Polysulfurated pyrene-cored dendrimers: Luminescent and electrochromic properties

Article abstract of DOI:10.1002/chem.200801198

We have synthesized a novel class of dendrimers, consisting of a polysulfurated pyrene core with appended poly(thiophenylene) dendrons (PyGO, PyG1, and PyG2, see Scheme 1), which exhibit remarkable photophysical and redox properties. In dichloromethane or cyclohexane solution they show a strong, dendron-localized absorption band with a maximum at around 260 nm and a band in the visible region with a maximum at 435 nm, which can be assigned to the pyrene core strongly perturbed by the four sulfur substituents. The dendrimers exhibit a strong (Φ = 0.6), short-lived (τ=2.5 ns) corelocalized fluorescence band with maximum at approximately 460 nm in cyclohexane solution at 293 K. A strong fluorescence is also observed in dichloromethane solution at 293 K, in dichloromethane/chloroform rigid matrix at 77 K, and in the solid state (powder) at room temperature. The dendrimers undergo reversible chemical and electrochemical one-electron oxidation with formation of a strongly colored deep blue radical cation. A second, reversible one-electron oxidation is observed at more positive potential values. The photophysical and redox properties of the three dendrimers are finely tuned by the length of their branches. The strong blue fluorescence and the yellow to deep blue color change upon reversible one-electron oxidation can be exploited for optoelectronic devices.

Full text of DOI:10.1002/chem.200801198

FULL PAPER
DOI: 10.1002/chem.200801198
Polysulfurated Pyrene-Cored Dendrimers: Luminescent and Electrochromic
Properties
Marc Gingras,*[a] Virginie Placide,[a] Jean-Manuel Raimundo,[a] Giacomo Bergamini,[b]
Paola Ceroni,*[b] and Vincenzo Balzani[b]
Abstract: We have synthesized a novel
class of dendrimers, consisting of a pol-
ysulfurated pyrene core with appended
poly(thiophenylene) dendrons (PyG0,
PyG1, and PyG2, see Scheme 1), which
exhibit remarkable photophysical and
redox properties. In dichloromethane
or cyclohexane solution they show a
strong, dendron-localized absorption
(F=0.6), short-lived (t=2.5 ns) core-
localized fluorescence band with maxi-
mum at approximately 460 nm in cyclo-
hexane solution at 293 K. A strong
fluorescence is also observed in di-
chloromethane solution at 293 K, in di-
chloromethane/chloroform rigid matrix
at 77 K, and in the solid state (powder)
at room temperature. The dendrimers
undergo reversible chemical and elec-
trochemical one-electron oxidation
with formation of a strongly colored
deep blue radical cation. A second, re-
versible one-electron oxidation is ob-
served at more positive potential
values. The photophysical and redox
properties of the three dendrimers are
finely tuned by the length of their
branches. The strong blue fluorescence
and the yellow to deep blue color
change upon reversible one-electron
oxidation can be exploited for opto-
band with
a maximum at around
260 nm and a band in the visible region
with a maximum at 435 nm, which can
be assigned to the pyrene core strongly
perturbed by the four sulfur substitu-
ents. The dendrimers exhibit a strong
Keywords: dendrimers
·
electro-
AHCTUNGTREGeNNUN lectronic devices.
chemistry · electrochromism · lumi-
nescence · pyrene
Introduction
thetic strategies it is possible to prepare dendrimers that
contain selected functional units in predetermined sites of
their structure. Such compounds can often exhibit remark-
able chemical, physical, and biological properties, with a
wide range of potential applications in different fields such
as medicine, biology, chemistry, physics, and engineering.[4]
In the last few years, several families of dendrimers con-
taining units capable of interacting with photons and/or
electrons have been synthesized, and their properties have
been the object of detailed investigations. Dendrimers con-
taining photoactive components,[5,6] in the core and/or in the
branches, are particularly interesting since: 1) luminescence
signals offer a handle to better understand the dendritic
structures and superstructures; 2) cooperation among the
photoactive components can allow the dendrimer to per-
form useful functions such as light harvesting; 3) changes in
the photophysical properties can be exploited for sensing
purposes with signal amplification; and 4) photochemical re-
actions can change the structure and other properties of
dendrimers and could also lead to a controlled release of
molecules.[2a] Dendrimers containing several equivalent elec-
troactive units in the branches may display multi-electron
transfer properties and play the role of nanobatteries.[7]
Dendrimers[1] are complex, repeatedly branched treelike
compounds that can be synthesized with well-defined com-
position and a high degree of order. They usually consist of
a core upon which radially branched layers are covalently
attached. Because of their treelike multi-branched structure,
dendrimers can form internal dynamic niches in which small
molecules or ions can be hosted.[2,3] By using suitable syn-
[a] Prof. Dr. M. Gingras, V. Placide, Dr. J.-M. Raimundo
UPR CNRS 3118 Interdisciplinary Center on Nanoscience at Mar-
seille (CINaM)
Campus de Luminy, Universitꢀ de la Mꢀditerranꢀe
Case 913, 13288 Marseille Cedex 09 (France)
[b] Dr. G. Bergamini, Prof. Dr. P. Ceroni, Prof. Dr. V. Balzani
Department of Chemistry “G. Ciamician”
University of Bologna
40126 Bologna (Italy)
Fax : (+39)051-2099456
E-mail: paola.ceroni@unibo.it
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801198.
Chem. Eur. J. 2008, 14, 10357 – 10363
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10357

When the electroactive component is the dendrimer core, its
electron transfer processes can be slowed down or complete-
ly prevented by the dendrimer branches.[8]
Herein we report on the synthesis, characterization, pho-
tophysical behavior (absorption spectra, emission spectra
and lifetime, fluorescence anisotropy), and redox properties
(chemical and electrochemical oxidation, and electrochrom-
ism) of a novel class of dendrimers (PyG0, PyG1, and
PyG2, Scheme 1) consisting of a polysulfurated pyrene core,
Results and Discussion
Synthesis and characterization: Most pyrene derivatives are
monosubstituted, but a practical precursor to tetrafunctional
derivatives is 1,3,6,8-tetrabromopyrene, which has been pro-
duced easily on the gram scale since 1937, by the bromina-
tion of pyrene at elevated temperatures in nitrobenzene.[19]
Bromine substitutions are often achieved by SNAr or by
À
metal-catalyzed C C bond coupling procedures. These
namely a 1,3,6,8-tetra
N
methods have opened up new routes to a family of C-func-
tionalized pyrene compounds.
ed thiophenylene units. Pyrene and its derivatives have in-
teresting photophysical and electrochemical properties, and,
for this reason, they have been widely used in the fields of
organic light-emitting devices,[9] field-effect transistors,[10]
liquid crystals,[11] biological markers,[12] ion sensors,[13] and
conformational probes.[14] On the other hand, polysulfurated
pyrene derivatives are unusual, in spite of the fact that
sulfur substituents directly bound to an aromatic core are
known to stabilize charged species, giving rise to complexes
with thiophilic metal ions and charge-transfer complexes
with organic molecules.[15] In particular, 1,3,6,8-tetrame-
We succeeded in the polysulfuration of 1,3,6,8-tetrabro-
mopyrene[19] by using simple nucleophilic aromatic substitu-
tions with thiolate anions in polar solvents.[16,17] As shown in
Scheme 1, we prepared PyG0 (90% yield) from 4-methyl-
benzenethiol after heating in DMF at 808C in the presence
of a strong base (NaH). This reference compound estab-
lished the basis of our studies on the whole dendrimer
family. The next generation pyrene dendrimers were similar-
ly prepared (PyG1: 70% yield; PyG2: 60% yield). They
were well characterized by elemental analysis and by vari-
ous NMR and mass spectrometry techniques (ESI, ESI-CI
with Ag+, MALDI-TOF, and HRMS). In all cases, the mo-
lecular ions (or the Ag+ complex) were obtained as the
main signals. No significant lack of thiophenylene arms were
observed, confirming full substitution. This was further sub-
stantiated by the symmetry observed in the 1H and
13C NMR spectra and the virtual absence of incomplete sub-
stitution products. Dendrons Dend-G1-SH or Dend-G2-SH
thylthiopyrene is
a
good organic p-conductor when
doped.[16,17]
The novelty of the present work is due both to the incor-
poration[18] of an uncommon tetrathiopyrene core into a
dendritic structure and to the presence of polysulfurated
dendrons containing thioether functions. These new features
lead to unprecedented photophysical, redox, and electro-
chromic properties useful for optoelectronic applications.
Scheme 1. Synthesis of polysulfurated pyrene dendrimers.
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Polysulfurated Pyrene-Cored Dendrimers
FULL PAPER
have already been described in the literature by one of our
group.[20] They were prepared in good overall yields on a
gram scale. 4-Methylbenzenethiol is commercially available.
Photophysical properties: Absorption spectra: The absorp-
tion spectra of compounds PyG0, PyG1, and PyG2 in di-
chloromethane solutions are shown in Figure 1, in which the
Figure 2. Emission spectra in cyclohexane (a) and in dichloromethane (b)
solution at 293 K of PyG0 (solid line), PyG1 (dashed line), and PyG2
(dashed-dotted line). lex =390 nm.
pyrene (Table 1). The energy separation between the two vi-
brational features (1400 cmÀ1) corresponds to a C=C aro-
matic vibration. The emission bands occur at slightly differ-
ent energies for the three dendrimers (Figure 2a), but they
exhibit the same quantum yield and the same lifetime
(Table 1). A remarkable difference compared to pyrene[21] is
that the excited state lifetime is so short that it is unaffected
by the presence of oxygen. A strong fluorescence is also ob-
served in a dichloromethane solution at 293 K (Figure 2b),
but in this solvent the fluorescence quantum yields and life-
times of PyG0 and PyG1 are somewhat lower than those of
PyG2 (Table 1). This result suggests the presence of a deac-
tivation path involving the solvent, which is prevented in
PyG2 by the shielding effect of the dendrons. In the rigid di-
chloromethane/chloroform 1:1 matrix at 77 K, the fluores-
cence band is blue-shifted by 15 nm compared to the solu-
tion spectrum, as expected for an excited state with some
charge-transfer character. There is no evidence of phosphor-
escence.
Figure 1. Absorption spectra of PyG0 (solid line), PyG1 (dashed line),
and PyG2 (dashed-dotted line) in dichloromethane solution at 293 K. For
comparison purposes the spectrum of pyrene (dotted line) is also shown.
spectrum of pyrene is also shown for comparison purposes.
The spectra of the dendrimers are quite different from that
of pyrene. The broad absorption band in the visible region
with a maximum at 435 nm, which is essentially the same for
the three dendrimers, can be straightforwardly assigned to
the pyrene core strongly perturbed by the four sulfur sub-
stituents. The band with a maximum around 260 nm, which
increases in intensity with the dendrimer generation, can be
assigned to the dendrimer branches. The displacement to
lower energy on increasing dendrimer generation and the
lack of simple correlation with the number of thiophenylene
units contained in the branches show that such chromophor-
ic groups do not behave independently from one another.
The strong fluorescence is present also in the solid state
(powder) as a broader band at lower energy (green emis-
sion) with the same lifetime. This result contrasts with the
behavior of pyrene, in which excimer formation strongly di-
minishes its emission quantum yield.
Emission spectra and lifetime: In cyclohexane solution at
293 K, the three dendrimers exhibit an intense fluorescence
band (Figure 2a), strongly red-shifted compared to that of
Fluorescence anisotropy: Fluorescent dendrimers often ex-
hibit fluorescence anisotropy.[22] In the case of dendrimers
with a fluorescent core, the only available depolarization
Table 1. Photophysical and electrochemical properties of the investigated compounds in deaerated solutions.
Absorption
dichloromethane
Emission
E1/2 [V] (vs. SCE)
dichloromethane
I II
Solvent
Compounds
cyclohexane
dichloromethane
lmax
[nm][a]
e
lmax
t
Fem
lmax
t
Fem
A
]
[nm]
[ns]
[nm]
[ns]
pyrene
PyG0
PyG1
PyG2
335
435
435
435
54000
39000
34000
36000
370
448
452
457
650
2.5
2.5
2.6
0.65
0.60
0.60
0.60
375
457
457
460
277
1.4
1.6
2.4
0.61
0.33
0.35
0.55
1.30
0.85
1.10
1.09
–
1.19
1.28
1.35
[a] Lowest energy band.
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10359

P. Ceroni, M. Gingras et al.
path is the rotation of the molecules during the excited state
lifetime.[23] In cyclohexane solution at 293 K, the anisotropy
value increases with dendrimer generation (0.04, 0.07, and
0.10 for PyG0, PyG1, and PyG2, respectively), as expected
because of the increase in dimension of the rotating species.
Redox behavior: We investigated the chemical and electro-
chemical oxidation of the three dendrimers in dichlorome-
thane solution.
À
Chemical oxidation: Titration of PyG0 with AuCl4 in di-
chloromethane solution causes strong changes in the absorp-
tion spectrum (Figure 3), namely the disappearance of the
Figure 4. Normalized emission intensity changes at 457 nm for PyG0 (cir-
cles), PyG1 (squares), and PyG2 (triangles) in dichloromethane solutions
upon titration with HAuCl4. lex =390 nm.
dination reaction with the sulfur units of the dendrimer
branches.
Electrochemical experiments: Cyclovoltammetric measure-
ments in dichloromethane solution with tetrabutylammoni-
um hexafluorophosphate (TBAPF6) as supporting electro-
lyte indicated that each dendrimer undergoes two consecu-
tive, reversible, one-electron oxidation processes followed
by another ill-defined irreversible process (Figure 5,
Table 1). Both the first and the second oxidation waves
move to more positive potentials on increasing dendrimer
generation.[24] They can be assigned to the perturbed pyrene
core, suggesting a stronger electron-donating character due
to the sulfur substituents.[16b] No evidence of decreasing het-
erogeneous electron-transfer rate with increasing dendron
size has been found.
Figure 3. Changes in the absorption spectra upon titration of a 3.3ꢂ
10À5 m dichloromethane solution of PyG0 with a 3.18ꢂ10À3 m acetonitrile
solution of HAuCl4. Solid curve: original solution of PyG0; dashed
curve: end of the titration (one-electron oxidation product).
band at 435 nm and the formation of a deep blue species
that exhibits a strong, structured, and narrow absorption
band with a maximum at 630 nm (e=72000 mÀ1 cmÀ1) and a
weaker and broader band with its maximum at 915 nm (e=
29000 mÀ1 cmÀ1). The changes in the absorption spectrum
are accompanied by the quenching of the dendrimer fluores-
cence. The oxidation reaction is quantitative for PyG0, as
shown by the complete fluorescence quenching (Figure 4).
The product obtained is the one-electron oxidation species
of the dendrimer, as shown by the electrochemical and spec-
troelectrochemical experiments described below. The ob-
served spectral changes show clearly that the oxidation pro-
cess involves the perturbed pyrene core.
Spectroelectrochemical experiments: The first one-electron
oxidation process leads to spectral changes (Figure 6) coinci-
À
dent with those observed on chemical oxidation with AuCl4
(Figure 3), that is, the disappearance of the core absorption
band with its maximum at 435 nm and the formation of a
very strong band at 630 nm and a weaker band at 915 nm.
The one-electron electrochemical oxidation is quantitative
for each one of the three dendrimers, contrary to what hap-
À
pens for the oxidation by AuCl4 (vide supra). The forma-
tion of the deep blue radical cation is fully reversible. Fur-
ther oxidation causes a decrease in the intensity of the 630
and 915 nm bands and the formation of a new, broader, and
lower intensity band with a maximum at 660 nm (Figure 6).
These spectral changes, which can be reversed by electro-
chemical reduction, can be assigned to a two-electron oxida-
tion product from the neutral, original dendrimer.
À
Titration of PyG1 and PyG2 with AuCl4 causes changes
in the absorption spectra and fluorescence intensity as in the
case of PyG0, but the oxidation reaction is not quantitative,
as shown by the fluorescence quenching plots in Figure 4.
Such different behavior of the two larger dendrimers can be
attributed to a competition for the added AuIII species be-
tween the redox reaction with the pyrene core and the coor-
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Polysulfurated Pyrene-Cored Dendrimers
FULL PAPER
Figure 6. Absorption spectra in dichloromethane solution of PyG0 (solid
curve) and its one-electron (dashed curve) and two-electron (dashed-
dotted curve) oxidation product.
cesses in dichloromethane solution. The first one-electron
oxidation process, which can also be performed using
À
AuCl4 as an oxidant, leads to the formation of a deep blue
radical cation. The photophysical and redox properties of
the three dendrimers are fine-tuned by the length of their
branches: 1) the dendron localized absorption band at
ꢀ260 nm increases strongly in intensity and moves slightly
to the red on increasing dendrimer generation; 2) in di-
chloromethane solution, the quantum yield and lifetime of
the fluorescence band and the values of the half-wave po-
tentials increase with dendrimer generation; 3) the dendri-
mer branches partially protect the core from oxidation by
À
AuCl4 . The strong blue fluorescence and the yellow to
deep blue color change upon reversible one-electron oxida-
tion might be exploited for optoelectronic and electrochro-
mic applications.
Experimental Section
Figure 5. Cyclic voltammetric curves for PyG0 (a), PyG1 (b), and PyG2
(c) in dichlorometane/TBAPF6 solution at 293 K. Scan rate=0.1 VsÀ1
Synthesis: General: 1H NMR (200.13 or 500.13 MHz) and 13C NMR
(50.32 or 125.77 MHz) spectra were recorded on Bruker instruments
AC200 or Avance500 respectively, in CDCl3 or DMSO-d6 (293 K, dried
over activated 4 ꢃ molecular sieves, chemical shifts (d) in ppm and cou-
pling constants (J) in Hz). Me4Si (0.00 ppm) served as an internal stan-
dard, or residual signals for CHCl3 (1H NMR, d=7.26 ppm; 13C NMR,
d=77,36 ppm) or DMSO (1H NMR, d=2.54 ppm; 13C NMR, d=
40,45 ppm). Mass spectra were recorded on an Ion-Trap ThermoFinnigan
LCQ (Thermo Electron) spectrometer using ESI mode (API: atmospher-
ic pressure ionization source, positive mode, ion-spray voltage 4.5–
5.0 kV; capillary temperature: 200–2508C) or EI mode (direct introduc-
tion, Automass probe (IPC), temperature range 60–3508C with
1008CminÀ1, max. 3 min). MALDI-TOF spectra were recorded on a
Bruker Reflex II and dithranol was used as a matrix (molar ratio of di-
thranol/sample was about 250:1). HRMS spectra were recorded on a
QStar Elite (Applied Biosystems SCIEX–API: atmospheric pressure ion-
ization source, positive mode, ion-spray voltage 5.5 kV). Melting points
(uncorrected) were determined in an open capillary with an Electrother-
mal 9100 apparatus (0.28CminÀ1). Microanalyses were performed at the
Spectropole de Marseille, France.
Conclusion
We have synthesized a new series of polysulfurated pyrene-
cored dendrimers PyG0, PyG1, and PyG2 (Scheme 1). They
exhibit remarkable photophysical and redox properties. In
cyclohexane solution they show a strong branch-localized
absorption band in the UV region, a core-localized absorp-
tion band in the visible region, and a strong core-localized
fluorescence band (lmax =460 nm, F=0.6, t=2.5 ns), even
in the presence of oxygen. Strong fluorescence is also exhib-
ited in dichloromethane solution at 293 K, in the rigid
matrix (CH2Cl2:CHCl3) at 77 K, and in the solid state at
room temperature. All the dendrimers undergo two succes-
sive one-electron reversible electrochemical oxidation pro-
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P. Ceroni, M. Gingras et al.
Chemicals: Aluminium TLC precoated silica gel plates from SDS 60F254
(15–60 mm) were used. Visualization: UV (254, 315, 365 nm), iodine-SiO2
CDCl3): d=8.65 (s, 4H; Pyr), 8.11 (s, 2H; Pyr), 7.16 (dapp
8.0 Hz, 32H; S-Ph-S), 7,03 (d, 3J
(H,H)=8.0 Hz, 32H; S-Ph-S), 6.82 (s,
, ACHTUNGTRENNUNG(H,H)=
3J
AHCTUNGTRENNUNG
12H), 6.71 (m, 24H), 2.28 ppm (s, 48H; CH3); 13C NMR (125.77 MHz,
CDCl3,): d=140.7, 139.2, 138.8, 138.5, 138.0, 133.8, 133.06, 130.6, 130.4,
129.9, 129.3, 129.2, 127.9, 126.8, 126.1, 21.6 ppm (CH3); MS (MALDI-
TOF, dithranol, THF): 3455 [M+H]+ (isotopic envelope); elemental
analysis calcd (%) for C200H154S28: C 69.52, H 4.49, S 25.98; found: C
69.56, H 4.53, S 26.21.
and/or
a
Ce/Mo developer (100 mL H2SO4, 900 mL H2O, 25 g
(SO4)2 - followed by heating). Column chro-
(NH4)6Mo7O24H2O, 10 g CeAHCTNUGTRENNNUG
matography purifications were achieved over silica gel 60 from SDS (40–
63 mm). Most reagents were purchased from Sigma-Aldrich or Acros Or-
ganics and used as received. DMF was dried over CaH2 overnight, dis-
tilled under reduced pressure and kept over freshly activated 3 ꢃ molec-
ular sieves (2508C for 3 h). Similarly, DMI was also kept over 3 ꢃ molec-
ular sieves. Powdered NaH (95%) was used as received. The synthesis of
some compounds has been reported previously: 1,3,6,8-tetrabromopyr-
ene,[19] Dend-G1-SMe,[20, 25] Dend-G1-SH,[20,24] Dend-G2-SMe,[20] Dend-
G2- SH.[20]
Photophysical experiments: The experiments were carried out in air-
equilibrated cyclohexane and dichloromethane solution at 298 K. Lumi-
nescence measurements at 77 K were performed in dichloromethane/
chloroform (1:1 v/v). UV/Vis absorption spectra were recorded with a
Perkin Elmer l40 spectrophotometer, using quartz cells with pathlength
of 1.0 cm. Fluorescence spectra were obtained with a Perkin Elmer LS-50
spectrofluorimeter, equipped with a Hamamatsu R928 phototube. The
estimated experimental errors are: 2 nm on the band maximum, 5% on
the molar absorption coefficient.
General procedure for pyrene dendrimers synthesis (PyG0, PyG1,
PyG2): The thiol (p-methylbenzenethiol, Dend-G1-SH or Dend-G2-SH
(4.58 equiv) and 1,3,6,8-tetrabromopyrene[12] (1.00 equiv) were weighed
in an oven-dried two-neck flask capped with septa. Under a flow of nitro-
gen, dry DMF or dry DMI (1,3-dimethyl-2-imidazolidinone) was added
using a syringe. NaH was weighed in a closed Gooch tube (U-shape) and
the latter was installed on the main flask after removing the septa. After
cooling in an ice-bath for a few minutes while stirring vigorously, NaH
was added carefully in small portions over a period of 5–10 mins, to con-
trol an effervescent and exothermic reaction. After release of the gas, the
mixture was stirred at 808C (oil bath temperature) for 24–60 h (1208C
for 30 h for PyG2). A color change was observed and a yellow precipitate
appeared over time (see separate procedure for PyG2, after this point).
The solid was collected and washed several times with ethanol, while stir-
ring vigorously each time for a few minutes. The final yellow solid was
collected and dried in vacuo for several hours.
Redox experiments: Cyclic voltammetric (CV) experiments were carried
out in argon-purged dichloromethane (Romil Hi-DryTM) solutions with
tetrabutylammonium hexafluorophosphate as supporting electrolyte at
room temperature with an Autolab 30 multipurpose instrument inter-
faced to a personal computer. The working electrode was a glassy carbon
electrode (0.08 cm2, Amel); its surface was routinely polished with
0.3 mm alumina-water slurry on a felt surface, immediately prior to use.
In all cases, the counter electrode was a Pt spiral, separated from the
bulk solution with a fine glass frit, and an Ag wire was used as a quasi-
reference electrode. Ferrocene (E1/2= +0.395 V vs. SCE) was present as
an internal standard.
Spectroelectrochemistry was performed in an optically transparent thin-
layer electrochemical (OTTLE) cell equipped with quartz windows, two
Pt minigrids as working and counter electrodes, and a silver wire as a
quasi-reference electrode. Prior to electrolysis, a thin-layer cyclic voltam-
mogram at a scan rate of 5 mVsÀ1 was recorded in order to choose the
proper electrolysis potential. Absorption spectra were recorded by an
Agilent Technologies 8543 diode array spectrophotometer.
PyG0: 4-Methylbenzenethiol (1.10 g, 8.87 mmol), 1,3,6,8-tetrabromopyr-
ene (1.00 g, 1.94 mmol), NaH (95%) (0.224 g, 9.33 mmol), DMI
(16.0 mL), temperature 808C for 60 h; PyG0 was obtained as a yellow
solid (1.205 g, 90%); m.p. 285–2888C; 1H NMR (200.13 MHz, CDCl3):
d=8.60 (s, 4H, Pyr), 7.87 (s, 2H, Pyr), 7.14 (dapp
,
3J
ACHTUNGTRENNUNG(H,H)=8.1 Hz, 8H; S-Ph-S), 2.32 ppm (s, 12H;
ACHTUNGTREN(NGNU H,H)=8.1 Hz, 8H,
S-PhS-), 7.03 (dapp
,
3J
CH3); 13C NMR (125.77 MHz, CDCl3): d=137.5, 134.2, 132.4, 132.0,
131.5, 130.6, 130.4, 126.1, 125.4, 21.5 ppm (CH3); MS (EI): m/z (%): 567.5
(9) [MÀCH3PhS], 690.3 (100) [M]+, 691.3 (50) [M+1]+, 692.3 (30)
[M+2]+, 693.3 (10) [M+3]+; HRMS (ESI, chem. ionization with AgOTf)
calcd for [C44H34S4
+
Ag+]: 799.0587 [M+Ag]+; found: 799.0565
Acknowledgements
[M+Ag]+; elemental analysis calcd (%) for C44H34S4: C 76.48, H 4.96, S
18.56; found: C 74.78, H 4.88, S 18.34.
We thank the Univ. de la Mꢀditerranꢀe (Marseille), the instrument
center Spectropole of Marseille, CNRS France. We acknowledge Dr. L.
Massi (mass spectrometry), Dr. H.-J. Raeder and Dr. A. Rouhanipour
(MALDI-TOF, Max Planck Institute for Polymer Research, Mainz, Ger-
many); Prof. A. Samat (Univ. de la Mꢀditerranꢀe), Dr. Y. M. Chabre
(UQAM, Montrꢀal), and Prof. R. Giasson (Univ. de Montrꢀal). This
work was funded by the France-Canada Funds (2000–2002) and by
MIUR (PRIN 2006034123_003) in Italy.
PyG1: Dend-G1-SH (3.15 g, 8.89 mmol), 1,3,6,8-tetrabromopyrene
(1.01 g, 1.95 mmol), solid NaH (purity 95%) (0.224 g, 9.33 mmol), DMF
(15.0 mL), bath temperature 808C for 26 h; the color changed from
orange to yellow; PyG1 was obtained as a yellow solid (2.20 g, 70%);
Rf =0.71 (petroleum ether in toluene, 70/30 v/v); m.p. 168–1718C;
1H NMR (200.13 MHz, CDCl3): d=8.54 (s, 4H; Pyr), 8.12 (s, 2H; Pyr),
7.11 (dapp, ACHTUNGTRENNUNG(H,H)=8,0 Hz, 16H; S-Ph-S), 6.86 (dapp, ACHUTNGTREG(NNNU H,H)=8.0 Hz,
3J 3J
16H; S-Ph-S), 6.77 (s, 4H), 6.67 (s, 8H), 2.78 ppm (s, 24H; CH3);
13C NMR (125.77 MHz, CDCl3): d=141.0, 138.8, 138.6, 133.8, 130.4,
129.8, 128.9, 126.7, 125.7, 125.5, 21.5 ppm (CH3); MS (ESI, chem. ioniza-
tion with AgOTf): m/z (%): 1611.3 (12) [M]+, 1719.2 (100) [M+Ag]+;
MS (MALDI-TOF, dithranol, THF): 1613.3 [M+H]+; HRMS (ESI,
chem. ionisation with AgOTf) calcd for [C96H74S12 + Ag+]: 1719.1469
[M+Ag]+; found: 1719.1494 [M+Ag]+; elemental analysis calcd (%) for
C96H74S12: C 71.51, H 4.63, S 23.86; found: C 69.55, H 4.51, S 23.57.
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PyG2: Dend-G2-SH (622 mg, 0.763 mmol), 1,3,6,8-tetrabromopyrene
(77.3 mg, 0.149 mmol), NaH (95%) (17.2 mg, 0.717 mmol), DMF
(1.5 mL), bath temperature 1208C for 3 h. After the mixture had been al-
lowed to cool, the orange solution was taken up in dichloromethane
(30 mL) and aqueous NaOH (30 mL, 1.0m). The aqueous solution was
discarded and the DCM phase was further washed with aqueous NaOH
(3ꢂ10 mL, 1.0m). After drying over anhydrous Na2SO4, filtration, and
evaporation of solvent, a yellow oil was obtained. Column chromatogra-
phy (SiO2, petroleum ether/toluene: 60/40 v/v), evaporation of solvents
and drying in vacuo afforded PyG2 (310 mg, 60%, yellow solid); Rf =
0.23 (toluene in petroleum ether, 40% v/v); 1H NMR (500.13 MHz,
10362
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ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 10357 – 10363

Polysulfurated Pyrene-Cored Dendrimers
FULL PAPER
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Received: June 18, 2008
Published online: October 8, 2008
Chem. Eur. J. 2008, 14, 10357 – 10363
ꢁ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10363