Fullerodendrimers with peripheral triethyleneglycol chains: Synthesis, mass spectrometric characterization, and photophysical properties

Article abstract of DOI:10.1039/b203272b

Poly(aryl ether) dendritic branches terminated with peripheral triethyleneglycol chains have been attached to C₆₀. The resulting fullerodendrimers have been characterised by electrospray mass spectrometry (ESMS), which appears to be a particularly interesting analytical tool for the unambiguous structural assignment of such high molecular weight fullerene derivatives. Their photophysical properties have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. The changes observed in the photophysical properties along the series suggest an increasing interaction between the poly(aryl ether) dendritic wedges and the fullerene core, which brings about an increasing isolation of the central chromophore from the exterior. Finally, thanks to their high solubility, fullerodendrimers 1-4 have been easily incorporated in mesoporous silica glasses and preliminary measurements on the resulting doped samples have revealed efficient optical limiting properties.

Full text of DOI:10.1039/b203272b

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Fullerodendrimers with peripheral triethyleneglycol chains: synthesis,
mass spectrometric characterization, and photophysical properties
a
Yannick Rio, Gianluca Accorsi, H e´ l e` ne Nierengarten, Jean-Luc Rehspringer,
b
c
a
a
a
a
Bernd H o¨ nerlage, Giedrius Kopitkovas, Alexey Chugreev, Alain Van Dorsselaer,*
c
b
Nicola Armaroli* and Jean-Fran c¸ ois Nierengarten*
a
a
Institut de Physique et Chimie des Mat e´ riaux de Strasbourg, Universit e´ Louis Pasteur et CNRS,
3 rue du Loess, 67037, Strasbourg cedex, France. E-mail: niereng@ipcms.u-strasbg.fr
Istituto per la Sintesi Organica e la Fotoreattivit a` , Laboratorio di Fotochimica, Consiglio Nazionale
della Ricerche, via Gobetti 101, 40129, Bologna, Italy. E-mail: armaroli@frae.bo.cnr.it
Laboratoire de Spectrom e´ trie de Masse Bio-Organique, Universit e´ Louis Pasteur et CNRS,
2
b
c
2
5 rue Becquerel, 67087, Strasbourg cedex 2, France. E-mail: vandors@chimie.u-strasbg.fr
Received (in Strasbourg, France) 25th March 2002, Accepted 15th April 2002
First published as an Advance Article on the web 6th August 2002
Poly(aryl ether) dendritic branches terminated with peripheral triethyleneglycol chains have been attached to
C60 . The resulting fullerodendrimers have been characterised by electrospray mass spectrometry (ESMS),
which appears to be a particularly interesting analytical tool for the unambiguous structural assignment of such
high molecular weight fullerene derivatives. Their photophysical properties have been systematically
investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. The changes observed in the
photophysical properties along the series suggest an increasing interaction between the poly(aryl ether)
dendritic wedges and the fullerene core, which brings about an increasing isolation of the central chromophore
from the exterior. Finally, thanks to their high solubility, fullerodendrimers 1–4 have been easily incorporated
in mesoporous silica glasses and preliminary measurements on the resulting doped samples have revealed
efficient optical limiting properties.
Following the development of efficient synthetic procedures
for the preparation of monodispersed cascade molecules, the
design of functional dendrimers is more and more emphasized
Results and discussion
Synthesis
1
–3
today. In particular, the ability of a dendritic shell to encap-
sulate a functional core moiety and to create a specific site-iso-
lated microenvironment capable of affecting the molecular
The synthesis of fullerene-functionalized dendrimers is cur-
6
rently an area of considerable interest. Dendrimers with a
3
7
8
properties has been explored in recent years. A variety of
experimental techniques has been employed to evidence the
shielding of the core moiety and to ascertain the effect of the
C60 core, peripheral C subunits or a C sphere at each
60 60
9
branching unit have already been described. As far as fullero-
dendrimers with C -type cores are concerned, it should be
6
0
3
dendritic shell. Among them, UV-Vis absorption and emis-
noted that the functionalization of the fullerene sphere with
dendritic branches dramatically improves the solubility of
sion spectroscopy has proven to be very helpful since specific
changes in the microenvironment of chromophoric cores can
be monitored by observing changes in the intensity, shape,
C
60 . In the design of fullerodendrimers 1–4, it was decided
to attach poly(aryl ether) dendritic branches terminated with
peripheral triethyleneglycol chains to obtain compounds solu-
ble in a wide range of solvents. The dendritic branches 5–8
4
or position of absorption and luminescence bands. On the
other hand, the bimolecular deactivation of excited states
resulting from the penetration of external quenchers through
the dendritic shell allows for an evaluation of the accessibility
1
1
2
have been prepared as previously described and MnO oxi-
dation afforded the corresponding aldehydes 9–12 (Scheme 1).
The synthetic approach to prepare compounds 1–4 relies upon
the 1,3-dipolar cycloaddition of the dendritic azomethine
ylides generated in situ from the corresponding aldehydes
and N-methylglycine. This methodology has proven to be a
powerful procedure for the functionalization of C60 due to
its versatility and the ready availability of the starting mat-
5
of the core. Despite the fact that in recent years C60 has
become a widely employed building block in dendrimer chem-
6
–9
istry,
studies aiming at evidencing dendritic effects on the
photophysical properties of a fullerene core have never been
reported. In this paper, we describe the ground state and
excited state properties as well as the singlet oxygen sensitiza-
1
0
12
tion of fullerodendrimers 1–4 in different solvents. The
changes of the photophysical properties observed along the
series suggest an increasing interaction between the dendritic
wedges and the central core, which brings about an increasing
isolation of the central chromophore from the exterior.
Finally, thanks to their high solubility, fullerodendrimers 1–4
have been easily incorporated in mesoporous silica glasses
and preliminary measurements on the resulting doped samples
have revealed efficient optical limiting properties.
erials. Thus, reaction of aldehydes 9–12 with N-methyl-
glycine and C60 in refluxing toluene gave the corresponding
fulleropyrrolidines 1–4 in 37 to 44% isolated yield after column
chromatography on silica gel followed by gel permeation
chromatography.
The stucture of fullerodendrimers 1–4 was confirmed by
analytical and spectroscopic data. The H-NMR spectra of
1
3
1–4 recorded in CDCl exhibit the expected features with the
signals arising from the poly(aryl ether) dendritic branches,
1
146
New J. Chem., 2002, 26, 1146–1154
DOI: 10.1039/b203272b
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2002

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an AB quartet and a singlet for the pyrrolidine protons as well
as a singlet for the N–CH group. It is also important to note
functionalized fullerenes by taking advantage of their electro-
9
b
chemical properties. In the present case, ionization (by pro-
tonation) and therefore detection of the compounds was
possible owing to the presence of the amine function and the
3
that the signals corresponding to the protons of the phenyl
group directly attached to the pyrrolidine ring are broad at
room temperature. As previously described for phenylfullero-
2 2
addition of 1% formic acid in the solvent (CH Cl ).
1
3
pyrrolidine derivatives, this indicates restricted rotation of
the phenyl substituent on the pyrrolidine ring. This was con-
firmed by variable-temperature NMR studies showing a clear
The ES mass spectra of 1 and 2 obtained in the positive
mode are depicted in Fig. 1. In each case, only the expected
singly charged ion resulting from the protonation of the com-
ꢀ
+
coalescence at ca. 10 C in all the cases and a reversible nar-
pound is observed: at m/z ¼ 1179.2 for [1 + H] (calcd m/
+
rowing was observed in the spectra of 1–4. The associated free
energy of activation for the rotation of the phenyl group on the
pyrrolidine ring was estimated by following the coalescence of
z ¼ 1179.2) and at m/z ¼ 1715.9 for [2 + H] (calcd m/z ¼
1715.9). The isotopic pattern of the two observed peaks corre-
sponds to the theoretical one, confirming the charge state of
the ions.
z
the aromatic C–H and found to be similar (DG ¼ 13 kcal
ꢁ
1
mol ) for the four compounds. The C-NMR spectra of
13
The ES mass spectra of 3 (not represented here) and 4
(Fig. 2) recorded under the same conditions also show the pre-
sence of one singly charged peak corresponding to the
expected protonated compound at m/z ¼ 2789.1 (calcd m/z
1
1–4 were also in full agreement with their C symmetry result-
ing from the presence of the asymmetric C atom in the pyr-
rolidine ring.
+
for [3 + H] ¼ 2789.1) and at m/z ¼ 4935.0 (calcd m/z for
+
+
[
4 + H ] ¼ 4935.5).
Mass spectrometry
An unequivocal structural analysis of compounds 1–4 requires
also their mass spectrometric analysis. Indeed, several ioniza-
tion techniques have been used successfully for the character-
ization of low molecular weight fullerene derivatives; electron
Photophysical studies
The electronic absorption spectra of 1–4 in toluene, dichloro-
methane, and acetonitrile (hereafter indicated as, respectively,
PhCH , CH Cl , and CH CN) are reported in Fig. 3–5.
3 2 2 3
Fullerodendrimers 2–4 are sticky glassy compounds at room
temperature, making precise weighting difficult; thus an accu-
rate experimental determination of their molar extinction coef-
ficients (e) was not possible. The spectrum in e units was
experimentally determined only for 1 in CH Cl , in all the
1
4
impact (EI),
(
matrix-assisted laser desorption/ionization
MALDI) or fast-atom bombardment (FAB). However,
1
5
16
for functionalized fullerenes of high molecular weight, these
mass spectrometric methods are difficult to handle (and/or
inefficient) and most often accompanied by high levels of frag-
mentation. Therefore, we propose here the use of electrospray
mass spectrometry (ESMS) as an alternative. Indeed, ESMS is
2
2
other cases the values reported are estimated by assuming
the same molar extinction coefficient at 520 nm (1100 M
1
7
ꢁ1
particularly suitable for large compounds and the gentle nat-
ure of the ES process yields usually a simple mass pattern with-
out fragments. In addition, we have already described a
fruitful ESMS strategy to detect neutral high molecular weight
ꢁ
1
cm ). This can be considered a reasonable approximation in
view of (i) the invariance of the C60 chromophoric unit
along the series; (ii) the similar spectral shape for the various
New J. Chem., 2002, 26, 1146–1154
1147

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2 2 2
Scheme 1 Preparation of compounds 1–4. Reagents and conditions: (i) MnO , CH Cl , room temperature; (ii) C60 , N-methylglycine, toluene, D.
dendrimers above 500 nm; (iii) the little or no dependence of
branches above 250 nm and around 280 nm (shoulder) in pas-
sing from 1 to 4 (Fig. 4 and 5), in agreement with the dendri-
mers’ structures. In all solvents changes of the absorption
spectral shapes are observed for 1–4. In particular we note:
1
8
fullerene e values on solvent polarity.
The absorption spectra in CH Cl
increasing contribution of the poly(aryl ether) dendritic
2
2
3
and CH CN reveal the
(
i) an intensity decrease of the fullerene bands in the 250–350
nm region, quite remarkable for 4 and (ii) a progressive loss
of spectral resolution in the visible region, particularly evident
from the marked intensity reduction of the diagnostic fullero-
pyrrolidine absorption peaks at 431 and 706 nm. This might
reflect a modification of the C60 chromophore solvation envir-
onment as a consequence of a tighter contact with the external
5
e
dendritic arms containing aromatic units, possibly promoted
1
9
by favourable electronic donor-acceptor interactions.
To bring some support to this hypothesis we note that the
above effect (ii) is the strongest in polar CH CN (Fig. 5), where
3
intramolecular stacking between the dendritic wedges and
the hydrophobic central core is expected to be particularly
effective.
Fig. 1 ES mass spectrum of 1 (top) and 2 (bottom) and isotopic pat-
terns observed for the two singly charged ions. Isotopic peaks are sepa-
rated by 1 m/z unit.
Fig. 2 ES mass spectrum of 3 recorded at V
resolution capability of the quadrupole analyser (R ¼ 1000) is not suf-
c
¼ 160 V; in this case the
ficient to obtain the isotopic pattern of the peak.
1
148
New J. Chem., 2002, 26, 1146–1154

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Fig. 5 Absorption spectra of 2–4 in CH
4
3
CN solution at 298 K; above
00 nm a scaling factor of 10 is applied. Inset: fluorescence (left,
Fig. 3 Absorption spectra of 1–4 in toluene solution at 298 K; above
400 nm a scaling factor of 5 is applied. Inset: fluorescence (left,
l
exc ¼ 370 nm, O. D. ¼ 0.30) and sensitised singlet oxygen lumines-
l
exc ¼ 370 nm, O. D. ¼ 0.30) and sensitised singlet oxygen lumines-
cence spectra (right, lexc ¼ 480 nm, O. D. ¼ 0.20) of 2–4. 2 (blue), 3
cence spectra (right, lexc ¼ 480 nm, O. D. ¼ 0.20) of 1–4. 1 (black),
(
mated according to the procedure described in the text.
red), 4 (green). 1 is not soluble in this solvent. The e values are esti-
2
the procedure described in the text.
(blue), 3 (red), 4 (green). The e values are estimated according to
bimolecular quenching processes. Thus, in order to test protec-
tive effects, the study of the much longer triplet lifetimes (hun-
dreds of ns in air-equilibrated solutions) can be more
advantageous, also when considering the high intersystem
crossing yield of fulleropyrrolidines (q90%).
The shape and position of triplet-triplet transient absorption
spectra are practically the same for 1–4 in all the investigated
The fluorescence spectra of 1–4 in the three solvents are also
shown in Fig. 3–5, and a summary of luminescence data is
reported in Table 1.
As a function of dendrimer size one can note: (i) a steady
red-shift of the band maxima (up to 10–15 nm) in all solvents
and (ii) a prolongation of the singlet lifetime for the largest
dendrimer 4, safely above the experimental uncertainty. These
trends could be the consequence of changes in the dendrimers
solvation environment, as suggested above.
2
0
solvents. As an example the spectrum of 4 in CH
reported in Fig. 6, which is quite comparable to those of sim-
2 2
Cl is
2
1
pler fulleropyrrolidines previously reported. By contrast, the
triplet lifetimes steadily increase on passing from 1 to 4, as dis-
played in the inset of Fig. 6 and summarized in Table 2.
The differences between triplet lifetimes measured in air-
equilibrated solutions (AER) with respect to the corresponding
values in air-free samples (DEA) is attributable to oxygen
quenching, a well investigated phenomenon in fullerene photo-
In a given solvent, the excited state singlet lifetimes of 1–3
and fluorescence quantum yields of 1–4 do not change within
the corresponding experimental uncertainties (see Experimen-
tal); the highest fluorescence yields are measured in toluene.
The very short singlet lifetime of fullerenes makes it unsuita-
ble to probe any dendritic protection effects since the very fast
intrinsic singlet excited state deactivation of fullerenes (around
2
0
chemistry. This originates from a triplet-singlet energy trans-
fer process following light irradiation of fullerenes (F) in the
presence of dioxygen; the whole reaction can be schematized
as follows:
1
ns) is expected to be much faster than the time needed for
hn
ISC
O2
1
ꢂ
3
ꢂ
1
ꢂ
Fꢁ! F ꢁ! F ꢁ!F þ O2
ð1Þ
where ISC denotes singlet ( F*) to triplet ( F*) intersystem
1
3
1
1
2 2 g
crossing, and O * stands for O ( D ), commonly called ‘‘sing-
let oxygen’’. The occurrence of the bimolecular energy transfer
process described in eqn. (1) has been probed by monitoring
1
the diagnostic O * luminescence band centred at 1270 nm,
22
2
whose relative intensity in a given solvent can be taken to eval-
uate the relative yields of singlet oxygen generation
2
3
(
1
Fig. 3–5). It must be pointed out that the concentration of
–4 under typical experimental conditions for spectroscopic
ꢁ6
ꢁ5
investigations (10 –10 M) is orders of magnitude lower
than that of molecular oxygen in air-equilibrated organic
solvents (10 –10 M).
For 1–4 interesting trends can be obtained from the analysis
ꢁ
2
ꢁ3
24
of triplet lifetimes in air-equilibrated solutions (Table 2) and of
the relative yields of formation of singlet oxygen, as derived
1
from the O
2
* NIR luminescence band intensities (Fig. 3–5).
Fig. 4 Absorption spectra of 1–4 in CH
4
l
2
Cl
00 nm a scaling factor of 20 is applied. Inset: fluorescence (left,
exc ¼ 370 nm, O. D. ¼ 0.30) and sensitised singlet oxygen lumines-
2
solution at 298 K; above
A steady increase of lifetimes is found by increasing the dendri-
mer size in all solvents, suggesting that dendritic wedges are
able to partially shield the fullerene core from contacts with
dioxygen molecules. This hypothesis can be supported by
the fact that the increase is particularly marked in polar
cence spectra (right, lexc ¼ 480 nm, O. D. ¼ 0.20) of 1–4. 1 (black),
(blue), 3 (red), 4 (green). The e values of 2–4 are estimated according
to the procedure described in the text.
5
b–d
2
New J. Chem., 2002, 26, 1146–1154
1149

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a
Table 1 Fluorescence data and singlet excited state lifetimes at 298 K.
PhCH CH Cl
max/nm max/nm
3
2
2
3
CH CN
b
4
b
4
b
4
l
F ꢃ 10
t/ns
l
F ꢃ 10
t/ns
lmax/nm
F ꢃ 10
t/ns
c
c
c
1
2
3
4
715
715
718
725
8
8
8
7
1.3
1.3
1.4
1.5
712
715
716
726
6
6
6
5
1.3
1.2
1.2
1.6
–
–
–
716
722
728
5
6
6
1.3
1.3
1.5
a
Fluorescence spectra and quantum yields (F) were obtained upon excitation at 370 nm; excited state lifetimes are upon excitation at 337 nm (see
Experimental). From spectra corrected for the photomultiplier response. Not soluble in this solvent.
b
c
CH
is expected (see above); in this case a 45% lifetime prolongation
is found in passing from 2 to 4 (23% and 28% only for PhCH
and CH Cl , respectively). It must be emphasized that triplet
3
CN, where a better shielding of the fullerene chromophore
passing from the reference methanofullerene molecule to the
2
6
fullerodendrimer. This is attributable to the high rigidity
of the dendritic wedge, which prevents close through-space
distances between the core and the periphery, unlike our
present case.
3
2
2
lifetimes of 4 in the three solvents are rather different from
each other, likely reflecting specific solvent-fullerene interac-
tions that affect excited state deactivation rates. This suggests
that, albeit a dendritic effect is evidenced, even the largest
wedges are not able to provide complete shielding of the cen-
tral fulleropyrrolidine core; indeed, this can be expected in
light of the dendrimer structures. In any case the dendritic
wedges are able to reduce the singlet oxygen sensitization cap-
ability of the fullerene chromophore, and 4 exhibits the lowest
singlet oxygen sensitization yield in all the investigated solvents
Incorporation in sol-gel glasses and optical limiting properties
Several studies on fullerene derivatives have shown the great
potential of this class of materials for optical limiting applica-
tions. In effect, the transmission of fullerene solutions
27
decreases upon increasing the light intensity. For short pulses
ps), the limiting action is ascribed to pure reverse saturable
(
absorption (RSA) whereas for longer pulses (ns–ms) additional
mechanisms of mainly thermal origin are invoked. Even if
(
Fig. 3–5).
Notably, in any solvent, the triplet lifetimes in oxygen-free
28
these solutions are efficient optical limiters, the use of solid
devices is largely preferred for practical applications due to
their greater ease of handling. Therefore, crystalline films of
solutions are also constantly increased by enlarging the dendri-
mers’ size (Table 2). This demonstrates that molecular oxygen
is not the only potential quencher of fullerene triplet states in
solution. This result is not surprising since long-lived triplet
states are known to be quenched by solvent impurities such
C
60 have been studied, but found to be inefficient against
pulses longer than tens of ps. This result is ascribed to a fast
de-excitation of the laser-created excited state due to the inter-
actions of neighbouring C60 molecules in the solid phase. In
contrast, it has been shown that C60 keeps its limiting proper-
2
5
as stabilizers and/or paramagnetic ions, which are com-
monly present in non-negligible amounts in spectroscopic
grade solvents. This trend in triplet lifetimes of air-purged sam-
ples may be taken as a further proof of a protective dendritic
effect in this series of dendrimers 1–4. Our results compare
29
ties after inclusion in solid matrices such as sol-gel glasses,
polymethyl methacrylate (PMMA) matrices and glass-poly-
30
31
mer composite samples. As far as sol-gel glasses are con-
2
6
interestingly with those of Schwell et al., who reported
photophysical investigations on a methanofullerene chromo-
phore bearing two large dendrimeric poly(aryl)acetylene units.
In that case no appreciable changes in the absorption, lumines-
cence, and singlet oxygen sensitization yields were observed in
cerned, faster de-excitation dynamics and reduced triplet
yields are typically observed when compared to the solutions.
The latter observations are mainly explained by two factors: (i)
perturbation of the molecular energy levels due to the interac-
tions with the sol-gel matrix and (ii) interactions between
2
8
neighbouring fullerene spheres due to aggregation. There-
fore, the encapsulation of the C60 core evidenced by the photo-
physical studies of fullerodendrimers 1–4 might be useful to
prevent such undesirable effects.
Incorporation of fullerodendrimers 1–4 in the sol-gel glasses
was easily achieved by soaking mesoporous silica glasses
2
8
with a solution of 1–4. In all the cases, the resulting glass com-
posites were dark brownish. Since the pore diameter is small,
the molecules should be relatively well dispersed in the sam-
ples. This assumption is also supported by the linear optical
absorption spectra. The spectra contain pronounced vibronic
Table 2 Triplet lifetimes as determined by transient absorption at 298
K in air-equilibrated (AER) and oxygen-free (DEA) solutions
PhCH
3
CH
2
Cl
2
3
CH CN
AER/ns DEA/ms AER/ns DEA/ms AER/ns DEA/ms
a
a
1
2
3
4
279
304
318
374
34.0
37.9
39.4
42.5
598
643
732
827
26.3
27.4
30.1
34.6
–
–
2 2
Fig. 6 Transient absorption spectrum of 4 at 298 K in CH Cl air-
330
412
605
14.0
21.7
25.5
equilibrated solution upon laser excitation at 355 nm (energy ¼ 3 mJ
per pulse). The spectra were recorded at delays of 100, 300, 600, 900,
and 2000 ns following excitation. The inset shows the different decay
time profiles of DA (700 nm) for the whole series of compounds: 1
a
Not soluble in this solvent.
(black), 2 (blue), 3 (red), 4 (green).
1
150
New J. Chem., 2002, 26, 1146–1154

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determine the influence of the dendritic branches on the optical
limiting behaviour of these composite materials.
Experimental
General methods
Reagents and solvents were purchased as reagent grade and
used without further purification. Compounds 5–8 were pre-
1
1
pared according to a previously reported procedure. All reac-
tions were performed in standard glassware under an inert Ar
atmosphere. Evaporation and concentration were done at
ꢁ
2
water aspirator pressure and drying in vacuo at 10 Torr.
For column chromatography silica gel 60 (230–400 mesh,
0
.040–0.063 mm) was purchased from E. Merck. Thin layer
chromatography (TLC) was performed on glass sheets coated
with silica gel 60 F254 purchased from E. Merck, with visuali-
zation by UV light. Melting points were measured on an Elec-
trothermal Digital Melting Point apparatus and are
uncorrected. UV/Vis spectra [lmax in nm (e)] were measured
Fig. 7 Transmission vs. incident fluence at 532 nm of a sol-gel sample
containing compound 3.
structures that suggest only weak intermolecular fullerene-full-
erene interactions; such vibronic features are absent in solu-
tions containing aggregates as well as in crystalline films of
fullerenes. Indeed, the spectra of the sol-gel samples obtained
from 1–4 are similar to those obtained in solutions where no
aggregates are present. It is therefore reasonable to conclude
that the samples contain mainly well-dispersed fullerodendri-
mer molecules.
ꢁ
1
on a Hitachi U-3000 spectrophotometer. IR spectra (cm
)
were measured on an ATI Mattson Genesis Series FTIR
instrument. NMR spectra were recorded on a Bruker AC
2
00 with solvent peaks as reference.
Syntheses
General procedure for the synthesis of dendritic benzaldehydes
–12. A mixture of the appropriate dendritic benzylic alcohol
In order to evaluate the potential of the doped samples for
optical limiting, their transmission has been determined as a
function of excitation intensity. The excitation source is the
frequency-doubled Nd:YAG laser emission at a wavelength
of 532 nm. The pulse duration is about 30 ps, which is consid-
erably shorter than the intersystem crossing time and the
observed increase in absorption is dominated by the popula-
tion of the excited singlet state. The optical transmission as a
function of the fluence of the laser pulses is shown in Fig. 7
for a sol-gel sample containing compound 3. Similar results
have been obtained with the other compounds. For all the
compounds, the transmission remains nearly constant for flu-
9
(
1 equiv.) and MnO (10 equiv.) in CH Cl was stirred vigor-
2
2
2
ously for 3 to 6 h. The mixture was filtered and evaporated
to dryness under reduced pressure. The crude product was
then purified as outlined in the following text.
9
.. It was prepared from 5 and purified by column chromato-
graphy (SiO , Et O–acetone 7 : 3) to give 9 as a colourless
glassy product: yield 84%; H NMR (CDCl , 200 MHz) d
2
2
1
3
3
.38 (s, 6H), 3.53–3.73 (m, 16H), 3.87 (t, J ¼ 5 Hz, 4H), 4.16
(
t, J ¼ 5 Hz, 4H), 6.77 (t, J ¼ 2 Hz, 1H), 7.25 (d, J ¼ 2 Hz,
1
3
ꢁ
2
3
2H), 9.89 (s, 1H); C NMR (CDCl , 50 MHz) d 58.76,
ences lower than 3 to 10 mJ cm . When the intensity increases
above this threshold, the effect of induced absorption appears,
and the transmission diminishes rapidly, thus showing the
potential of these materials for optical limiting applications.
6
1
7.57, 69.27, 70.31, 70.39, 70.58, 71.65, 107.69, 107.99,
38.03, 160.13, 191.58.
10.. It was prepared from 6 and purified by column chromato-
graphy (SiO , Et O–acetone 7 : 3) to give 10 as a colourless
2
2
1
3
glassy product: yield 80%; H NMR (CDCl , 200 MHz) d
Conclusions
3
4
6
.38 (s, 12H), 3.53–3.76 (m, 32H), 3.85 (t, J ¼ 5 Hz, 8H),
.12 (t, J ¼ 5 Hz, 8H), 5.01 (s, 4H), 6.46 (t, J ¼ 2 Hz, 2H),
.58 (d, J ¼ 2 Hz, 4H), 6.84 (t, J ¼ 2 Hz, 1H), 7.08 (d,
Poly(aryl ether) dendritic branches terminated with peripheral
triethyleneglycol chains have been attached to C60 by the 1,3-
dipolar cycloaddition of the azomethine ylides generated in situ
from the corresponding aldehydes and N-methylglycine. The
resulting fullerodendrimers have been characterized by electro-
spray mass spectrometry (ESMS), which appears to be a par-
ticularly interesting analytical tool for the unambiguous
structural assignment of such high molecular weight fullerene
derivatives. The results of the photophysical investigations
reveal that, by enlarging the dendrimer size, changes of the
core solvation environment occur, most likely as a conse-
quence of a tighter contact between the fullerene unit and
the external dendritic wedges due to favourable electronic
donor/acceptor interactions. This provides some shielding
of the fulleropyrrolidine chromophore from contacts with
external molecules such as dioxygen. As a consequence, a
reduction of the potent singlet oxygen sensitizing character
of the fullerene unit is obtained. Finally, thanks to their high
solubility, the fullerodendrimers have been easily incorporated
in mesoporous silica glasses and preliminary measurements on
the resulting doped samples have revealed efficient optical lim-
iting properties. Further studies are now underway in order to
1
3
J ¼ 2 Hz, 2H), 9.89 (s, 1H); C NMR (CDCl
3
, 50 MHz) d
9.01, 67.47, 69.61, 70.54, 70.61, 70.78, 71.88, 101.16, 106.03,
06.17, 108.23, 108.61, 138.42, 159.97, 160.24, 191.79.
5
1
11.. It was prepared from 7 and purified by column chromato-
graphy (SiO
glassy product: yield 82%; H NMR (CDCl
2 2
, Et O–acetone 2 : 3) to give 11 as a colourless
1
3
, 200 MHz) d
.35 (s, 24H), 3.51–3.70 (m, 64H), 3.82 (t, J ¼ 5 Hz, 16H),
3
4
.07 (t, J ¼ 5 Hz, 16H), 4.95 (s, 8H), 5.01 (s, 4H), 6.43 (t,
J ¼ 2 Hz, 4H), 6.54 (t, J ¼ 2 Hz, 2H), 6.57 (d, J ¼ 2 Hz, 8
H), 6.64 (d, J ¼ 2 Hz, 4H), 6.85 (t, J ¼ 2 Hz, 1H), 7.08 (d,
1
3
1
9
J ¼ 2 Hz, 2H), 9.87 (s, 1H); C NMR (CDCl , 50 MHz) d
3
5
1
1
8.90, 67.32, 69.51, 69.86, 70.10, 70.42, 70.50, 70.66, 71.78,
00.95, 101.53, 105.91, 106.23, 108.15, 108.42, 138.25, 138.45,
38.82, 159.95, 160.14, 191.71.
12.. It was prepared from 8 and purified by column chromato-
graphy (SiO , CH Cl –acetone 2 : 3) to give 12 as a colourless
glassy product: yield 95%; H NMR (CDCl , 200 MHz) d 3.35
2
2
2
1
3
(s, 48H), 3.50–4.15 (m, 192H), 4.95 (m, 28H), 6.30–6.80
New J. Chem., 2002, 26, 1146–1154
1151

View Article Online
(
(
m, 42H), 6.85 (t, J ¼ 2 Hz, 1H), 7.09 (d, J ¼ 2 Hz, 2H), 9.87
4.. This was prepared from 12 and purified by column chroma-
tography (SiO , toluene–acetone 3 : 2) followed by gel permea-
1
3
s, 1H); C NMR (CDCl , 50 MHz) d 58.95, 67.39, 69.57,
3
2
6
1
9.91, 70.49, 70.55, 70.71, 71.84, 101.03, 101.48, 106.02,
06.39, 108.23, 138.92, 160.01, 191.74.
tion chromatography (Biorads, Biobeads SX-1, CH
give 4 as a brown glassy product: yield 44%; H NMR
2
Cl
2
) to
1
(
(
4
7
3
CDCl , 400 MHz) d 2.80 (s, 3H), 3.37 (s, 48H), 3.47–3.77
m, 128H), 3.76 (t, J ¼ 5 Hz, 32H), 4.10 (t, J ¼ 5 Hz, 32H),
General procedure for the synthesis of fullerodendrimers 1–4.
.23 (d, J ¼ 9.5 Hz, 1H); 4.92 (m, 30H), 6.44–7.05 (m, 43H),
.12 (br, 2H); Anal. calcd. for C279 78N.CH Cl : C
A mixture of the appropriate dendritic benzaldehyde (1
equiv.), C60 (1 equiv.) and N-methylglycine (10 equiv.) in
toluene was refluxed for 12 h. The mixture was cooled to room
temperature, filtered and evaporated to dryness under reduced
pressure. The crude product was then purified as outlined in
the following text.
H
319
O
2
2
67.05, H 6.37, N 0.28, O 24.88, found: C 66.73, H 6.53, N
.28, O 24.86.
0
Electrospray mass spectrometry (ESMS)
Positive ES mass spectra were obtained on a ES triple quadru-
pole mass spectrometer Quattro II with a mass-to-charge (m/
z) ratio range extended to 8000 (Micromass, Altrincham, UK).
The electrospray source was heated to 45 C. The sampling
c
cone voltage (V ) was at 160 V to allow the transmission of
1
.. It was prepared from 9 and purified by column chromato-
graphy (SiO , toluene–acetone 4 : 1) followed by gel permea-
tion chromatography (Biorads, Biobeads SX-1, CH Cl ) to
2
ꢀ
2
2
1
give 1 as a brown glassy product: yield 40%; H NMR
ions with m/z > 4000 without fragmentation processes. Under
these conditions reproducible spectra were also obtained. Sam-
ple solutions were introduced into the mass spectrometer
source with a syringe pump (Harvard type 55 1111: Harvard
Apparatus Inc., South Natick, MA, USA) with a flow rate
(
(
CDCl , 200 MHz) d 2.80 (s, 3H), 3.37 (s, 6H), 3.52–3.85
m, 20H), 4.12 (t, J ¼ 5 Hz, 4H), 4.24 (d, J ¼ 9.5 Hz, 1H),
3
4
1
5
8
1
1
1
1
3
.82 (s, 1H), 4.96 (d, J ¼ 9.5 Hz, 1H), 6.46 (t, J ¼ 2 Hz,
3
1
3
H), 6.98 (br, 2H); C NMR (CDCl , 50 MHz) d 40.05,
9.06, 67.50, 69.02, 69.57, 69.89, 70.55, 70.61, 70.79, 71.91,
3.60, 101.99, 135.69, 136.46, 136.57, 139.22, 139.59, 139.84,
40.10, 141.66, 141.79, 141.92, 142.01, 142.11, 142.55, 142.95,
43.13, 144.36, 144.60, 144.68, 145.24, 145.41, 145.75, 145.92,
46.08, 146.29, 146.42, 146.96, 147.28, 153.41, 153.58, 154.08,
ꢁ
1
of 6 mL min . Calibration was performed using protonated
horse myoglobin. Scanning was performed in the MCA (multi
channel analyzer) mode, and several scans were summed to
obtain the final spectrum.
Samples for ESMS were prepared by dissolving the com-
39 8 2
56.12, 159.96; Anal. calcd. for C83H O N.H O: C 83.34, H
.45, N 1.17, O 12.04, found: C 83.61, H 3.49, N 1.17, O 11.73.
2 2
pound under study in a solution of CH Cl containing 1% for-
ꢁ
4
mic acid to achieve a concentration of 10 M. After stirring at
room temperature for 1 min, the clear red solution was directly
analyzed by ESMS.
2.. It was prepared from 10 and purified by column chromato-
graphy (SiO
2
, toluene–acetone 4 : 1) followed by gel permea-
tion chromatography (Biorads, Biobeads SX-1, CH Cl ) to
2
2
Spectroscopic and photophysical measurements
1
give 2 as a brown glassy product: yield 37%; H NMR
The photophysical investigations were carried out in toluene,
dichloromethane, and acetonitrile (Carlo Erba, spectrofluori-
metric grade). The samples were normally placed in fluori-
metric 1 cm path cuvettes. Absorption spectra were recorded
with a Perkin-Elmer l40 spectrophotometer. Uncorrected
emission spectra were obtained with a Spex Fluorolog II spec-
trofluorimeter (continuous 150 W Xe lamp), equipped with a
Hamamatsu R-928 photomultiplier tube. The corrected spec-
tra were obtained via a calibration curve determined with a
(
(
CDCl , 200 MHz) d 2.82 (s, 3H), 3.38 (s, 12H), 3.52–3.74
3
m, 32H), 3.83 (t, J ¼ 5 Hz, 8H), 4.08 (t, J ¼ 5 Hz, 8H),
4
1
7
5
7
1
1
1
1
1
1
0
.23 (d, J ¼ 9.5 Hz, 1H), 4.82 (s, 1H), 4.93 (d, J ¼ 9.5 Hz,
H), 4.98 (s, 4H), 6.41 (t, J ¼ 2 Hz, 2H), 6.50–6.65 (m, 5H),
1
3
.08 (br, 2H); C NMR (CDCl , 50 MHz) d 39.93, 40.04,
3
3.41, 59.05, 67.41, 68.99, 69.43, 70.01, 70.55, 70.63, 70.77,
1.91, 83.43, 100.79, 101.16, 102.52, 105.84, 106.68, 135.70,
36.24, 136.57, 139.14, 139.41, 139.78, 140.02, 140.12, 141.57,
41.62, 141.68, 141.89, 141.92, 141.97, 142.00, 142.09, 142.19,
42.53, 142.64, 142.92, 142.97, 144.31, 144.55, 144.65, 145.01,
45.11, 145.22, 145.45, 145.49, 145.75, 145.91, 146.04, 146.12,
46.18, 146.28, 146.42, 146.80, 147.27, 153.36, 154.03, 156.07,
60.05; Anal. calcd. for C111H O N: C 77.75, H 4.64, N
3
2
procedure described earlier. Fluorescence quantum yields
obtained from spectra on an energy scale (cm ) were mea-
ꢁ1
3
sured with the method described by Demas and Crosby using
3
2
+
as standards air-equilibrated solutions of [Os(phen)
acetonitrile (Fem ¼ 0.005).
3
]
in
79
18
3
4
.82, O 16.79, found: C 77.74, H 4.67, N 0.85, O 16.74.
The steady-state IR luminescence spectra were obtained
with an apparatus available at the Chemistry Department of
the University of Bologna (Italy) and described in detail ear-
3.. It was prepared from 11 and purified by column chromato-
graphy (SiO , toluene–acetone 3 : 2) followed by gel permea-
tion chromatography (Biorads, Biobeads SX-1, CH
give 3 as a brown glassy product: yield 39%; H NMR
(
(
3
2
lier. A continuous 450 W xenon lamp was used as the light
source; excitation was performed at 480 nm. The determina-
tion of the relative yields of singlet oxygen sensitization in a
given solvent can be obtained by monitoring the singlet oxygen
luminescence intensity at 1270 nm of solutions displaying the
2
2
Cl
2
) to
1
CDCl
m, 64H), 3.83 (t, J ¼ 5 Hz, 16H), 4.09 (t, J ¼ 5 Hz, 16H),
.22 (d, J ¼ 9.5 Hz, 1H), 4.82 (s, 1H), 4.90 (s, 8H), 4.94 (d,
3
, 200 MHz) d 2.82 (s, 3H), 3.38 (s, 24H), 3.52–3.75
2
3
4
same optical density (0.3) at the excitation wavelength.
J ¼ 9.5Hz, 1H), 5.03 (s, 4H), 6.43–7.09 (m, 19H), 7.08 (br,
Emission lifetimes on the nanosecond time scale were deter-
mined with an IBH single photon counting spectrometer
equipped with a thyratron gated nitrogen lamp working in
the range of 2–40 KHz (lexc ¼ 337 nm, 0.5 ns time resolution);
the detector was a red-sensitive (185–850 nm) Hamamatsu R-
3237–01 photomultiplier tube.
1
3
2
6
7
1
1
1
1
1
1
3
H); C NMR (CDCl , 50 MHz) d 40.02, 59.03, 67.47,
7.68, 68.97, 69.64, 69.80, 69.98, 70.55, 70.63, 70.79, 70.97,
1.90, 83.37, 101.16, 101.51, 102.66, 106.03, 106.19, 135.65,
35.68, 136.17, 136.57, 138.87, 139.33, 139.46, 139.75, 139.99,
40.08, 141.53, 141.62, 141.89, 141.97, 142.03, 142.09, 142.16,
42.44, 142.51, 142.62, 142.88, 142.92, 144.30, 144.52, 144.60,
44.92, 145.08, 145.21, 145.46, 145.72, 145.89, 146.02, 146.07,
46.16, 146.25, 146.40, 146.75, 147.23, 153.33, 153.36, 154.02,
Transient absorption spectra in the nanosecond–microse-
cond time domain were obtained by means of a flash-photoly-
3
5
sis system described in detail earlier.
Excitation was
56.09, 159.84; Anal. calcd. for C167
H
159
O
38N.H
2
O: C 71.48,
performed with the third harmonic (355 nm) of a Nd:YAG
laser (J.K. Lasers Ltd.) with 20 ns pulse duration and 1–2
mJ of energy per pulse. Triplet lifetimes were obtained by
H 5.78, N 0.50, O 22.24, found: C 71.55, H 5.88, N 0.50, O
2
2.07.
1
152
New J. Chem., 2002, 26, 1146–1154

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averaging at least five different decays recorded around the
maximum of the absorption peak (680–720 nm). When neces-
sary, oxygen was removed by at least four freeze-thaw-pump
References
1
G. R. Newkome, C. N. Moorefield, F. V o¨ gtle, Dendrimers and
Dendrons: Concepts, Syntheses, Applications, VCH, Weinheim,
ꢁ6
cycles by means of a diffusive vacuum pump at 10 Torr
CH Cl , PhMe) or by bubbling argon for several minutes
through the solution (CH CN).
2
001.
(
2
2
2
(a) V. Balzani, S. Campagna, G. Denti, A. Juris, S. Serroni and
M. Venturi, Acc. Chem. Res., 1998, 31, 26; (b) H. Frey, Angew.
Chem., Int. Ed., 1998, 37, 2193; (c) A. Archut and F. V o¨ gtle,
Chem. Soc. Rev., 1998, 27, 233; (d ) C. Gorman, Adv. Mater.,
3
Experimental uncertainties are estimated to be ꢄ7% for life-
time determinations, ꢄ20% for emission quantum yields, and
ꢄ2 nm for absorption and emission peaks.
1
998, 10, 295; (e) M. A. Hearshaw and J. R. Moss, Chem. Com-
mun., 1999, 1; ( f ) G. R. Newkome, E. He and C. N. Moorefield,
Chem. Rev., 1999, 99, 1689; (g) A. J. Berresheim, M. M u¨ ller and
K. M u¨ llen, Chem. Rev., 1999, 99, 1747; (h) M. Fischer and F.
V o¨ gtle, Angew. Chem., Int. Ed., 1999, 38, 884; (i) F. Zeng and
S. C. Zimmerman, Chem. Rev., 1997, 97, 1681; ( j) H.-F. Chow,
T. K.-K. Mong, M. F. Nongrum and C.-W. Wan, Tetrahedron,
Mesoporous silica glasses
A solution of tetramethoxysilane (TMOS) in MeOH was
added to a mixture of water, MeOH, nitric acid and forma-
1
998, 54, 8543; (k) D. K. Smith and F. Diederich, Chem. Eur.
J., 1998, 4, 1353; (l) A. W. Bosman, H. M. Janssen and E. W. Mei-
jer, Chem. Rev., 1999, 99, 1665; (m) A. Adronov and J. M. J.
Fr e´ chet, Chem. Commun., 2000, 1701; (n) K. Inoue, Prog. Polym.
Sci., 2000, 25, 453; (o) V. Balzani, P. Ceroni, A. Juris, M. Venturi,
S. Campagna, F. Puntoriero and S. Serroni, Coord. Chem. Rev.,
mide; the final composition of TMOS–MeOH–H
CHONH –HNO was 1 : 10 : 5 : 1 : 0.063 (molar ratio).
2
O–
3
6
2
3
The reaction was followed by FTIR, which showed that full
hydrolysis of TMOS occurred within a few seconds. The con-
densation reaction then took place and gelation occured within
2
001, 219–221, 545; (p) S. M. G. Grayson and J. M. J. Fr e´ chet,
Chem. Rev., 2001, 101, 3819.
ꢀ
2
gels were cast in small PMMA round boxes (diameter: 25 mm,
to 3 h, depending on the temperature, normally at 40 C. The
3
4
For reviews on dendritic encapsulation, see: (a) S. Hecht and
J. M. J. Fr e´ chet, Angew. Chem., Int. Ed., 2001, 40, 74; (b) C. B.
Gorman and J. C. Smith, Acc. Chem. Res., 2001, 34, 60.
(a) C. J. Hawker, K. L. Wooley and J. M. J. Fr e´ chet, J. Am.
Chem. Soc., 1993, 115, 4375; (b) C. Devadoss, P. Bharathi and
J. S. Moore, Angew. Chem., Int. Ed. Engl., 1997, 36, 1633; (c)
D. K. Smith and L. M u¨ ller, Chem. Commun., 1999, 1915.
(a) R.-H. Jin, T. Aida and S. Inoue, J. Chem. Soc., Chem. Com-
mun., 1993, 1260; (b) F. V o¨ gtle, M. Plevoets, M. Nieger, G. C.
Azzellini, A. Credi, L. De Cola, V. De Marchis, M. Venturi and
V. Balzani, J. Am. Chem. Soc., 1999, 121, 6290; (c) J. Issberner,
F. V o¨ gtle, L. De Cola and V. Balzani, Chem. Eur. J., 1997, 3,
ꢀ
height: 8 mm) and dried at 40 C in a drying oven for 2 days.
During this step extensive shrinkage occurred, leading to
pieces of transparent xerogels of 10 mm in diameter and
0
.4 mm in height. These xerogel pieces were further heat trea-
ꢀ
ted at 500–600 C. The samples were mesoporous as shown by
physisorption measurements. The mean pore diameter was
5
3
.46 nm and the maximum pore diameter was 4.9 nm with a
3
ꢁ1
porous volume of 0.2133 cm g . The resulting silica glasses
were prepared by the sol-gel process and soaked in a concen-
trated THF solution of compound 1, 2, 3 or 4. After 30 min,
7
06; (d ) M. Plevoets, F. V o¨ gtle, L. De Cola and V. Balzani,
New J. Chem., 1999, 23, 63; (e) M. S. Matos, J. Hofkens, W. Ver-
heijen, F. C. De Schryver, S. Hecht, K. W. Pollak, J. M. J. Fre-
chet, B. Forier and W. Dehaen, Macromolecules, 2000, 33, 2967.
J.-F. Nierengarten, Chem. Eur. J., 2000, 6, 3667.
(a) G. Accorsi, N. Armaroli, J.-F. Eckert and J.-F. Nierengarten,
Tetrahedron Lett., 2002, 43, 65; (b) B. Dardel, D. Guillon, B.
Heinrich and R. Deschenaux, J. Mater. Chem., 2001, 11, 2814;
the samples were removed from the solutions and dried at
ꢀ
4
0 C for 1 h.
6
7
Optical limiting measurements
(c) F. Langa, M. J. Gomez-Escalonilla, E. Diez-Barra, J. C. Gar-
cia-Martinez, A. de la Hoz, J. Rodriguez-Lopez, A. Gonzalez-
To study the optical limiting properties, the transmission of the
doped glass samples was determined as a function of the
incoming fluence at room temperature. A frequency-doubled
Cortes and V. Lopez-Arza, Tetrahedron Lett., 2001, 42, 3435;
d ) J. L. Segura, R. Gomez, N. Martin, C. Luo, A. Swartz and
(
D. M. Guldi, Chem. Commun., 2001, 707; (e) A. G. Avent,
P. R. Birkett, F. Paolucci, S. Roffia, R. Taylor and N. K. Wach-
ter, J. Chem. Soc., Perkin Trans. 2, 2000, 1409; ( f ) A. Herzog,
A. Hirsch and O. Vostrowsky, Eur. J. Org. Chem., 2000, 171;
(g) F. Djojo, E. Ravanelli, O. Vostrowsky and A. Hirsch, Eur.
J. Org. Chem., 2000, 1051; (h) B. Dardel, R. Deschenaux, M. Even
and E. Serrano, Macromolecules, 1999, 32, 5193; (i) M. Brettreich
and A. Hirsch, Tetrahedron Lett., 1998, 39, 2731; ( j) J.-F. Nieren-
garten, T. Habbicher, R. Kessinger, F. Cardullo, F. Diederich, V.
Gramlich, J.-P. Gisselbrecht, C. Boudon and M. Gross, Helv.
Chim. Acta., 1997, 80, 2238; (k) V. J. Catalano and N. Parodi,
Inorg. Chem., 1997, 36, 537; (l) C. J. Hawker, K. L. Wooley
and J. M. J. Fr e´ chet, Chem. Commun., 1994, 925; (m) K. L. Woo-
ley, C. J. Hawker, J. M. J. Fr e´ chet, F. Wudl, G. Srdanov, S. Shi,
C. Li and M. Kao, J. Am. Chem. Soc., 1993, 115, 9836.
(a) J.-F. Nierengarten, D. Felder and J.-F. Nicoud, Tetrahedron
Lett., 1999, 40, 269; (b) J.-F. Nierengarten, D. Felder and J.-F.
Nicoud, Tetrahedron Lett., 1999, 40, 273; (c) N. Armaroli, C.
Boudon, D. Felder, J.-P. Gisselbrecht, M. Gross, G. Marconi,
J.-F. Nicoud, J.-F. Nierengarten and V. Vicinelli, Angew. Chem.,
Int. Ed., 1999, 38, 3730; (d ) D. Felder, J.-L. Gallani, D. Guillon,
B. Heinrich, J.-F. Nicoud and J.-F. Nierengarten, Angew. Chem.,
Int. Ed., 2000, 39, 201.
(
active/passive mode locked) Nd:YAG laser at 532 nm with
a pulse duration of 30 ps and a repetition rate of 5 Hz was used
for these measurements. At this wavelength, the linear trans-
mission of the samples was typically 40 to 60%. To take into
account the intensity fluctuations of the laser source, a refer-
ence beam created by a beam splitter from the same laser beam
as the excitation branch was used. The exciting pulses were
focussed onto the sample by a lens of f ¼ 16 cm into a spot
2
of 6400 mm . The transmitted light of the measurement pulses,
as well as that of the reference pulses, was sent onto the same
optical multichannel analyzer. The incident intensity at the
sample position was changed by means of calibrated neutral
density filters.
8
Acknowledgements
This work was supported by the CNRS, the French Ministry
of Research (ACI Jeunes Chercheurs) and the CNR. We thank
Prof. A. Juris (University of Bologna) for allowing the use
of the IR spectrofluorimeter, L. Oswald and M. Minghetti
for technical help, and M. Schmitt for NMR measurements.
Y. R. thanks the French Ministry of research, G. A. the
MIUR (Progetto 5%), A. C. the INTAS (RFBR 00-03-
9
0
(a) J.-F. Nierengarten, D. Felder and J.-F. Nicoud, Tetrahedron
Lett., 2000, 41, 41; (b) D. Felder, H. Nierengarten, J.-P. Gissel-
brecht, C. Boudon, E. Leize, J.-F. Nicoud, M. Gross, A. Van
Dorsselaer and J.-F. Nierengarten, New J. Chem., 2000, 24, 687;
(
c) J.-F. Nierengarten, J.-F. Eckert, Y. Rio, M. P. Carreon,
J.-L. Gallani and D. Guillon, J. Am. Chem. Soc., 2001, 123, 9743.
Y. Rio, J.-F. Nicoud, J.-L. Rehspringer and J.-F. Nierengarten,
Tetrahedron Lett., 2000, 41, 10 207.
1
3
3016), and G. K. the ERASMUS/SOCRATES programme
for their fellowships. N. A. and A. V. D. are grateful to EU
for the TMR contract no. CT98-0226.
11 M. J. Hannon, P. C. Mayers and P. C. Taylor, J. Chem. Soc., Per-
kin Trans. 1, 2000, 1881.
New J. Chem., 2002, 26, 1146–1154
1153

View Article Online
Lett., 1992, 199, 14; (c) D. G. McLean, R. L. Sutherland, M. C.
1
1
2
3
M. Prato and M. Maggini, Acc. Chem. Res., 1998, 31, 519.
(a) J.-F. Eckert, J.-F. Nicoud, J.-F. Nierengarten, S-G. Liu, L.
Echegoyen, F. Barigelletti, N. Armaroli, L. Ouali, V. Krasnikov
and G. Hadziioannou, J. Am. Chem. Soc., 2000, 122, 7467; (b)
P. de la Cruz, A. de la Hoz, L. M. Font, F. Langa and M. C.
Perez-Rodriguez, Tetrahedron Lett., 1998, 39, 6053; (c) T. Gu,
C. Bourgogne and J.-F. Nierengarten, Tetrahedron Lett., 2001,
Brant and D. M. Brandelik, Opt. Lett., 1993, 18, 858; (d ) C. Li,
L. Zhang, R. Wang, Y. L. Song and Y. Wang, J. Opt. Soc. Am.
B, 1994, 11, 1356; (e) S. Couris, E. Koudoumas, A. A. Ruth
and S. Leach, J. Phys. B, 1995, 28, 4537; ( f ) C. Li, J. H. Si, M.
Yang, R. B. Wang and L. Zhang, Phys. Rev. A, 1995, 51, 569;
(g) Y.-P. Sun, G. E. Lawson, J. E. Riggs, B. Ma, N. Wang and
D. K. Moton, J. Phys. Chem. A, 1998, 102, 5520; (h) J. E. Riggs
and Y.-P. Sun, J. Phys. Chem. A, 1999, 103, 485; (i) L. Smilowitz,
D. McBranch, V. Klimov, J. M. Robinson, A. Koskelo, M. Gri-
gorova, B. Mattes, H. Wang and F. Wudl, Opt. Lett., 1996, 21,
922; ( j) Y.-P. Sun, J. E. Riggs and B. Liu, Chem. Mater., 1997,
9, 1268.
42, 7249.
14
S. K. Srivastava, G. Jong, S. Leifer and W. Saunders, Rapid Com-
mun. Mass Spectrom., 1993, 7, 610.
D. C. Brune, Rapid Commun. Mass Spectrom., 1999, 13, 384.
C. G. Juo, L. L. Shiu, C. K. F. Shen, T. Y. Luh and G. R. Her,
Rapid Commun. Mass Spectrom., 1995, 9, 604.
1
1
5
6
1
7
(a) H. Rogniaux, A. Van Dorsselaer, P. Barth, J.-F. Biellmann, J.
Barbanton, M. van Zandt, B. Chevrier, E. Howard, A. Mitschler,
N. Potier, L. Urzhumtseva, D. Moras and A. Podjarny, J. Am.
Soc. Mass Spectrom., 1999, 10, 635; (b) H. Nierengarten, E. Leize,
E. Breuning, A. Garcia, F. Romero-Salguero, J. Rojo, J.-M. Lehn
and A. Van Dorsselaer, J. Mass Spectrom., 2002, 37, 56.
B. Ma, C. E. Bunker, R. Guduru, X. F. Zhang and Y. P. Sun,
J. Phys. Chem. A, 1997, 101, 5626.
J.-F. Eckert, D. Byrne, J.-F. Nicoud, L. Oswald, J.-F. Nierengar-
ten, M. Numata, A. Ikeda, S. Shinkai and N. Armaroli, New J.
Chem., 2000, 24, 749.
K. Kordatos, T. Da Ros, M. Prato, S. Leach, E. J. Land and
R. V. Bensasson, Chem. Phys. Lett., 2001, 334, 221.
N. Armaroli, F. Barigelletti, P. Ceroni, J. F. Eckert, J. F. Nicoud
and J. F. Nierengarten, Chem. Commun., 2000, 599.
N. Armaroli, G. Accorsi, D. Felder and J. F. Nierengarten, Chem.
Eur. J., 2002, 8, 2314.
C. Wirp, H. G u¨ sten and H.-D. Brauer, Ber. Bunsenges. Phys.
Chem., 1996, 100, 1217.
S. L. Murov, I. Carmichael and G. L. Hug, Handbook of Photo-
chemistry, Marcel Dekker Inc., New York, 2nd edn., 1993.
J. B. Birks, Photophysics of Aromatic Molecules, Wiley-Inter-
science, London, 1970.
M. Schwell, N. K. Wachter, J. H. Rice, J. P. Galaup, S. Leach, R.
Taylor and R. V. Bensasson, Chem. Phys. Lett., 2001, 339, 29.
(a) L. W. Tutt and A. Krost, Nature, 1992, 356, 225; (b) F. Henari,
J. Callaghan, H. Stiel, W. Blau and D. J. Cardin, Chem. Phys.
28 J. Schell, D. Felder, J.-F. Nierengarten, J.-L. Rehspringer, R.
L e´ vy and B. H o¨ nerlage, J. Sol-Gel Sci. Technol., 2001, 22, 225.
29 (a) J. Schell, D. Brinkmann, D. Ohlmann, B. H o¨ nerlage, R. Levy,
M. Joucla, J.-L. Rehspringer, J. Serughetti and C. Bovier, J.
Chem. Phys., 1998, 108, 8599; (b) J. Schell, D. Ohlmann, D. Brink-
mann, R. L e´ vy, M. Joucla, J.-L. Rehspringer and B. H o¨ nerlage, J.
Chem. Phys., 1999, 111, 5929; (c) F. Bentivegna, M. Canva, P.
Georges, A. Brun, F. Chaput, L. Malier and J.-P. Boilot, Appl.
Phys. Lett., 1993, 62, 1721; (d ) R. Signorini, M. Zerbetto, M.
Meneghetti, R. Bozio, M. Maggini, C. De Faveri, M. Prato and
G. Scorrano, Chem. Commun., 1996, 1891; (e) M. Maggini, C.
De Faveri, G. Scorrano, M. Prato, G. Brusatin, M. Guglielmi,
M. Meneghetti, R. Signorini and R. Bozio, Chem. Eur. J., 1999,
5, 2501.
30 A. Kost, L. Tutt, M. B. Klein, T. K. Dougherty and W. E. Elias,
Opt. Lett., 1993, 18, 334.
31 R. Gvishi, J. D. Bhawalkar, N. D. Kumar, G. Ruland, U. Nar-
ang, P. N. Prasad and B. A. Reinhardt, Chem. Mater., 1995, 7,
2199.
32 N. Armaroli, G. Marconi, L. Echegoyen, J. P. Bourgeois and
F. Diederich, Chem. Eur. J., 2000, 6, 1629.
33 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991.
34 E. M. Kober, J. V. Caspar, R. S. Lumpkin and T. J. Meyer, J.
Phys. Chem., 1986, 90, 3722.
1
8
9
1
2
2
2
2
2
2
2
2
0
1
2
3
4
5
6
7
35 L. Flamigni, J. Phys. Chem., 1992, 96, 3331.
36 N. Viart and J.-L. Rehspringer, J. Non-Cryst. Solids, 1996, 195,
223.
1
154
New J. Chem., 2002, 26, 1146–1154