9, 111.2, 108.4, 84.7, 74.8, 65.6, 49.4, 45.5, 21.0, 12.1 ppm.
Compound 16: Air was removed from a solution of 5a[10] (4.267 g,
8.047 mmol) and 15b (1.06 g, 2.681 mmol) in toluene/Et3N (5:1, 13 mL)
by blowing argon for 20 min. Then CuI (10.3 mg, 0.054 mmol), [Pd-
Compound 3: Aqueous NaOH (1.5 mL, 0.5m) was added to a solution of
18 (80 mg, 0.087 mmol) in THF/EtOH (2:1, 4.5 mL). The mixture was
stirred at 208C for 25 min, then aqueous HCl (7.5 mL, 0.1m) was added.
After addition of water, extraction with CH2Cl2, and drying (Na2SO4),
the solvents were removed under reduced pressure. The residue was puri-
fied by column chromatography (CH2Cl2, then CH2Cl2/AcOEt 98:2) to
ACHTUNGTRENNUNG(PPh3)2Cl2] (37.9 mg, 0.054 mmol), and TBAF (1m in THF, 2.8 mL,
2.8 mmol) were added, and the mixture was stirred at 408C for 15 h.
After evaporation of the solvents, the residue was purified by column
chromatography (heptane/CH2Cl2 80:20, then 70:30) to yield 16 (1.052 g,
54%). Rf =0.48 (heptane/CH2Cl2 80:20); 1H NMR (200.13 MHz, CDCl3):
d=7.73 (s, 1H), 7.70 (d, J=7.6 Hz, 1H), 7.66 (d, J=8.0 Hz, 1H), 7.53 (d,
yield
(200.13 MHz, CDCl3): d=7.62 (d, J=8.1 Hz, 2H), 7.47 (d, J=8.1 Hz,
2H), 7.46 (m, 2H), 7.43 and 6.68 (AA’XX’, J(A,X)=8.8 Hz, 8H), 6.76
3
(72 mg, 98%). Rf =0.41 (CH2Cl2/AcOEt 95:5); 1H NMR
J=8.0 Hz, 1H), 7.51 (s, 1H), 7.49 and 6.74 (AA’XX’, J
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
4H), 7.46 (d, J=7.6 Hz, 1H), 7.05 and 6.92 (AA’BB’, JAHCTUNGTRENNUNG
(m, 8H), 4.58 (s, 2H), 4.07 (t, J=6.0 Hz, 4H), 3.72 (t, J=6.0 Hz, 4H),
3.50 (q, J=6.9 Hz, 4H), 1.97 (m, 4H), 1.22 (t, J=6.9 Hz, 6H), 1.09 (m,
4H), 0.67 (t, J=7.3 Hz, 6H), 0.59 ppm (m, 4H); 13C NMR (50.32 MHz,
CDCl3): d=152.7, 150.9, 149.7, 147.4, 140.1, 132.9, 130.3, 125.5, 122.5,
119.7, 116.0, 115.5, 111.4, 109.8, 90.8, 88.4, 66.0, 55.0, 49.6, 45.6, 40.3, 25.8,
23.0, 13.8, 12.2 ppm; HRMS (ES+): m/z calcd for C57H60N2O4Na
[M+Na]+: 859.4451; found: 859.4407; m/z calcd for C57H60N2O4K
[M+K]+: 875.4190; found: 875.4149.
4H), 4.16 (t, J=5.9 Hz, 2H), 3.80 (t, J=5.9 Hz, 2H), 3.55 (q, J=7.1 Hz,
2H), 2.32 (s, 3H), 1.93 (m, 4H), 1.23 (t, J=7.1 Hz, 3H), 1.09 (m, 4H),
0.68 (t, J=7.0 Hz, 6H), 0.57 ppm (m, 4H); 13C NMR (50.32 MHz,
CDCl3): d=169.7, 156.2, 153.3, 150.0, 147.3, 144.4, 140.2, 139.5, 135.9,
133.0, 132.0, 130.4, 125.5, 123.1, 122.9, 121.5, 119.7, 115.0, 111.4, 109.8,
92.7, 91.0, 88.3, 65.7, 55.2, 49.5, 45.6, 40.1, 25.8, 23.0, 21.0, 13.8, 12.2 ppm.
Compound 2: Air was removed from
a solution of 16 (0.952 g,
1.31 mmol) and 11a (0.546 g, 1.574 mmol) in toluene/Et3N (5:1, 8.5 mL)
Compound 1: Air was removed from
1.146 mmol) and 5a (0.303 g, 0.571 mmol) in THF/Et3N (4:1, 5.5 mL) by
blowing argon for 20 min. Then CuI (4.9 mg, 0.026 mmol), [Pd(PPh3)2Cl2]
(18 mg, 0.026 mmol), and TBAF (1m in THF, 1.8 mL) were added, and
deaeration was continued for 10 min. Thereafter the mixture was stirred
at 508C for 16 h. The solvents were removed under reduced pressure,
and the crude product was purified by column chromatography (heptane/
CH2Cl2 95:5, then 90:10) to yield 1 (286 mg, 59%). Rf =0.29 (heptane/
a solution of 11a (0.410 g,
by blowing argon for 20 min. Then CuI (5.2 mg, 0.027 mmol), [Pd-
ACHTUNGTRENNUNG(PPh3)2Cl2] (18.9 mg, 0.027 mmol), and TBAF (1m in THF, 1.7 mL,
ACHTUNGTRENNUNG
1.7 mmol) were added, and the mixture was stirred at 408C for 15 h.
After evaporation of the solvents, the residue was purified by column
chromatography (heptane/CH2Cl2 60:40 then 50:50) to yield 17 (0.868 g,
75%). Rf =0.39 (heptane/CH2Cl2 50:50); 1H NMR (200.13 MHz, CDCl3):
d=7.62 (d, J=7.8 Hz, 2H), 7.47 (d, J=7.5 Hz, 2H), 7.45 (m, 2H), 7.43
and 6.68 (AA’XX’, JACHTUNGTRENNUNG(A,X)=8.6 Hz, 4H), 7.39 and 6.58 (AA’XX’, J-
16460
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 16450 – 16462

Water-Soluble Organic Nanodots
FULL PAPER
CH2Cl2 90:10); 1H NMR (300.13 MHz, CDCl3): d=7.62 (d, J=7.8 Hz,
2H), 7.47 (dd, J=7.8 Hz, 1.5 Hz, 2H), 7.46 (m, 2H), 7.40 and 6.58
(AA’XX’, JACHTUNGTRENNUNG(A,X)=9.0 Hz, 8H), 3.28 (m, 8H), 1.97 (m, 4H), 1.59 (m,
8H), 1.32 (m, 24H), 1.09 (m, 4H), 0.91 (t, J=6.8 Hz, 12H), 0.67 (t, J=
7.4 Hz, 6H), 0.59 ppm (m, 4H); 13C NMR (50.32 MHz, CDCl3): d=151.3,
148.3, 140.4, 133.2, 130.7, 125.9, 123.1, 120.1, 111.6, 109.2, 91.5, 88.6, 55.4,
51.4, 40.7, 32.1, 27.6, 27.2, 26.3, 23.5, 23.1, 14.2 ppm; HRMS (ES+): m/z
calcd for C61H85N2 [M+H]+: 845.6713; found: 845.6716; elemental analy-
sis calcd (%) for C61H84N2 (845.33): C 86.67, H 10.02, N 3.31; found: C
86.40, H 10.16, N 3.41.
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Photophysical methods: All photophysical properties were analyzed with
freshly prepared air-equilibrated solutions at room temperature (298 K).
UV/Vis absorption spectra were recorded using a Jasco V-570 spectro-
photometer. Steady-state and time-resolved fluorescence measurements
were performed on dilute solutions (approximately 10ꢀ6 m, optical density
<0.1) contained in standard 1 cm quartz cuvettes using an Edinburgh In-
struments (FLS920) spectrometer in photon-counting mode. Fully cor-
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photon counting (TCSPC) by using the same FLS 920 fluorimeter. Exci-
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(repetition rate 40 kHz). The instrument response (full width at half-max-
imum (FWHM) approximately 1 ns) was determined by measuring the
light scattered by a Ludox suspension. The TCSPC traces were analyzed
by standard iterative reconvolution methods implemented in the software
of the fluorimeter. All compounds displayed strictly monoexponential
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which saturation or photodegradation did not occur.
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Received: August 7, 2012
Published online: November 8, 2012
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