A rational design of catechol-based compounds: An experimental and theoretical study of optical properties

Article abstract of DOI:10.1002/chem.200802325

The synthesis and optical properties of 4,5-disubstituted (tert-butyldimethylsilyloxy)-protected catechol derivatives are reported. One or two carbon - carbon triple bond functions were introduced through the Sonogashira cross-coupling reaction. The effec

Full text of DOI:10.1002/chem.200802325

FULL PAPER
DOI: 10.1002/chem.200802325
A Rational Design of Catechol-Based Compounds: An Experimental and
Theoretical Study of Optical Properties
Christophe Aronica,[a] Anna Venancio-Marques,[a] Jꢀrꢁme Chauvin,[b]
Vincent Robert,*[a] and Gilles Lemercier*[a, c]
Abstract: The synthesis and optical
properties of 4,5-disubstituted (tert-bu-
tyldimethylsilyloxy)-protected catechol
derivatives are reported. One or two
these catechol derivatives with elec-
tron-withdrawing or -donating substitu-
ents have been investigated. The exper-
imental chemical-structure–polarisabili-
ty relationship has been studied by
using the Lippert–Mataga correlation
and compared with the results of a the-
oretical study carried out with DFT
calculations. These compounds are
promising candidates for the fine-
tuning of internal charge transfer, but
also as potential non-linear chromo-
phores and ligands within multifunc-
tional coordination complexes.
ꢀ
carbon carbon triple bond functions
were introduced through the Sonoga-
shira cross-coupling reaction. The ef-
fects on the optical properties of mono-
substitution at the 4-position or disub-
stitution at the 4- and 5-positions of
Keywords:
density functional calculations
charge transfer
·
·
luminescence · nonlinear optics ·
polarizability
Introduction
would be desirable. With this goal in mind, one may wonder
how much the natures and positions of different groups con-
trol the optical properties and more particularly the polaris-
abilities of a material. Part of the answer is to be found in
the modulation of the electron-transfer processes, which in-
volve the donor (D) and acceptor (A) partners. As shown,
for example, with substituted tetraethynylethenes,[3] the opti-
cal properties can be selectively varied by varying the substi-
tution pattern and the nature of the substituents around the
p-conjugated system. Thus, starting from a catecholate back-
bone, we contemplated the substitution of the 3- to 6-posi-
tions (see Scheme 1) with a view to generating disubstituted
derivatives that could then be used for further complexation
to a metal centre. Because our goal was to enhance the po-
larisabilities of a molecule for non-linear optical (NLO) ap-
plications, the design of molecules with large intramolecular
charge transfer through chemical engineering is favoured.
This can be achieved by concentrating on the 4- and 5-posi-
tions (see Scheme 1). At this stage, (D,D), (D,A) and (A,A)
pairs of substituents were considered as promising candi-
dates. Indeed, the (D,D) and (A,A) combinations should
allow for charge transfer (CT) between the catecholate posi-
tions and the substituents. On the other hand, (D,A) sub-
stituents are likely to favour inter-substituent CT. The
former candidates are expected to significantly modify the
electron distribution in the region of the catecholates. In
view of the chelating ability of such a motif, one can also an-
ticipate metal-to-ligand and ligand-to-metal charge transfer
The prevalence of intramolecular charge-transfer (ICT) in
organic molecules and related polymers[1] have motivated a
large number of studies in the field of optoelectronics, for
example, in electroluminescence devices (LEDs), thin-film
transistors, solar cells and optical storage devices.[2] These
compounds are commonly based on conjugated electron-
withdrawing and -donating groups linked through a p-conju-
gated system. To target specific properties and applications,
knowledge of a material’s structure–property relationship
[a] Dr. C. Aronica, A. Venancio-Marques, Dr. V. Robert,
Prof. G. Lemercier
Universitꢀ de Lyon, Laboratoire de Chimie, ENS-Lyon, CNRS
46, Allꢀe d’Italie, 69364 Lyon Cedex 07 (France)
Fax : (+33)472728860
E-mail: vincent.robert@ens-lyon.fr
[b] Dr. J. Chauvin
Universitꢀ Joseph Fourier, CNRS 5250, ICMG FR-2607
Dꢀpartement de Chimie Molꢀculaire, B.P. 5
38402 St Martin d’Hꢁres (France)
[c] Prof. G. Lemercier
Universitꢀ Reims Champagne-Ardenne, ICMR–UMR CNRS 6229
Groupe Chimie de Coordination
B.P. 1039, 51687 Reims Cedex 2 (France)
Fax : (+33)326913243
E-mail: gilles.lemercier@univ-reims.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802325.
Chem. Eur. J. 2009, 15, 5047 – 5055
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5047

catechols pCat-I-PENO2, pCat-
I-PENMe2, pCat-di-PEOMe
and pCat-di-PECF3 were ob-
tained by Sonogashira cross-
coupling reactions[4] starting
from 1 and 2 (1 equiv) or 3
(1 equiv) or
4 (2 equiv) and
commercially available 1-ethyn-
yl-4-trifluoromethylbenzene (5),
respectively, and starting from
compound pCat-I-PENO2 and
3 (1 equiv) or 4 (1 equiv) to
obtain
compounds
pCat-
PENO2-PENMe2 and pCat-
PENO2-PEOMe, respectively
(see Scheme 1).
The yields were quite poor
for
monosubstituted
com-
pounds pCat-I-PENO2 and
pCat-I-PENMe2 (around 20%,
also obtained with the disubsti-
tuted product) and ranged from
40 to 53% for the disubstituted
compounds
PENMe2,
pCat-PENO2-
pCat-PENO2-
PEOMe, pCat-di-PEOMe and
pCat-di-PECF3 (see the Experi-
mental Section).
Scheme 1. Synthesis and general atom numbering scheme, also used for NMR assignments (see Experimental
Section), of catechol compounds pCat-I-PENO2, pCat-I-PENMe2, pCat-PENO2-PENMe2, pCat-PENO2-
PEOMe, pCat-di-PEOMe2 and pCat-di-PECF3. TBDMS=tert-butyldimethylsilyl.
The electronic absorption
spectra of the compounds in
CH2Cl2 are shown in Figure 1.
(MLCT and LMCT, respectively). This is to be contrasted
with the use of a (D,A)-substituted ligand, which should
favour ILCT (intra-ligand CT) over MLCT and LMCT.
Therefore, the synthesis, characterisation and theoretical
analysis of these target systems should provide new insights
into the rational design of chromophores and NLO-phore
ligand-type materials. In this study, the tuning of the optical
properties of a novel class of 4,5-[(4-substituted-phenyl-
ethynyl)] TBDMS-protected catecholate molecules is re-
ported. Substitution of an electron donor and/or acceptor
group at the 4- and 5-position(s) gives rise to different CT
strengths and pathways within the chromophore. A correla-
tion between these optical properties and the structures is
suggested and complementary theoretical investigations per-
formed. Density functional theory has allowed the calcula-
tion of polarisabilities and offers a quantitative analysis of
the substituent effects.
Three types of bands are observed. 1) Bands at around
230 nm that depend slightly on the substituent. These can be
mainly attributed to p–p* electronic transitions centred on
the aromatic ring. 2) Lower-energy absorption bands lying
in the 280–420 nm spectral range (revealing a shoulder at a
higher wavelength), which may be mainly assigned to a
donor–acceptor CT. 3) A broad band between 420 and
500 nm (the longest-wavelength lmax) ascribed to the lower-
energy CT between the strongest donor (for example,
NMe2) and the acceptor (NO2). The low e values are consis-
tent with the less-effective non-linear-conjugated pathway
followed in this CT, which confirms the influence of the
nature of the substituents and their positions on the maxi-
mum absorption wavelengths and e values.
Interestingly, the pCat-PENO2-PENMe2 absorption spec-
trum is clearly very close to the arithmetic sum of the UV/
Vis absorption of compounds pCat-I-PENO2 and pCat-I-
PENMe2, except for the lowest-energy absorption band at-
tributed to a so-called “bent-conjugated pathway”,[5] which
also confirms that the energy of the CT optical band-gap is
further minimised in donor/acceptor-substituted compounds.
The absorption observed at 290 nm for the dimethoxy-
substituted compound (pCat-di-PEOMe) is red-shifted to
320 nm in the spectrum of the bis(dimethylamino) com-
pound (pCat-di-PENMe2) with a more efficient donor group
(see Figure 1a). The same red-shift is observed for pCat-di-
Results and Discussion
Synthesis: Compounds 1–3 (see Scheme 1), pCat-di-PENO2
and pCat-di-PENMe2 (Z=NO2 and NMe2, respectively, as
shown in Scheme 1) were prepared according to procedures
previously described in the literature (see the Experimental
Section for references). 4,5-Disubstituted TBDMS-protected
5048
www.chemeurj.org
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5047 – 5055

Design of Catechol-Based Compounds
FULL PAPER
Figure 2. UV/Vis spectra of compounds pCat-di-PENMe2 in several sol-
vents (the insert represents a normalised section of the spectra).
PENMe2 in relation to its absorption and emission proper-
ties are presented in Figures 2 and 4, respectively.
The CT bands display a positive solvatochromism, in
good agreement with the increase in the dipole moment
from the ground to the excited states (e.g., lmax for pCat-di-
PENMe2: cyclohexane, 315 nm; diethyl ether, 316 nm; ethyl
acetate, 318 nm; THF, 320 nm; dichloromethane, 322 nm;
CH3CN, 322 nm; DMSO, 328 nm). The UV/Vis spectra of
molecules possessing only donor or acceptor functionalities
usually lack CT transitions and display much reduced sol-
vent dependencies.
Fluorescence spectroscopy: Several of the examined com-
pounds showed fluorescence emission in solution at room
temperature, as summarised in Table 1, but no (or very
weak) emission was observed for the nitro-substituted com-
pounds. The use of CF3 is therefore interesting because it is
the only acceptor group that allows experimental analysis of
the luminescent properties. The luminescence spectra (dis-
played in Figure 3) exhibit broad bands centred at 370, 390
and 415 nm for compounds pCat-di-PEOMe, pCat-I-
Figure 1. UV/Vis spectra of a) compounds pCat-di-PEOMe, pCat-di-
PENMe2, pCat-di-PENO2 and pCat-di-PECF3, b) compounds pCat-I-
PENMe2, pCat-I-PENO2 and pCat-PENO2-PENMe2 and c) compounds
pCat-PENO2-PEOMe and pCat-PENO2-PENMe2 in dichloromethane.
Table 1. Absorption and emission properties of all the studied protected-
compounds at room temperature and in the THF.
Compounds
labs [nm] (e
[Lmolꢀ1 cmꢀ1]) [nm] shift
[cmꢀ1
]
lem
Stokes
F[a]
t[a]
[ns]
A
pCat-I-PENO2
pCat-I-PENMe2
pCat-PENO2-
PENMe2
pCat-PENO2-
PEOMe
355 (24275)
337 (47100)
338 (59560)
420 4359
418 5750
420 5776
<10ꢀ4 2.11
0.001
0.003
2.81
2.88
PECF3 and the dinitro analogue, which shows the intermedi-
ate character of the methoxy and trifluoromethyl substitu-
ents. It can also be seen in Figure 2 that this band is red-
shifted as the polarity of the solvent is increased. The largest
red-shift is observed for the dinitro compound pCat-di-
PENO2 due to the electron-donating character of the two
OTBDMS groups in the para positions.
A systematic study of the linear optical properties of
these compounds using different solvents has been accom-
plished. As an example, the results obtained for pCat-di-
307 (32200)
376 (10360)
290 (88000)
320 (42500)
329 (35000)
360 (29500)
322 (72760)
321 (20200)
543 8180
362 3626
2ꢃ10ꢀ4 0.71
pCat-di-PEOMe
0.15
1.26
pCat-di-PENO2
500 7778
415 6960
395 5900
0.001
0.21
0.14
0.59
2.63
2.03
pCat-di-PENMe2
pCat-di-PECF3
[a] In acetonitrile.
Chem. Eur. J. 2009, 15, 5047 – 5055
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5049

V. Robert, G. Lemercier et al.
cordance with a large delocalisation of the electronic density
from the PEOMe donor branch to the PENO2 acceptor one.
The Stokes shift has been plotted against the solvent
Reichardt ENT parameter[7] and its orientation polarisability
DfACHTNUTRGNEUNG(e,n) (see Figure 5a and b, respectively; see also Table 2
Figure 3. Normalised fluorescence emission of compounds pCat-di-
PEOMe, pCat-I-PENMe2, pCat-di-PECF3 and pCat-di-PENMe2 in di-
chloromethane.
PENMe2 and pCat-di-PENMe2, respectively. Maximum ab-
sorption and emission wavelengths, Stokes shifts (DnST, de-
fined as the loss of energy between the absorption and emis-
sion of light), quantum yields and excited-state lifetimes of
all the compounds are reported in Table 1. A strong fluores-
cence has already been observed for a similar catechol sub-
stituted with two pyridine groups,[6] which was attributed to
a p–p* transition. In our case, the dependence of the maxi-
mum emission wavelength on solvent polarity (see Figure 4
Figure 5. a) Plot of the Stokes shift (DnST) against the normalized Reich-
ardtꢄs ETN parameter. b) Correlation of the Stokes shift and the Lippert–
Mataga polarity parameter according to Equation (1) for compounds
&
^
*
pCat-di-PENMe2 ( ), pCat-di-PEOMe ( ) and pCat-di-PECF3 ( ) in the
seven solvents listed in Table 2 (R2 =0.93, 0.87 and 0.85 for compounds
pCat-di-PENMe2, pCat-di-PEOMe and pCat-di-PECF3, respectively).
Table 2. Relative permittivity (e) at 258C, refractive index (n), orienta-
tional polarisability (Df) and Reichardtꢄs ETN values of solvents.
Solvents
e258C
n2D0
Df
G
ETN
cyclohexane
diethyl ether
ethyl acetate
THF
dichloromethane
CH3CN
2.0
4.2
6.0
7.6
8.9
1.426
1.353
1.372
1.407
1.424
1.344
1.479
ꢀ0.00396
0.16223
0.19943
0.20987
0.21692
0.30459
0.26308
0.006
0.117
0.228
0.207
0.309
0.460
0.444
Figure 4. Emission spectra of compound pCat-di-PENMe2 in different
solvents.
35.9
46.4
DMSO
for compound pCat-di-PENMe2) suggests that the fluores-
cence properties are instead due to a CT-type excited state.
The photophysical properties of pCat-PENO2-PEOMe
and pCat-di-PENO2 are markedly different from the other
protected catecholates. The emission is dominated by a
broad and red-shifted band with a larger Stokes shift, a
lower quantum yield and a shorter emission lifetime.
These results suggest a larger rearrangement of the elec-
tronic distribution in the excited state of these structures
prior to relaxation. For pCat-PENO2-PEOMe, this is in ac-
for further details). The relationship between the Stokes
shift and the solvent polarity is usually given by the Lip-
pert–Mataga equation [Eq. (1)].[8] This correlation is the
equation most widely used to describe the effects of the
physical properties of the solvent on the emission spectra of
fluorophores. It has been used here to estimate the variation
(mCTꢀmg) in the dipole moment between the ground and the
excited states (polarisability) with a representing the value
of the Onsagar cavity radius in which the fluorophore re-
sides,[9] h is Planckꢄs constant, c is the speed of light, e0 is the
5050
www.chemeurj.org
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5047 – 5055

Design of Catechol-Based Compounds
FULL PAPER
vacuum permittivity and DfACTHNURGTNE(UNG e,n) is defined by Equation (2)
in which e is the static dielectric constant and n is the refrac-
tive index of the solvent.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
2
DnST ¼ Dn0ST
þ
ꢁ ðmCT ꢀ mgÞ ꢁ Dfðe; nÞ
ð1Þ
ð2Þ
ð4pe0Þðhca3Þ
e ꢀ 1
n2 ꢀ 1
Dfðe; nÞ ¼
ꢀ
2e þ 1 2n2 þ 1
The plots were linear for compounds pCat-di-PENMe2,
pCat-di-PEOMe and pCat-di-PECF3 with correlation factors
of R2 =0.93, 0.87 and 0.85, respectively (for the plots against
the ENT parameter), which suggests that dipole–dipole inter-
actions between the solute and solvent are mainly responsi-
ble for the solvent-dependent fluorescence shift.
On the basis of Equation (1) and by assuming that the
cavity radius a is comparable for compounds pCat-di-
PENMe2, pCat-di-PECF3 and pCat-di-PEOMe, the differ-
ence in the dipole moment between the ground and the ex-
cited states in solution is larger for the diamino compound
than for the trifluoromethyl- and methoxy-substituted ones.
With pCat-di-PEOMe as a reference (due to the homoge-
nous OR-type tetrasubstitution of the central aromatic
ring), the slope, which is proportional to (mCTꢀmg)2 according
to Equation (1), is 4.3- and 1.7-fold larger for pCat-di-
PENMe2 and pCat-di-PECF3, respectively. This indicates
that the polarisability should be larger for pCat-di-PENMe2
and that, as reported recently in the literature,[10] a higher
efficiency in non-linear optics may be expected. The emis-
sion lifetime decay of the compounds in deoxygenated
CH3CN, recorded at 480 nm after excitation at 400 nm, are
all mono-exponential. The emission decay times t (see
Table 1) of around a few nanoseconds are in good agree-
ment with a singlet excited-state emission.
Figure 6. X-ray structures of Cat-di-PENO2 and Cat-I-PENO2 after de-
protection (atom numbering for compound Cat-di-PENO2 is used in
Table 3).
Theoretical analysis: To support and rationalise our experi-
mental data, complementary calculations based on DFT
were performed. Our goal was to use a theoretical investiga-
tion to complement the experimental data obtained for
pCat-di-PENMe2, pCat-di-PEOMe and pCat-di-PECF3. Al-
though these compounds exhibit rather low polarisabilities,
(see Figure 5b, the Lippert–Mataga plot), the pCat-di-
PENMe2 system looks like a promising candidate for non-
linear optics applications.
In addition, the lack of experimental data on pCat-di-
PENO2 and pCat-PENO2-PENMe2 (which do not exhibit
any fluorescence under the experimental conditions used for
this study) strongly supports the need for complementary
theoretical inspections. How much the structures and combi-
X-ray structures: Single crystals of deprotected Cat-I-
PENO2 and Cat-di-PENO2 were obtained by slow evapora-
tion of methanol and diethyl ether, respectively, after depro-
tection of the silyl groups in a tetrabutylammonium fluoride
solution in THF.[11] On the molecular scale (Figure 6), Cat-I-
PENO2 is totally planar with all bonds having the expected
bond lengths.
The dinitro compound Cat-di-
PENO2 exhibits a small dihe-
dral C17-C5-C4-C9 angle (see
Table 3) and the two nitrophen-
yl fragments are twisted from
the catechol ring by 108, thus
the molecule exhibits an imper-
fect planarity. This particular
geometry may be caused by
steric interactions between the
hydrogen atoms of each substi-
tuted aromatic cycle.
Table 3. Geometric data extracted from X-ray analysis of pCat-di-PENO2 and DFT-optimised parameters of
pCat-di-PENO2 and pCat-di-PENMe2. The relative orientations of the NO2 groups and aryl rings are given.[a]
Optimised parameter
X-ray data
pCat-di-PENO2
pCat-di-PENMe2
C17-C5-C4-C9
(N13-O3-O4)/(C10-C12-C14)
1.75
8.00
3.11
0.34
3.39
1.19
A
8.66
0.31
1.16
9.02
19.44
15.61
16.63
1.23
21.56
17.46
17.48
1.23
G
10.48
10.51
1.17
(C17-C19-C21)/ACTHNUGTRNEUNG(C1-C3-C5)
ꢀ
C15 C16
ꢀ
C7 C8
1.19
1.23
1.23
[a] All angles are in 8 and distances in ꢅ.
Chem. Eur. J. 2009, 15, 5047 – 5055
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5051

V. Robert, G. Lemercier et al.
nations of donor and acceptor substituents compete in the
generation of high polarisabilities might be scrutinised on
the basis of ab initio calculations. First, a comparison was
made between available experimental structures and calcu-
lated ones to validate the optimisation procedure. To reduce
the computational cost, the OTBDMS groups were changed
to methoxy groups; such a modification is unlikely to signifi-
cantly modify the investigated properties (for convenience,
the same “protected” term and “pCat” abbreviation will be
used). Then we performed linear-response-type calculations
to evaluate the polarisabilities. Finally, the impact upon the
polarisabilities of the geometrical changes was estimated by
allowing substituent changes without performing geometry
optimisation.
The commonly accepted B3LYP (Becke–Lee–Yang–Parr)
exchange-correlation functional was used throughout the ge-
ometry optimisations and linear-response-type polarisability
calculations. Nevertheless, particular attention was paid to
the dependence of the optical properties on the basis set
used. In fact, it is known from the literature that sufficiently
large basis sets are recommended to evaluate polarisabili-
ties.[12] Such a procedure allows us to estimate the error bars
in the polarisability calculations. Thus, we used the following
strategy: First, full geometry optimisations of the disubstitut-
ed systems were carried out because the crystal structures
were not available. These DFT calculations were conducted
by using the B3LYP functional and the 6-311G basis set
available in the Gaussian 03 package.[13] Such a combination
of basis set and functional is known to produce very satisfac-
tory optimised geometries for organic molecules. The calcu-
lated structure of pCat-di-PENO2 is in good agreement with
our X-ray data. In particular, this (A,A) compound exhibits
a dihedral angle close to 38, as expected from experimental
diffraction data (1.88). Therefore, a similar procedure was
used for the whole series of compounds. The structural data
for pCat-di-PENO2 and pCat-di-PENMe2 are reported in
Table 3.
Figure 7. Theoretical values of the polarisabilities (in Bohr3) determined
by different quality basis sets.
Let us first concentrate on the polarisabilities calculated
for the protected pCat-di-PENO2, pCat-di-PECF3, pCat-di-
PEOMe and pCat-di-PENMe2 species by using the 6-311G
basis set. CF3 and MeO are known to be weak acceptor and
donor substituents, respectively. Therefore, the correspond-
ing systems display the lowest polarisabilities (ꢂ360 and
370 Bohr3, respectively) in the series. The significant en-
hancement observed for the pCat-di-PENMe2 compound
(410 Bohr3) is in good agreement with the increase in the
slope observed in Figure 5. As expected, the stronger donor
character of the NMe2 group relative to the methoxy group
leads to a significant change in the polarisability. Even
though experimental data for the pCat-di-PENO2 molecule
were not accessible, our calculations suggest that its polaris-
ability should be comparable (see Figure 7a). One may
therefore wonder why the (A,A) and (D,D) combinations
represented by the pCat-di-PENO2 and pCat-di-PENMe2
synthetic compounds induce similar polarisability values.
Part of the answer is to be found in the geometrical changes
that accompany the changes of the substituents. Thus, bear-
ing in mind that we are seeking to design molecules through
a chemical engineering approach, we investigated this par-
ticular issue by using the X-ray and geometry-optimised
structures obtained.
Based on these optimised geometries, polarisabilities were
also calculated by using different basis sets and the molecu-
lar orbitals (MOs) were analysed to clarify the origins of the
variations of the optical properties. The DFT-based polarisa-
bilities are shown in Figure 7a as a function of basis-set
quality. Even though it is traditionally accepted that 6-31G*
gives satisfactory estimates, we felt that a detailed inspection
of the basis-set dependence for this class of compounds
would be useful. As seen in Figure 7a, the variations in the
polarisabilities with the different basis sets are very similar
for the target molecules.
Not only do the parallel variations suggest that DFT cal-
culations anticipate the relative polarisabilities, but one can
also estimate the errors inherent in the numerical simula-
tions. Hence, a 12% variation is observed as the basis set is
modified. Let us stress that the calculations performed with
5052
www.chemeurj.org
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5047 – 5055

Design of Catechol-Based Compounds
FULL PAPER
more elaborate basis sets than 6-311+G remained out of
reach due to the relatively large size of the studied systems.
From this preliminary inspection, pCat-di-PENO2 and
particularly pCat-di-PENMe2 and pCat-PENO2-PENMe2
are observed to exhibit comparable polarisabilities
(ꢂ400 Bohr3). These values were calculated by using the
corresponding DFT-optimised structures. Thus, one may
wonder how sensitive the polarisability is to geometrical
changes. Because X-ray diffraction data are available for
Cat-di-PENO2, a comparison between the polarisabilities
obtained from 1) the X-ray data, 2) DFT-optimised data and
3) the optimised pCat-di-PENMe2 structure was performed
(see Figure 7b; the third value was determined by using the
optimised structure of pCat-di-PENMe2 to evaluate the in-
fluence of the geometrical changes ascribed to the substitu-
ents). A similar analysis was carried out for pCat-di-
PENMe2 for which X-ray data are not accessible (see Fig-
ure 7c). As seen in Figure 7b, the polarisability values are
very sensitive to geometrical changes. The X-ray and opti-
mised structures are very similar, but the corresponding po-
larisabilities differ by ꢂ60 Bohr3. A comparable difference
is noted for calculations performed by using the pCat-di-
PENMe2 optimised structure. This is clear evidence of the
important geometry dependency of the optical properties of
pCat-di-PENO2. This is to be contrasted with the behaviour
observed for pCat-di-PENMe2 c(Figure 7c). Whatever the
geometry (i.e., optimised pCat-di-PENMe2 or pCat-di-
PENO2), the polarisability of pCat-di-PENMe2 is in the
430 Bohr3 range. One may argue that the acceptor character
of the NO2 substituent enhances CT within the molecule be-
cause the OMe group (OTBDMS analogue in the theoreti-
cal study) has a donor character. In turn, geometrical
changes are likely to modify the polarisability. In particular,
for complexes involving the pCat-di-PENO2 deprotected an-
alogue as a ligand (Cat-di-PENO2), significant variations
can be anticipated. Conversely, the behaviour of the pCat-
di-PENMe2 molecule is different because the donor sub-
stituents NMe2 and the OTBDMS analogue compete and
reduce the sensitivity of the polarisability to geometrical
modifications.
Figure 8. HOMO and LUMO valence MO diagrams for compound pCat-
di-PENMe2, pCat-di-PENO2 and pCat-PENO2-PENMe2.
zoannuleno)benzenes,[5] the donor and acceptor substituents
tend to localise the disjoint frontier molecular orbitals
(FMOs) on the corresponding branches of the so-called
“cruciform”-type chromophores. Such compounds are
known to exhibit remarkable optical properties, which have
been studied, for instance, in diarylpyrazoline derivatives
and exploited as biological sensory frameworks.[15] Because
our compounds possess a “hemi-cruciform”-type structure,
the presented catechol-derivatives provide an insight into
CT behaviour.
Finally, the valence molecular orbitals HOMO and
LUMO were drawn to support the donor versus acceptor
characteristics of the substituents. As shown in Figure 8, the
LUMO has a strong NO2 moiety character in pCat-di-
PENO2 and pCat-PENO2-PENMe2. The electron flow
should be oriented towards NO2 (see the arrows in
Figure 8), in agreement with the substituent properties. As
expected, the NMe2 group exhibits donor characteristics be-
cause the HOMO in the pCat-PENO2-PENMe2 compound
is mostly localised on the NMe2 moiety and the intramolecu-
lar CT to the LUMO can be selectively controlled. Note
that the MeO substituent (introduced into the calculations
to replace the OTBDMS moiety) does not seem to be in-
volved in the CT in the pCat-PENO2-PENMe2 analogue
compound. As recently reported in the literature for dialkyl-
amino- and/or pyridine-containing functional chromo-
phores[14] and tetrakis(phenylethynyl)- or bis(dehydroben-
Conclusions
The synthesis and optical characteristics of NLO target mol-
ecules have been presented by following a chemical engi-
neering approach. As far as molecular polarisability is con-
cerned, it has been shown that their optical properties can
be fine-tuned by an optical property–structure correlation.
A low efficiency, red-shifted CT through a bent-conjugated
pathway has been identified and compared with a more effi-
cient linear-conjugated pathway. A theoretical study has
also been performed and the results compared favourably
with the experimental data. A systematic basis-set polarisa-
bility dependency was explored to validate the use of DFT/
B3LYP calculations as theoretical probes. These calculations
shed light on the crucial roles of structural and substituent
effects. Related polarisability values and NLO properties
were estimated. After the removal of the silyl-protecting
Chem. Eur. J. 2009, 15, 5047 – 5055
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5053

V. Robert, G. Lemercier et al.
(vw),
685 cmꢀ1
(m);
UV/Vis
(THF):
lmax
(e)=355 nm
groups, the use of these molecules as ligands within com-
plexes is under investigation and should lead to multifunc-
tional coordination complexes, merging magnetic and opti-
cal properties. Because these substituted catecholate di-
anions are good metal-binding candidates, this preliminary
study opens up new routes to multifunctional coordination
complexes involving non-innocent ligands.[16]
(24275 molꢀ1 dm3 cmꢀ1); HRMS: m/z calcd for C26H36Si2O4IN+Na+:
632.1125; found: 632.1120; elemental analysis calcd (%) for
C26H36Si2O4I1N1 (609.64): C 51.22, H 5.95, N 2.30; found: C 51.30, H 5.94,
N 2.18.
pCat-I-PENMe2: Compound 1 (1.70 mmol), [PdCl2ACHTUNTRGNEUNG(PPh3)2] (0.08 mmol),
CuI (0.21 mmol) in THF (20 mL), Et3N (10 mL) and 3 (1.70 mmol) gave
180 mg of a pale-yellow solid (18% yield); 1H NMR (200 MHz, CDCl3,
300 K): d=7.46 (AA’, 2H), 7.27 (s, 1H), 6.98 (s, 1H), 6.86 (BB’, 2H),
2.98 (s, 6H), 0.99 (s, 18H), 0.22 ppm (s, 12H); 13C NMR (50 MHz,
CDCl3, 300 K): d=150.2, 147.7, 147.1, 132.7, 130.8, 124.0, 123.6, 111.9,
110.0, 92.7, 90.5, 89.7, 40.3, 25.9, 18.5, ꢀ4.10 ppm; IR (KBr): n˜ =3093 (vw,
Experimental Section
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
aryl C H), 2954 (w, C H), 2929 (w, C H), 2893 (w, C H), 2858 (w, C
ꢃ
H), 2206 (vw, C C), 1608 (w), 1579 (w), 1523 (w), 1481 (s), 1383 (w),
General: All operations were performed under argon by using standard
Schlenk-line techniques. All reagents and 4 were purchased from com-
1360 (w), 1321 (vw), 1257 (s), 1190 (w), 1128 (vw), 995 (vw), 906 (vw),
881 (vw), 854 (w), 839(m), 814 (m), 783 (m), 712 (w), 532 (vw), 363 cmꢀ1
(m); UV/Vis (THF): lmax (e)=337 nm (47100 molꢀ1 dm3 cmꢀ1); HRMS:
m/z calcd for C28H43Si2O2I1N1 +H+: 608.1877; found: 608.1862; elemental
analysis calcd (%) for C28H42Si2O2IN·0.2CH2Cl2 (624.71): C 54.23, H 6.84,
N 2.24; found: C 54.44, H 6.93, N 2.11.
mercial sources and used as received. Compounds 1,[17] 2,[18] 3,[18] pCat-di-
[19]
PENO2 and pCat-di-PENMe2
were prepared according to literature
procedures.
1
Instrumental: H and 13C NMR spectra were recorded with a Bruker AC
200 FT NMR spectrometer. Elemental analyses were obtained from the
“Service Central d’Analyse de Vernaison—CNRS”. Infrared spectra were
recorded in the range of 4000–200 cmꢀ1 as KBr pellets with a Mattson
3000 spectrometer. UV/Vis spectra were recorded with a Jasco V-550
spectrophotometer using spectro grade solvents. The steady-state emis-
sion spectra were recorded with a Photon Technology International
(PTI) SE-900M spectrofluorimeter. All samples were prepared in a glove
box in deoxygenated CH2Cl2 and contained in 1 cm quartz cell. The sam-
ples were maintained in aerobic conditions with a Teflon cap. Emission
quantum yields fL were determined in deoxygenated CH3CN at 258C
after irradiation at 360 nm (except for pCat-PENO2-PEOMe for which
an excitation wavelength of 340 nm was used) and by using a solution of
anthracene in EtOH (ꢀLRef =0.27[20]) as a standard according to Equa-
tion (3) in which IL, the emission intensity, was calculated from the spec-
trum area sI(l)dl, OD represents the optical density at the excitation
wavelength, the superscripts “S” and “Ref” refer to the sample and the
standard, respectively, and n is the refractive index of the solvents. The
time-dependant emission experiments were performed after irradiation
at l=400 nm obtained by the second harmonic of a titanium:sapphire
laser (picosecond Tsunami laser spectra physics 3950-M1BB) at a 8 MHz
repetition rate. Fluotime 200 from AMS technologies was used for decay
acquisition. It consists of a GaAs microchannel plate photomultiplier
pCat-PENO2-PENMe2:
[PdCl2A(PPh3)2] (0.01 mmol) and CuI (0.02 mmol) in THF (10 mL) with
A mixture of pCat-I-PENO2 (0.30 mmol),
CTHUNGTRENNUNG
Et3N (5 mL) and 3 (0.43 mmol) yielded a pale-yellow solid (95 mg, 51%
yield); 1H NMR (200 MHz, CDCl3, 300 K): d=8.17 (AA’, 2H), 7.64
(BB’, 2H), 7.40 (AA’, 2H), 6.98 (s, 2H), 6.64 (BB’, 2H), 2.99 (s, 6H),
0.99 (s, 18H), 0.22 ppm (s, 12H); 13C NMR (50 MHz, CDCl3, 300 K): d=
150.2, 148.6, 147.0, 146.7, 133.7, 132.6, 132.1, 130.9, 124.1, 123.8, 121.2,
117.5, 111.9, 110.0, 94.6, 94.0, 90.1, 85.8, 40.2, 25.9, 18.5, ꢀ4.10 ppm; IR
ꢀ
ꢀ
ꢀ
(KBr): n˜ =3102 (vw, aryl C H), 2953 (w, C H), 2926 (w, C H), 2885 (w,
ꢀ
ꢀ
ꢃ
C H), 2856 (w, C H), 2205 (vw, C C), 1608 (w), 1588 (w), 1527 (s, NO2),
1356 (w), 1337 (s, NO2), 1251 (s), 1191 (w), 1133 (vw), 1080 (vw), 923
(vw), 838 (vw), 779 (w), 685 cmꢀ1 (m); UV/Vis (THF): lmax (e)=338 nm
(59560 molꢀ1 dm3 cmꢀ1); HRMS: m/z calcd for C36H46Si2O4N2 +H+:
627.3074; found: 627.3071; elemental analysis calcd (%) for
C36H46Si2O4N2 (626.93): C 68.97, H 7.40, N 4.47; found: C 68.97, H 7.29,
N 4.50.
pCat-PENO2-PEOMe: A mixture of pCat-I-PENO2 (0.30 mmol), [PdCl2-
AHCTUNGTRENNUNG
;
10-H), 7.46 (AA’, 2H), 6.98 (s, 2H; 3-H, 6-H), 6.87 (BB’, 2H), 2.99 (s,
3H), 0.99 (s, 18H), 0.22 ppm (s, 12H); 13C NMR (50 MHz, CDCl3,
300 K): d=159.8, 148.6, 147.4, 146.8, 132.9, 132.0, 130.7, 124.1, 124.0,
123.7, 120.5, 117.8, 115.4, 114.1, 113.7, 94.2, 92.6, 91.4, 86.5, 55.4, 25.9,
tube (Hamamatsu model R3809U-50) and
a time-correlated single-
photon counting system from picoquant (PicoHarp300). The ultimate
time resolution of the system was close to 40 ps. These measurements
were recorded using the technical support from the chemistry platform
“NanoBio Campus” in Grenoble (France).
ꢀ
ꢀ
18.5, ꢀ4.01 ppm; IR (KBr): n˜ =3116 (vw, aryl C H), 2954 (w, C H),
ꢀ
ꢀ
ꢀ
ꢃ
2927 (w, C H), 2895 (w, C H), 2856 (w, C H), 2208 (vw, C C), 1590
(w), 1513 (s, NO2), 1406 (w), 1340 (s, NO2), 1247 (s), 1172 (w), 1083 (vw),
1028 (vw), 926 (vw), 837 (vw), 785 (w), 684 cmꢀ1 (m); UV/Vis (THF):
lmax (e)=307 (32200), 376 nm (10360 molꢀ1 dm3 cmꢀ1); HRMS: m/z calcd
for C35H43Si2O5N+Na+: 636.2578; found: 636.2556; elemental analysis
calcd (%) for C35H43Si2O5N (613.89): C 68.48, H 7.06, N 2.28; found: C
68.47, H 7.07, N 2.06.
Ref
ILSð1 ꢀ 10ꢀOD Þ n2S
FLS
¼
FRLef
ð3Þ
S
ILRefð1 ꢀ 10ꢀOD Þ nR2 ef
Typical general synthetic procedure for compounds Cat-I-PEX (X=NO2,
NMe2), Cat- PENO2-PEY (Y=NMe2, OMe) and Cat-di-PEY (Y=OMe,
CF3): Compound 2 (0.5 g, 3.40 mmol) was added to a mixture of 1 (2 g,
pCat-di-PEOMe: A mixture of 1 (1 mmol), [PdCl
2ACHTUNGTRENN(NUG PPh3)2] (0.14 mmol)
and CuI (0.32 mmol) in THF (15 mL) with Et3N (7.5 mL) and
4
3.39 mmol), [PdCl2ACHTUNGTRENNUNG(PPh3)2] (0.12 g, 0.17 mmol) and CuI (0.08 g,
(2.2 mmol) yielded a pale-yellow solid (382 mg, 46% yield); 1H NMR
(200 MHz, CDCl3, 300 K): d=7.47 (AA’, 2H), 6.96 (s, 2H), 6.84 (BB’,
2H), 3.81 (s, 6H), 0.98 (s, 18H), 0.22 ppm (s, 12H); 13C NMR (50 MHz,
CDCl3, 300 K): d=159.5, 147.3, 134.0, 133.6, 123.8, 119.6, 114.0, 91.9,
0.42 mmol) in THF (100 mL) and Et3N (50 mL). The black solution was
heated at 408C for 1.5 h (2 h for Cat-di-PECF3), cooled to room tempera-
ture and the solvent was evaporated under vacuum. The remaining black
solid was purified by chromatography on silica gel (dichloromethane/pe-
troleum ether, 2:3—except for Cat-I-PENO2, 1:3).
ꢀ
87.1, 55.3, 25.9, 18.5, ꢀ4.10 ppm; IR (KBr): n˜ =3005 (vw, aryl C H), 2952
ꢀ
ꢀ
ꢀ
ꢀ
ꢃ
(w, C H), 2929 (w, C H), 2896 (w, C H), 2858 (w, C H), 2208 (vw, C
C), 1604 (w), 1515 (s, NO2), 1493 (w), 1353 (w), 1294 (vw), 1254 (s, NO2),
1171 (w), 1030 (vw), 931 (vw), 842 (vw), 825 (vw), 785 cmꢀ1 (w); UV/Vis
(THF): lmax (e)=290 nm (88000), 320 (42500 molꢀ1 dm3 cmꢀ1); HRMS:
m/z calcd for C36H46Si2O4 +Na+: 621.2832; found: 621.283; elemental
analysis calcd for C36H46Si2O4 (598.9): C 72.19, H 7.74; found: C 72.26, H
7.46.
pCat-I-PENO2: Obtained as a pale-yellow solid (400 mg, 20% yield).
1H NMR (200 MHz, CDCl3, 300 K): d=8.20 (AA’, 2H), 7.69 (BB’, 2H),
7.25 (s, 1H), 6.99 (s, 1H), 0.98 (s, 18H), 0.22 ppm (s, 12H); 13C NMR
(50 MHz, CDCl3, 300 K): d=149.3, 147.3, 147.0, 132.1, 131.0, 130.3, 124.7,
123.7, 121.4, 97.0, 90.9, 89.4, 25.8, 18.5, ꢀ4.10 ppm; IR (KBr): n˜ =3112
ꢀ
ꢀ
ꢀ
ꢀ
(vw, aryl C H), 2956 (w, C H), 2929 (w, C H), 2885 (w, C H), 2858 (w,
ꢀ
ꢃ
C H), 2208 (vw, C C), 1593 (w), 1577 (w), 1537 (w), 1514 (s, NO2), 1494
(w), 1479 (w), 1386 (vw), 1340 (s, NO2), 1324 (w), 1257 (vw), 1332 (vw),
1105 (vw), 998 (vw), 916 (w), 885(m), 864 (m), 849 (m), 785 (w), 750
pCat-di-PECF3: A mixture of 1 (2.9 mmol), [PdCl2CAHTUNGERTN(NUNG PPh3)2] (0.57 mmol)
and CuI (1.05 mmol) in THF (70 mL) with Et3N (35 mL) and
5
5054
www.chemeurj.org
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5047 – 5055

Design of Catechol-Based Compounds
FULL PAPER
(6.1 mmol) yielded a pale-yellow solid (1.02 g, 53% yield); 1H NMR
(200 MHz, CDCl3, 300 K): d=7.60 (s, 8H), 7.02 (s, 2H), 1.01 (s, 18H),
0.26 ppm (s, 12H); 13C NMR (50 MHz, CDCl3, 300 K): d=148.2, 131.6,
130.3, 126.6, 125.3, 125.2, 121.2, 118.9, 90.8, 90.5, 25.9, 18.5, ꢀ4.10 ppm;
[8] a) N. Mataga, Bull. Chem. Soc. Jpn. 1963, 36, 654–659; b) J. R. La-
kowicz, Principles of Fluorescence Spectroscopy, Plenum Press, New
York, 1983.
[9] The simplest method for estimating the cavity radius is to assume
1
=
IR (KBr): n˜ =2214 cmꢀ1 (vw, C C); UV/Vis (THF): lmax (e)=321 nm
a=(3V/4p) , in which V is the volume of the solute.
3
ꢃ
(20200 molꢀ1 dm3 cmꢀ1); HRMS: m/z calcd for C36H40Si2O2F6 +Na+:
697.2369; found: 697.2368; elemental analysis calcd (%) for C36H46Si2O4
(598.9): C 64.1, H 5.97; found: C 63.8, H 5.90.
[10] F. Terenziani, C. Le Droumaguet, C. Katan, O. Mongin, M. Blan-
chard-Desce, ChemPhysChem 2007, 8, 723–734.
[11] CCDC-706650 and 706651 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[12] P. J. P. de Oliveira, F. E. Jorge, Chem. Phys. Lett. 2008, 463, 235–239.
[13] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
Acknowledgements
AHCTUNGERTGeNNUN ry, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millan, S. S. Iyen-
The authors thank the “Centre de Diffractomꢀtrie H. Longchambon” of
the University of Lyon for use of its X-ray diffraction facilities.
gar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adano, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford CT, 2004.
[1] a) J. H. Burroughes, D. D. C. Radley, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burns, A. B. Holmes, Nature 1990, 347,
539–541; b) R. H. Friends, R. W. Gymer, A. B. Holmes, J. H. Bur-
roughes, R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos,
J. L. Brꢀdas, M. Lçgdlund, W. R. Salaneck, Nature 1999, 397, 992–
996; c) T.-C. Chao, Y.-T. Lin, C.-Y. Yang, T. Shi Hung, H.-C. Chou,
C.-C. Wu, K.-T. Wong, Adv. Mater. 2005, 17, 992–996; d) S. W. Tho-
mas III, G. D. Joly, T. M. Swager, Chem. Rev. 2007, 107, 1339–1386.
[2] a) Special Issue: Chem. Rev. 1994, 94, 1–278; b) J. Cornil, D. Bel-
jonne, J.-P. Calbert, J.-L. Brꢀdas, Adv. Mater. 2001, 13, 1053–1067;
c) Special Issue: Chem. Mater. 2004, 16, 4381–4846.
[3] a) R. R. Tykiwinski, M. Schreiber, V. Gramlich, P. Seiler, F. Dieder-
ich, Adv. Mater. 1996, 8, 226–231; b) C. Bosshard, R. Spreiter, P.
Gꢆnter, R. R. Tykwinski, M. Shreiber, F. Diederich, Adv. Mater.
1996, 8, 231–234.
[14] A. J. Zucchero, J. N. Wilson, U. H. F. Bunz, J. Am. Chem. Soc. 2006,
128, 11872–11881.
[15] C. J. Fahmi, L. Yang, D. G. Vanderveer, J. Am. Chem. Soc. 2003,
125, 3799–3812.
[4] K. Sonogashira in Metal-Catalyzed Cross-Coupling Reactions (Eds.:
F. Diederich, P. J. Stang) Wiley-VCH, Weinheim, 1998, pp. 203–230.
[5] J. A. Marsden, J. J. Miller, L. D. Shirtcliff, M. M. Haley, J. Am.
Chem. Soc. 2005, 127, 2464–2476.
[6] a) S. Shotwell, P. Windscheif, M. Smith, U. Bunz, Org. Lett. 2004, 6,
4151–4154; b) M. G. Lauer, J. W. Leslie, A. Mynar, S. A. Stamper,
A. D. Martinez, A. J. Bray, S. Negassi, K. McDonald, E. Ferraris, A.
Muzny, S. McAvoy, C. P. Miller, K. A. Walters, K. C. Russell, J. Org.
Chem. 2008, 73, 474–484.
[16] E. Evangelio, D. Ruiz-Molina, Eur. J. Inorg. Chem. 2005, 2957–
2971.
[17] J. D. Kinder, W. J. Youngs, Organometallics 1996, 15, 460–463.
[18] S. Takahashi, Y. Kuroyama, K. Sonogashira, N. Hagihara, Synthesis
1980, 628–630.
[19] V. Kriegisch, C. Lambert, Eur. J. Inorg. Chem. 2005, 4509–4515.
[20] W. R. Dawson, M. W. Windsor, J. Phys. Chem. 1968, 72, 3251–3260.
Received: November 8, 2008
[7] C. Reichardt, Chem. Rev. 1994, 94, 2319–2358.
Published online: March 31, 2009
Chem. Eur. J. 2009, 15, 5047 – 5055
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5055