Design of new fluorinated bridged push-pull stilbenes and preparation of LB films for second harmonic generation in the blue domain

Article abstract of DOI:10.1039/b005056n

In order to prepare alternating Y-type multilayers involving push-pull stilbenes giving second harmonic generation (SHG) in the blue domain, we have synthesized two new bridged compounds, 1 and 2, with the hydrophobic chain grafted onto the donor group. The photophysical properties of these dyes in both solution and LB films are reported. The SHG signal of monolayer LB films containing 1 and 2 are close to that of the analog 3 and 4 having the hydrophobic chain grafted onto the acceptor group. Finally, multilayer LB films based on one, two and four bilayers of 1/3 or 2/4 were prepared and the SHG measurements show a regular noncentrosymmetric arrangement for 2/4 films only.

Full text of DOI:10.1039/b005056n

View Article Online / Journal Homepage / Table of Contents for this issue
Design of new Ñuorinated bridged push–pull stilbenes and preparation
of LB Ðlms for second harmonic generation in the blue domain¤
Stephanie Desrousseaux,a Bernard Bennetau,a Jean-Pierre Morand,b Christophe Mingotaud,c
Jean-Francois Letard,*d Sebastien Montante and Eric Freysze
a L aboratoire de Chimie Organique et Organometallique (CNRS UMR 5802), Universite de
Bordeaux I, 351 Cours de la L iberation, F-33405 T alence cedex, France
b L aboratoire dÏAnalyse Chimique par Reconnaissance Moleculaire, Ecole Nationale Superieure
de Chimie et de Physique de Bordeaux, Av. Pey-Berland BP 108, F-33402 T alence, France
c Centre de Recherche Paul Pascal, Av. du Docteur A. Schweitzer, F-33600 Pessac, France
d L aboratoire des Sciences Moleculaires, Institut de Chimie de la Matiere Condensee de Bordeaux
(CNRS UPR 9048), Universite de Bordeaux I, Av. du Docteur A. Schweitzer, F-33608 Pessac,
France. E-mail: L etard=chimsol.icmcb.u-bordeaux.fr
e Centre de Physique Moleculaire Optique et Hertzienne (CNRS UMR 5798), Universite de
Bordeaux I, 351 Cours de la L iberation, F-33405 T alence, France
Received (in Montpellier, France) 22nd June 2000, Accepted 9th October 2000
First published as an Advance Article on the web 21st November 2000
In order to prepare alternating Y-type multilayers involving pushÈpull stilbenes giving second harmonic generation
(SHG) in the blue domain, we have synthesized two new bridged compounds, 1 and 2, with the hydrophobic chain
grafted onto the donor group. The photophysical properties of these dyes in both solution and LB Ðlms are
reported. The SHG signal of monolayer LB Ðlms containing 1 and 2 are close to that of the analog 3 and 4 having
the hydrophobic chain grafted onto the acceptor group. Finally, multilayer LB Ðlms based on one, two and four
bilayers of 1/3 or 2/4 were prepared and the SHG measurements show a regular noncentrosymmetric arrangement
for 2/4 Ðlms only.
During the last few decades the potential development of
optoelectronic devices, based on nonlinear optical processes
induced in molecular materials, has attracted considerable
attention.1h5 It is now well-known that organic materials
exhibit higher efficiency than inorganic compounds as far as
second-order nonlinear optical (SONLO) properties are con-
cerned. Moreover, in addition to the wide range of active mol-
ecules, the processability of such materials is considerably
improved, making them all the more attractive.4h6
membered ring in order to reduce photochemical processes.17
The hydrophobic long perÑuoroalkyl (ÈC F ) chain was
8 17
selected because of its self-assembling property, observed
when the perÑuoroalkyl chain is longer than heptane.18
On the basis of a two-state model,1 it has been suggested
and experimentally conÐrmed that conjugated systems substi-
tuted by donorÈacceptor groups exhibit large optical
responses. In the blue spectral region, the pushÈpull stilbenes
represent an important class of Ñuorescent dyes.7,8 The photo-
physical and photochemical properties of these compounds
are very appealing because of their particularly strong charge
transfer in the excited state.9,10 Nevertheless, increasing the
strength of the donorÈacceptor groups induces a red-shift of
the absorption spectrum7 and therefore limits the applications
in the blue domain. Ulman et al.8 showed that a ÈSO È group,
2
which is a strong r-acceptor, induces a lower absorption red-
shift than the p-acceptor ÈNO group, despite similar p and
2
p
p~ values.11 In addition, the ability of stilbene molecules to
form H-aggregates in LangmuirÈBlodgett (LB) Ðlms,12,13
which are characterized by a hypsochromic absorption shift,14
emphasises the interest in such sulfonyl stilbenes as good can-
didates for SONLO response in the blue domain. Along these
lines, Le Breton et al.15,16 have synthesized some bridged
derivatives of polyphilic stilbenes (3 and 4, see Fig. 1). The
central double bond has been incorporated into a Ðve-
Fig. 1 Molecular structure of 1È4: 1 \ 4-M6-[ethyl(1H,1H,2H,2H-
perÑuorooctyl)amino]benzofuran-2-ylNbenzoic acid ethyl ester;
2 \ 2-M4-[methyl(1H,1H,2H,2H-perÑuorooctyl)amino]phenylN-1H-
indole-6-carboxylic acid ethyl ester; 3 \ 2-(4@-heptadecaÑuorooctyl-
sulfonylphenyl)-6-(N,N-dimethyl)aminobenzofuran and 4 \ 2-[4@-(N,
N-dimethyl)aminophenyl]-6-heptadecaÑuorooctylsulfonylindole.
¤ This paper is dedicated to the memory of Olivier Kahn.
DOI: 10.1039/b005056n
New J. Chem., 2000, 24, 977È985
977
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2000

View Article Online
Fig. 2 Display of X- and Z-type structures of LB multilayers ((a) and
(b)). Alternating layers of 1È4 molecules when deposited in a Y-type
conÐguration (c).
Monolayer LB Ðlms of 3 and 4 have been prepared and the
SONLO response from the surface set-up gave a molecular
quadratic hyperpolarizability b of 200 ] 10~30 esu.16
The LB technique is a widely developed method for build-
ing ordered arrays of molecules, in particular as a means of
imposing the non-centrosymmetric structure necessary to the
generation of a second harmonic response at the macroscopic
level. Nevertheless, most compounds adopt centrosymmetric
head-to-head or tail-to-tail arrangements (Fig. 2). It is neces-
sary to alternate the optically active layers with inactive
spacers,19 or to include interdigitating arrangements20,21 or to
depose two di†erent active molecules.22 Each species is alter-
nating deposited, the hydrophobic chain being grafted onto
the acceptor of the Ðrst species (DIR) and the donor group of
the second species (INV). The nonlinear susceptibility
resulting from the addition of the individual nonlinearities of
each monolayer is expected to be quite large, with the addi-
tional advantage of a high degree of order and a better stabil-
ity of the structure.
In this work, we describe the preparation of alternating
Y-type multilayers involving pushÈpull stilbenes with second
harmonic generation in the blue domain. We present the syn-
thesis of two new bridged stilbenes, 1 and 2 (Fig. 1), which are
the analogs of 3 and 4 having the hydrophobic chain grafted
onto the donor group. The photophysical properties of 1 and
2 were studied both in solution and in LB Ðlms. The SONLO
responses using SHG-surface technique are Ðrstly reported for
LB Ðlms containing only the 1 and 2 dyes. Alternating layers
of 1/3 and 2/4 were also prepared and their SONLO proper-
ties are described.
Results and discussion
Synthesis of compounds 1 and 2
1 and 2 are two new polyphilic compounds with an ester
hydrophilic head, a stilbene rigid core and a hydrophobic
Ñuorinated chain. In these molecules, the central double bond
is incorporated in a Ðve-membered ring in order to prevent
transÈcis photoisomerization.15h17 A spacer containing two
carbon atoms is introduced between the perÑuorinated chain
and the amino group in order to reduce the inÑuence of the
electronic e†ect of Ñuorine atoms on the donor capacity of the
nitrogen atom. The weak acceptor ester group is selected in
order to obtain a good transparency in the blue domain.
Scheme 1 Route followed for the synthesis of 1.
formulated at the para position to the amino group with N,N-
dimethylformamide and phosphorus oxychloride; this
VilsmeierÈHaack reaction23,24 a†orded the aldehyde 9. Par-
ticular experimental conditions (see Experimental) prevented
the formation of the product diformylated at the para posi-
tions to the amino and hydroxyl groups. Starting from com-
pound 10, the withdrawing moiety of dye 1 was obtained by
radical benzylic bromination with N-bromosuccinimide to
yield the brominated ester 11 as the major product of the
reaction. An ether bridge was then created between the donat-
ing 9 and the withdrawing 11 moieties by nucleophilic substi-
tution under basic conditions.25 Benzofuran derivative 1 was
Ðnally obtained by an intramolecular Knoevenagel reaction
on 12 using alumina-supported potassium Ñuoride;26 in spite
of the strong character of this base, anhydrous conditions pre-
vented the hydrolysis of the ester function.
1 was synthesized according to the multi-step pathway
described on Scheme 1. Both the perÑuorinated chain and the
spacer were introduced on the donating moiety during the
Ðrst step by nucleophilic substitution between C F (CH ) I
6 13
2 2
and m-anisidin 5, an excess of this amine leading to the sec-
ondary amine 6 as the only substituted product. The tertiary
amine 7 was synthesized by ethylation of 6 under basic condi-
tions. The hydroxyl group of 8 was released by the deprotec-
tion method using BBr in dichloromethane; 2 equiv. of BBr
3
3
were necessary because boron atoms complex both oxygen
The synthesis of 2 was performed following the pathway
shown on Scheme 2. The introduction of the Ñuorinated
and nitrogen. The amino phenol compound 8 was mono-
978
New J. Chem., 2000, 24, 977È985

View Article Online
18 with an excess of thionyl chloride and then performing an
alcoholysis with absolute ethanol. Compound 19 was after-
ward submitted to a radical benzylic bromination with N-
bromosuccinimide to give the brominated ester derivative 20
as the major product. Finally, the phosphonium salt 21 was
obtained by reaction between triphenylphosphine and the
bromobenzyl derivative 20. The trans-stilbene 22 was obtained
by a Wittig reaction28 involving the donating 16 and the with-
drawing 21 moieties under basic conditions. The indolic deriv-
ative 2 was obtained in the last step by cyclization of the
stilbene with an excess of triethyl phosphite, probably accord-
ing to a mechanism described by Sundberg.29
Absorption and emission properties in solution
The absorption maxima measured in solvents of increasing
polarity are reported in Table 1. A small bathochromic shift of
the longest wavelength band is observed from n-hexane to
acetonitrile, suggesting that the FranckÈCondon electronic
excitation involves a relatively small charge transfer. It is
worth noting that even in polar solvent the absorption
maxima never exceed 390 nm for 1 and 362 nm for 2. This
result is important for designing SONLO materials in the blue
domain.
The Ñuorescence maxima are reported in Table 1 as a func-
tion of the solvent polarity. Fig. 3 shows the Ñuorescence
spectra of
2 in n-hexane, diethyl ether and dimethyl-
formamide. In nonpolar solvents the spectra are structured. In
mildly and strongly polar solvents (for 2) and in polar solvents
only (for 1) the spectra are structureless. The position of the
Ñuorescence maxima (jmax) is strongly red-shifted from n-
fluo
hexane to acetonitrile, indicating a larger dipole moment in
the excited state than in the ground state. The dipole moment
of the excited state (k ) can be determined by the solvatochro-
e
mic method. The equations to calculate k were Ðrst derived
e
by Ooshika,30 Lippert,31 Liptay32 and Mataga et al.33 All are
Scheme 2 Route followed for the synthesis of 2.
hydrophobic tail was realized as described for the preparation
of compound 6, using aniline 1327 as the nucleophilic reagent
instead of m-anisidin 5. The secondary amine 14 was then
methylated under basic conditions to give the tertiary amine
15. The donating moiety 16 was Ðnally obtained by for-
mylation at the para position using the VilsmeierÈHaack reac-
tion. Starting from the disubstituted benzoic acid 17, the
withdrawing moiety of 2 was synthesized according to the fol-
lowing procedure. The ester derivative 19 was obtained in a
one-pot reaction by Ðrst forming the acid chloride compound
Fig. 3 Normalized Ñuorescence spectra of 2 at room temperature in
n-hexane (*f @ \ 0.092), diethyl ether (Et O, *f @ \ 0.256) and
2
dimethylformamide (DMF, *f @ \ 0.378).
Table 1 Absorption (jmax) and Ñuorescence (jmax) maxima, Ñuorescence quantum yields (/ ), lifetimes (q ) and radiative (k ) and non-radiative
abs
fluo
f
f
f
(k ) rate constants in solvents of di†erent polarity at room temperature
nr
Compound
Solvent
jmax/nm
jmax/nm
/
q /ns
k /109 s~1
k /107 s~1
abs
fluo
f
f
f
nr
1
n-Hexane
369
374
374
382
390
384
347
352
351
355
362
356
398
451
444.5
479
525
524
370
389
386
410
440
440
0.39
0.32
0.44
0.32
0.42
0.44
0.38
0.42
0.47
0.54
0.47
0.47
BuOMe
EtO
THF
2
0.2
25
2
DMF
CH CN
2.8
1.2
0.2
0.3
25
49
3
2
n-Hexane
BuOMe
EtO
THF
1.3
0.4
45
2
DMF
CH CN
1.6
0.3
34
3
New J. Chem., 2000, 24, 977È985
979

View Article Online
based on the Onsager description of a solute-induced reaction
Ðeld inside a spherical solvent cavity of radius o.34 This
parameter is estimated from the molecular volume calculated
from the molecular weight and density of ethyl benzoate
(1.051 g cm~3). With the usual assumptions,35,36 the excited
Ñuorescence quenching (state P*) and therefore raises the Ñuo-
rescence quantum yield.40 When the central double bond is
chemically bridged in a Ðve-membered ring40 the P* state is
not available. In bis-donor stilbenes, the quantum yield of
Ñuorescence remains high whatever the solvent polarity.42 In
pushÈpull stilbenes with a strong acceptor group, like a
nitro43 or a pyridinium ion,44,45 the Ñuorescence quantum
yield falls in polar solvents as a result of TICT state formation
with non-emissive character. For 3 and 4 bearing a strong
state dipole moment (k ) is given by eqn. (1):
e
lmax \ [2k (k [ k )*f @/hco3 ] Const
(1)
fluo
e
e
g
The polarity parameter *f @ is deÐned by [(e [ 1)/(2
e ] 1)] [ 0.5[(n2 [ 1)/(2n2 ] 1)] where e and n are the dielec-
tric constant and the optical refractive index, respectively. The
solvatochromic slopes determined by the plot of Ñuorescence
acceptor substituent (ÈSO C F ), we e†ectively demonstrated
2 8 17
the presence of a non-emissive TICT state in polar solvent
and then explained the decrease of / in polar solvents.17 For
f
1 and 2, the / values remain nearly solvent-independent (Fig.
maxima (lmax) vs. *f @ are gathered in Table 2. The dipole
f
fluo
4). Moreover, the Ñuorescence decays (q ) measured at room
temperature (Table 1) and satisfactorily Ðtted by a single-
moment of the ground state (k ) has been calculated, in a Ðrst
f
g
approximation, by the semi-empirical AM1 method.37 The
exponential model, are relatively independent of the solvent
resulting k values are listed in Table 2 and compared to those
e
polarity. Similarly, the radiative rate constants (k ) calculated
of compounds 3 and 4. Note that these values are only
f
from / /q and the non-radiative rate constants (k ) obtained
approximate because of (i) the rough evaluation of o and (ii)
the nonlinearity of the bridged compounds, which may induce
di†erent orientations of the dipole moment for the ground
and excited states. Nevertheless, these data show that 1È4
possess large excited state dipole moments. Moreover, the
change of the dipole moment between the ground and the
f f
nr
from k (1// [ 1) remain una†ected by the solvent polarity.
This behavior shows the absence of TICT states in polar
solvent, as expected from the weak acceptor property of the
ester function.
f
f
excited states (*k ) is larger for 1 and 2 than for 3 and 4 due
LB Ðlms with 1 and 2
eg
to the smaller ground state dipole moments associated with
Fig. 5 shows the surface pressureÈarea (nÈA) isotherms for
monolayers of 1 and 2 while Table 3 collects the compression
isotherm data for dyes 1È4.16 For all compounds, the shape of
the isotherms indicates good Ðlm-forming ability and no
apparent phase transition during compression. Nevertheless,
the nÈA isotherms of 2–4 are more abrupt than for 1, as reÑec-
the ester acceptor group.
The Ñuorescence quantum yields (/ ) of 1 and 2 in di†erent
f
solvents are collected in Table 1. Fig. 4 shows the plot of / as
f
a function of the solvent parameter *f @ for 1È4. The Ñuores-
cence quantum yields of 1 and 2 are not signiÐcantly a†ected
by the solvent polarity and remain around 0.4, whatever the
solvent polarity, whereas for 3 and 4 a strong decrease occurs
in polar solvents.17 Let us recall that pushÈpull stilbenes, like
4-N,N-dimethylamino-4@-cyano stilbene (DCS),38h40 are
strongly altered in their photophysical properties by the Ñex-
ibility or non-Ñexibility of their single and double bonds. In
DCS, double bond twisting leads to Ñuorescence quenching
(state P*), whereas twisting the adjacent single bonds popu-
lates lower-lying emissive charge transfer states (A*, twisted
intramolecular charge transfer, TICT),41 which competes with
ted by the values of A (see Table 3). The abrupt character of
0
the 2–4 isotherms can be attributed to a molecule organiz-
ation similar from the beginning to the end of monolayer for-
Table 2 Solvatochromic slope m [cm~1 (*f @)~1] using the data of
Table 1, Onsager parameter (o) and ground (k ) and excited (k ) state
g
e
dipole moments
1
2
3
4
Slope m
[20 890
6.28
3.1
[15 050
6.23
2.5
[20 610
6.11
6.5
[18 160
6.10
6.5
o/g cm~1
k /D
g
Fig. 5 Compression isotherm of Langmuir Ðlms at the airÈwater
interface at room temperature for 1 (solid line) and 2 (dotted line).
k /D
24
20
24
23
e
Table 3 Compression isotherm data of monolayer LB Ðlms of 1È4:
absorption maxima (jmax) area per molecule at zero surface pressure
abs
(A ), limiting area per molecule at the collapse point (A ) and surface
0
c
pressure of the collapse point (P ), wavelength of the titanium sapp-
c
hire laser (j ), molecular second harmonic hyperpolarizability (b)
exc
and average tilt angle (h )
0
1
2
3
4
jmax/nm
364
65
34
337
36
28
341
44
30
329
47
30
abs
A /A
Ž
2 molecule~1
0
A /A
Ž
2 molecule~1
c
P /mN m~1
31
32
34
35
c
j
/nm
800
300
32
800
290
32
788
200
32
788
190
31
exc
b/10~30 esua
h /deg
0
Fig. 4 Fluorescence quantum yields as a function of solvent for (=)
1, (…) 2, (L) 3 and (K) 4.
a esu \ electrostatic unit; b \ 1 m4 V~1 \ 4.189 ] 10~10 esu.
980
New J. Chem., 2000, 24, 977È985

View Article Online
mation, while the gradual behavior of 1 reÑects di†erent
for mono- and multi-layer LB Ðlms of trans-stilbene sur-
factants, containing nonpolar groups11,12 or p-donor and p@-
acceptor substituents,13 even in dilute conditions.11h13 This
blue absorption shift was attributed to an H-aggregate
arrangement in which the chromophore transition moments
are aligned with an angle h inferior to 36 degrees.12,13 In fact,
a tilt angle larger than 36¡ induces a bathochromic shift of the
absorption and is characteristic of J-aggregates, according to
the model of Kasha et al.,14 as reported for 4-octadecylamino-
4@-nitro stilbene.49 In the case of 1 and 2, the blue-shift of the
absorption spectra (Fig. 7) suggests that H-aggregation is the
predominant arrangement.
conÐgurations involved during Ðlm formation.
From the nÈA isotherms the collapse pressure (P , Table 3)
c
is estimated to be around 35 mN m~1 for 3 and 4 and 30 mN
m~1 for 1 and 2. This demonstrates a good stability of the LB
Ðlms, as expected with perÑuorinated chains. The lower stabil-
ity recorded for 1 and 2 is directly related to the shorter length
of the Ñuorinated chain. The limiting area per molecule, deter-
mined when the monolayer starts to collapse (A , Table 3), is
c
close to the area of perÑuoroundecanoic acid (C
F
COOH,
10 21
33.2 AŽ 2 molecule~1)46 but larger than the A values obtained
c
for surfactant derivatives containing the trans-stilbene
chromophore (22 A2 molecule~1)47 and larger than the esti-
mated value of the molecular cross-sectional area of the Ñu-
orocarbon chain (28 A
Ž
Second harmonic generation
Ž
2).48 This slight increase of the
For Ðlms of both 1 and 2, the s-polarized component of the
second harmonic signal, although measurable, is very weak
for s- and p-polarized incident radiation. On the contrary, an
intense signal is observed for the p-polarized component at 2u
for 1 and 2 when the incident beam is polarized either s or p.
To obtain the average molecular orientation in the Ðlm and
the second-order molecular polarizability we have followed
the now classical method Ðrst proposed by Blombergen and
Pershan50 and subsequently reÐned by Shen.51 For stilbenes,
molecular cross-sectional area can reÑect a tilted arrangement
of the dyes in the LB Ðlms (see absorption and SHG
measurements).
After stabilization of the Langmuir Ðlm, transfer is achieved
at a constant pressure of 28 mN m~1 for 1 and 30 mN m~1
for 2. The absorption spectra have been measured for an
increasing number N of superposed monolayers (Fig. 6). For
up to nine monolayers, the absorbance remains proportional
to N, showing a regular organization in this LB Ðlm. Fig. 7
shows a comparison between the normalized absorption
spectra of 2 in chloroform solution and as Ðve superposed
only one component, a(2) \ b, of the molecular second-order
mmm
polarizability tensor is signiÐcant. The surface nonlinear sus-
ceptibility tensor s(2) is a function of NSa(2)T where N is the
mmm f{
monolayers on a CaF support. The absorption band of the
molecular surface density, m is the direction of the molecular
2
LB Ðlm is wider and the maximum is blue-shifted. These
dipole moment and f denotes the monolayer orientational dis-
tribution function. The m direction is approximately given by
the donorÈacceptor direction. In the xy plane (z axis normal
to the substrate) only two distinct nonzero elements have to
be taken into account: s(2) and s(2) \ s(2) \ s(2) , where i \ x,
changes in absorption spectra can be explained by the forma-
tion of aggregates. The proximity of the molecules in a LB
Ðlm induces intermolecular interactions that a†ect both
ground and excited state energies.14 Similar changes in the
absorption spectra (hypsochromic shift) have been observed
zzz
zii
izi
iiz
y. The average tilt angle h of the molecular axis can be esti-
o
mated from s(2)( \ Na(2) cos3 h ) and s(2)(\(N/2)a(2) sin2 h
zzz
mmm
o
zyy
mmm
o
cos h ) with the assumption that the h distribution is well
peaked, that is, f (h) \ d(h [ h )/sin h .
o
o
o
Our monolayer symmetry implies that the second-order s-
polarized Ðeld is null: that is, Es?s(2u) \ Ep?s(2u) \ 0. In this
notation, u is the frequency of the incident radiation, the Ðrst
subscript indicates the polarization (s or p) of this incident
radiation and the second subscript denotes the polarization (s
or p) of the SH signal. The nonzero second-order p-polarized
electric Ðelds are proportional to the surface nonlinear tensor
elements, as deÐned by eqn. (2) and (3), where the three con-
stants A, B and C are related to the angle of incidence and to
the dielectric indices of the glass substrate and of the Ðlm at u
and 2u.
Es?p(2u) P As(2)[Ep(u)]2
(2)
(3)
zyy
Ep?p(2u) P (Bs(2) ] Cs(2))[Ep(u)]2
Fig. 6 Absorption spectra of LB Ðlms of 2 as a function of the
zyy
zzz
number of layers.
Table 3 collects the tilt angle h and the molecular second-
o
order hyperpolarizability b found from the SHG experiment
of deposited single monolayer LB Ðlms containing 1 and 2.
Data previously reported for 3 and 4 are also gathered in
Table 3. The azimutal tilt angle of 32¡ for 1 and 2 is consistent
with the H-aggregate arrangement proposed according to our
absorption data. The dipole moment direction of the mol-
ecules is certainly close to the long axis of the chromophores
and as a result, the benzoic acid ethyl ester moieties of 1 and 2
are probably perpendicular to the substrate.
The b values of 1 and 2 arranged in monolayer LB Ðlms are
estimated to be around 300 ] 10~30 esu, close to the
200 ] 10~30 esu found for 3 and 4. This result opens inter-
esting perspectives for the design of noncentrosymmetric
multilayers containing alternatingly layers of 1È4. Firstly, we
elaborate Y-type multilayers containing an odd number of
layers and, as expected, the SHG intensity is equivalent to
that of the signal recorded for a single monolayer. This con-
Ðrms a head-to-head organization of the Y-type multilayers.
Fig. 7 Normalized absorbance spectra of 2 in chloroform and in LB
Y-type multilayers (5 superposed monolayers) on a hydrophobic Ñuo-
rine substrate.
New J. Chem., 2000, 24, 977È985
981

View Article Online
Table 4 Intensity of the p-polarized component (N ) of the SHG
melting point apparatus and are uncorrected. 1H NMR
spectra were recorded on a Bruker AC 200 at 200 MHz or on
a Bruker AC 250 spectrometer at 250 MHz. 13C NMR
spectra were recorded on a Bruker AC 250 spectrometer at 63
MHz. Infrared spectra were recorded on a Paragon 1000
PerkinÈElmer infrared spectrophotometer with polystyrene as
standard (Ðlm on NaCl or dispersion in KBr).
pp
signal in multilayer LB Ðlms constituted of N bilayers of 2/4). The
signal recorded for the quartz crystal is also reported
N
N
N1@2
pp
pp
1
2
4
2400
13 000
50 000
2400
49
114
224
49
Langmuir Ðlms of 1 and 2 were prepared under a constant
nitrogen Ñow in a dark KSV 5000 double trough. Ultrapure
water puriÐed in a Milli-Q-System (Millipore) was used as
subphase (resistivity 18.2 M) cm). Stock solution concentra-
tion was 10~3 mol l~1 in chloroform (Prolabo, HPLC grade)
for 1 and in toluene containing 1% methanol (Prolabo, HPLC
grade) for 2. The compression was started 30 min after spread-
ing of the solution (ca. 200 ll). The monolayer was com-
pressed at room temperature at a barrier speed of 100 mm
min~1. Surface pressure was monitored with a Pt-Wilhelmy
Quartz crystal
Then, we prepared bilayer LB Ðlms (Y-type structure, see Fig.
2) containing 1/3 or 2/4. As expected, the SHG signal is not
negligible and suggests a noncentrosymmetric arrangement
with dipolar moments oriented in the same direction. The
study of the di†erent SHG components reveals in fact that the
s-polarized component is not negligible for s- and p-polarized
incident radiation. This behavior shows the absence of an in-
plane isotropic molecular orientation within the bilayer LB
Ðlms. For instance, one may consider that the transfer process
Ðxes a preferential axis along which the bilayer could re-
arrange during the transfer. Such rearrangement may occur
due to an imperfect match of the limiting area per molecule
within the two LB Ðlms of the bilayer. If such a rearrangement
balance. The transfer on hydrophilic CaF slides was realized
2
under a constant pressure using a transfer speed of 1.75 mm
min~1. When several monolayers were superposed, the drying
period between two depositions was set to 20 min under nitro-
gen. Alternating layers were prepared using a KSV 5000
double-trough according the same experimental conditions as
described for the LB Ðlm formation. Transfer was realized on
happens, the bilayer would have a C symmetry that would
hydrophobic CaF slides previously prepared by depositing
1v
2
account for the observed phenomena. Note that if such a
three layers of behenic acid on hydrophilic slides and was per-
rearrangement is induced one would expect to observe a more
pronounced e†ect for the 1/3 bilayer Ðlm.
Multilayer LB Ðlms based on one, two and four bilayers of
1/3 or 2/4 have been prepared. The SHG signals measured as
a function of the number of 2/4 bilayers are collected in Table
4. As expected, the intensity of the p-polarized components
increases with the number of layers. Moreover, the increase of
formed at a surface pressure of 15 mN m~1 with a dipping
and lifting speed of 5 mm min~1.
Absorption and emission spectra were recorded on a Cary
5E spectrophotometer and Edinburgh Instruments spectro-
meter, respectively. Fluorescence spectra were recorded in
quartz cells with right angle detection. Solvents were of spec-
troscopic quality. Fluorescence quantum yields were relative
the square root of N is proportional to the number of layers,
to 3 in diethyl ether (/ \ 0.49).17 Fluorescence decays of
pp
f
indicating a regular noncentrosymmetric arrangement at least
aerated solutions were measured using a single-photon-
up to four bilayers. Similar SHG measurements have been
performed on multilayers constituted by 1/3. Unfortunately,
the p-polarized component remains una†ected by the number
of bilayers. The organization of the 1/3 multilayers is certainly
responsible for such behavior. This is therefore a clear indica-
tion that to preserve a good polar orientation within a single
LB Ðlm the limiting area per molecule within the two LB Ðlms
has to be as close as possible. In fact, according to our data
and discarding any other contributions to the disorganization
of the multilayer, a mismatch of about 10% in the area per
molecule within the layers drastically and rapidly a†ects the
multilayer arrangement.
counting setup from Edinburgh Instruments.
The sapphire surface SHG measurements were made using
a mode-locked titanium sapphire laser operating at a 76 MHz
repetition rate and with a wavelength of 800 nm. The incident
radiation, polarized parallel (p) or perpendicular (s) to the
plane of incidence, was focused on the CaF slide and directed
2
at a 45¡ angle to the substrate normal.16 The SHG signal,
resolved into s- and p-polarized components, was detected at
90¡ to the pumping direction by a photon-counting photomul-
tiplier at the output of a monochromator. Sample regions free
of any LB Ðlm exhibit no SHG. The SHG detected signal was
calibrated against a properly oriented Z-cut quartz crystal.
Conclusion
Synthesis of 1
A new family of organic molecules for SONLO, displaying an
interesting compromise in terms of the nonlinearity/
transparence trade-o†, has been investigated. We have demon-
strated that it was possible to form LB Ðlms of 1 and 2. The
observed changes in absorption have been explained by H-
(1H,1H,2H,2H-PerÑuorooctyl)-3-methoxyphenylamine (6).
1H,1H,2H,2H-PerÑuoro-1-iodooctane (10 g, 21.1 mmol) was
added dropwise to 3-methoxyaniline (13 g, 105.5 mmol) at
90 ¡C. After complete addition, the mixture was stirred at
140 ¡C for 3 h (the reaction was monitored by GPC). After
cooling, the organic layer was washed with 2 N aqueous
sodium hydroxide (100 ml) and the aqueous layer extracted
with diethyl ether (3 ] 30 ml). Then, the organic layer was
washed with water and dried with sodium sulfate. The solvent
was removed under reduced pressure and the excess 3-
methoxyaniline was distilled o† under reduced pressure to
give a brown residue. The crude product was puriÐed by chro-
matography on a silica gel column eluting with dichloro-
aggregation and a tilt angle h of ca. 32¡ was estimated by
o
SHG measurements.
A
molecular quadratic hyperpolar-
izability b of 300 ] 10~30 esu has been recorded for both 1
and 2 in LB Ðlms. Multilayer LB Ðlms containing both 1/3 or
2/4 have been prepared. The proportional increase of the
SHG signal with the number of bilayers for 2/4 proves the
regular organization of these LB Ðlms.
Experimental
methane to give the product 6 as a clear oil (9.7 g, 98%). d
H
(250 MHz, CDCl ): 2.42 (m, 2H), 3.54 (m, 2H), 3.80 (s, 3H),
3
Apparatus and methods
3.80 (s, 1H), 6.18È7.18 (m, 4H); d (63 MHz, CDCl ): 30.6
C
3
The course of the reactions and the purity of the Ðnal pro-
ducts were monitored by thin-layer chromatography (TLC).
Melting points were determined on a Mettler FP 62 capillary
(2J \ 21.0), 35.8 (3J \ 4.3 Hz), 55.1, 99.0, 103.2, 105.9,
CF
CF
130.3, 148.3, 161.0; IR l
(cm~1): 3409, 1675, 1515, 1240,
max
1145.
982
New J. Chem., 2000, 24, 977È985

View Article Online
Ethyl[1H,1H,2H,2H-perÑuorooctyl)-3-methoxyphenyl]-
amine (7). Ethyl iodide (9.2 g, 58.8 mmol) was added dropwise
to a stirred solution of 6 (6.9 g, 14.4 mmol), powdered sodium
carbonate (6.2 g, 58.8 mmol) and acetone (20 ml) at room tem-
perature. After complete addition, the mixture was reÑuxed for
72 h (the reaction was monitored by TLC). After cooling, the
mixture was poured into water (50 ml) and standard ethereal
work-up (3 ] 40 ml) provided the crude amine, which was
puriÐed by chromatography on a silica gel column eluting
with 40% petroleum ether in dichloromethane to give the
product 7 as a clear oil (5.8 g, 80%). d (250 MHz, CDCl ):
4-{2-Formyl-5-[ethyl(1H,1H,2H,2H-perÑuorooctyl)-
amino]phenoxymethyl}benzoic acid ethyl ester (12). A solution
of 9 (686 mg, 1.34 mmol), 11 (373 mg, 1.53 mmol) and pow-
dered potassium carbonate (0.5 mg, 3.62 mmol) in dimethyl-
formamide (10 ml) was stirred at 100 ¡C for 20 h. After
cooling, the solvent was eliminated under reduced pressure
and water (50 ml) was added. The aqueous phase was separat-
ed, extracted with dichloromethane, washed with water and
dried over magnesium sulfate. Chromatography on a silica gel
column eluting with dichloromethane gave 12 as a red solid
(366 mg, 40%). Mp 101 ¡C; d (250 MHz, CDCl ): 1.17 (t, 3H,
H
3
H
3
1.20 (t, 3H, 3J \ 7), 2.39 (m, 2H, 3J \ 8, 3J \ 19), 3.38
3J \ 7.0), 1.39 (t, 3H, 3J \ 7.2), 2.33 (m, 2H), 3.40 (q, 2H,
HH
HH
HF
HH HH
(q, 2H, 3J \ 7 Hz), 3.66 (m, 2H) 3.80 (s, 3H), 6.25È7.24 (m,
3J \ 7), 3.64 (m, 2H), 4.37 (q, 3H, 3J \ 7.2 Hz) 5.2 (s, 2H),
HH
HH
HH
4H); d (63 MHz, CDCl ): 12.4, 28.7 (2J \ 21.0), 42.2
6.0È7.7 (m, 3H), 7.47, 7.51, 8.05, 8.08 (AA@BB@, 4H), 10.3 (s,
1H); d (63 MHz, CDCl ): 12.4, 45.5, 69.4, 28.7 (2J \ 21.0
C
3
CF
(3J \ 4.8 Hz), 45.3, 55.0, 98.7, 101.4, 105.1, 130.3, 148.3,
CF
C
3
CF
161.2; IR l (cm~1): 1613, 1501, 1380, 1238, 1145.
Hz), 42.3 (3J \ 5.7 Hz), 14.3, 61.1, 94.5, 104.6, 115.4, 126.5,
max
CF
130.0, 130.3, 131.0, 141.4, 152.8, 162.8, 166.2, 187.2; IR l
max
3-[Ethyl(1H,1H,2H,2H-perÑuorooctyl)amino]phenol (8). A
1.0 M boron tribromide solution in dichloromethane (22 ml,
22.2 mmol) was added dropwise to a stirred solution of 7 (5.1
g, 10.2 mmol) in dichloromethane (40 ml) at 0 ¡C. After com-
plete addition, the reaction mixture was stirred for 24 h at
room temperature. The mixture was poured into ice-cold
water, then extracted with dichloromethane (3 ] 40 ml) and
dried with magnesium sulfate. Removal of solvent gave a
purple oily residue, which was puriÐed by chromatography on
a silica gel column eluting with 30% petroleum ether in
dichloromethane to give the product 8 as an orange oil (3.1 g,
63%). d (200 MHz, CDCl ): 1.22 (t, 3H, 3J \ 7.1), 2.40 (m,
(cm~1): 1708, 1598, 1518, 1238, 1140.
4-{6-[Ethyl(1H,1H,2H,2H-perÑuorooctyl)amino]-
benzofuran-2-yl}benzoic acid ethyl ester (1). The reagent pot-
assium Ñuoride/alumina was Ðrst prepared according to the
following procedure. Potassium Ñuoride (4 g, 68.84 mmol) was
mixed with alumina (6 g) in water (20 ml) for 1 h. Water was
removed in a rotary evaporator and the impregnated alumina
was dried under vacuum at 80 ¡C for 12 h. A solution of 12
(530 mg, 0.8 mmol) and powdered potassium Ñuoride/alumina
(1.2 g, 0.79 mmol), in dimethylformamide (5 ml) was stirred at
120 ¡C for 4 h (the reaction was monitored by TLC). After
cooling, the solid material was Ðltered o† and washed with
ether. Removal of solvent under reduced pressure gave a
yellow-brown oily residue. The product was puriÐed by
column chromatography on silica gel eluting with dichloro-
methane to give 1 as a yellow solid (144 mg, 24%). Mp 110 ¡C;
H
3
HH
2H, 3J \ 7.8, 3J \ 19.9), 3.39 (q, 2H, 3J \ 7.1 Hz), 3.67
HH HF HH
(m, 2H), 5.04 (s, 1H), 6.23È7.30 (m, 4H); d (50 MHz, CDCl ):
C
3
12.4, 28.7 (2J \ 21.7 Hz), 42.1, 45.2, 99.1, 103.7, 104.8, 130.5,
CF
148.5, 156.9; IR l
(cm~1): 3361, 1614, 1504, 1384, 1205,
max
1144.
d
(250 MHz, CDCl ): 1.17 (t, 3H, 3J \ 7.0), 1.35 (t, 3H,
2-Hydroxy-4-[ethyl(1H,1H,2H,2H-perÑuorooctyl)-
H
3
HH
3J \ 7.2), 2.35 (m, 2H), 3.37 (q, 2H, 3J \ 7.0), 3.66 (m,
amino]benzaldehyde (9). A mixture of dimethylformamide (4 g,
54.3 mmol) and phosphorus oxychloride (0.8 g, 5.2 mmol) was
stirred at 0 ¡C for 1 h under nitrogen atmosphere, then at
room temperature for 1.5 h to give an orange solution. The
latter was cannulated into a mixture of 8 (2.5 g, 5.2 mmol) and
dimethylformamide (1 ml). The resulting solution was stirred
at 95 ¡C for 15 h. After cooling, the reaction mixture was
poured into ice-cold water, washed with aqueous sodium
hydroxide (10%) and the aqueous layer was extracted with
dichloromethane (3 ] 50 ml). The organic layer was washed
with water (3 ] 30 ml) and dried with magnesium sulfate.
Removal of the solvent gave a red oil, which was puriÐed by
chromatography on a silica gel column eluting with 30% pet-
roleum ether in dichloromethane to give the product 9 as a
grey solid (1 g, 38%). Mp 68È69 ¡C; d (250 MHz, CDCl ):
HH
HH
2H), 4.33 (q, 3H, 3J \ 7.2 Hz), 6.97 (s, 1H), 6.65È7.39 (m,
HH
3H), 7.83, 7.86, 8.07, 8.10 (AA@BB@, 4H); d (63 MHz, CDCl ):
12.5, 14.4, 28.3 (2J \ 21.0), 61.0, 42.8 (3J \ 5.7 Hz), 45.9,
C
3
CF
CF
94.6, 103.8, 110.1, 119.5, 121.8, 123.8, 129.1, 130.1, 134.8, 145.9,
152.8, 157.4, 166.4; IR l
(cm~1): 1708, 1606, 1503, 1381,
max
1271, 1139; MS (EI) m/z: 655 (M`, 100), 222 (M`
[ CH C F , 10).
2 6 13
Synthesis of 2
(1H,1H,2H,2H-PerÑuorooctyl)phenylamine (14). 1H,1H,2H,
2H-PerÑuoro-1-iodooctane (20.4 g, 43 mmol) was added drop-
wise to aniline (16 g, 171.8 mmol) at 90 ¡C. After complete
addition, the mixture was stirred at 140 ¡C for 15 h (the reac-
tion was monitored by GPC). After cooling, the organic layer
was washed with 2 N aqueous sodium hydroxide (100 ml) and
the aqueous layer extracted with diethyl ether (3 ] 40 ml).
Then, the organic layer was washed with water and dried with
magnesium sulfate. Solvent was removed under reduced pres-
H
3
1.22 (m, 2H, 3J \ 7.1), 2.36 (tt, 2H, 3J \ 8.1, 3J \ 20.2),
HH
HH
HF
3.40 (q, 2H, 3J \ 7.1 Hz), 3.68 (m, 2H), 6.08È6.31 (m, 3H),
HH
9.51 (s, 1H, CHO), 10.54 (s, 1H, OH); d (50 MHz, CDCl ):
C
3
12.4, 28.8 (2J \ 21.8 Hz), 42.3, 45.4, 97.2, 104.1, 112.2, 135.7,
CF
sure and the residue was puriÐed by distillation, bp
153.5, 164.4, 192.6; IR l
(cm~1): 1636, 1519, 1344, 1235,
0.0026 atm
max
116È117 ¡C, to give the product 14 as a clear colorless liquid
1186.
(15.9 g, 85%). d (250 MHz, CDCl ): 2.42 (tt, 2H, 3J \ 7.1,
H
3
HH
4-Bromomethylbenzoic acid ethyl ester (11). A well-stirred
mixture of 4-methylbenzoic acid ethyl ester 10 (1.2 g, 7.3
mmol), N-bromosuccinimide (1.4 g, 7.8 mmol) and benzoyl
peroxide (20 mg) in dry carbon tetrachloride (15 ml) was
reÑuxed for 15 h. The hot mixture was Ðltered and the Ðltrate
was evaporated to give a white residue, which was puriÐed by
chromatography on a silica gel column eluting with 30%
dichloromethane in petroleum ether to give the product 11 as
a colorless oil (1.1 g, 67%). d (200 MHz, CDCl ): 1.36 (t, 3H,
3J \ 18.8), 3.57 (t, 2H, 3J \ 7.1 Hz), 3.77 (s, 1H), 6.64È
HF
HH
7.29 (m, 5H); d (63 MHz, CDCl ): 30.7 (2J \ 20.0 Hz),
C
3
HF
(cm~1): 3417, 1605,
35.8, 112.9, 118.8, 129.6, 146.9; IR l
max
1510, 1365, 1240, 1145.
Methyl[(1H,1H,2H,2H-perÑuorooctyl)phenyl]amine
(15).
Methyl iodide (5.9 g, 41.5 mmol) was added dropwise to a
stirred solution of 14 (10 g, 22.8 mmol), powdered sodium car-
bonate (2.5 g, 23 mmol) and acetone (20 ml) at room tem-
perature. After complete addition, the mixture was reÑuxed for
72 h (the reaction was monitored by GPC). After cooling, the
mixture was poured onto water (70 ml), the organic layer
separated and the aqueous phase extracted with dichloro-
H
3
3J \ 7.1), 4.35 (q, 2H, 3J \ 7.1 Hz), 4.46 (m, 2H), 7.39,
HH
HH
7.43, 7.97, 8.01 (AA@BB@, 4H); d (50 MHz, CDCl ): 14.0, 32.0,
60.8, 128.7, 129.7, 130.1, 142.2, 165.6; IR l
C
3
(cm~1): 1716,
max
1611, 1278, 1108.
New J. Chem., 2000, 24, 977È985
983

View Article Online
methane (3 ] 40 ml). The organic phase was washed with
water and dried with magnesium sulfate. Solvent was removed
under reduced pressure to give a residue, which was puriÐed
by chromatography on a silica gel column eluting with 40%
dichloromethane in petroleum ether to give the product 15 as
a clear colorless liquid (9 g, 85%). d (250 MHz, CDCl ): 2.36
8.0), 8.17 (dd, 1H, 3J \ 8.0, 4J \ 1.6), 8.57 (d, 1H, 4J
HH HH
\
HH
1.6 Hz); d (63 MHz, CDCl ): 14.2, 27.9, 62.1, 126.4, 132.0,
C
3
132.7, 134.1, 136.9, 148.5, 164.5; IR l
1347, 1290, 1265.
(cm~1): 1720, 1535,
max
(4-Ethoxycarbonyl-2-nitrobenzyl)triphenylphosphonium
bromide (21). A solution of 20 (1.8 g, 6.2 mmol) and tri-
phenylphosphine (1.9 g, 7.2 mmol) in dry toluene (25 ml) was
stirred at 110 ¡C for 16 h. After cooling, the product was Ðl-
tered o† and evaporated to dryness to give the phosphonium
H
3
(tt, 2H, 3J \ 7.6, 3J \ 19.0), 2.98 (s, 3H), 3.74 (t, 2H,
HH HF
3J \ 7.6 Hz), 6.73È7.33 (m, 5H); d (50 MHz, CDCl ): 27.5
HH
C
3
(2J \ 21.8 Hz), 38.2, 44.3, 112.3, 117.2, 129.5, 148.0; IR l
(cm~1): 1602, 1508, 1365, 1240, 1145.
CF
max
salt as a pale brown solid (3.1 g, 91%). Mp 197 ¡C; d (250
H
4-[Methyl(1H,1H,2H,2H-perÑuorooctyl)amino]-
MHz, CDCl ): 1.31 (t, 3H, 3J \ 7.1), 4.32 (q, 2H, 3J
\
3
HH
HH
benzaldehyde (16). A mixture of dimethylformamide (5.1 g,
70.4 mmol) and phosphorus oxychloride (3.1 g, 19.4 mmol)
was stirred at 0 ¡C for 1.75 h under a nitrogen atmosphere,
then at room temperature for 1.25 h to give an orange solu-
tion. To the resulting solution, 15 (8 g, 17.6 mmol) was added
dropwise and the resulting mixture was stirred at 100 ¡C for
15 h. After cooling, the reaction mixture was poured into ice-
cold water (50 ml), washed with 2 N aqueous sodium hydrox-
ide (10%), the organic layer was separated and the aqueous
layer extracted with dichloromethane (4 ] 50 ml). The organic
layer was washed with water (3 ] 25 ml) and dried with mag-
nesium sulfate. Removal of the solvent under reduced pressure
gave a brown oily residue, which was puriÐed by chromatog-
raphy on a silica gel column eluting with 20% petroleum ether
in dichloromethane to give the product 16 as a pale yellow
solid (7 g, 80%). Mp 44 ¡C; d (250 MHz, CDCl ): 2.35 (tt,
7.1), 6.06 (s, 2H, 2J
\ 15.3 Hz), 7.55È7.78 (m, 15H), 8.11
HP`
(AB, 2H), 8.44 (s, 1H); d (63 MHz, CDCl ): 13.9, 28.3
C
3
(1J
CP`
(cm~1): 1718, 1536, 1438, 1300, 1268, 1110.
\ 48.7 Hz), 61.9, 126È137 (18 C , 2C ), 163.7; IR l
max
H
q
4º-[Methyl(1H,1H,2H,2H-perÑuorooctyl)amino]-2-nitro-
trans-stilbene-4-carboxylic acid ethyl ester (22). A mixture of
16 (2.6 g, 5.4 mmol), 21 (3 g, 5.4 mmol) and powdered pot-
assium carbonate (1.6 g, 11.5 mmol) in dimethylformamide (20
ml) was stirred at 90 ¡C for 20 h. After cooling, the excess of
dimethylformamide was removed under vacuum and water
(50 ml) was added. The aqueous layer was extracted with
dichloromethane (3 ] 50 ml); the organic layer was washed
with water (3 ] 25 ml) and dried with magnesium sulfate.
Removal of the solvent under reduced pressure gave a red
solid residue. This was puriÐed by chromatography on a silica
gel column eluting with 30% petroleum ether in dichloro-
methane to give 22 as a red solid (1.5 g, 40%). Mp 105È
106 ¡C; d (250 MHz, CDCl ): 1.42 (t, 3H, 3J \ 7.1); 2.37
H
3
2H, 3J \ 7.5, 3J \ 18.8), 3.06 (s, 3H), 3.76 (t, 2H, 3J
\
HH
HF
HH
C
7.5 Hz), 6.67, 6.71, 7.72, 7.75 (AA@BB@, 4H), 9.91 (s, 1H); d (63
MHz, CDCl ): 27.9 (2J \ 22.0 Hz), 38.4, 44.3, 111.1, 126.1,
3
CF
H
3
HH
132.2, 152.4, 190.3; IR l
(cm~1): 1683, 1593, 1527, 1383,
(m, 2H, 3J \ 7.3, 3J \ 19.0); 3.03 (s, 3H); 3.75 (t, 2H,
HH HF
3J \ 7.3), 4.42 (q, 2H, 3J \ 7.1), 6.68, 6.71, 7.46, 7.49
max
1240, 1164.
HH
HH
(AA@BB@, 4H), 7.18 (d, 1H, 3J
\ 16), 7.42 (d, 1H,
3-Nitro-4-methylbenzoyl chloride (18). 3-Nitro-4-methyl-
benzoic acid (10 g, 55.2 mmol) was added in small amounts to
thionyl chloride (50 g, 420 mmol) at room temperature. After
the addition, the solution was reÑuxed for 3 h. The excess of
thionyl chloride was removed under reduced pressure and the
solution azeotroped with toluene (3 ] 100 ml) to give the
benzoyl chloride 18 as a pale green oil (11.2 g, quantitative
HHtrans
C
3J
\ 16 Hz), 8.54 (s, 1H); d (63 MHz, CDCl ): 14.3,
HHtrans
3
27.7 (3J \ 22 Hz), 38.3, 44.4, 61.7, 112.1, 117.8, 125.1, 126.2,
CF
127.2, 129.0, 129.2, 133.1, 136.1, 137.3, 147.4, 148.6, 164.6.
2-{4-[Methyl(1H,1H,2H,2H-perÑuorooctyl)amino]phenyl}-
1H-indole-6-carboxylic acid ethyl ester (2). A mixture of 22
(1 g, 1.5 mmol) and triethyl phosphite (10 ml) was reÑuxed for
18 h. After cooling, the excess of triethyl phosphite was
removed by distillation (bp 156È157 ¡C). Water (30 ml) was
added, the organic layer separated and the aqueous layer was
extracted with diethyl ether (3 ] 30 ml). The organic layer was
washed with water (10 ml) and dried with magnesium sulfate.
Removal of the solvent under reduced pressure gave an
orange solid residue. This was reprecipated by adding
dichloromethane to give the product 2 as a yellow solid (0.1 g,
10%). Mp 212 ¡C; d (200 MHz, acetone-d ): 1.40 (t, 3H,
yield); the product was used without further puriÐcation. d
H
(250 MHz, CDCl ): 2.67 (s, 3H), 7.46 (d, 1H, 3J \ 8.1), 8.16
3
HH
(dd, 1H, 3J \ 8.1, 4J \ 1.9), 8.65 (d, 1H, 4J \ 1.8 Hz);
HH
HH
HH
d
(63 MHz, CDCl ): 20.8, 127.2, 132.2, 133.6, 134.2, 141.1,
C
3
150.1, 167.2.
3-Nitro-4-methylbenzoic acid ethyl ester (19). Ethanol (40
ml) was added dropwise to 18 (11 g, 54 mmol) at room tem-
perature. After complete addition, the solution was reÑuxed
for 8 h. The excess of ethanol was removed under reduced
pressure. The residue was dried under vacuum and was puri-
Ðed by chromatography on a silica gel column eluting with
dichloromethane to give the product 19 as a colorless oil (10.7
g, 95%). d (250 MHz, CDCl ): 1.38 (t, 3H, 3J \ 7.1), 2.62
H
6
3J \ 7.1), 2.60 (m, 2H, 3J \ 7.3, 3J \ 20.1), 3.12 (s, 3H),
HH HH HF
3.91 (t, 2H, 3J \ 7.3), 4.36 (q, 2H, 3J \ 7.1 Hz), 6.91, 6.95,
HH
HH
7.79, 7.83 (AA@BB@, 4H), 6.84È8.12 (m, 4H), 10.83 (s, 1H); d (63
C
MHz, acetone-d ): 14.7, 30.1, 38.3, 44.4, 60.8, 98.8, 113.3,
6
H
3
HH
113.6, 119.8, 121.4, 123.5, 126.9, 127.6, 132.9, 137.1, 137.8,
(s, 3H), 4.38 (q, 2H, 3J \ 7.1), 7.40 (d, 1H, 3J \ 8.0), 8.11
HH HH
144.1, 167.3; IR l
(cm~1): 3365, 1689, 1610, 1506, 1369,
(dd, 1H, 3J \ 8.0, 4J \ 1.7), 8.54 (d, 1H, 4J \ 1.7 Hz);
max
HH
HH
HH
1233, 1189; MS (EI) m/z: 640 (M`, 100), 307 (M`
d
(63 MHz, CDCl ): 14.2, 20.5, 61.6, 125.7, 129.7, 132.9,
C
3
[ CH C F , 13).
133.3, 138.2, 149.8, 164.4; IR l
1290, 1265.
(cm~1): 1720, 1535, 1347,
2 6 13
max
References
4-Bromomethyl-3-nitrobenzoic acid ethyl ester (20). A well-
stirred mixture of 19 (5 g, 23.9 mmol), N-bromosuccinimide
(4.2 g, 23.9 mmol) and benzoyl peroxide (20 mg) in dry carbon
tetrachloride (45 ml) was reÑuxed for 15 h. The hot mixture
was Ðltered and the Ðltrate was evaporated to give a white
solid residue, which was puriÐed by chromatography on a
silica gel column eluting with 25% dichloromethane in pet-
roleum ether to give the product 20 as a yellow solid (4.1 g,
1
2
J. L. Oudar, J. Chem. Phys., 1977, 67, 446.
J. F. Nicoud and R. Tweig, in Nonlinear Optical Properties of
Organic Molecules and Crystals, eds. D. S. Chemla and J. Zyss,
Academic Press, New York, 1987, p. 227.
3
4
5
Molecular Nonlinear Optics: Materials, Physics, and Devices, ed.
J. Zyss, Academic Press, Boston, 1993.
D. M. Burland, R. D. Miller and C. A. Walsh, Chem. Rev., 1994,
94, 31.
T. J. Marks and M. A. Ratner, Angew. Chem., Int. Ed. Engl., 1995,
34, 155.
60%). Mp 43 ¡C; d (250 MHz, CDCl ): 1.35 (t, 3H, 3J
\
\
H
HH
3
HH
HH
7.1), 4.36 (q, 2H, 3J \ 7.1), 4.77 (s, 2H), 7.60 (d, 1H, 3J
984
New J. Chem., 2000, 24, 977È985

View Article Online
6
7
C. Sanchez and B. Lebeau, Pure Appl. Opt., 1996, 5, 689.
L. T. Cheng, W. Tam and A. E. Feiring, Mol. Cryst. L iq. Cryst.
Sci. T echnol., Sect. B: Nonlinear Optics, 1992, 3, 69È71.
A. Ulman, C. S. Willand, W. Kohler, D. R. Robello, D. J. Wil-
liams and L. Handley, J. Am. Chem. Soc., 1990, 112, 7085.
J.-F. Letard, R. Lapouyade and W. Rettig, J. Am. Chem. Soc.,
1993, 115, 2441.
29 R. J. Sundberg, J. Org. Chem., 1973, 30, 3604.
30 Y. Ooshika, J. Phys. Soc. Jpn., 1954, 9, 594.
31 E. Lippert, Z. Naturforsch. A, 1955, 10, 541.
32 W. Liptay, Z. Naturforsch. A, 1965, 20, 1441.
8
9
33 N. Mataga, Y. Kaifu and M. Koizumi, Bull. Chem. Soc. Jpn.,
1956, 29, 465.
34 L. Onsager, J. Am. Chem. Soc., 1936, 58, 1486.
35 P. Suppan, Chem. Phys. L ett., 1983, 94, 272.
36 W. Baumann, H. Bischof, J. C. Frohling, C. Brittinger, W. Rettig
and K. Kotkiewiez, J. Photochem. Photobiol. A: Chem., 1992, 64,
49.
10 R. Lapouyade, A. Kuhn, J.-F. Letard and W. Rettig, Chem. Phys.
L ett., 1993, 208, 48.
11 E. M. Kosower, Physical Organic Chemistry, Wiley, New York,
1968.
12 W. F. Mooney, III and D. G. Whitten, J. Am. Chem. Soc., 1986,
37 Cerius2 Quantum Mechanics, Chemistry, MOPAC, AM1 Hamil-
tonian approximation method. Molecular Simulations Inc., San
Diego, CA, USA, 1998.
38 W. Rettig and W. Majenz, Chem. Phys. L ett., 1989, 154, 335.
39 W. Rettig, W. Majenz, R. Lapouyade and G. Haucke, J. Photo-
chem. Photobiol. A: Chem., 1992, 62, 415.
108, 5712.
13 I. Furman, H. C. Geiger, D. G. Whitten, T. L. Penner and A.
Ulman, L angmuir, 1994, 10, 837.
14 M. Kasha, H. R. Rawls and M. A. El-Bayoumi, Pure Appl. Chem.,
1965, 11, 371.
15 H. Le Breton, B. Bennetau, J. Dunogues, J.-F. Letard, R.
Lapouyade, L. Vignau and J.-P. Morand, L angmuir, 1995, 11,
1353.
16 H. Le Breton, J.-F. Letard, R. Lapouyade, A. Le Calvez, R.
Maleck Rassoul, E. Freysz, A. Ducasse, C. Belin and J.-P.
Morand, Chem. Phys. L ett., 1995, 242, 604.
17 H. Le Breton, B. Bennetau, J.-F. Letard, R. Lapouyade and W.
Rettig, J. Photochem. Photobiol. A: Chem., 1996, 95, 7.
18 J. Hoepken and M. Moeller, Macromolecules, 1992, 25, 2482.
19 J. Zyss, J. Mol. Electron., 1985, 1, 25.
20 S. Ma, X. Lu, W. Wang and Z. Zhang, J. Phys. D, 1997, 30, 2651.
21 G. J. Ashwell, J. Mater. Chem., 1999, 9, 1991.
22 I. Ledoux, D. Josse, J. Zyss, T. McLean, P. F. Gordon, R. A.
Hann and S. Allen, J. Chim. Phys., 1988, 85, 1085.
23 E. Campaigne and W. L. Archer, Org. Synth., 1953, 33, 27.
24 E. Campaigne and W. L. Archer, J. Am. Chem. Soc., 1953, 75,
989.
40 R. Lapouyade, K. Czeschka, W. Majenz, W. Rettig, E. Gilabert
and C. Rulliere, J. Phys. Chem., 1992, 96, 9643.
41 K. Rotkiewicz, K. H. Grellmann and Z. R. Grabowski, Chem.
Phys. L ett., 1973, 19, 315; K. Rotkiewicz, K. H. Grellmann and Z.
R. Grabowski, Chem. Phys. L ett., 1973, 21, 212 (erratum).
42 J.-F. Letard, R. Lapouyade and W. Rettig, Chem. Phys. L ett.,
1994, 222, 209.
43 R. Lapouyade, A. Kuhn, J.-F. Letard and W. Rettig, Chem. Phys.
L ett., 1993, 208, 48.
44 H. Ephardt and P. Fromherz, J. Phys. Chem., 1989, 93, 7717; H.
Ephardt and P. Fromherz, J. Phys. Chem., 1991, 95, 6792.
45 P. Fromherz and A. Heilemann, J. Phys. Chem., 1992, 96, 6864.
46 H. Nakahama, S. Miyata, T. T. Wang and S. Tasaka, T hin Solid
Films, 1986, 141, 165.
47 S. P. Spooner and D. G. Whitten, J. Am. Chem. Soc., 1994, 116,
1240.
48 A. Laschewsky, H. Ringsdorf and G. Schmidt, T hin Solid Films,
25 G. Grynkiewicz, M. Poenie and R. Y. Tsien, J. Biol. Chem., 1985,
1985, 134, 153.
260, 3440.
49 M. E. Lippitsch, S. Draxler and E. Koller, T hin Solid Films, 1992,
217, 161.
26 J. Yamawari, T. Kawate, T. Ando and T. Hanafusa, Bull. Chem.
Soc. Jpn., 1983, 56, 1885.
50 N. Blombergen and P. S. Pershan, Phys. Rev., 1962, 128, 606.
51 Y. R. Shen, Annu. Rev. Phys. Chem., 1989, 40, 327.
27 R. Sureau and J. Pechmeze, Ger. Pat., 2.353.293, 1974.
28 B. E. Maryano† and A. B. Reitz, Chem. Rev., 1989, 89, 863.
New J. Chem., 2000, 24, 977È985
985