Synthetic strategies to derivatizable triphenylamines displaying high two-photon absorption

Article abstract of DOI:10.1021/jo702002y

(Chemical Equation Presented) A versatile synthetic strategy to access a set of highly fluorescent π-conjugated triphenylamines bearing a functional linker at various positions on one phenyl ring is described. These compounds were designed for large two-photon absorption (2PA) and in particular for labeling of biomolecules. The monoderivatized trisformylated or trisiodinated intermediates described herein allow introduction of a large variety of electron-withdrawing groups required for large 2PA as well as a panel of chemical functions suitable for coupling to biomolecules. The monoderivatized three-branched compounds and in particular the benzothiazole (TP-3Bz) series show remarkable linear (high extinction coefficients and high quantum yield) and nonlinear (high 2-photon cross sections) optical properties. Interestingly the presence of functional side chains does not disturb the two-photon absorption. Finally, monoderivatized two-branched derivatives also appear to be valuable candidates. Altogether the good optical properties of the new derivatizable π-conjugated TPA combined with their small size and their compatibility with bioconjugation protocols suggest that they represent a new chemical class of labels potentially applicable for the tracking of biomolecules using two-photon scanning microscopy.

Full text of DOI:10.1021/jo702002y

Synthetic Strategies to Derivatizable Triphenylamines Displaying
High Two-Photon Absorption
Re´my Lartia,§ Cle´mence Allain, Guillaume Bordeau,† Falk Schmidt,|
Ce´line Fiorini-Debuisschert,‡ Fabrice Charra,‡ and Marie-Paule Teulade-Fichou*,†
Institut Curie, CNRS UMR-176, bat 110, Centre UniVersitaire, 91405 Orsay Cedex, France, and
CEA-Saclay, DSM/DRECAM/SPCSI, 91191 Gif-sur-YVette, France
marie-paule.teulade-fichou@curie.fr
ReceiVed September 12, 2007
A versatile synthetic strategy to access a set of highly fluorescent π-conjugated triphenylamines bearing
a functional linker at various positions on one phenyl ring is described. These compounds were designed
for large two-photon absorption (2PA) and in particular for labeling of biomolecules. The monoderivatized
trisformylated or trisiodinated intermediates described herein allow introduction of a large variety of
electron-withdrawing groups required for large 2PA as well as a panel of chemical functions suitable for
coupling to biomolecules. The monoderivatized three-branched compounds and in particular the
benzothiazole (TP-3Bz) series show remarkable linear (high extinction coefficients and high quantum
yield) and nonlinear (high 2-photon cross sections) optical properties. Interestingly the presence of
functional side chains does not disturb the two-photon absorption. Finally, monoderivatized two-branched
derivatives also appear to be valuable candidates. Altogether the good optical properties of the new
derivatizable π-conjugated TPA combined with their small size and their compatibility with bioconjugation
protocols suggest that they represent a new chemical class of labels potentially applicable for the tracking
of biomolecules using two-photon scanning microscopy.
Introduction
photon of energy hν and two-photon absorption (2PA) is based
upon simultaneous absorption of two photons of half the
excitation energy (hν/2 each) by a single molecule. In view of
biological applications and in vivo imaging the two-photon
process offers many advantages:1,2 better in-depth penetration,
reduced cell damage, and higher spatial resolution. As a
consequence, two-photon microscopy experiences an increasing
popularity. Unfortunately, the two-photon absorption process
is statistically disfavored and hence performances of classical
one-photon fluorophores are usually low due to their two-photon
absorption cross section (δ).3,4 As a consequence, many efforts
have been devoted to design fluorophores displaying higher δ.
Optical imaging of living cells is a common method in
molecular biology and hence many fluorescent dyes are routinely
used as molecular probes. Fluorescence is characterized by
emission of a photon from a molecular excited state. However,
at least two main processes are known to populate such a state:
one-photon absorption (1PA) results from absorption of a single
§ Present address: De´partement de Chimie Mole´culaire, UMR 5250, ICMG
FR 2607, CNRS, Universite´ Joseph Fourier, BP 53, 38041 Grenoble Cedex 9,
France.
Present address: Laboratoire de Chimie Inorganique et Mate´riaux Mole´cu-
laires, UMR CNRS 7071, Universite´ Pierre et Marie Curie, 4 place Jussieu,
75252 Paris, France.
† Institut Curie.
(1) Xu, C.; Zipfel, W.; Shear, J. B.; Williams, R. M.; Webb, W. W.
Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 10763-10768.
(2) Zipfel, W. R.; Williams, R. M.; Webb, W. W. Nat. Biotechnol. 2003,
21, 1369-1377.
| Present address: Eckert & Ziegler Eurotope GMbH, Robert-Ro¨ssle-Strasse
10, D-13125 Berlin, Germany.
‡ CEA-Saclay.
10.1021/jo702002y CCC: $40.75 © 2008 American Chemical Society
Published on Web 02/02/2008
1732
J. Org. Chem. 2008, 73, 1732-1744

Triphenylamines Displaying High Two-Photon Absorption
Since intramolecular charge transfer (ICT) contributes strongly
to increase the 2PA capacity, many two-photon fluorophores
are built up from electron-donating and/or withdrawing groups
bridged by π-conjugated systems.5-8 Therefore, classical ap-
proaches toward optimization of 2PA cross section consist of
extending the π-electron conjugation throughout additional
double bonds and aromatic moieties.9-11 Following these
guidelines, many dendrimeric, highly conjugated large-sized
compounds have been designed.12,13 However, most of them
lack suitable functionalities for conjugation to biomolecules.14-16
In addition, their large size and strong aromatic characteristics
are likely to perturb the properties of the biomolecule they might
be linked with. Also, a key issue is solubilization in water of
these large aromatic systems, albeit several strategies based on
the attachment of hydrophilic substituents such as charged
groups or polyethyleneglycol (PEG) chains can be applied to
improve this parameter.17-20 A challenging task is thus to design
efficient two-photon fluorophores compatible both with the con-
straints of biolabeling and with the synthetic protocols for conju-
gation to biomolecules. In addition to exhibiting solubility and
stability in aqueous media, the ideal 2PA biolabel should meet
the following specific requirements: (i) advantageous balance
between as small as possible size and high two-photon absorp-
tion cross section and (ii) the presence of a functional linker
for labeling with a negligible effect on the optical properties.
For many years, triphenylamine (TPA) derivatives have been
shown to be promising materials for two-photon absorption.
TPA is an electron-rich, propeller-shaped molecule exhibiting
a C3 symmetry thus displaying an octupolar feature.21 By
introduction of electron-withdrawing groups on the three
positions para to the central nitrogen, very efficient 2PA
fluorophores were recently obtained.22,23 Hence TPA represents
an excellent scaffold for the design of new 2PA dyes for
biolabeling. However, most of the derivatives currently available
are large-sized π-extended systems displaying the previously
mentioned drawbacks. In addition, the chemistry of derivatizable
TPA remains largely unexplored.24-29 More importantly, no
studies were reported on the influence of lateral chains on 2PA
properties of TPA that are known to be highly sensitive to
symmetry and electron density.
In our ongoing research aimed on nucleic acids/small
molecules interactions, we recently described vinylpyridinium
triphenylamine derivatives (TP-py) displaying enhanced two-
photon excited fluorescence upon binding to double-stranded
DNA.30 DNA-bound TP-py compounds exhibit a strong fluo-
rescence in the far-red range (680 nm) upon two-photon
excitation in the NIR (700-800 nm) and are highly efficient
for visualization of nuclear DNA in cells via laser scanning two-
photon microscopy. This study demonstrated for the first time
that TPA derivatives are suitable as labels for biological
purposes and hence it was extremely stimulating to continue to
develop 2PA biolabels based on the TPA core.
The present paper describes the building of a versatile
derivatizable set of TPA synthons and of their development
toward two-photon fluorophores suitable for biolabeling. Ad-
ditionally a structure-property correlation based on the sys-
tematic comparison of the photophysical properties of the
derivatized and nonderivatized TPA series bearing various
functional groups is proposed.
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Results and Discussion
The synthetic strategies to construct π-conjugated tripheny-
lamines are essentially based on metal-catalyzed cross-coupling
reactions with halogenated derivatives or on Wittig-Horner
condensations via formylated precursors. Therefore we focused
on the preparation of trishalogeno and trisformyl TPA bearing
a functional group on one of the three phenyl rings (Figure 1).
The choice of the additional functional group (OH or COOH)
was dictated by chemical reactivity consideration, since OH or
carboxylate groups can be easily engaged in chain elongation
strategies, and by the availability of starting materials as detailed
below.
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Synthesis of Derivatizable Halogenated TPAs. 4,4′,4′′-
TrishaloTPA are convenient precursors of various two-photon
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J. Org. Chem, Vol. 73, No. 5, 2008 1733

Lartia et al.
Bromination of 1 following known procedures (Br2 in CHCl3
at 0 °C33 or NBS in DMF34) led to mixtures of under- and
overhalogenated compounds. Because the high electron-donating
ability of the methoxy group should strongly perturb the
electrophilic bromination, conversion of 1 to the moderately
activated arene 2 was performed, which enabled easy and
regioselective access to 3 by trisbromination.33,35 Iodination was
revealed to be more problematic: TPA 2 in the presence of the
widely used reagents Ag2SO4/I2,36 I2/In(OTf),37 AgOTf/I2,38 or
FIGURE 1. General structure of functionalized TPA precursors.
R4N+, ICl2 salt39 either reacts extremely slowly or leads to
-
intractable mixtures. Finally a HgO/iodine mixture40 leads to
clean conversion of 2 into 4 within 3 days. By using this reagent,
the trisiodination, albeit slow, was revealed to be particularly
efficient since the fairly deactivated TPA 5 was converted into
6 within 10 days at room temperature, while the strongly
deactivated 7 was quantitatively and regioselectively trisiodi-
nated into 9 in hot n-propanol accompanied by transesterifica-
tion41 with the same reaction time. Its parent brominated
compound 8 was also obtained under forced conditions (3 days
in refluxing CHCl3)42 as compared to the unsubstituted TPA.
In summary, this set of reactions enables us to develop a pool
of regiospecifically halogenated TPA bearing one electron-
donating or electron-withdrawing group in position 2 or 3 of
the phenyl ring. Hence, the synthesized key intermediates (3,
4, 6, 8, and 9) open the way for the application of palladium-
catalyzed reactions.
SCHEME 1. Synthesis of Trishalogenated TPAa
Synthesis of Derivatizable Formylated TPA. Beside halo-
genated TPA, formylated TPA are convenient precursors for
conjugated TPA since they can be converted into vinylated
analogues by Knoevenagel or Wittig reactions which have been
exemplified in many studies.22,43,44 However, few reports are
known on the synthesis of their 2- or 3-monofunctionalized
derivatives,28 hence hampering the design of derivatizable
fluorescent TPA (Figure 1).
a Reagents and conditions: (a) BBr3, CH2Cl2, -78 °Cfrt, 2 h; (b) Ac2O,
pyridine, reflux, 1 h; (c) Br2, CHCl3, 0 °Cfrt, 3 h; (d) HgO, I2, CH2Cl2, rt,
3 days; (e) HgO, I2, CH2Cl2, rt, 10 days; (f) NBS, CHCl3, reflux, 3 days;
(g) HgO, I2, 1-propanol, 90 °C, 10 days.
Several attempts to directly formylate the monofunctionalized
TPA core failed: Repeated halogen-metal exchange reactions
from compound 10, followed by quenching by DMF or ethyl
formate lead to the expected compound in low yield and poor
reproducibility. In a second attempt, we choose to introduce
formyl groups directly by palladium-catalyzed coupling between
two properly functionalized moieties. The corresponding precur-
sors 11 and 12 were synthesized and their condensation on the
corresponding diphenylamines 13 and 14 attempted (Scheme
fluorescent TPA dyes since they can be functionalized by
numerous palladium-catalyzed reactions. However, little re-
search was published on such compounds bearing a fourth
derivatizable reactive group (R) in position 2 or 3 of one phenyl
ring, in addition to the three reactive functions in position 4.
To the best of our knowledge there are no methods of
trisbromination/iodination of monofunctionalized TPA described
to date. This can be explained by difficulties that rely mainly
on three points: first, introduction of a side chain increases or
decreases the electron density of the corresponding phenyl ring
leading potentially to over- or underhalogenation, respectively;
second, iodination is commonly performed using strong oxidants
(to oxidize I2 into the more electrophilic I+) whereas the central
nitrogen atom of the TPA core is oxidation sensitive,31,32 and
last, putative regioisomers are virtually inseparable from the
desired products.
We investigated several halogenation reagents/conditions and
developed an efficient set of reactions to obtain regioselectively
4,4′,4′′-trishalo, 2-(or 3-)functionalized TPA (Scheme 1). Among
the starting materials, 1 is commercially available whereas
compound 5 was obtained by Ullmann coupling from 2-ami-
nobenzoic acid followed by esterification and compound 7 by
Buchwald-Hartwig coupling from methyl 3-aminobenzoate.
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1734 J. Org. Chem., Vol. 73, No. 5, 2008

Triphenylamines Displaying High Two-Photon Absorption
SCHEME 2. First Attempts of Synthesis of Trisformylated TPA
SCHEME 3. Synthesis of Trisformylated TPAa
SCHEME 4. Synthesis of Functionalized Precursors for
Two-Branched TPAa
a Reagents and conditions: (a) PhBr, Pd(OAc)2, P(tBu)3, Cs2CO3, toluene,
reflux, o/n; (b) POCl3, DMF, 95 °C, 4 h; (c) NBS, CHCl3, reflux, 2 h.
on the trisbranched TPA the preparation of derivatizable
precursors leading to two-branched TPA was explored. As
depicted in Scheme 4, bisbromo and bisformyl precursors
bearing a methoxycarbonyl function on the third phenyl ring
(19 and 20) were easily obtained following classical synthetic
procedures. Comparatively, this straightforward access emp-
hazises the difficulties to be solved in the synthesis of the
monofunctionalized trisbranched series.
Synthesis of π-Conjugated Derivatizable Triphenylamines.
The versatile set of synthons was further used as starting
materials for the introduction of various electron-withdrawing
groups via vinylation. The biscyanomethyl, 4-pyridinyl, and
2-benzothiazolyl moieties were chosen since they are relatively
small, have been proved to be efficient electron-withdrawing
groups, and have been successfully incorporated into various
push-pull nonlinear optics materials23,42,48 and water-soluble
fluorophores.49,50
Thus, the highly fluorescent TPA 22, 23, and 26 were
obtained by Heck coupling,51 whereas 24 was synthesized by
Wittig reaction52 and 21 and 25 by Knoevenagel condensation.44
It should be noticed that, in spite of the anhydrous conditions
used, reaction of 4 in Heck conditions resulted in the concomi-
tant ester hydrolysis to yield the phenolic derivative 23. The
derivatizable TPA 21-26 (Scheme 5) display a large structural
a Reagents and conditions: (a) 4-BrC6H4COOMe, Cs2CO3, Pd(OAc)2,
P(tBu)3, toluene, reflux, o/n; (b) Red-Al, NMP, THF, 7 h, 0 °C; (c) LiAlH4,
THF, reflux, 1 h; (d) MnO2, CH2Cl2, rt, 48 h.
2). Unfortunately, the application of the palladium-catalyzed
procedure led in all cases to recovery of starting materials.
Then a new route was devised to access trisformylated key
intermediates and we focused our effort on the preparation of
the methoxy, trisformylated key compound 17 (Scheme 3). This
goal was achieved by construction of the corresponding triester
15 followed by a controlled reduction of all three esters.
Although direct reduction of aliphatic esters into aldehydes is
well documented,45 the parent reaction on aromatic esters was
revealed to be more difficult. Recently, a report on 2,6-
naphthalene-biscarbaldehyde synthesis, using modified Red-Al
reagent,46 prompted us to apply this reagent to our target system.
Unfortunately, despite repeated trials, the best yield was only a
poor overall yield of 38%. Unexpectedly, the unsymmetrical
monoester was isolated as the major byproduct and increasing
reaction time or hydrid concentration led only to complex
mixtures of over-reduced TPA. Finally, the classical two-step
sequence based on reduction into alcohol and smooth reoxy-
dation into aldehyde afforded 17 in far better yield (88%)
(Scheme 3).
As previously observed by us30 and others43,47 two-branched
TPA represent an alternative design of highly fluorescent
materials, which were also used for comparative purposes in
the photophysical studies. Therefore, in parallel with our work
(48) Rogers, J. E.; Slagle, J. E.; McLean, D. G.; Sutherland, R. L.; Brant,
M. C.; Heinrichs, J.; Jakubiak, R.; Kannan, R.; Tan, L. S.; Fleitz, P. A. J.
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Prasad, P. N. J. Phys. Chem. B 1999, 103, 10741-10745.
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J. Org. Chem, Vol. 73, No. 5, 2008 1735

Lartia et al.
SCHEME 5. Fluorescent Derivatizable TPA
SCHEME 6. Fluorescent Naked TPA
pattern diversity differing by the number of branches (from
trisbranched 21-24 to bisbranched 25 and 26) and the electronic
character of the functional group (21, 23, and 24 bear a donor
group whereas 22, 25, and 26 bear the acceptor COOMe). The
presence of the functional group induces distortion from the C3
symmetry and should also influence the electron density
repartition of the resulting TPA. Given that 2PA fluorescence
is expected to be sensitive to these two parameters, this
molecular set of derivatizable TPA will enable evaluation of
the structural determinants and optimization of the optical
properties aimed at selection of the best candidates for biola-
beling.
nucleophilic phosphonate anion. It is worth noting that the
“naked” triphenylamines prepared herein belong to the so-called
star-shaped chromophores and that some derivatives (29a and
29b) already have been described.23,44,54
Synthesis of TPA Suitable for Biolabeling. To achieve
biolabeling subsequent elongation of the initially grafted
functional group was then examined in the pyridine and
benzothiazole series. In the pyridine series compound 22 was
submitted to amidation with a monoprotected diamino PEG
linker after saponification, which afforded the derivative 31 in
a satisfactory yield (Scheme 7).
In the benzothiazole series, cleavage of the methoxy group
of derivative 24 with BBr3 failed likely due to complexation of
the borate reagent with the nitrogens of the benzothiazole
moieties as seen from MS analysis. Thus elongation was
attempted on the key trisformylated intermediate 17 (Scheme
8). Treatment of 17 with BBr3 led quantitatively to a tetrabro-
minated intermediate.55 Although the latter could be converted
into the desired compound 32 by AgNO3, yields and purity were
revealed to be poorly reproducible and use of other cleavage
agents (BI3 Me3SiCl/NaI, p-MeC6H4SNa) failed. Finally, AlCl3
in dichloromethane under gentle reflux afforded quantitatively
pure trisformylated phenol 32. Subsequent alkylation with 1,8-
Nonfunctionalized TPA. For comparative purposes a series
of “naked” (i.e., nonderivatizable) TPA were synthesized
following procedures similar to those described precedently. The
mono-, bis-, and trisbranched TPA series 27-29 were thus
obtained from their corresponding iodinated30 or formylated53
counterparts which bear three various vinyl groups: (biscyano)-
vinyl (a), vinylpyridine (b) and vinylbenzothiazole (c) (Scheme
6). It should be noted that yields of Wittig-Horner reaction
increased from 67% to 95% along with increasing number of
introduced benzothiazole moieties reflecting presumably the
electron-withdrawing character of this group and, hence, the
increased sensitivity of the remaining formyl group toward the
(54) Yan, Y.; Tao, X.; Sun, Y.; Yu, W.; Wang, C.; Xu, G.; Yang, J.;
Wu, Y.; Zhao, X.; Jiang, M. J. Mol. Struct. 2005, 733, 83-87.
(55) Lansinger, J. M.; Ronald, R. C. Synth. Commun. 1979, 9, 341-
349.
(53) Lai, G. F.; Bu, X. R.; Santos, J.; Mintz, E. A. Synlett 1997, 1275-
1276.
1736 J. Org. Chem., Vol. 73, No. 5, 2008

Triphenylamines Displaying High Two-Photon Absorption
SCHEME 7. Synthesis of Trispyridine TPA Suitable for Bioconjugationa
a Reagents and conditions: (a) LiOH, THF, H2O, rt, o/we; (b) EDCI, HOAt, DMF, rt, 7 days.
dibromooctane was easily performed under Williamson condi-
tions to afford 33. In parallel a carboxylic acid terminated linker
was introduced by use of ethyl ω-bromobutyrate, which afforded
34. Intermediates 33 and 34 were conveniently converted to
the highly fluorescent trisbenzothiazole derivatives 35 and 37
with phosphonate 4056 under Wittig-Horner conditions. Com-
pound 37 was converted to acid 38 and activated ester 39. On
the other hand, bromide 35 could be efficiently converted into
N-alkylmaleimide 36 by the method described by Turnbull.57
These reactional sequences provide us with a pool of highly
fluorescent TPA displaying a large set of reactivity for coupling
to biomolecules. For example, a haloalkylated terminated
compound, such as 35, might be linked on the 5′ end of
oligonucleotides by thiophosphate chemistry under nonaqueous
conditions.58 Equally, acid 38 might be coupled to oligonucle-
otides as well as to protein amino residues by in situ activation,
whereas 39 is expected to react similarly without the need of
prior activation. Last, maleimide derivatives (such as 36) may
serve for selective coupling with cysteine residues, which is
routinely applied for labeling proteins.59 Finally introduction
of an amino PEG linker should provide water solubility60 while
also allowing amidation reactions.
Optical Measurements. (a) Linear Spectroscopy. The
photophysical properties of fluorophores 21-29 were studied
in dichloromethane and are summarized in Table 1. All the
compounds show an intense π-π* absorption band (ꢀ g 40 000
L‚mol-1‚cm-1) with absorption maxima between 385 and 476
nm. The two- and three-branched compounds are significantly
red-shifted (∼28-30 nm) as compared to the monoderivatives
indicating some degree of conjugation between the vinyl
conjugated arms. The strongest absorption is obtained in the
benzothiazole (Bz) series with ꢀ up to 94 700 L‚mol-1‚cm-1
for compound 24. As expected the molar extinction coefficient
ꢀ increases with the number of π-conjugated branches. For
example, in the biscyano (BCN) series ꢀ is increasing from
39 400 L‚mol-1‚cm-1 for the monosubstituted derivative to
49 000 L‚mol-1‚cm-1 for the di- and 82 600 L‚mol-1‚cm-1 for
the trisubstituted compound. Importantly, the presence of a
lateral functionalized linker does not influence the UV/vis
absorption, neither in the two-branched nor in the three-branched
series, indicating that the electronic structure is not affected by
the linker.
In polar solvents, all fluorophores exhibit a broad structureless
emission characteristic of intramolecular charge transfer at
excited states61,62 (Figure 2, and the Supporting Information).
All compounds display high quantum yields in dichloromethane
(0.13 < η < 0.6) and large Stokes shifts (50 to 150 nm) (see
Table 1). In the benzothiazole series the quantum yield increases
with the dimensionality of the molecule since the two- and three-
branched compounds exhibit significantly higher quantum yields
than their mono counterpart. The same is observed for the two
other series but given the low one-photon fluorescence of the
monoderivatives the quantum yield was not determined. Most
importantly, in the three series introduction of the lateral chain
does not have a detrimental influence on the fluorescence
emission albeit a decrease in quantum yield of 20-30% is
systematically observed (see, for example, compounds 29c and
24 or compounds 29b and 22).
All the fluorophores (mono, bis, and tris) display a strong
emission solvatochromism that is reflected by a large batho-
chromic shift of their fluorescence emission maxima with
increasing solvent polarity. In contrast the absorption is not
shifted. This solvatochromic behavior, which results from the
stabilization of the highly polar emitting state by polar solvents,
is typical for compounds presenting an internal charge transfer
upon excitation and has been fully documented for numerous
fluorophores containing donor-acceptor units including triph-
enylamine derivatives.43,61,62 To examine in detail the solvent
effect, the emission spectra of compound 29c were recorded in
various media from nonpolar to polar solvents: as can be seen
in Figure 2 the maximum emission wavelength of 29c is red-
shifted by 100 nm from cyclohexane (455 nm) to methanol (560
nm). Interestingly in apolar media (toluene, cyclohexane) the
vibronic structure is restored likely due to the decrease of polar-
ity in the solvation shell and hence a better vibronic coupling.
The solvatochromic behavior is accompanied by a decrease of
the fluorescence quantum yield when the polarity of the solvent
increases. The origin of this quenching phenomenon is attributed
(56) Cai, G.; Bozhkova, N.; Odingo, J.; Berova, N.; Nakanishi, K. J.
Am. Chem. Soc. 1993, 115, 7192-7198.
(57) Clevenger, R. C.; Turnbull, K. D. Synth. Commun. 2000, 30, 1379-
1388.
(58) Asseline, U.; Thuong, N. T.; Helene, C. New J. Chem. 1997, 21,
5-17.
(59) Gorin, G.; Martic, P. A.; Doughty, G. Arch. Biochem. Biophys. 1966,
115, 593-597.
(61) Diwu, Z.; Zhang, C.; Klaubert, R. P.; Haughland, J. J. Photochem.
Photobiol. A 2000, 131, 95-100.
(62) Detert, H.; Schmidt, V. J. Phys. Org. Chem. 2004, 17, 1051-1056.
(60) Hayek, A.; Ercelen, S.; Zhang, X.; Bolze, F.; Nicoud, J. F.; Schaub,
E.; Baldeck, P. L.; Mely, Y. Bioconj. Chem. 2007, 18, 844-851.
J. Org. Chem, Vol. 73, No. 5, 2008 1737

Lartia et al.
SCHEME 8. Synthesis of Trisbenzothiazole TPA Suitable for Bioconjugationa
a Reagents and conditions: (a) AlCl3, CH2Cl2, reflux, o/n; (b) excess Br(CH2)8Br, K2CO3, acetone, 45 °C, 24 h; (c) Br(CH2)3COOEt, K2CO3, DMF, rt,
24 h; (d) 40, NaH, 15-crown-5, THF, rt, o/we; (e) (i) rac-7-oxabicyclo-[2.2.1]-heptene-2,3-dicarboxylic imide, K2CO3, DMF, 55 °C, o/n, (ii) anisole, reflux,
2 h; (f) LiOH, THF/H2O, rt, o/n; (g) NHS, DCC, CH2Cl2, rt, 24 h.
to the lowered energies of the ICT states62 but still remains
unclear and its amplitude rather unpredictable.63-65
determination of the 2PA cross section, if equal one- and two-
photon fluorescence quantum yields are assumed.3,4
(b) Two-Photon Absorption (2PA) Properties. 2PA spectra
of the TP dyes were obtained after two-photon-induced fluo-
rescence (TPIF) measurements, with a femtosecond Ti:sapphire
laser source delivering 90 fs pulses at 76 MHz repetition rate
over the spectral range from 740 to 840 nm. The TPIF intensities
of the samples were measured relative to a solution of
fluorescein, the ratio of the fluorescent signals enabling further
2PA cross section of the monosubstituted compounds was
revealed to be low, on the order of magnitude of that of standard
fluorophores (1-10 GM, 1 GM ) 10-50 cm4‚s‚photon-1), and
for this reason was not systematically determined. In the Bz
and BCN series, 2PA excitation spectra of two- and three-
branched TPA strongly differ in shape (Figure 3A,B). While
two-branched compounds have their maximum 2PA wavelength
between 760 and 820 nm, three-branched compounds exhibit
an absorption maximum below 740 nm, which is the lowest
excitation wavelength allowed by the titanium-sapphire laser
used in this study. Thus, the maximum 2PA wavelength appears
blue-shifted relative to twice the maximum 1PA wavelength,
(63) Le Droumaguet, C.; Mongin, O.; Werts, M. H. V.; Blanchard-Desce,
M. Chem. Commun. 2005, 2802-2804.
(64) Woo, H. Y.; Liu, B.; Kohler, B.; Korystov, D.; Mikhailovsky, A.;
Bazan, G. C. J. Am. Chem. Soc. 2005, 127, 14721-14729.
(65) Allain, C. Ph.D. Dissertation, Universite´ Pierre et Marie Curie, Paris,
2006.
1738 J. Org. Chem., Vol. 73, No. 5, 2008

Triphenylamines Displaying High Two-Photon Absorption
TABLE 1. Linear Optical Data and Two-Photon Absorption Properties
compd
λ
abs (nm)a
ꢀ (L‚mol-1‚cm-1
)
λ
em (nm)b
ηc
δ
max (GM)d
δ
max/M (GM‚g-1‚mol)
Bz series
27c (TP-1Bz)
28c (TP-2Bz)
29c (TP-3Bz)
24 (TP-3Bz-OMe)
37 (TP-3Bz-Oalk-ester)
403
431
433
432
428
19 700
59 400
89 200
94 700
90 000
531
0.24
0.59
0.54
0.45
0.38
16 (740 nm)
158 (760 nm)
345 (740 nm)
341 (740 nm)
365 (745 nm)
0.04
0.28
0.48
0.45
0.43
530
538
542
540
BCN series
27a (TP-1BCN)
28a (TP-2BCN)
25 (TP-2BCN-COOMe)
29a (TP-3BCN)
21 (TP-3BCN-OMe)
446
476
467
461
464
39 400
49 000
42 300
82 600
40 300
609
535
515
509
539
ndf
ndf
ndf
0.34e
0.20e
0.22e
0.14
205 (780 nm)
136 (780 nm)
204 (745 nm)
140 (745 nm)
0.52
0.30
0.43
0.28
Py series
27b (TP-1Py)
28b (TP-2Py)
26 (TP-2Py-COOMe)
29b (TP-3Py)
23 (TP-3Py-OH)
22 (TP-3Py-COOMe)
384
402
385
406
408
402
32 000
50 400
47 200
63 900
71 000
66 100
494
497
488
519
521
550
ndf
ndf
ndf
0.64
0.81
0.53
0.36
0.37
102 (820 nm)
34 (820 nm)
90 (820 nm)
73 (820 nm)
97 (820 nm)
0.23
0.07
0.16
0.13
0.16
a One-photon maximum absorption wavelength in dichloromethane. b Maximum fluorescence emission wavelength in dichloromethane. c Fluorescence
emission quantum yield, measured using quinine bisulfate in 1 N H2SO4 as a reference. d Maximum two-photon absorption cross section. e Measurements
were performed in chloroform. f nd: not determined.
stituted with pyridine groups have smaller two-photon absorption
cross sections, which remain slightly under 100 GM. On the
whole, in the Bz series the cross section increases strongly with
the number of branches and three-branched compounds exhibit
significantly increased two-photon absorption properties com-
pared to their two-branched and monobranched counterparts.
This increase is not linear with respect to the number of
branches, which is consistent with a cooperative enhancement
effect already observed for other vinyl triphenylamines43,47 and
for multimeric molecular systems.67 The δmax enhancement is
dramatic when the number of branches is increased from one
to two (approximately 10-fold from compound 27c to 28c) and
then more modest but still significant when increasing from two
to three (approximately 2-2.5-fold from 28c to 29c). This is
consistent with a strong electronic coupling between at least
two/several units and implies that bisbranched systems could
display both dipolar and quadrupolar characteristics. However,
the mechanism of this enhancement still remains to be fully
established.43,47
This trend is not observed in the BCN series and in the Py
series showing that the 2PA performance of the designed
triphenylamine dyes is dependent on several structural param-
eters (at least on the electron-withdrawing group and the number
of branches) thus confirming the difficulty to predict optimized
molecular structures.
However, in the three families (BCN, Bz, and Py) the two-
branched derivatives still reach a satisfying 2PA level, which
falls in the 100-200 GM range. This activity combined with
the easy synthetic access of these two-branched structures and
with their high quantum yields make these compounds worth
considering for biolabeling applications.
Finally and very interestingly no significant difference was
observed between the two-photon absorption cross section of
compounds bearing a derivatizable linker and that of their
unsubstituted counterparts. This can be exemplified in the Bz
series where a systematic comparison can be conducted, i.e.,
compare 29c, 24, and 37. This important feature was observed
in the case of the two- and three-branched series irrespective
FIGURE 2. Normalized emission spectra of compound 29c recorded
in various solvents.
indicating that higher order excited states may also contribute
to the signal.4,43 Additionally this indicates that the maximum
2PA wavelength is not reached in the scanned optical window
(740-840 nm), and suggests that it would be of interest to test
the three-branched compounds at lower excitation wavelengths.66
This trend is not observed in the Py series where the 2PA
maximum is situated around 820 nm for all compounds (Figure
3C). The pyridine group being much less electron-withdrawing
than the Bz and BCN functions, this indicates that the EW
character of the end group and thus the magnitude of the ICT
is a determinant of the 2PA spectral shape. In addition variations
of charge transfer occurring on each single branch are likely to
induce differences in the coupling between branches.
Determination of the 2PA cross section of the compounds at
their respective absorption maxima (δmax) was achieved and the
obtained values are listed in Table 1. As can be seen triphenyl-
amines substituted by 3 benzothiazole units (29c, 24, and 37)
and three biscyanovinyl groups (29a) are the most efficient
compounds, with two-photon absorption cross sections δmax
reaching respectively 365 and 204 GM. Triphenylamines sub-
(67) Karotki, A.; Drobizhev, M.; Dzenis, Y.; Taylor, P. N.; Anderson,
H. L.; Rebane, A. Phys. Chem. Chem. Phys. 2004, 6, 7-10.
(66) Xu, F.; Wang, Z.; Gong, Q. Opt. Mater. 2007, 29, 723-727.
J. Org. Chem, Vol. 73, No. 5, 2008 1739

Lartia et al.
FIGURE 3. Two-photon absorption cross sections of compounds in dichloromethane and fluorescein (/) in aqueous KOH (pH 10-11): (A)
benzothiazole series 28c (TP-2Bz, 2), 29c (TP-3Bz, 9), 37 (TP-3Bz O-alkyl-ester, 0); (B) biscyano series 28a (TP-2BCN, 2), 29a (TP-3BCN, 9),
21 (TP-3BCN-OMe, 0); and (C) pyridine series 28b (TP-2Py, 2), 29b (TP-3Py, 9), 22 (TP-3Py -COOMe, 4).
of the electron-withdrawing group present on the TPA and of
the linker length (Figure 3 and Table 1). This result indicates
that the distortion from the C3-symmetry induced by the linker
does not influence significantly the two-photon absorption
ability. This observation, made for the first time, fully validates
our initial design (Figure 1), which is especially important for
future applications.
On the whole, the cross-section values obtained for the most
efficient compounds fall in the range obtained for recently
optimized 2PA dyes dedicated to biolabeling.60,68 Nevertheless,
δ values remain 1 order of magnitude below that of the extended
π-conjugated TPA reported so far in the literature.9,23 But the
large size of the latter represents a major issue for the labeling
of biomolecules. In this respect and in order to compare the
2PA performances of different chromophoric series, the two-
photon absorption/molecular weight ratio (δ/MW) is a relevant
figure of merit. In this regard, our compounds fall in the range
of the best chromophores reported so far with a δ/MW ratio
around 0.5 GM‚g-1‚mol for compounds 29c (TP-3Bz) and 28a
(see Table 1) compared to values of 0.5-1.0 GM‚g-1‚mol
described for large-sized systems optimized for 2-photon
absorption.9,66,67
allows introduction of side chains of various nature and length
and terminated with chemically reactive groups suitable for
conjugation to biomolecules. The one-photon and two-photon
characterizations in organic solvents show high extinction
coefficients, high quantum yields, and high 2PA cross sections.
Comparison of the derivatized series with their nonderivatized
counterparts shows that the former retain all of the desirable
nonlinear optical properties. This indicates that the presence of
the linker although affecting the C3-symmetry does not have
significant consequences on the 2PA absorption, which fully
validates the initial three-branched monosubstituted design.
Interestingly the good 2PA performances of the two-branched
series highlight this design as a valuable alternative for
fluorescent labeling. Finally the relatively small size of our
compounds allows us to anticipate that water solubility could
be provided either by quaternerization of heterocyclic ring
nitrogens30 or by the use of highly hydrophilic linkers (PEG or
polyammonium and peptides chains)69 which will be the next
step in exploring fully the biolabeling potential of the newly
synthesized triphenylamines.
Experimental Section
In the aggregate, our data fully validate the initial design of
derivatizable vinyl triphenylamines for covalent labeling of
biomolecules and subsequent tracking using multiphoton mi-
croscopy. They also demonstrate that 2-branched compounds
might be good candidates to consider given their good perfor-
mance and the short and easy synthetic access of the deriva-
tizable derivatives. As a result, we are currently focusing our
efforts in the development of functionalized TPA based on both
designs.
2-Bromo-5-(N,N-Bis(4-bromophenyl)amino)phenyl Acetate
(3). Compound 2 (153 mg, 525 µmol) was dissolved in chloroform
(3 mL) and cooled to 0 °C and bromine (79 µL, 1.54 mmol) in
solution in chloroform (5 mL) was added dropwise during 1 h.
The reaction mixture was stirred at rt for 2 h. Then it was diluted
in CH2Cl2 and washed with a Na2S2O3 solution (0.1 M), a NaHCO3
solution (10%), and water. The organic layers were collected, dried
(Na2SO4), and evaporated to afford 225 mg (426 µmol) of a light
green powder in 81% yield (product is spoiled by a few isomers).
Alternatively, 3 could be prepared from 2 (450 mg, 1.48 mmol,
1 equiv) and benzyltrimethylammonium tribromide (1.70 g, 4.45
Conclusions
(68) Hayek, A.; Bolze, F.; Nicoud, J.-F.; Baldeck, P. L.; Mely, Y.
Photochem. Photobiol. Sci. 2006, 5, 102-106.
(69) Meltola, N. J.; Wahlroos, R.; Soin, A. E. J. Fluorescence 2004, 14,
635-647.
In conclusion, new synthetic methodologies were developed
opening access to three series of novel fluorescent π-conjugated
triphenylamines. The versatility of the synthetic routes described
1740 J. Org. Chem., Vol. 73, No. 5, 2008

Triphenylamines Displaying High Two-Photon Absorption
mmol, 3 equiv) dissolved in a CHCl3/MeOH mixture (10 mL, 1:1,
v/v) containing excess CaCO3. Once the solution became colorless,
the crude mixture was filtered, washed with water, dried (Na2SO4),
concentrated, and purified by column chromatography (n-hexane/
CH2Cl2, 3:1, v/v) affording the title compound in lower yield (67%)
but isomer free.
Mp 242-244 °C. 1H NMR (CDCl3) δ 1.00 (d, J ) 7.2 Hz, 3H),
1.80 (hex, J ) 7.2 Hz, 2H), 4.27 (t, J ) 7.2 Hz, 2H), 6.93-6.90
(m, 5H), 7.44 (d, J ) 2.7 Hz, 1H), 7.59 (d, J ) 8.7 Hz, 4H), 7.80
(d, J ) 8.4 Hz, 1H). 13C NMR (CDCl3) δ 10.6, 21.9, 67.5, 85.3,
87.4, 125.3, 126.4, 127.3, 137.2, 138.7, 141.9, 146.1, 146.9, 166.5.
HRMS (MALDI+) calcd for C22H18NO2I3 708.8466, found 708.8442.
Mp 68-70 °C; IR (KBr pellet) 1774 (νCdO, ester), 1579 (Ar),
1486 (Ar) cm-1; 1H NMR (acetone-d6) δ 2.27 (s, 3H), 6.89 (dd, J
) 2.7 Hz, 8.4 Hz, 1H), 7.07 (d, J ) 9.0 Hz, 4H), 7.51 (d, J ) 9.0
Hz, 4H), 7.56 (d, J ) 8.4 Hz, 1H). 13C NMR (CDCl3) δ 20.8, 109.1,
116.9, 118.1, 121.8, 126.2, 132.7, 134.6, 145.6, 147.2, 148.9, 167.4.
HRMS (FAB+) calcd for C20H1479Br281BrNO2 538.8555, found
538.8556. HRMS (FAB+) calcd for C20H1479Br81Br2NO2 540.8536,
found 540.8541.
2-Iodo-5-(N,N-bis(4-iodophenyl)amino)phenyl Acetate (4). To
a well-stirred solution of 2 (77 mg, 254 µmol) in CH2Cl2 (2 mL)
was added an excess of iodine (449 mg, 1.77 mmol, 7 equiv). After
complete dissolution, red mercury oxide (384 mg, 1.77 mmol, 7
equiv) was added and the solution was stirred for 3 d at rt. The
suspension was filtered through a pad of Celite and washed with
Na2S2O3 (0.1 M) and water. The organic layers were collected, dried
(Na2SO4), and concentrated to dryness to afford dark brown residue.
This residue was purified by chromatography on a short column
(eluant: n-hexane/CH2Cl2 (2/1, v/v)) to afford the title compound
as a white foam (153 mg, 223 µmol) in 88% yield.
Methyl 2-Methoxy-4-(N,N-bis(4-methoxycarbonylphenyl)ami-
no)benzoate (15). To dry and degassed toluene (30 mL) were
introduced Pd(OAc)2 (186 mg, 828 µmol, 5%) and P(t-Bu)3 (7.7
mL, 2.48 mmol, 15%, 10% in hexanes (w/w)). After 15 min of
stirring, methyl 4-bromobenzoate (10.7 g, 49.7 mmol, 3 equiv),
methyl 2-methoxy-4-aminobenzoate (3.0 g, 16.6 mmol, 1 equiv),
and Cs2CO3 (13.5 g, 41.4 mmol, 2.5 equiv) were added. The
solution was refluxed overnight, cooled to rt, and diluted with CH2-
Cl2 (100 mL). The crude mixture was filtered through a Celite pad,
evaporated to dryness, and purified by silica gel column chroma-
tography (n-hexane/CH2Cl2 (2:1, v/v) to CH2Cl2 gradient) to afford
a light yellow powder (6.35 g, 14.8 mmol) in 89% yield.
Mp 77-79 °C. IR (KBr pellet) 2839 (νC-OMe), 1719 (νCdO, ester),
1597 (Ar), 1507 (Ar) cm-1. 1H NMR (CDCl3) δ 3.76 (s, 3H), 3.91
(s, 3H), 3.94 (s, 6H), 6.68 (m, 2H), 7.17 (d, J ) 8.7 Hz, 4H), 7.80
(d, J ) 9.0 Hz, 1H), 7.98 (d, J ) 8.7 Hz, 4H). 13C NMR (CDCl3)
δ 166.3, 165.8, 160.6, 151.0, 150.2, 133.2, 131.1, 125.4, 123.8,
116.0, 115.5, 108.0, 56.0, 52.0, 51.8. HRMS (DCI+) calcd for
C25H24NO7 450.1553, found 450.1548.
Mp 74 °C; IR (KBr pellet) 1771 (νCdO, acetate), 1575 (Ar), 1483
(Ar) cm-1. 1H NMR (acetone-d6) δ 2.28 (s, 3H), 6.77 (dd, J ) 8.7
Hz, 2.7 Hz, 1H), 6.89 (d, J ) 2.7 Hz, 1H), 6.94 (d, J ) 9.0 Hz,
4H), 7.69 (d, J ) 9.0 Hz, 4H), 7.75 (d, J ) 8.7 Hz, 1H). 13C NMR
(CDCl3) δ 21.2, 81.9, 87.4, 117.7, 122.3, 126.6, 138.6, 139.5, 146.2,
148.2, 152.0, 168.4. HRMS (ESI-) calcd for C18H11I3NO [M -
Ac] 637.7975, found 637.7977.
Alternatively, compound 4 was prepared by stirring 2 (100 mg,
330 mol) and silver(I) trifluoroacetate (219 mg, 991 µmol, 3 equiv)
and iodine (251 mg, 989 mol, 3 equiv) in chloroform (5 mL) for 3
d at rt. Yield: 80%.
Methyl 5-[Bis(4-bromophenyl)amino]-2-bromobenzoate (8).
A solution of 3-(diphenylamino)benzoic acid methyl ester 7 (5.20
g, 17.1 mmol, 1 equiv) and NBS (6.71 g, 37.7 mmol, 2.2 equiv) in
CHCl3 was heated at reflux. The reaction course was followed by
1H NMR. After 2 h, a second portion of NBS (6.10 g, 34.3 mmol,
2.0 equiv) was added. After 2 d of reflux, the chloroform was
removed in vacuo and the residue was filtered through a short silica
pad and washed with CH2Cl2/n-pentane (1:1, v/v) to give 8 (8.78
g, 95%) as a light brown solid. The compound purity was estimated
by 1H NMR to be >95%, and it was used without further
purification.
(4-{Bis[4-(hydroxymethyl)phenyl]amino}-2-methoxyphenyl)-
methanol (16). To a slurry of LiAlH4 (1.7 g, 45 mmol, 15 equiv)
in dry THF (30 mL) was added a solution of 15 (1.35 g, 3 mmol)
in THF (20 mL) dropwise at -78 °C. The reaction mixture was
allowed to warm to rt and then was stirred at reflux for 1 h. The
mixture was cooled again to -78 °C then diluted in CH2Cl2, and
water (10 mL) was added. The solids were filtered and washed
thoroughly with CH2Cl2 and the filtrate was washed with water
and brine, dried (Na2SO4), and concentrated to afford a green paste
(1.05 g, 2.88 mmol) in 97% yield.
1
Mp 138 °C. H NMR (acetone-d6) δ 3.67 (s, 3H), 3.90 (t, J )
5.7 Hz, 1H), 4.17 (t, J ) 5.7 Hz, 2H), 4.59 (s, 4H), 4.61 (s, 2H),
6.57 (dd, J ) 1.8 Hz, 8.1 Hz, 1H), 6.67 (d, J ) 1.8 Hz, 1H), 7.00
(d, J ) 8.4 Hz, 4H), 7.29 (d, J ) 8.4 Hz, 4H), 7.30 (d, J ) 8.1 Hz,
1H). 13C NMR (acetone-d6) δ 54.8, 59.0, 63.5, 106.4, 115.8, 123.7,
125.2, 127.8, 128.4, 136.9, 146.8, 148.1, 157.5. MS (DCI+) m/z
348 (100%) [M - H2O + H]+. HRMS (ESI+) calcd for C22H23-
NO4Na 388.1525, found 388.1509.
4-[Bis(4-formylphenyl)amino]-2-methoxybenzaldehyde (17).
To a solution of 16 (27 mg, 74 µmol) in CH2Cl2 (2 mL) was added
MnO2 (40 mg, 444 µmol). The resulting suspension was stirred
for 48 h at rt and filtered. Solids were washed well with CH2Cl2
and the filtrate was concentrated to afford the product as a yellow
solid (25 mg, yield 91%).
Mp 109-111 °C; IR (KBr pellet) 1486 (Ar), 1580 (Ar), 1732
1
(νCdO) cm-1. H NMR (CD2Cl2) δ 3.87 (s, 3H), 6.99 (d, J ) 9.0
Hz, 4H), 7.05 (dd, J ) 8.7 Hz, 2.7 Hz, 1H), 7.40-7.46 (m, 5H),
7.54 (d, J ) 8.7 Hz, 1H). 13C (CDCl3) δ 52.4, 114.0, 116.5, 125.5,
126.0, 127.2, 132.6, 133.5, 135.1, 145.7, 146.3, 166.1. HRMS
(DCI+) calcd for C20H15Br3NO2 537.8653 (79Br)3, 539.8633 (79-
Alternatively, 17 could be obtained directly from 15 as follows:
In a dry flask and under an inert atmosphere, Red-Al solution
(3.70 mL, 65% in toluene (w/w)) was diluted in dry toluene (5
mL). After cooling to 0 °C, freshly distilled N-methylpiperazine
(1.48 mL) was added dropwise. The resulting Red-Al-modified
colorless solution was stirred 20 min and stored at rt.
Br)2
+ +
81Br, 541.8614 (81Br)2 79Br, 543.8598 (81Br)3, found
537.8661, 539.8623, 541.8602, 543.8574.
Propyl 2-Iodo-5-(N,N-bis(4-iodophenyl)aminobenzoate (9). To
a solution of 7 (134 mg, 441 µmol, 1 equiv) dissolved in technical
n-propanol (5 mL) were added iodine (1.12 g, 4.41 mmol, 10 equiv)
and red mercury oxide (956 mg, 4.41 mmol, 10 equiv). The resulting
suspension was heated at 85 °C for 2 weeks. Regularly after ca. 72
h, I2 (2 equiv) and HgO (2 equiv) were added portionwise again.
Then the crude mixture was filtered through a Celite pad and
abundantly washed with hot toluene. Mother liquors were concen-
trated to dryness, redissolved in a few milliliters, and filtered again.
This procedure was repeated until removal of excess HgO. The
crude mixture (215 mg) contained the expected product along with
the methyl ester (in a 5.6:1 ratio) as impurity and was purified by
preparative TLC (n-hexane/Et2O, 95:5, v/v) to afford the title
compound as a yellow oil (160 mg) in 51% yield.
To a solution of 15 (300 mg, 667 µmol, 1 equiv) dissolved in
dry toluene (10 mL) cooled to 0 °C was added Red-Al-modified
solution dropwise (1.90 mL, 2.30 mmol hydride, 3.44 equiv). Light
green coloration occurred rapidly. After 8 h of stirring at rt, the
appearance of the expected product (Rf 0.29 in n-hexane/THF, 7:3,
v/v) and residual monoester was noticed. Water was added (2 mL)
and the resulting biphasic mixture was filtered through a Celite
pad. Mother liquor was decanted, diluted by CH2Cl2, and washed
several times with HCl (10 mM) and water. After evaporation to
dryness, the residue was redissolved in THF/LiOH saturated solution
(20 mL, 1:1, v/v) and stirred for 2 h. Once disappearance of residual
monoester derivative was noticed by TLC (in n-hexane/THF, 7:3,
v/v), the mixture was treated using classical procedures and purified
J. Org. Chem, Vol. 73, No. 5, 2008 1741

Lartia et al.
by column chromatography (n-hexane/THF, 3:1, v/v) to afford 92
mg (256 µmol) in 38% yield.
Mp 130 °C dec. IR (KBr pellet) 1715 (νCdO), 1631 (νCdC), 1588
1
(Ar), 1504 (Ar) cm-1. H NMR (CD2Cl2) δ 3.88 (s, 3H), 6.95 (d,
J ) 16.2 Hz, 1H), 7.02 (d, J ) 16.2 Hz, 2H), 7.17 (d, J ) 8.7 Hz,
4H), 7.32 (s, 1H), 7.32 (dd, J ) 2.7 Hz, 8.4 Hz, 1H), 7.36-7.46
(m, 7H), 7.55 (d, J ) 8.7 Hz, 4H), 7.70 (d, J ) 2.7 Hz, 1H), 7.73
Mp 130-131 °C. IR (KBr pellet) 2841 (νS, CH3), 2735 (νC-H
,
formyl), 1697 (νCdO, formyl), 1592 (Ar), 1504 (Ar) cm-1. NMR
1H (CDCl3) δ 3.81 (s, 3H), 6.71 (s, 1H), 6.77 (dd, J ) 8.4 Hz, 0.9
Hz, 1H), 7.29 (d, J ) 8.4 Hz, 4H), 7.84 (d, J ) 8.4 Hz, 1H), 7.88
(d, J ) 8.4 Hz, 4H), 9.89 (s, 2H), 10.39 (s, 1H). 13C NMR (CD2-
Cl2) δ 55.8, 107.5, 116.8, 121.5, 124.6, 129.8, 131.2, 132.6, 151.3,
152.6, 163.1, 187.8, 190.4. HRMS (DCI+) calcd for C22H18NO4
360,1236, found 360.1229.
(d, J ) 8.4 Hz, 1H), 8.15 (d, J ) 16.2 Hz, 1H), 8.58 (br, 6H). 13
C
NMR (CDCl3) δ 167.2, 150.2, 147.0, 146.8, 144.8, 144.6, 132.6,
132.2, 131.8, 131.1, 130.3 128.3, 127.7, 127.6, 125.6, 125.2, 124.4,
121.0, 120.7, 52.4. HRMS (DCI+) calcd for C41H33N4O2 613.2604,
found 613.2599.
Tris[4-(2,2-dicyanovinyl)phenyl]amine (29a). Molecular sieve
(1.00 g, 3 Å), malononitrile (101 mg, 1.53 mmol, 3.6 equiv), acetic
acid (few drops), and ammonium acetate (1 crystal) were added to
a solution of tris(4-formylphenyl)amine (140 mg, 430 µmol, 1
equiv) in dry pyridine (15 mL). After a few minutes of stirring at
rt, the solution turned red. After 2.5 h of stirring at rt, pyridine
was removed in vacuo, and the residue was dissolved in CH2Cl2,
filtered through a Celite pad, and washed with water. The organic
phase was dried over Na2SO4 and its volume was reduced to ca. 1
mL. Then 29a was obtained as a red powder (164 mg, 344 µmol)
in 80% yield by precipitation with hexane.
Mp 180 °C dec. IR (KBr pellet) 1497 (Ar), 1581 (Ar), 2222
(νCN) cm-1. 1H NMR (CDCl3) δ 7.29 (d, J ) 8.7 Hz, 6H), 7.73 (s,
3H), 7.96 (d, J ) 8.7 Hz, 6H). 13C NMR (CDCl3) δ 81.70, 112.8,
113.8, 124.9, 127.7, 132.8, 150.1, 157.5. HRMS (DCI+) calcd for
C30H16N7 474.1467, found 474.1458.
{4-[(E)-2-(Benzothiazol-2-yl)vinyl]}-N,N-bis{4-[(E)-2-(ben-
zothiazol-2-yl)vinyl]phenyl}aniline (29c). Phosphonate 40 (574
mg, 2.01 mmol, 3.3 equiv), NaH (60% dispersion, 54 mg, 2.25
µmol, 3.7 equiv), and one drop of 15-crown-5 were dissolved in
dry THF (5 mL). To this reddish solution was added tris(4-
formylphenyl)amine (200 mg, 607 µmol, 1 equiv) in dry THF (20
mL) dropwise. After 70 h of stirring, disappearance of tris(4-
formylphenyl)amine was noticed by TLC and the solution became
yellow greenish fluorescent. The reaction was quenched with water,
diluted with diethyl ether, decanted, and washed with water. After
evaporation, the resulting yellow powder was triturated in n-pentane
affording the title compound as a yellow powder (412 mg, 570
µmol) in 94% yield.
Mp 154 °C dec. IR (KBr pellet) 1625 (νCdC), 1591 (Ar), 1505
(Ar), 1454 (Ar) cm-1. 1H NMR (DMSO-d6) δ 7.14 (d, J ) 8.7 Hz,
6H), 7.43 (dt, J ) 1.2 Hz, 8.1 Hz, 3H), 7.51 (dt, J ) 1.2 Hz, 8.1
Hz, 3H), 7.53 (d, J ) 16.2 Hz, 3H), 7.65 (d, J ) 16.2 Hz, 3H),
7.78 (d, J ) 8.7 Hz, 6H), 7.96 (d, J ) 7.8 Hz, 3H), 8.09 (d, J )
7.8 Hz, 2H). 13C NMR (CDCl3) δ 167.1, 154.0, 147.7, 136.8, 134.4,
130.1, 128.7, 126.3, 125.3, 124.5, 122.9, 121.5, 121.0. HRMS
(DCI+) calcd for C45H31N4S3 723.1702, found 723.1721.
5-(Bis{4-[(E)-2-(pyridin-4-yl)vinyl]phenyl}amino)-2-[(E)-2-
(pyridin-4-yl)vinyl]benzoic Acid (30). The methyl ester 22 (50
mg, 82 µmol) was dissolved in 2 mL of THF. Aqueous LiOH (1
mL, 20 mg‚mL-1) was added and the mixture was stirred at rt in
the dark for 72 h. The solvents were removed under reduced
pressure; the residue was dissolved in ethanol and filtered. The
filtrate was concentrated under reduced pressure to give 30 as a
red powder with quantitative yield.
Before LiOH treatment, asymmetric monoester could be isolated
(12% yield). Despite increased reaction time, its presence was
always noticed.
Methyl 4-(N,N-Bis(4-formylphenyl)amino)benzoate (19). Dry
DMF (2.9 mL, 37.5 mmol) was cooled to 0 °C and POCl3 (3.7
mL, 40 mmol) was added dropwise under nitrogen atmosphere.
The mixture was stirred for 1 h at 0 °C and in case it became solid,
warmed until melted. To this mixture 18 (500 mg, 1.6 mmol) was
added with vigorous stirring during the addition. The reaction was
carried out at 95 °C for 4 h. After cooling to rt, the reaction mixture
was poured onto ice and neutralized by addition of NaOH pellets.
The product was extracted with CH2Cl2. The organic phase was
washed with brine and dried over sodium sulfate. The crude product
was purified by column chromatography (n-hexane/AcOEt, 3:1,
v/v). The expected product was obtained as an orange foam (205
mg, 553 µmol) in 35% yield and the monoformylated byproduct
as a yellow oily major byproduct (358 mg, 1.04 mmol) in 65%
yield.
Mp 129 °C. 1H NMR (CDCl3) 3.96 (s, 3H), 7.27 (m, 6H), 7.85
(d, J ) 8.7 Hz, 4H), 8.04 (d, J ) 8.7 Hz, 2H), 9.96 (s, 2H). 13C
NMR (CDCl3) δ 52.2, 124.0, 124.8, 126.6, 131.4 (2C), 132.2, 149.8,
151.4, 166.3, 190.5. HRMS (DCI+) calcd for C22H18NO4 360.1236,
found 360.1223.
4-(2,2-Dicyanovinyl)-3-methoxy-[N,N-(4-(2,2-dicyanovinyl)-
phenyl)]aniline (21). To aldehyde 17 (61 mg, 170 µmol, 1 equiv)
in dry pyridine (5 mL) were added malononitrile (40 mg, 606 µmol,
3.6 equiv), AcONH4 (one crystal), AcOH (one drop), and crushed
molecular sieve (3 Å). The reaction mixture was stirred 16 h at rt.
Pyridine was removed under reduced pressure. The residue was
redissolved in CH2Cl2 and filtered through a Celite pad. The mother
liquor was washed with diluted HCl and water, and then concen-
trated to dryness, redissolved in CH2Cl2, and filtered through a short
silica plug. The residue was triturated in n-hexane and Et2O to afford
the title compound as a red powder (53 mg, 105 µmol) in 62%
yield.
Mp 125 °C. IR (KBr pellet) 1503 (Ar), 1573 (Ar), 2224 (νCN
)
cm-1. NMR 1H (CD2Cl2) δ 8.26 (s, 1H), 8.25 (d, J ) 8.4 Hz, 1H),
7.95 (d, J ) 8.7 Hz, 4H), 7.77 (s, 2H), 7.29 (d, J ) 8.4 Hz, 4H),
6.83 (dd, J ) 8.7 Hz, 2.9 Hz, 1H), 6.72 (d, J ) 2.9 Hz, 1H), 3.80
(s, 3H). 13C (CDCl3) δ 56.3, 80.3, 81.6, 107.0, 112.8, 113.4, 113.8,
114.6, 117.4, 117.5, 124.8, 127.6, 130.5, 132.7, 150.0, 151.9, 152.1,
157.5, 160.4. HRMS (DCI+) calcd for C31H18N7O 504.1573, found
504.1574.
Methyl 5-{N,N-Bis{4-[(E)-2-(pyridin-4-yl)vinyl]phenyl}}amino-
2-[(E)-2-(pyridin-4-yl)vinyl]benzoate (22). To a dry and degassed
TEA/DMF (9 mL, 2:1, v/v) mixture were added Pd(OAc)2 (191
mg, 85 µmol, 8%) and P(o-tolyl)3 (78 mg, 255 µmol, 24%) and
the suspension was stirred 10 min. Then 8 (575 mg, 1.06 mmol, 1
equiv) and 4-vinylpyridine (574 µL, 5.30 mmol, 5 equiv) were
added and the resulting mixture was heated to 85 °C for 18 h. The
crude mixture was allowed to cool to rt, diluted with CH2Cl2, and
washed with a NaHCO3 solution (10%) and water. The organic
layer were collected, dried, and evaporated to dryness. The resulting
red oil was diluted with a few drops of CH2Cl2 then redissolved
by n-pentane and the resulting precipitate was filtered to afford
impure title compound (741 mg). The red powder was subjected
to column chromatography (CH2Cl2 to CH2Cl2/MeOH (96:4, v/v)
to afford 495 mg of the product as an orange powder (495 mg,
806 µmol) in 76% yield.
Mp >260 °C. IR (KBr pellets) 1505 (Ar), 1587 (Ar), 1630 (νCd
1
C), 1759 (νCdO) cm-1. H NMR (MeOD) δ 7.05-7.18 (m, 8H),
7.30 (d, J ) 2.1 Hz, 1H), 7.50 (d, 2H, J ) 16.2 Hz), 7.56-7.62
(m, 10H), 7.77 (d, J ) 8.7 Hz, 1H), 8.05 (d, J ) 16.2 Hz, 1H),
8.45 (m, 6H). 13C NMR (MeOD + D2O) δ 121.0, 121.2, 122.7,
123.8, 124.0, 124.1, 124.6, 126.6, 128.1, 128.3, 131.4, 132.2, 133.2,
142.5, 146.2, 146.6, 146.7, 147.3, 148.8, 148.9, 175.6. MS (FAB+)
m/z 605.5 ([M + Li]+, 15%), m/z 599 ([M + H]+, 10%), m/z 314.2
([M + 2Li]2+/2, 25%). HRMS (ESI+) calcd for C40H31N4O2
599.2447, found 599.2398.
[2-(2-{2-[5-{Bis-[4-(2-pyridin-4-ylvinyl)phenyl]amino}-2-(2-
pyridin-4-ylvinyl)benzoylamino]ethoxy}ethoxy)ethyl]-
carbamic Acid tert-Butyl Ester (31). To a solution of 2-[2-(2-
aminoethoxy)ethoxy]ethylcarbamate (19 mg, 76.5 µmol, 1.2 equiv)
1742 J. Org. Chem., Vol. 73, No. 5, 2008

Triphenylamines Displaying High Two-Photon Absorption
in DMF (2 mL) were added acid 30 (39.5 mg, 6.53 × 10-2 mmol,
1.0 equiv), EDCI (13.7 mg, 71.5 µmol, 1.1 equiv), and HOAt (11
mg, 80.8 µmol, 1.2 equiv). The mixture was stirred 7 days at rt in
the dark. The mixture was then diluted with CH2Cl2 (60 mL) and
washed with water (3 × 15 mL). The aqueous phase was extracted
with CH2Cl2 (10 mL). The organic phases were combined and dried
over Na2SO4. The product was dried under reduced pressure to
remove DMF and then purified by preparative TLC (SiO2 2 mm,
elution with CH2Cl2/MeOH 95/5) to give 31 as an orange solid
(16 mg, 30% yield).
chromatography (elution with a MeOH gradient 0 to 1% in CH2-
Cl2) to afford the product as an orange powder (275 mg, 530 µmol)
in 75% yield.
1
Mp 80 °C. H NMR (CDCl3) δ 1.23 (t, J ) 6.6 Hz, 3H), 2.12
(quint, J ) 6.6 Hz, 2H), 2.50 (t, J ) 6.6 Hz, 2H), 3.96 (t, J ) 6.6
Hz, 2H), 4.11 (q, 6.6 Hz, 2H), 6.69 (br, 1H), 6.73 (br, d, J ) 8.4
Hz, 1H), 7.25 (br, dd, J ) 8.7 Hz, 4H), 7.77 (d, J ) 8.1 Hz, 1H),
7.84 (d, J ) 8.7 Hz, 4H), 9.93 (s, 2H), 10.35 (s, 1H). 13C NMR
(CDCl3) δ 14.2, 24.2, 30.5, 60.6, 67.5, 108.1, 117.0, 121.7, 122.8,
124.6, 130.1, 131.4, 132.6, 151.1, 152.5, 162.3, 172.8, 187.9, 190.5.
HRMS (ESI+) calcd for C27H25NaNO6 482.1580, found 482.1563.
1H NMR (CDCl3) δ 1.44 (s, 9H), 3.22 (br s, 2H), 3.44 (t, J )
5.4 Hz, 4H), 3.49 (d, J ) 5.1 Hz, 2H), 3.68 (br s, 4H), 4.91 (br s,
1H, NH), 6.43 (br s, 1H, NH), 6.95 (d, J ) 16.2 Hz, 1H), 6.98 (d,
J ) 16.2 Hz, 2H), 7.17 (d, J ) 8.4 Hz, 4H), 7.22 (d, J ) 8.4 Hz,
1H), 7.27 (d, J ) 2.4 Hz, 1H), 7.31 (d, J ) 16.2 Hz, 2H), 7.41 (br
s, 6H), 7.51 (d, J ) 8.4 Hz, 4H), 7.67 (d, J ) 8.4 Hz, 1H), 7.70 (d,
J ) 16.2 Hz, 1H), 8.63 (br s, 6H). 13C NMR (CDCl3) δ 28.4, 39.9,
40.3, 69.7, 39.8, 70.1, 70.3, 79.5, 122.2, 124.7, 125.2, 127.1, 127.6,
128.3, 129.0, 129.9, 131.8, 132.3, 144.7, 146.9, 147.1, 150.1, 155.9.
MS (FAB+) m/z 829.5 (75%) [M + H]+, m/z 729.5 (18%) [M -
Boc + H]+, m/z 581.3 (88%) [M + H - (NH-((CH)2O)2 -(CH2)2-
NH2)]+. HRMS (DCI+) calcd for C51H53N6O 828.3999, found
829.4048.
4-[Bis(4-formylphenyl)amino]-2-hydroxybenzaldehyde (32).
To a suspension of AlCl3 (575 mg, 4.31 mmol, 5 equiv) in dry
CH2Cl2 (10 mL) at -10 °C was added a solution of 17 (310 mg,
860 µmol) in CH2Cl2 (5 mL) dropwise. The mixture was stirred at
reflux overnight then poured into an ice/water mixture and
vigorously stirred for 10 min. The mixture was extracted with CH2-
Cl2. The combined organic layers were washed with water and
brine, dried (Na2SO4), and concentrated to afford a crude solid that
was triturated in n-hexane to give 32 as a yellow powder (260 mg,
754 µmol) in 87% yield.
3-[8-(2,5-Dioxo-1-aza)cyclopent-3-enyl]octyloxy- 4-[(E)-2-
(benzothiazol-2-yl)vinyl]-N,N-(bis{4-[(E)-2-(benzothiazol-2-yl)]-
vinyl}phenyl)aniline (36). Compound 35 (24 mg, 25.8 µmol), rac-
7-oxabicyclo[2.2.1]heptene-2,3-dicarboxylic imide (5 mg, 28.4
µmol, 1.1 equiv), and K2CO3 (18 mg, 129 µmol, 5 equiv) were
dissolved in dry DMF (500 µL). The resulting suspension was
stirred at 55 °C overnight. The reaction course was monitored by
TLC. Once starting material disappearance was noticed, the crude
mixture was diluted in CH2Cl2 and washed with water. The
combined organic phases were dried and concentrated. The residue
was redissolved in anisole (5 mL) and refluxed 2 h. Anisole was
vacuum distilled and the residue was purified by preparative TLC
(CH2Cl2/MeOH, 400:3, v/v) repeatedly, until separation. The title
compound was isolated as an orange powder (11 mg, 12 µmol) in
47% yield.
Mp 80 °C. IR (KBr pellet) 1508 (Ar), 1590 (Ar), 1702 (νCdO
)
cm-1. 1H NMR (CDCl3) δ 1.30-1.60 (br, 10H), 1.85 (quint, 2H),
3.52 (t, J ) 7.2 Hz, 2H), 3.93 (t, J ) 6.3 Hz, 2H), 6.67 (s, 4H),
6.72 (d, J ) 1.8 Hz, 1H), 6.77 (dd, J ) 1.8 Hz, 8.4 Hz, 1H), 7.22
(d, J ) 8.4 Hz, 4H), 7.33-7.60 (m, 16 H), 7.84 (d, J ) 16.2 Hz,
1H), 7.90 (m, 3H), 8.01 (d, J ) 7.6 Hz, 1H), 8.03 (d, J ) 7.6 Hz,
2H). 13C NMR (CDCl3) δ 26.1, 26.6, 28.5, 29.0, 29.1, 29.2, 37.9,
68.6, 108.0, 116.9, 120.4, 121.0, 121.4, 121.5, 122.7, 122.9, 124.4,
125.0, 125.2, 126.3, 126.4, 128.7, 128.9, 130.6, 132.7, 134.0, 134.4
(2C), 136.8, 147.6, 148.9, 153.9, 154.0, 158.1, 167.3, 168.6, 171.0.
HRMS (FAB+) calcd for C57H47N5O3S3 946.2919, found 946.2884.
Mp 242-244 °C. 1H NMR (CDCl3) δ 6.64 (d, J ) 1.8 Hz, 1H),
6.71 (dd, J ) 1.8, 8.4 Hz, 1H), 7.30 (d, J ) 8.4 Hz, 4H), 7.49 (d,
J ) 8.4 Hz, 1H), 7.88 (d, J ) 8.4 Hz, 4H), 9.78 (s, 1H), 9.97 (s,
2H), 11.33 (s, 1H). 13C NMR (CDCl3) δ 110.9, 115.0, 117.1, 125.4,
131.5, 133.1, 135.1, 150.8, 153.3, 163.4, 190.5, 194.3. HRMS
(DCI+) calcd for C21H16NO4 346.1079, found 346.1088.
2-(8-Bromooctyloxy)-4-[N,N-bis(4-formylphenyl)]aminoben-
zaldehyde (33). Compound 32 (100 mg, 290 µmol), 1,8-dibro-
mooctane (800 µL, 1.18 g, 4.34 mmol, 15 equiv), and K2CO3 (100
mg, 723 µmol, 2.5 equiv) were dissolved in dry acetone (10 mL).
The white suspension was stirred at 45 °C for 24 h. Diethyl ether
was added and the mixture filtered through a Celite pad. After
concentration, the residue was purified by column chromatography
(CH2Cl2/n-hexane 1:1 to 4:1 then CH2Cl2 and CH2Cl2/MeOH 99.5:
0.5). The title compound was isolated as a yellow solid (130 mg,
242 µmol) in 84% yield.
4-{5-[Bis(4-[(E)-2-(1,3-benzothiazol-2-yl)vinyl]phenyl)amino]-
2-[(E)-2-(1,3-benzothiazol-2-yl)vinyl]phenoxy}butanoic Acid (38).
A mixture of ester 37 (60 mg, 0.070 mmol) in THF (2 mL) and a
saturated aqueous LiOH solution (2 mL) was stirred overnight at
rt. The reaction was acidified to pH 2 and extracted with CH2Cl2.
The combined organic layers were washed with water and brine,
dried (Na2SO4), and concentrated to afford a crude oil. Purification
by silica gel column chromatography (CH2Cl2/MeOH, 98:2, v/v)
afforded the product as an orange powder (52 mg, 63 µmol) in
90% yield.
1
Mp 146-149 °C. H NMR (CDCl3) δ 2.32 (br, 2H), 2.59 (br,
2H), 4.01 (t, J ) 6.0 Hz, 2H), 6.67 (d, J ) 1.8 Hz, 1H), 6.75 (dd,
J ) 1.8 Hz, 8.4 Hz, 1H), 7.21 (d, J ) 8.4 Hz, 4H), 7.30-7.65 (m,
16H), 7.86-7.91 (m, 3H), 8.01-8.04 (m, 3H), 8.14 (d, J ) 15.0
Hz, 1H). 13C NMR (CDCl3) δ 25.0, 32.0, 68.6, 107.5, 116.9, 119.4,
120.1, 121.0, 121.5, 122.2, 122.8, 124.6, 125.0, 125.2, 126.5, 128.5,
128.7, 130.9, 132.8, 134.1, 134.3, 137.0, 147.5, 149.0, 153.1, 153.9,
158.1, 167.2, 168.7. HRMS (FAB+) calcd for C49H36N4O3S3
825.1980, found 825.2030.
Mp 80 °C. IR (KBr pellet) 2852 (νC-H, formyl), 2738 (νC-H
,
formyl), 1696 (νCdO), 1588 (Ar), 1505 (Ar) cm-1. 1H NMR (CDCl3)
δ 1.30-1.55 (br, 8H), 1.79 (quint, J ) 6.6 Hz, 2H), 1.88 (quint, J
) 6.6 Hz, 2H), 3.43 (t, J ) 6.6 Hz, 2H), 3.91 (t, J ) 6.6 Hz, 2H),
6.68 (d, J ) 1.8 Hz, 1H), 6.74 (dd, J ) 1.8, 8.4 Hz, 1H), 7.28 (d,
J ) 8.4 Hz, 4H), 7.82 (d, J ) 8.4 Hz, 1H), 7.87 (d, J ) 8.4 Hz,
4H), 9.98 (s, 2H), 10.42 (s, 1H). 13C NMR (CDCl3) δ 25.9, 28.0,
28.6, 28.9, 29.1, 32.7, 33.9, 68.7, 108.2, 116.9, 121.7, 124.5, 130.0,
131.4, 132.6, 151.2, 152.5, 162.7, 188.1, 190.5. HRMS (DCI+)
calcd for C29H3179BrNO4 536.1436, found 536.1437. HRMS (DCI+)
calcd for C29H3181BrNO4 538.1421, found 538.1434.
Succinimidyl 4-{5-[Bis(4-[(E)-2-(1,3-benzothiazol-2-yl)vinyl]-
phenyl)amino]-2-[(E)-2-(1,3-benzothiazol-2-yl)vinyl]phenoxy}-
butanoate (39). A solution of compound 38 (40 mg, 48.5 µmol, 1
equiv), N-hydroxysuccinimide (9 mg, 78 µmol, 1.6 equiv), and DCC
(11 mg, 56 µmol, 1.1 equiv) in dry CH2Cl2 was stirred for 24 h.
The cloudy suspension was filtered, concentrated, and redissolved
in CH2Cl2. The procedure was repeated five times to afford the
title compound as a yellow powder (25 mg, 27 µmol) in 66% yield.
Ethyl 4-{5-[Bis(4-formylphenyl)amino]-2-formylphenoxy}-
butanoate (34). To a solution of 32 (280 mg, 810 µmol) in dry
DMF (12 mL) was added K2CO3 (1.1 g, 8.0 mmol, 10 equiv). The
reaction was stirred for 15 min and ethyl bromobutanoate (175 µL,
1.22 mmol, 1.5 equiv) was added slowly. The mixture was stirred
24 h at rt and concentrated. The residue was redissolved in CH2-
Cl2 and water and extracted with CH2Cl2. The combined organic
layers were washed with water and brine, dried (Na2SO4), and
concentrated to afford a crude solid purified by silica gel column
1
Mp 80 °C. H NMR (CDCl3) δ 2.34 (quint, J ) 6.3 Hz, 2H),
2.83 (s, 4H), 2.93 (t, J ) 6.3 Hz, 2H), 4.06 (t, J ) 6.0 Hz, 2H),
6.73 (d, J ) 1.8 Hz, 1H), 6.80 (dd, J ) 1.8 Hz, 8.4 Hz, 1H), 7.22
(d, J ) 8.4 Hz, 4H), 7.35-7.65 (m, 16H), 7.83 (d, J ) 16.5 Hz,
J. Org. Chem, Vol. 73, No. 5, 2008 1743

Lartia et al.
1H), 7.90 (m, 3H), 8.00 (d, J ) 8.4 Hz, 2H), 8.02 (d, J ) 8.4 Hz,
1H). 13C NMR (CDCl3) δ 22.7, 25.6 (3C), 66.8, 108.0, 117.3, 120.2,
121.0, 121.4, 121.5, 122.7, 122.8, 124.6, 125.1, 125.3, 126.2, 126.4,
128.5, 128.7, 130.8, 132.3 134.3, 138.9, 147.6, 148.8, 153.9, 154.0,
157.4, 167.2, 168.2, 168.3, 169.0. HRMS (FAB+) calcd for
C53H39N5O5S3 921.2113, found 921.2099.
Optical Measurements. Fluorescence spectra were recorded at
a temperature maintained between 19.9 and 20.5 °C with a
thermostated cell holder. The solvents were of spectrophotometric
grade. Measurements were performed with solutions of OD e 0.1
to avoid reabsorption of the emitted light, and data were corrected
with a blank sample and from the variations of the detector with
the emitted wavelength.
Measurements of Two-Photon Absorption Cross Sections.
Two-photon induced fluorescence (TPIF) measurements were
performed with a mode-locked Ti-sapphire laser delivering 90 fs
pulses with a 76 MHz repetition rate, with fluorescein as reference.
The experimental setup used was adapted from the experiment
described already.4 The Ti-Saph excitation beam was focused in
a 1 cm long and 2 mm wide cuvette filled with moderately
concentrated solutions, with use of a 20 mm focal length lens. The
signal was collected at an angle of 90° from the excitation source
with use of a high NA lens: a spectrometer was used for detailed
study of the emission spectra. The laser beam was linearly polarized
and a set of half-wave plates and polarizers were used to vary the
fundamental beam intensity. Excitation spectra were determined
from measurements of the whole emitted light with use of an
amplified photodiode equipped with filters cutting the fundamental
beam. For each dye, the quadratic dependence of the signal with
the pump beam was checked.
Measurements of Fluorescence Quantum Yields. Fluorescence
quantum yields were measured with use of quinine bisulfate in H2-
SO4 (1 N) as a reference. The quantum yield was calculated with
eq 1, where the indices s and u stand for the standard and the
Acknowledgment. This research was supported by a joint
fellowship from the CEA and CNRS to C.A, by a postdoctoral
fellowship from the CNRS to F.S., and by a E.U. postdoctoral
fellowship to R.L. (FP6 STREP no. NMP4-CT-2003-505-669).
2
(1 - 10-A )Fun
s
φu )
2φs
(1)
(1 - 10-A )Fsn0
u
Supporting Information Available: Experimental details and
analytical and spectroscopic data for compounds 2, 6, 7, 11, 12,
14, 20, 23-26, 27c, 28c, 35, 37, and 40. This material is available
free of charge via the Internet at http://pubs.acs.org.
compound to measure, respectively. F represents the area of the
fluorescence spectrum, A the absorbance of the solution, and n and
n0 the refraction indices of the solvents in which the compound
and the standard were dissolved. Experimental errors can be
estimated to (10%.
JO702002Y
1744 J. Org. Chem., Vol. 73, No. 5, 2008