Synthesis, fluorescence, and two-photon absorption of bidentate phosphane oxide derivatives: Complexation with Pb2+ and Cd2+ cations

Article abstract of DOI:10.1002/chem.200800084

A series of fluorescent phosphane oxide derivatives based on diphenylphosphanoethane (DPPE) and diphenylphosphanomethane (DPPM) skeletons has been prepared by means of Grignard reactions and Sonogashira cross-couplings. The photophysical properties and th

Full text of DOI:10.1002/chem.200800084

FULL PAPER
DOI: 10.1002/chem.200800084
Synthesis, Fluorescence, and Two-Photon Absorption of Bidentate
Phosphane Oxide Derivatives: Complexation with Pb2+ and Cd2+ Cations
Minh-Huong Ha-Thi,[c] Mal Penhoat,[b] Delphine Drouin,[a]
Mireille Blanchard-Desce,*[a] VØronique Michelet,*[b] and Isabelle Leray*[c]
Abstract: A series of fluorescent phos-
phane oxide derivatives based on di-
phenylphosphanoethane (DPPE)and
diphenylphosphanomethane (DPPM)
skeletons has been prepared by means
of Grignard reactions and Sonogashira
cross-couplings. The photophysical
properties and the linear and nonlinear
spectra of these compounds have been
investigated. An edge-to-face confor-
mation resulting in the formation of an
excimer was confirmed by fluorescence
lifetime measurements of these multi-
chromophoric derivatives. Upon com-
plexation with heavy metal ions such as
Pb2+ and Cd2+, a red shift of the one-
and two-photon excitation spectra was
observed in the absorption and emis-
sion spectra. Furthermore, enhance-
ment of the electron-withdrawing char-
acter of the phosphane oxide resulted
in a significant enhancement of the
two-photon absorption cross-section,
leading to the first biphotonic Cd2+
sensors combining high affinity for
Cd2+
,
large two-photon absorption
cross-sections, and significant enhance-
ment of the two-photon excited fluo-
rescence in the presence of the cation.
Such derivatives are highly promising
for incorporation into devices for the
detection of heavy metal ions in water
and effluents.
Keywords: charge
transfer
·
fluorescence · phosphane oxide ·
sensors · two-photon absorption
Introduction
methods, the use of fluorescence offers distinct advantages
in terms of sensitivity, selectivity, response times, and capaci-
ty for local observations (e.g., by fluorescence imaging spec-
troscopy). The development of one-photon fluorescent mo-
lecular sensors[2] has been one of the most studied aspects in
the international community. However, such systems have
various disadvantages, in particular due to the low excitation
wavelength that they require. In contrast, systems based on
fluorescence induced by two-photon absorption (TPA)[3] are
very attractive and offer many advantages: i)a highly con-
fined excitation and three-dimensional (3D)sub-micrometer
spatial resolution can be obtained by employing the tech-
nique of two-photon laser scanning microscopy (TPLSM),[4]
ii)they permit a non-destructive method that allows the use
of excitation wavelengths in the 700–1000 nm region, thus
allowing iii)better penetration into cells and tissues (due to
reduced scattering losses), and iv) a reduction in the back-
ground fluorescence. Of particular importance in this con-
text is the use of fluorophores and fluorescent probes with
much higher TPA cross-sections (typically larger by orders
of magnitude)than those of endogenous chromophores.
This should allow selective excitation of engineered two-
photon probes, which is of major importance for biological
applications. Indeed, it has recently been shown that suitable
“photophysical” molecular engineering can yield photoac-
Over the past few years, significant efforts have been direct-
ed towards the development of new fluorescent molecules
for various applications, such as molecular labelling, probing
environments, and sensing.[1,2] Compared to other analytical
[a] D. Drouin, Dr. M. Blanchard-Desce
Synth›se et ElectroSynth›se Organiques
(CNRS, UMR 6510), Institut de Chimie, UniversitØ de Rennes 1
Campus Scientifique de Beaulieu, Bât 10A
35042 Rennes Cedex (France)
Fax : (+33)223236955
E-mail: mireille.blanchard-desce@univ-rennes1.fr
[b] Dr. M. Penhoat, Dr. V. Michelet
Laboratoire de Synth›se SØlective Organique
et Produits Naturels, E.N.S.C.P., UMR7573
11 rue P. et M. Curie, 75231 Paris Cedex 05 (France)
Fax : (+33)144-071-062
E-mail: veronique-michelet@enscp.fr
[c] M.-H. Ha-Thi, Dr. I. Leray
Laboratoire de Photophysique et Photochimie
SupramolØculaires et MacromolØculaires (CNRS UMR 8531)
ENS-Cachan, 61 avenue du PrØsident Wilson
94235 Cachan Cedex (France)
Fax : (+33)147-402-454
E-mail: icmleray@ppsm.en
Chem. Eur. J. 2008, 14, 5941 – 5950
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5941

tive molecules for which two-photon excitation allows more
selective photo-addressing than the corresponding one-
photon excitation.[5] Such selective excitation will reduce the
background fluorescence (thus providing an enhanced
signal-to-noise ratio and therefore improved sensitivity)and
also decrease photo-damage due to concomitant excitation
of endogenous compounds. Webb and co-workers, who pio-
neered the TPLSM technique, have characterised the TPA
spectra of endogenous chromophores in the spectral range
of interest for biological imaging, showing most of them to
have TPA cross-sections considerably lower than a few Gçp-
pert–Mayer (GM)(1 GM =10ꢀ50 cm4 sphotonꢀ1).[4] Hence,
the design of “two-photon” or “biphotonic” fluorescent
probes with TPA cross-sections of several hundred GM or
much higher is a current challenge for bio-related applica-
tions. Only recently have a few examples of two-photon
fluorescent molecular sensors for metallic cations been de-
scribed in the literature, focussing mainly on sensors[6] for
Ca2+, Mg2+, and Zn2+ in biological matrices. The molecular
designs of these TP cation sensors are based on a TP chro-
mophore, most commonly derived from a quadrupolar struc-
ture,[6d–i] or occasionally from dipolar[6c] or octupolar deriva-
tives.[6j] The donor moiety,[6d–i] or more rarely the acceptor
moiety,[6c,j] is therefore part of the complexing unit. As a
result, the presence of the cation can lead either to a de-
crease (as observed in the case of complexation on the
donor side in quadrupolar-type derivatives[6d–f,h,i])or to an in-
crease in the TPA response (as observed in the case of com-
plexation at the acceptor side in dipolar or octupolar deriva-
tives[6j]). In most reported cases, a quenching of two-photon
excited fluorescence (TPEF)is observed upon complexa-
tion.[6a,d–f,h,i,7]
we decided to focus on dipolar-type two-photon absorber
chromophores,[9] in which the acceptor moiety shows affinity
for heavy metal cations (Scheme 1).
Scheme 1. Design of multidentate biphotonic sensors for heavy metal cat-
ions.
It was anticipated that such systems would lead to very
large TPA cross-sections and an enhancement of the TPA
response in the presence of the cation. In view of the com-
plexing ability of phosphane oxide derivatives with heavy
metals,[10] and based on our experience of the synthesis of
phosphane oxides,[11] we decided to prepare some analogues
of diphenylphosphanoethane (DPPE)and diphenylphospha-
nomethane (DPPM)and to study their photophysical and
complexation properties. In this paper, we report the synthe-
sis of some new derivatives of this type (Scheme 2), and
their linear and two-photon spectroscopic properties in the
presence of heavy metal ions.
Critical issues for the sensitivity of the detection are the
complexation strength (as expressed by pKD), its selectivity,
and the amplitude of the variation in the fluorescence char-
acteristics as a function of cation concentration. For TP sen-
sors, another critical issue is the magnitude of the response
to two-photon excitation (i.e., the TPA cross-section), a
higher TPA cross-section being beneficial for both a low de-
tection threshold by reduction of background fluorescence
and faster scanning for imaging purposes.
Only rare examples of two-photon sensors for heavy
metals such as Pb2+ have been reported,[6f,g] and to the best
of our knowledge no efficient TP sensors for Cd2+ have
been described. Within this framework, our goal has been
the design of sensitive biphotonic Pb2+ and Cd2+ fluorescent
sensors. Our strategy was to design fluorophores that com-
bine high complexing ability with much larger TPA cross-
sections than those of classical fluorophores[4] or “ordinary”
fluorescent contaminants,[8] and that show enhancement of
their TPEF in the presence of the target cations.
Results and Discussion
Synthesis: The structures of ligands 1 and 2 were designed
with a view to increasing the solubility of phosphane oxides
in organic solvents while retaining the fluorescent properties
of phenylethynyl derivatives. Anticipating that the presence
of four phenylethynyl arms was likely to influence the pho-
tophysical properties and the stability of the corresponding
phosphane oxide, we also decided to prepare the unsymmet-
rical derivative 3. A Grignard derivative was first prepared
from the commercially available (4-bromophenyl)trimethyl-
silylacetylene (5), phosphorylation of which with bis(dichlor-
ophosphano)methane or 1,2-bis(dichlorophosphano)ethane
afforded
the
respective
tetraarylated
phosphanes
(Scheme 3). The phosphorus atoms were oxidised in the
presence of H2O2, and this was followed by desilylation. The
phosphane oxides 6 and 7 were isolated in yields of 31%
and 26%, respectively, over the three steps. Sonogashira
cross-coupling reactions[12] between the phosphano products
6/7 and the iodide 8[13] were then performed in the presence
of 10 mol% of Pd catalyst and 10 mol% of copper iodide.
This reaction allowed the introduction of four aryl groups,
leading to the desired phosphane oxides, DPPMO (1)and
In order to enhance the sensitivity for detection purposes,
we decided to prepare fluorescent sensors that could act as
two-photon antennae. Our idea was to graft several TP ab-
sorbers (with significant TPA response)bearing the binding
unit part onto a multidentate complexing unit (with high af-
finity for heavy metal ions). Based on these requirements,
5942
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5941 – 5950

Bidentate Phosphane Oxides for Heavy Metal Complexation
FULL PAPER
phane oxide as an electrophile,
gave the desired phosphane
monooxide in an unoptimised
27% yield. Another route in-
volving the more reactive
chlorodiphenylphosphane and
a phosphorus oxidation step
did not lead to higher yields.
Desilylation using K2CO3 in a
mixture of CH2Cl2/MeOH was
followed by the Sonogashira
cross-coupling reaction, which
led to the desired unsymmetri-
cal phosphane DPPMO-Ph2
(3)in 23% overall yield. Phos-
phane oxide TPPO (4)was
prepared according to a previ-
ously described procedure.[11]
Photophysical properties of
the ligands: The absorption
Scheme 2. Phosphane oxide fluorescent probes.
and fluorescence properties of
the phosphane oxide deriva-
DPPEO (2), in isolated yields of 71 and 50%, respectively
(Scheme 3).
tives are collected in Table 1, and their absorption and emis-
sion spectra are shown in Figure 1a)and b,) respectively.
The fluorophores show an intense absorption band in the
Scheme 3. Syntheses of the ligands DPPMO (1)and DPPEO ( 2): i) Mg,
THF, 508C, 1.5 h then Cl2PCH2CH2PCl2 or Cl2PCH2PCl2, THF, RT, 20 h,
35% (n = 0), 26% (n = 1); ii) H 2O2, CH2Cl2/MeOH, RT, 88% (n = 0),
100% (n = 1); iii) K 2CO3, MeOH/CH2Cl2, RT, 4 h, 70% (n = 0), 80%
Scheme 4. Synthesis of DPPMO-Ph2 ligand 3: i)Mg, THF, 50 8C, 1.5 h
then Cl2POCH3 (9), THF, RT, 20 h, 44%; ii) LTMP (2.5 equiv), THF,
ꢀ408C, then ClPOPh2, 27%; iii)K 2CO3, MeOH/CH2Cl2, RT, 4 h, 84%;
(n
=
1); iv) 10 mol% [Pd CAHTRE(UGN PPh3)4], 10 mol% CuI, I-C6H4-C6H4O-
(CH2)3CO2Et (8) , EtN, toluene, 508C, 71% (n = 0), 50% (n = 1).
iv)10 mol% [Pd ACHTRE(UNG PPh3)4], 10 mol% CuI, 8, Et3N, toluene, 508C, 28%.
As a desymmetrisation step was not conceivable starting
Table 1. Photophysical properties of phosphane oxide derivatives in
from 6, we changed our strategy and decided to take advant-
age of methyldichlorophosphane oxide (9). Scheme 4 out-
lines the synthesis of the DPPM ligand 3 bearing two fluo-
rescent arms. Here, the Grignard derivative of (4-bromophe-
nyl)trimethylsilylacetylene 5 was quenched with methyldi-
chlorophosphane oxide (9). The resulting phosphane oxide
was isolated in a modest yield of 44%. Treatment with a
hindered base such as lithium 2,2,6,6-tetramethylpiperidide
(LTMP),[14] followed by the addition of chlorodiphenylphos-
CH3CN/CHCl3 8:2. Maxima of the one-photon absorption labs [nm] and
of steady-state emission lem [nm], molar absorption coefficient
e
[104 mꢀ1 cmꢀ1], fluorescence quantum yield FF .
[a]
Product
labs [nm]
e [104 mꢀ1 cmꢀ1
]
lem [nm]
FF
TPPO (4)331
6
426
0.77
DPPMO-Ph2 (3)334
DPPEO (2)334
DPPMO (1)335
12
424
0.72
25
24
434
455
0.71
0.54
[a] Fluorescence quantum yield with a 10% random error.
Chem. Eur. J. 2008, 14, 5941 – 5950
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5943

M. Blanchard-Desce, V. Michelet, I. Leray et al.
near-UV region. After normalisation to the same number of
chromophores, the molar absorption coefficients at the
wavelength of maximum absorption are similar for the dif-
ferent fluorophores, indicating weak interaction between the
chromophores in the ground state of the multichromophoric
fluorophores.[15] All of these molecules show an intense fluo-
rescence emission in the visible region, with fluorescence
quantum yields ranging from 0.54 to 0.77. A large Stokes
shift and the unresolved vibronic structure of the fluores-
cence spectra observed for these fluorophores suggest the
formation of an intramolecular charge transition. In contrast
to the absorption spectra, significant differences are ob-
served in the shapes of the emission spectra and the fluores-
cence quantum yields for the different compounds. The
In order to further characterise the photophysical proper-
ties, time-resolved fluorescence measurements were per-
formed by the single-photon counting method with picosec-
ond laser excitation. The fluorescence decays for the differ-
ent phosphane oxides are shown in Figure 2. For TPPO (4)
emission spectra of TPPO (4)and DPPMO-Ph (3)are per-
2
fectly superimposable, suggesting weak interaction between
the chromophores. Similar behaviour was observed in the
case of a star-shaped fluorophore bearing three phenyle-
thynyl fluorescent arms.[11] In contrast, a broadening of the
emission and a decrease in the fluorescence quantum yield
were observed for the compounds DPPMO (1)and DPPEO
(2). This effect was found to be more pronounced in the
case of DPPMO (1).
Figure 2. Fluorescence decays of the phosphane oxide derivatives in
CH3CN/CHCl3 8:2.
and DPPMO-Ph2 (3), the decays are mono-exponential in
form. In contrast, satisfactory fits were obtained by consider-
ing three exponentials for DPPEO (2)and DPPMO ( 1).
The fluorescence decays at different emission wavelengths
were subjected to global analysis. The time constants thus
obtained are reported in Table 2. A component of around
Table 2. Fluorescence decay components ai and ti [ns] of the phosphane
oxide derivatives in CH3CN/CHCl3 8:2.
Product
lem [nm] t1 [ns] (a1) t2 [ns] (a2) t3 [ns] (a3) cr2
TPPO (4)425
DPPMO-Ph2 (3)425
1.–12 (1)
–
1.16
–
1.07 (1) –
1.12
430
470
510
530
450
500
550
640
0.03 (0.1) 0.99 (0.88)5.89 (0.02)1.12
0.03 (0.12)0.99 (0.84)5.89 (0.04)1.14
0.03 (0.14)0.99 (0.80)5.89 (0.05)1.14
0.03 (0.16)0.99 (0.78)5.89 (0.06)0.96
0.12 (0.35)0.78 (0.6) 8.65 (0.05)1.27
0.12 (0.28)0.78 (0.56)8.65 (0.16)1.11
0.12 (0.21)0.78 (0.50)8.65 (0.29)1.08
0.12 (0.15)0.78 (0.46)8.65 (0.39)1.17
DPPEO (2)
DPPMO (1)
0.9 ns, which is predominant in the region 380–430 nm, may
be attributed to the monomer emission. The longest compo-
nent (5.9 and 6.9 ns, respectively), the contribution of which
increases at long wavelengths, may be attributed to excimer
formation. It should be noted that the contribution of the
longest component is higher in the case of DPPMO (1).
This may be attributed to a stronger interaction between the
chromophores in the excited state of 1 as a result of their
proximity. These fluorescence decay measurements thus
permit evaluation of the spectra associated with each spe-
cies. A higher proportion of the excimer band is observed in
the case of the methylene chelate. This effect can be ration-
Figure 1. a)Absorptions of phosphane oxide derivatives in CH 3CN/
CHCl3 8:2. b)Corrected normalised emission spectra of the phosphane
oxide derivatives in CH3CN/CHCl3 8:2.
5944
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5941 – 5950

Bidentate Phosphane Oxides for Heavy Metal Complexation
FULL PAPER
alised in terms of the shorter distance between the fluoro-
phores. The shortest component (0.03 and 0.12 ns), which is
predominant in the blue region of the spectra, can be attrib-
uted to the decay of the monomer capable of forming an ex-
cimer.[16] However, it is important to note that no rise time
resulting from excimer formation was detected at 520 nm on
the shortest accessible timescale with our instrumentation
(around 20 ps); this means that the excimers were pre-
formed, as previously reported for b-cyclodextrins with
seven appended naphthalenic fluorophores.[17] All of these
data suggest, as previously observed for bichromophoric sys-
tems,[18] the presence of different conformers: one may en-
visage the presence of an expanded structure (leading to
monomer emission)and a near-sandwich geometry (respon-
sible for preformed excimer emission).
tra a)and emission spectra b)of DPPMO ( 1)upon com-
plexation with cadmium are given in Figure 4. Cation com-
plexation induces a bathochromic shift of the absorption
and emission spectra, which may be rationalised in terms of
Cation-induced photophysical changes: Complexation stud-
ies of the phosphane oxide derivatives with cadmium and
lead were performed in CH3CN/CHCl3 8:2 in order to
ensure good dissociation of the ion pair and good solubility
of the complexes. Figure 3 displays the evolution of the ab-
sorption spectra (a)and the emission spectra (b)of DPPEO
(2)upon complexation with cadmium. The absorption spec-
Figure 4. a)Absorption and b)corrected emission spectra of DPPMO
(2”10ꢀ6 m) (lexc =338 nm)in the presence of increasing concentrations of
Cd2+ in CH3CN/CHCl3 8:2.
an enhancement of the electron-withdrawing character of
the phosphane oxide group due to interaction of its oxygen
atoms with the cation. This effect may be correlated with
the charge density of the cation, since a more pronounced
effect was observed for the Cd2+ cation as compared to
Pb2+. The shifts towards higher wavelength upon cation
complexation are much more pronounced for the emission
spectra as compared to the absorption spectra, reflecting the
efficient intramolecular charge-transfer character of the
transition. These spectral characteristics clearly indicate an
increase in the electron density on the phosphane oxide
moiety in the excited state, thus resulting in stabilisation
(and hence a red-shift)of the emissions of the complexed
species.
Careful analysis of the emission spectra upon addition of
the cations by means of the SPECFIT program reveals that
different complexes are formed with the following different
stoichiometries 1:2, 1:1, and 2:1. Table 3 presents the stabili-
Figure 3. a)Absorption and b)corrected emission spectra of DPPEO
(2”10ꢀ6 m) (lexc =338 nm)in the presence of increasing concentrations of
Cd2+ in CH3CN/CHCl3 8:2.
Chem. Eur. J. 2008, 14, 5941 – 5950
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5945

M. Blanchard-Desce, V. Michelet, I. Leray et al.
Table 3. Stability constants of phosphane oxide derivatives with Pb2+
in the excimer emission is observed, which may be rational-
ised in terms of a rigidification of the chelate upon complex-
and Cd2+
Product
TPPO
.
Cation
logb12
logK11
logK21
ation. Similar effects are observed for the phosphane oxide
2+
Pb2+
Pb2+
Pb2+
Pb2+
Cd2+
Cd2+
Cd2+
Cd2+
–
3.7ꢂ0.02
7.8ꢂ0.2
7.6ꢂ0.2
6.6ꢂ0.1
3.0ꢂ0.02
8.0ꢂ0.2
6.7ꢂ0.1
6.9ꢂ0.1
–
–
DPPEO (2)with both Pb
and Cd2+. This demonstrates
DPPMO-Ph2
DPPEO
DPPMO
TPPO
DPPMO-Ph2
DPPEO
DPPMO
14.5ꢂ0.2
13.8ꢂ0.4
14ꢂ0.2
–
15.2ꢂ0.2
12.8ꢂ0.2
14.2ꢂ0.2
that DPPEO (2)may be used as a ratiometric fluorescent
sensor for Pb2+ and Cd2+, and may additionally serve as a
fluorescence lifetime sensor for these heavy metals. In con-
trast, a higher proportion of the excimer fluorescence is
maintained in the case of the complex between DPPMO (1)
and Cd2+, which may be due to the geometry of the com-
plex. Thus, with regard to imaging applications (FLIM: fluo-
rescence lifetime imaging), the DPPEO ligand 2 shows
better characteristics.
11.2ꢂ0.2
–
–
11.4ꢂ0.2
12.4ꢂ0.2
10.5ꢂ0.2
ty constants of the complexes formed with the Pb2+ and
Cd2+ cations, calculated from the results of the titration ex-
periments. Scheme 5 shows the possible complexes formed
upon complexation of the cations. It should be noted that
very high stability constants are observed upon complexa-
tion with the heavy metal ions.
Two-photon absorption: The TPA properties of the ligands
and complexes were investigated by performing two-photon
excited fluorescence (TPEF)measurements in solution ac-
cording to the methodology developed by Webb and co-
workers.[6a] The branched structures of DPPMO (1)and
DPPEO (2)show notable and similar TPA responses in the
target spectral region (s2 at lTmPaAx ꢁ 100 GM), which is con-
sistent with the weak interactions between the two chromo-
phores in the ligands. The first (lowest-energy)TPA band,
the maximum for which is located at around 740 nm, is red-
shifted with respect to the corresponding one-photon al-
lowed lowest-energy band, and is clearly overlapped by a
much more intense blue-shifted band. Such behaviour is typ-
ical of a branched system composed of two interacting dipo-
lar chromophores.[9] This is reminiscent of the behaviour of
triphenylamine derivatives, except that in their case the di-
polar chromophores interact through a common electron-
withdrawing moiety[9b] (which is also the complexing unit).
This indicates that the phosphane oxide moiety allows co-
herent coupling between the branches, thus opening an in-
teresting route as an original “joint” module for the molecu-
lar engineering of branched systems with enhanced TPA.[9c]
As illustrated in Figure 6, the ML2 complexes show a
marked increase in their TPA in the region 700–800 nm.
This is consistent with the reinforcement of the photoin-
duced charge transfer in the chromophoric parts of the li-
gands as a result of the increased electron-withdrawing abili-
ty of the phosphane oxide moiety when complexed with the
heavy metal cation. We observe that this leads to an in-
crease in the TPA cross-section at 740 nm (normalised with
respect to the number of fluorescent ligands)by a factor 1.7
for Pb2+ and by a factor 2.8 for Cd2+. The stronger TPA
modulation induced by Cd2+ in the presence of DPPMO
ligand 1 may be correlated with the higher charge density of
the Cd2+ cation. The bidentate DDPMO ligand 1 is thus
found to be a convenient biphotonic fluorescent sensor for
Cd2+ ions, since it combines high affinity for the cation
(large association constant), large TPA cross-sections of the
complex species (larger than those of classical fluorophores
commonly used in the biology community),[4b,6a] and signifi-
cant modulation of the TPEF signal in the presence of the
Cd2+ cation (Table 4).
2+
Scheme 5. Model of the binding of DPPEO (2)with Cd
or Pb2+
.
Time-resolved fluorescence decays were measured upon
cation complexation. Figure 5 displays the decays obtained
2+
for DPPMO (1)upon Pb
complexation. A sharp decrease
Figure 5. Fluorescence decays of DPPMO (4.1”10ꢀ7 m)in the presence of
increasing concentrations of Pb2+ (0 to 2400 equiv). Channel width=
34 ps.
5946
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5941 – 5950

Bidentate Phosphane Oxides for Heavy Metal Complexation
FULL PAPER
Table 4. TPA properties of phosphane oxide derivatives in CH3CN/
detection of toxic heavy metals in water and effluents. This
is a critical issue with regard to the selective detection of
heavy metal ions in enforcing the environmental health offi-
cial regulations imposed by the World Health Organisation
and the European Community.[19]
TPA
CHCl3 8:2. First maximum (lowest energy)of the TPA band [ l ]. TPA
max
cross-section s2 [1 GM=10ꢀ50 cm4 sꢀ1 photonꢀ1].
abs
max
TPA
max1
Compound
2l
l
s2 [GM] at
F
s2 F [GM] at
TPA
TPA
[nm]
[nm]
l
l
max
max
DPPMO
A
670
675
677
ꢁ740
ꢁ740
ꢁ740
95
320
520
0.54
0.03
0.44
51
10
229
C
Experimental Section
General: Reagents were obtained commercially from Acros, Aldrich, or
Avocado and were used without further purification unless otherwise
stated. Cyclohexane, dioxane, chloroform, dichloromethane, dimethyl
sulfoxide, and acetonitrile (spectrometric grade from Aldrich or SDS)
were employed as solvents for absorption and fluorescence measure-
ments. Column chromatography was performed on 0.040–0.063 mm Art.
11567 silica gel (E. Merck). 1H, 13C, and 31P NMR spectra were recorded
on Bruker AV300 or AV400 instruments. All signals (d)are expressed in
units of ppm downfield from Me4Si for 1H and 13C NMR and from
H3PO4 for 31P NMR, used as internal standards. Coupling constants (J)
are reported in Hz and refer to apparent peak multiplicities. Melting
points were measured in open capillary tubes. FTIR spectra were record-
ed on a Thermo-Optek Nexus spectrometer. Mass spectrometric analyses
were performed on a Hewlett-Packard HP 5989A instrument at the
Ecole Nationale SupØrieure de Chimie de Paris. Direct introduction ex-
periments were performed by chemical ionisation with ammonia. Ele-
mental analyses were performed at the Institut de Chimie des Substances
Naturelles (Gif-sur-Yvette).
Bis(4-trimethylsilylethynylphenyl)diphosphanomethane: A solution of (4-
bromophenylethynyl)trimethylsilane (4.66 g, 18.4 mmol) in anhydrous
THF (12.5 mL)was added in one portion to activated Mg (485 mg,
20.24 mmol)under argon. The mixture was heated at 55 8C for 2 h and
Figure 6. TPA spectra of DPPMO (1)and corresponding complexes in
*
^
CH3CN/CHCl3 8:2; : DPPMO2Cd, ”: DPPMO2PB, : DPPMO.
then cannulated into
a solution of DPPMCl4 in anhydrous THF
(12.5 mL)at 0 8C. The reaction mixture was stirred at 08C for 30 min and
then at room temperature for 18 h. The reaction was then quenched by
the addition of saturated aqueous NH4Cl solution (10 mL)and water
(10 mL). After extraction with diethyl ether, the organic phase was dried
(Na2SO4)and filtered, the volatiles were evaporated, and the crude oil
was purified by flash chromatography (CH2Cl2/cyclohexane 1:9!1:1)to
afford the desired product as a colorless solid (1.22 g, 35%). The product
was used directly for the synthesis of methylene bis(4-trimethylsilylethy-
nylphenyl)diphosphane oxide. 1H NMR (CDCl3, 300 MHz): d=0.25 (s,
36H), 2.73 (s, 2H), 7.30 ppm (m, 16H); 13C NMR (CDCl3, 75 MHz): d=
0.0, 27.8, 95.7, 104.6, 123.8, 131.8, 132.6, 132.8, 139.0 ppm; 31P NMR
(CDCl3, 121 MHz): d=ꢀ21.6 ppm.
Methylene bis(4-trimethylsilylethynylphenyl)diphosphane oxide: 30%
H2O2 (1.06 mL)was added dropwise to a solution of bis(4-trimethylsilyl-
ethynylphenyl)diphosphanomethane (1.18 g, 1.53 mmol) in dichlorome-
thane (5 mL)and methanol (10 mL). The reaction mixture was stirred at
room temperature for 4 h. The excess H2O2 was then reduced with aque-
ous Na2SO3 solution (15 mL)and AcOEt (20 mL)was added. The organ-
ic phase was dried over MgSO4 and filtered, and the volatiles were
evaporated in vacuo to afford a colorless solid (1.093 g, 88%). M.p.
>2508C; 1H NMR (300 MHz, CDCl3): d=7.62–7.52 (m, 8H), 7.44–7.40
(m, 8H), 3.48 (t, J=15 Hz, 2H), 0.25 ppm (s, 36H); 13C NMR (75 MHz,
CDCl3): d=132.5, 132.1, 132.0, 131.9, 131.1, 131.0, 130.9, 127.4, 126.9,
103.8, 98.0, 34.6, 0.0 ppm; 31P NMR (121 MHz, CDCl3): d=24.6 ppm; MS
(ESI): C45H54O2P2Si4: m/z: 801 [M+H]+; elemental analysis calcd (%)for
C45H54O2P2Si4: C 67.46, H 6.79; found: C 67.27, H 7.01.
Conclusions
In conclusion, we have synthesised a series of phenylethynyl
phosphane oxide derivatives bearing two or four fluorescent
arms starting from simple materials. These novel derivatives
show an intense absorption band in the near-UV region and
an intense fluorescence emission in the visible region, with
fluorescence quantum yields ranging from 0.54 to 0.77. We
have also shown that weak interactions between the chro-
mophores occur in the ground state for the multichromo-
phoric fluorophores. The observed large Stokes shift and the
unresolved vibronic structure of the fluorescence spectra
also suggest the formation of an intramolecular charge tran-
sition.
Addition of a heavy metal cation such as Cd2+ induces a
bathochromic shift of the absorption and emission spectra
due to an enhancement of the electron-withdrawing charac-
ter of the complexed phosphane oxide group. As a result,
these newly designed fluorophores show considerable prom-
ise as ratiometric sensors for Cd2+ ions. In addition, these
sensors have been found to exhibit large TPA cross-sections,
which are significantly enhanced in the presence of the
cation. This may be ascribed to the increased electron-with-
drawing character of the complexing moieties of the phos-
phane oxide due to the interaction of the oxygen atom with
the cation. These derivatives are therefore of great interest
as first prototypical biphotonic sensors for Cd2+ cations, and
hold much promise for the development of devices for the
Methylene bisCAHTRE[UNG bis(4-ethynylphenyl)phosphane oxide] (6): K2CO3
(770 mg, 5.2 mmol)was added to a solution of methylene bis(4-trimethyl-
silylethynylphenyl)diphosphane oxide (1.093 g, 1.36 mmol) in anhydrous
dichloromethane (8 mL)and methanol (16 mL)under argon, and the re-
action mixture was stirred for 4 h at room temperature. The reaction was
then quenched by the addition of water (10 mL), and dichloromethane
(20 mL)was added. After extraction, the organic layer was dried
(Na2SO4)and filtered, and the volatiles were evaporated in vacuo. The
Chem. Eur. J. 2008, 14, 5941 – 5950
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5947

M. Blanchard-Desce, V. Michelet, I. Leray et al.
resulting pale-yellow solid was then triturated with the minimum volume
of AcOEt and diethyl ether (10 mL)to afford the desired desilylated
product 6 as a colorless solid (490 mg, 70%). M.p. >2508C; 1H NMR
(300 MHz, CDCl3): d=7.68–7.65 (m, 8H), 7.46 (d, J=7.0 Hz, 8H), 3.47
(t, J=15 Hz, 2H), 3.20 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=
133.0, 132.2, 132.1, 132.0, 131.5, 130.9, 130.8, 130.7, 126.2, 82.3, 80.1,
34.6 ppm; 31P NMR (121 MHz, CDCl3): d=23.9 ppm; MS (ESI):
C33H22O2P2: m/z: 513 [M+H]+; MALDI HRMS: m/z: calcd for
C33H22O2P2Na: 535.0993; found: 535.0997 [M+Na+].
32H), 6.84 (d, J=8.7 Hz, 8H), 4.15 (q, J=7.2 Hz, 8H), 4.02 (t, J=6.1 Hz,
8H), 3.54 (t, J=15 Hz, 2H), 2.52 (t, J=7.3 Hz, 8H), 2.14 (m, 8H),
1.26 ppm (t, J=7.4H, 12H); 13C NMR (75 MHz, CDCl3): d=173.2, 159.2,
133.3, 131.8, 131.6, 131.5, 131.1, 127.4, 124.2, 122.0, 115.2, 114.7, 92.3,
91.9, 90.0, 87.9, 67.0, 60.6, 30.9, 24.7, 14.4 ppm; 31P NMR (121 MHz,
CDCl3): d=24.3 ppm; IR (powder): n˜ =2948 (m), 2213 (s), 1735 (s), 1595
(s), 1438 (s), 1285 (s), 1245 (s), 1175 (s), 1106 (s), 1035 cmꢀ1 (s); HRMS
(MALDI): m/z: calcd for
C
113H95O14P2: 1737.6191; found: 1737.6161
[M+H]+; UV/Vis:
105 mꢀ1 cmꢀ1).
l
(CH3CN/CHCl3 8:2)=335 nm (e=2.4”
1,2-Bis(4-trimethylsilylethynylphenyl)diphosphanoethane: A solution of
(4-bromophenylethynyl)trimethylsilane (2.183 g, 8.624 mmol) in anhy-
drous THF (4 mL)was added in one portion to activated Mg (230 mg,
9.48 mmol)under argon. The mixture was heated at 55 8C for 2 h and
then cannulated into a solution of DPPECl4 in anhydrous THF (8 mL)at
08C. The reaction mixture was stirred at 08C for 30 min and then at
room temperature for 18 h. Thereafter, the reaction was quenched by the
addition of saturated aqueous NH4Cl solution (10 mL)and water
(10 mL). After extraction with diethyl ether, the organic phase was dried
(Na2SO4)and filtered, the volatiles were evaporated, and the crude oil
was purified by chromatography on silica gel (CH2Cl2/cyclohexane 2:8)
to afford a pale-yellow solid (424 mg, 26%). The product was used di-
rectly for the synthesis of ethylene 1,2-bis(4-trimethylsilylethynylphenyl)-
diphosphane oxide. 1H NMR (CDCl3, 300 MHz): d=0.24 (s, 36H), 1.98
(t, J=4.1 Hz, 4H), 7.18 (m, 8H), 7.37 ppm (dd, J=0.5 and 8 Hz, 8H);
13C NMR (CDCl3, 75 MHz): d=0.0, 23.7, 95.7, 104.6, 123.7, 131.9, 132.4,
132.5, 132.6, 138.4 ppm; 31P NMR (CDCl3, 121 MHz): d=ꢀ12.0 ppm;
HRMS (MALDI TOF): m/z: calcd for C46H56P2Si4 [M+]: 783.3007;
found: 783.3004.
1,2-Bis-4-{ethyl 4-[4-di(phenylene ethynylene)phenoxy]butyrate}diphos-
phanoylethane (2): Iodoaryl building block (536 mg, 1.235 mmol,
6.5 equiv)was added to a solution of 7 (100 mg, 0.19 mmol)in toluene
(30 mL)and triethylamine (10 mL.) The mixture was degassed under
argon, CuI (4 mg, 5mol%)and [Pd ACTHER(UNG PPh3)4] (22 mg, 5mol%)were added,
8
and the reaction mixture was stirred for 20 h at 508C under argon. The
volatiles were then evaporated in vacuo and the residue was dissolved in
dichloromethane (10 mL). The organic phase was washed with 10%
aqueous HCl, dried (Na2SO4), filtered, and the solvents were evaporated
under reduced pressure. The crude product was then purified by flash
chromatography (silica gel; CH2Cl2 ! CH2Cl2/acetone 1:1)to afford the
desired phosphane oxide 2 as a colorless solid (50%). M.p. 2568C;
1H NMR (300 MHz, CDCl3): d=7.7–7.6 (m, 16H), 7.48–7.43 (m, 24H),
6.86 (dd, J=2 and 6.9 Hz, 8H), 4.15 (q, J=7.2 Hz, 8H), 4.04 (t, J=
6.1 Hz, 8H), 2.52 (m, 12H), 2.14 (m, 8H), 1.25 ppm (t, J=7.2 Hz, 12H);
13C NMR (75 MHz, CDCl3): d=173.2, 159.7, 133.3, 132.1, 131.9, 131.8,
130.9, 127.5, 124.3, 122.0, 115.2, 114.7, 92.4, 91.9, 89.9, 87.9, 67.0, 60.6,
30.9, 29.8, 24.7, 14.3 ppm; 31P NMR (121 MHz, CDCl3): d=32.1 ppm; IR
(powder): n˜ =2925 (m), 2207 (s), 1726 (s), 1589 (s), 1472 (s), 1250 (s),
1175 (s), 1105 (s), 1035 cmꢀ1 (s); HRMS (MALDI): m/z: calcd for
Ethylene 1,2-bis(4-trimethylsilylethynylphenyl)diphosphane oxide: 30%
H2O2 (360 mL)was added dropwise to a solution of 1,2-bis(4-trimethylsi-
lylethynylphenyl)diphosphanoethane (394 mg, 0.5 mmol) in dichlorome-
thane (1.5 mL)and methanol (6 mL). The reaction mixture was stirred at
room temperature for 4 h. The excess H2O2 was then reduced with aque-
ous Na2SO3 solution (6 mL)and dichloromethane (10 mL)was added.
The organic phase was dried over MgSO4 and filtered, and the volatiles
were evaporated under reduced pressure to afford the desired product as
a colorless solid (408 mg, 100%). M.p. >2508C; 1H NMR (300 MHz,
CDCl3): d=7.55 (m, 16H), 2.43 (t, J=2.4 Hz, 4H), 0.24 ppm (s, 36H);
13C NMR (75 MHz, CDCl3): d=132.5, 132.4, 130.7, 127.6, 103.7, 98.2,
29.9, 27.1, 0.0 ppm; 31P NMR (121 MHz, CDCl3): d=32.2 ppm; MS (CI,
C
114H97O14P2: 1751.6348; found: 1751.6358 [M+H]+.
Methylene-bis[4-(trimethylsilylethynyl)phenyl]phosphane oxide: A solu-
tion of (4-bromophenylethynyl)trimethylsilane (19 g, 75.3 mmol) in anhy-
drous THF (50 mL)was added in one portion to activated Mg (1.98 g,
82.7 mmol)under argon. The mixture was heated at 55 8C for 2 h and
then cannulated into a solution of CH3P(O)Cl2 (5 g, 37.6 mmol)in anhy-
drous THF (20 mL)at 0 8C. The reaction mixture was stirred at 08C for
30 min and then at room temperature for 18 h. The reaction was then
quenched by the addition of saturated aqueous NH4Cl solution (50 mL)
and water (10 mL). After extraction with diethyl ether, the organic phase
was dried (Na2SO4)and filtered, the volatiles were evaporated, and the
crude oil was purified by flash chromatography (CH2Cl2/AcOEt 1:1)to
NH3) : C H56O2P2Si4: m/z: 815 [M+H]+.
46
Ethylene 1,2-bisACHTREUNG[bis(4-ethynylphenyl)phosphane oxide] (7): K2CO3
afford the product as
a colorless solid (6.81 g, 44%). M.p. 1968C;
(68 mg)was added to a solution of ethylene 1,2-bis(4-trimethylsilylethy-
nylphenyl)diphosphane oxide (393 mg, 0.48 mmol) in anhydrous dichloro-
methane (4 mL)and methanol (6 mL)under argon, and the reaction mix-
ture was stirred at room temperature for 4 h. The reaction was then
quenched with water (10 mL), and AcOEt (20 mL) was added. After ex-
traction, the organic layer was dried (Na2SO4)and filtered, and the vola-
tiles were evaporated in vacuo to afford the desired desilylated product 7
as a colorless solid (200 mg, 80%). M.p. >2508C; 1H NMR (300 MHz,
CDCl3): d=7.62 (m, 16H), 3.20 (s, 4H), 2.47 ppm (d, 4H, J=2.7 Hz);
13C NMR (75 MHz, CDCl3): d=132.6, 132.5, 132.4, 131.7, 131.1, 130.6,
126.4, 82.3, 80.2, 29.7, 21.4 ppm; 31P NMR (121 MHz, CDCl3): d=
31.8 ppm; HRMS (ES): m/z: calcd for C34H24O2P2Na: 549.1149; found:
549.1164 [M+Na]+.
1H NMR (300 MHz, CDCl3): d=7.65–7.51 (m, 8H), 2.00 (d, J=13.2 Hz,
3H), 0.24 ppm (s, 18H); 13C NMR (75 MHz, CDCl3): d=134.5, 133.1,
132.3, 132.1, 130.6, 130.4, 127.1, 103.9, 97.7, 16.5 (d, J=74 Hz), 0.0 ppm;
31P NMR (121 MHz, CDCl3): d=29.5 ppm; MS: C23H29OPSi2: m/z: 409
[M+H]+; UV/Vis (CH3CN/CHCl3 8:2): l=334 nm (e=2.5”105 mꢀ1 cmꢀ1).
Bis[4-(trimethylsilylethynyl)phenyl]phosphanoyl-diphenyl phosphanoyl-
methane: A solution of LTMP was prepared by treating a solution of
TMPH (195 mL, 1.15 mmol)in THF (1 mL)with 2.5 m nBuLi (460 mL,
1.15 mmol)for 5 min at 0 8C under argon. This solution was then cannu-
lated at ꢀ408C into a solution of methylene-bis[4-(trimethylsilylethynyl)-
phenyl]phosphane oxide (204 mg, 0.5 mmol)in THF (2 mL)under argon.
The mixture was stirred for 1.5 h at 408C and then diphenylphosphanic
chloride (114 mL, 0.6 mmol)was added dropwise at ꢀ408C under argon.
The resulting mixture was stirred for 4 h at ꢀ408C and then the reaction
was quenched by the addition of saturated aqueous NH4Cl solution
(5 mL). After extraction with dichloromethane (5 mL), the organic layer
was dried (Na2SO4), filtered, and concentrated under reduced pressure.
The crude yellow solid was purified by flash chromatography (AcOEt,
Rf =0.4)and the solid obtained was triturated with the minimum volume
Bis-4-{ethyl 4-[4-di(phenylene ethynylene)phenoxy]butyrate}diphospha-
noylmethane (1): Iodoaryl building block
8 (434 mg, 1.01 mmol,
6.5 equiv)was added to a solution of 6 (80 mg, 0.16 mmol)in toluene
(25 mL)and triethylamine (7 mL.) The mixture was degassed under
argon, CuI (7.15 mg, 24mol%)and [Pd ACHTRE(UNG PPh3)4] (21 mg, 12mol%)were
added, and the reaction mixture was stirred for 20 h at 508C under
argon. The volatiles were then evaporated in vacuo and the residue was
dissolved in dichloromethane (10 mL). The organic phase was washed
with aqueous HCl (10%), dried (Na2SO4), filtered, and the solvents were
evaporated under reduced pressure. The crude product was then purified
by flash chromatography (silica gel; CH2Cl2 ! CH2Cl2/acetone 1:1)to
afford the desired phosphane oxide 1 as a colorless solid (197 mg, 71%).
1
of AcOEt to afford a colorless solid (70 mg, 27%). M.p. 1968C; H NMR
(300 MHz, CDCl3): d=7.67–7.65 (m, 8H), 7.39–7.36 (m, 8H), 3.50 (t, J=
13.3 Hz, 2H), 0.25 ppm (s, 18H); 13C NMR (75 MHz, CDCl3): d=133.3,
132.9, 132.0, 131.8, 131.1, 131.0, 128.8, 128.6, 127.1, 104.0, 97.7, 34.9,
0.0 ppm; 31P NMR (121 MHz, CDCl3): d=24.7, 24.3 ppm; MS:
C23H29OPSi2: m/z: 608.
1
M.p. 2548C; H NMR (300 MHz, CDCl3): d=7.28 (m, 8H), 7.52–7.43 (m,
5948
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5941 – 5950

Bidentate Phosphane Oxides for Heavy Metal Complexation
FULL PAPER
Bis(4-ethynylphenyl)phosphanoyl-diphenylphosphanoylmethane
(10):
sorption cuvette containing the sample. The average applied laser power
arriving at the sample was between 0.5 and 15 mW, leading to a time-
K2CO3 (26 mg, 0.1 mmol)was added to a solution of bis[4-(trimethyl-
silylethynyl)phenyl]phosphanoyl-diphenylphosphanoylmethane (50 mg,
0.08 mmol)in a mixture of dichloromethane (1 mL)and MeOH (2 mL),
and the reaction mixture was stirred at room temperature for 4 h. After
complete conversion, water (4 mL)was added and the mixture was ex-
tracted with dichloromethane (5 mL). The organic layer was then dried
(Na2SO4), filtered, and concentrated in vacuo. The crude oil was then tri-
turated with Et2O/cyclohexane 1:1 to afford 10 as a colorless solid
(31 mg, 84%). M.p. 2228C; 1H NMR (300 MHz, CDCl3): d=7.55–7.45
(m, 8H), 7.44–7.34 (m, 10H), 3.32 (t, J=14.7 Hz, 2H), 2.99 ppm (s, 2H);
13C NMR (75 MHz, CDCl3): d=133.1, 132.1, 131.9, 131.1, 130.9, 130.9,
130.7, 128.6, 128.5, 126.0, 82.5, 79.84, 34.3 ppm; 31P NMR (121 MHz,
CDCl3): d=24.6 (d, J=11.5 Hz), 24.1 ppm (d, J=11.5); HRMS (ES):
m/z: calcd for C29H22O2P2Na 487.0993; found 487.0983 [M+Na]+.
averaged light flux in the focal volume of the order of 0.1–1 mWmmꢀ2
.
The generated fluorescence was collected in epi-fluorescence mode,
through the microscope objective, and reflected by a dichroic mirror
(675dcxru, Chroma Technology Corporation, USA). Residual excitation
light was removed using a barrier filter (e650–2p, Chroma)and the fluo-
rescence was coupled into a 600 mm multimode fiber by an achromatic
doublet. The fiber was connected to a compact CCD-based spectrometer
(BTC112-E, B&WTek, USA), with which the two-photon excited emis-
sion spectrum was measured. The emission spectra were corrected for
the wavelength-dependence of the detection efficiency using correction
factors established through measurements on reference compounds with
known fluorescence emission spectra. Briefly, the set-up allowed the re-
cording of corrected fluorescence emission spectra under multiphoton ex-
citation at variable excitation power and wavelength.
Bis-4-{ethyl 4-[4-di(phenylene ethynylene)phenoxy]butyrate}phosphano-
yl-diphenylphosphanoylmethane (3): Iodoaryl building block 8 (86 mg)
was added to a solution of 10 (31 mg)in anhydrous toluene (4 mL)and
triethylamine (2 mL), the mixture was degassed with argon, and then
Absolute values for the two-photon excitation action cross-sections s2F
were obtained according to the method described by Xu and Webb, using
10ꢀ4 m fluorescein in 0.01m aqueous NaOH as a reference.[6a] DPPMO (1)
and DPPEO (2)were dissolved in CH 3CN/CHCl3 (80:20)at concentra-
tions of 3.8”10ꢀ5 and 2”10ꢀ5 m, respectively. The complexation studies
were performed using 0.5 equiv of heavy metal ions in order to ensure a
high proportion of the ML2 complex.
[PdACHTREUNG(PPh3)4] (7.7 mg)and CuI (1.5 mg, 10mol%)were added. The reac-
tion mixture was stirred at 508C under argon for 20 h. After cooling to
room temperature, the mixture was washed with saturated aqueous
NH4Cl solution (10 mL)and extracted with AcOEt (10 mL). The organic
layer was dried (Na2SO4), filtered, and the volatiles were removed under
reduced pressure. The residue was purified by flash chromatography
(silica gel; AcOEt)to afford 3 as a colorless solid (20 mg, 28%). M.p.
2108C; 1H NMR (300 MHz, CDCl3): d=7.77–7.68 (m, 10H), 7.49–7.34
(m, 24H), 6.87 (d, J=8 Hz, 4H), 4.15 (q, J=7 Hz, 4H), 4.03 (t, J=
6.1 Hz), 3.54 (t, J=15.6 Hz, 2H), 2.52 (t, J=7.2 Hz, 4H), 2.12 (m, 4H),
1.26 ppm (t, J=7 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=173.1, 159.1,
133.1, 132.6, 131.9, 131.7, 131.5, 131.4, 131.1, 131.0, 130.9, 130.8, 128.6,
128.5, 127.0, 124.1, 122.0, 115.0, 114.6, 91.9, 91.7, 90.0, 87.8, 66.8, 60.5,
34.8 (t), 30.7, 24.5, 14.2 ppm; 31P NMR (121 MHz, CDCl3): d=24.6 (d,
J=14 Hz), 24.3 ppm (d, J=14 Hz); HRMS (MALDI): m/z: calcd for
C69H59O8P2:1077.3680; found 1077.3692 [M+H]+.
Solvents and salts: Acetonitrile from Aldrich (spectrometric grade)and
Millipore-filtered water (conductivity <6”108 Wꢀ1 cmꢀ1 at 208C)were
employed as solvents for the absorption and fluorescence measurements.
Sodium thiocyanate, potassium thiocyanate, calcium perchlorate, zinc
perchlorate, cadmium perchlorate, and lead(II)thiocyanate, from Aldrich
or Alfa Aesar, were of the highest quality available and were vacuum-
dried over P2O5 prior to use.
Acknowledgements
This work was supported by the French Research Ministry program “ACI
Jeune Chercheur 2004–2006”. We are grateful to J.-P. Lefevre and J.-J.
Vachon for their assistance in tuning the single-photon timing instru-
ments. M.H.H.T. is grateful to the Minist›re de l’Education et de la Re-
cherche for a grant (2004–2007). M.B.D. gratefully acknowledges Rennes
MØtropole for financial support.
Spectroscopic measurements: UV/Vis absorption spectra were recorded
on a Varian Cary 5E spectrophotometer and corrected emission spectra
were obtained on a Jobin-Yvon Spex Fluorolog 1681 spectrofluorimeter.
Fluorescence quantum yields were determined by using quinine sulfate
dihydrate in sulfuric acid (0.5 n; FF =0.546[20])as a standard. For the
emission measurements, the absorbances at the excitation wavelengths
were below 0.1 and so the concentrations were below 105 molLꢀ1. Fluo-
rescence intensity decays were obtained by the single-photon timing
method with picosecond laser excitation using a Spectra Physics set-up
composed of a titanium sapphire Tsunami laser pumped by an argon ion
laser, a pulse detector, and doubling (LBO)and tripling (BBO)crystals.
Light pulses were selected by optoacoustic crystals at a repetition rate of
4 MHz. Fluorescence photons were detected through a long-pass filter
(375 nm)by means of a Hamamatsu MCP R3809U photomultiplier con-
nected to a constant-fraction discriminator. The time-to-amplitude con-
verter was purchased from Tennelec. Data were analysed by a nonlinear
least-squares method with the aid of Globals software (Globals Unlimit-
ed, University of Illinois at Urbana-Champaign, Laboratory of Fluores-
cence Dynamics). Complexation constants were determined by global
analysis of the evolution of all absorption and/or emission spectra by
using the Specfit Global Analysis System V3.0 for 32-bit Windows
system. This software uses singular value decomposition and nonlinear
regression modelling by the Levenberg–Marquardt method.[21]
[1] B. Valeur, Molecular Fluorescence: Principles and Applications,
Wiley-VCH, Weinheim, 2002.
[2] a)A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M.
Huxley, C. P. McCoy, J. T. Rademacher, T. E. Rice, Chem. Rev. 1997,
97, 1515–1566; b)B. Valeur, I. Leray, Coord. Chem. Rev. 2000, 205,
3–40; c)B. Valeur, I. Leray, Inorg. Chim. Acta 2007, 360, 765–774.
[3] W. R. Zipfel, R. M. Williams, W. W. Webb, Nat. Biotechnol. 2003, 21,
1369.
[4] a)W. Denk, J. H. Strickler, W. W. Webb, Science 1990, 248, 73–76;
b)C. Xu, W. Zipfel, J. B. Shear, R. M. Williams, W. W. Webb, Proc.
Natl. Acad. Sci. USA 1996, 93, 10763–10768.
[5] A.-C. Robin, S. Gmouh, O. Mongin, V. Jouikov, M. H. V. Werts, C.
Gautier, A. Slama-Schwok, M. Blanchard-Desce, Chem. Commun.
2007, 1334–1336.
[6] a)C. Xu, W. W. Webb, J. Opt. Soc. Am. B 1996, 13, 481–491; b)C.
Xu, R. M. Williams, W. Zipfel, W. W. Webb, Bioimaging 1996, 4,
198–207; c)M. Taki, J. L. Wolford, T. V. OꢁHalloran, J. Am. Chem.
Soc. 2004, 126, 712–713; d)H. M. Kim, M.-Y. Jeong, H. C. Ahn, S.-
J. Jeon, B. R. Cho, J. Org. Chem. 2004, 69, 5749–5751; e)S. J. K.
Pond, O. Tsutsumi, M. Rumi, O. Kwon, E. Zojer, J.-L. Bredas, S. R.
Marder, J. W. Perry, J. Am. Chem. Soc. 2004, 126, 9291–9306;
f)H. C. Ahn, S. K. Yang, H. M. Kim, S. Li, S.-J. Jeon, B. R. Cho,
Chem. Phys. Lett. 2005, 410, 312–315; g)J. S. Kim, H. J. Kim, H. M.
Kim, S. H. Kim, J. W. Lee, S. K. Kim, B. R. Cho, J. Org. Chem. 2006,
71, 8016–8022; h)R. Bozio, E. Cecchetto, G. Fabbrini, C. Ferrante,
M. Maggini, E. Menna, D. Pedron, R. Ricco, R. Signorini, M. Zer-
Two-photon excited fluorescence spectroscopy: Two-photon excited fluo-
rescence spectroscopy was performed using a mode-locked Ti:sapphire
laser generating 150 fs wide pulses at a rate of 76 MHz, with a time-aver-
aged power of several hundreds of mW (Coherent Mira 900 pumped by
a 5 W Verdi). The laser light was attenuated using a combination of half-
wave plates and a Glan laser polariser, and the excitation power was fur-
ther controlled using neutral density filters of varying optical density
mounted in a computer-controlled filter wheel. After five-fold expansion
through two achromatic doublets, the laser beam was focused by a micro-
scope objective (10”, NA 0.25, Olympus, Japan)into a standard 1 cm ab-
Chem. Eur. J. 2008, 14, 5941 – 5950
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5949

M. Blanchard-Desce, V. Michelet, I. Leray et al.
betto, J. Phys. Chem. A 2006, 110, 6459–6464; i)F. Huang, Y. Tian,
C.-Y. Chen, Y.-J. Cheng, A. Cody Young, A. K.-Y. Jen, J. Phys.
Chem. C 2007, 111, 10673–10681; j)A. Bhaskar, G. Ramakrishna,
R. J. Twieg, T. Goodson III, J. Phys. Chem. C 2007, 111, 14607–
14611.
d)M.-H. Ha-Thi, V. Souchon, M. Penhoat, F. Miomandre, J.-P.
GenÞt, I. Leray, V. Michelet, Lett. Org. Chem. 2007, 4, 185–188.
[12] R. Chinchilla, C. Najera, Chem. Rev. 2007, 107, 874–922.
[13] P. J. Hajduk, G. Sheppard, D. G. Nettesheim, E. T. Olejniczak, S. B.
Shuker, R. P. Meadows, D. H. Steinman, G. M. Carrera, P. A. Mar-
cotte, J. Severin, K. Walter, H. Smith, E. Gubbins, R. Simmer, T. F.
Holzman, D. W. Morgan, S. K. Davidsen, J. B. Summers, S. W. Fesik,
J. Am. Chem. Soc. 1997, 119, 5818–5827.
[14] G. Bartoli, M. Bosco, L. Sambri, Tetrahedron Lett. 1996, 37, 7421–
7424.
[15] I. Aujard, J.-P. Baltaze, J.-B. Baudin, E. Cogne, F. Ferrage, L. Jullien,
E. Perez, V. PrØvost, L. M. Qian, O. Ruel, J. Am. Chem. Soc. 2001,
123, 8177–8188.
[16] S. Akimoto, H. Nishizawa, T. Yamazaki, I. Yamazaki, Y. Hayashi,
M. Fujimaki, K. Ichimura, Chem. Phys. Lett. 1997, 276, 405–410.
[17] M. N. Berberan-Santos, J. Canceill, J. C. Brochon, L. Jullien, J. M.
Lehn, J. Pouget, P. Tauc, B. Valeur, J. Am. Chem. Soc. 1992, 114,
6427–6436.
[18] B. H. Boo, D. Kang, J. Phys. Chem. A 2005, 109, 4280–4284.
[19] a) Guidelines for drinking-water quality, 2nd ed., Vol. 2, World
Health Organisation, Geneva, 1996, p. 940; b)G. H. Scoullos, M. J.
Vonkeman, L. Thorton, Z. Makuch, in Mercury, Cadmium, Lead:
Handbook for Sustainable Heavy Metals Policy and Regulation (En-
vironment and Policy, V. 31), Kluwer, Norwell, 2001.
[7] More subtle designs involve bischromophoric units, whereby com-
plexation prevents the RET mechanism (resulting in quenching of
fluorescence), thus resulting in enhanced TPEF (ref. [6g]).
[8] The fluorescence response can be disturbed by the presence of fluo-
rescent contaminants such as tryptophan or polycyclic aromatic
compounds.
[9] Branching of dipolar units has been reported as a useful strategy for
enhancing TPA responses: a)D. Beljonne, W. Wenseleers, E. Zojer,
Z. Shuai, H. Vogel, S. J. K. Pond, J. W. Perry, S. R. Marder, J.-L.
BrØdas, Adv. Funct. Mater. 2002, 12, 631; b)C. Katan, F. Terenziani,
O. Mongin, M. H. V. Werts, L. Porr›s, T. Pons, J. Mertz, S. Tretiak,
M. Blanchard-Desce, J. Phys. Chem. A 2005, 109, 3024. However,
this effect strongly depends on the nature of the branching unit,
which controls coherent coupling between the branches: c)F. Teren-
ziani, C. Le Droumaguet, C. Katan, O. Mongin, M. Blanchard-
Desce, ChemPhysChem 2007, 8, 726–738.
[10] a)P. Perez-Lourido, J. Romero, J. A. Garcia-Vazquez, A. Sousa,
Y. F. Zheng, J. R. Dilworth, J. Zubieta, J. Chem. Soc. Dalton Trans.
2000, 769–774; b)P. A. W. Dean, L. Polensek, Can. J. Chem. 1980,
58, 1627–1632.
[11] a)R. Metivier, R. Amengual, I. Leray, V. Michelet, J.-P. GenÞt, Org.
Lett. 2004, 6, 739–742; b)M.-H. Ha-Thi, M. Penhoat, V. Michelet, I.
Leray, Org. Lett. 2007, 9, 1133–1136; c)M. H. Ha-Thi, V. Souchon,
A. Hamdi, R. Metivier, V. Alain, K. Nakatani, P. G. Lacroix, J.-P.
GenÞt, V. Michelet, I. Leray, Chem. Eur. J. 2006, 12, 9056–9065;
[20] J. N. Demas, G. A. Crosby, J. Phys. Chem. 1971, 75, 991–1024.
[21] H. Gampp, M. Maeder, C. J. Meyer, A. D. Zuberbꢂhler, Talanta
1985, 32, 95–101.
Received: January 15, 2008
Published online: May 15, 2008
5950
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5941 – 5950