Alkynyl expanded donor-acceptor calixarenes: Geometry and second-order nonlinear optical properties

Article abstract of DOI:10.1002/chem.200700615

A number of wide- and narrow-rimmed functionalized alkynylcalix[4] arenes have been synthesized by Sonogashira coupling. With respect to their optical properties, these donor-acceptor systems are treated as ensembles of covalently linked, electronically i

Full text of DOI:10.1002/chem.200700615

FULL PAPER
DOI: 10.1002/chem.200700615
Alkynyl Expanded Donor–Acceptor Calixarenes: Geometry and Second-
Order Nonlinear Optical Properties
Gunther Hennrich,*[a] Ma Teresa Murillo,[a] Pilar Prados,[a] Hassan Al-Saraierh,[b]
Abdelmeneim El-Dali,[b] David W. Thompson,[b] Julie Collins,[b] Paris E. Georghiou,*[b]
Ayele Teshome,[c] Inge Asselberghs,[c] and Koen Clays*[c]
Abstract:
A
number of wide- and
depend on the electron-withdrawing
nature of the terminal ethynylphenyl
substituent (NO2, CF3, H). The nitro
derivatives display high values of the
quadratic hyperpolarizability b. Not
only do the (nonlinear) optical proper-
ties of the target compounds depend
on the number and relative disposition
of the subchromophores, but also on
the geometry of the calixarenes. In par-
ticular, the opening angle of the calix-
arene cavity can be determined by the
substitution pattern of the calixarene
scaffold (wide- versus narrow-rim sub-
stitution) and the number of the acety-
lene functions introduced. Both the
NLO properties and the conformation-
al issues are conveniently assessed by
using hyper-Rayleigh scattering (HRS)
in solution, and supported by X-ray
crystallography in the solid state.
narrow-rimmed functionalized alkynyl-
calix[4]arenes have been synthesized
by Sonogashira coupling. With respect
to their optical properties, these
donor–acceptor systems are treated as
ensembles of covalently linked, elec-
tronically independent tolane subchro-
mophores. Linear UV/visible and fluo-
rescence spectroscopic investigations
revealed that the charge-transfer char-
acter of the electronic transitions in
calixarenes, and also the second-order
nonlinear optical (NLO) properties
Keywords: alkynes · calixarenes ·
conformation analysis · nonlinear
optics · Sonogashira coupling
Introduction
creasing importance over the past years.[2] Enlarged supra-
molecular scaffolds for molecular recognition of larger guest
molecules, the possibility of utilizing large container mole-
cules to carry out chemical reactions in their interior, and
the construction of noncovalent assemblies in nanoscale di-
mensions has, among other incentives, led to an intensifica-
tion of synthetic efforts to access deep calixarenes by means
of covalent synthesis.[3] Among various methods, the palladi-
um-catalyzed Sonogashira cross-coupling of halogenated cal-
ixarene precursors with terminal acetylenes has been estab-
lished as one of the most efficient strategies to achieve this
goal.[4] Various research groups have reported alkynylcalix-
arenes as molecular receptors,[5] building blocks for supra-
molecular assemblies,[6] coordination compounds,[7] and elec-
tro-optical devices.[8] A particularly attractive challenge is
the exploitation of the flexibility of the cavitand scaffold for
the purpose of transferring molecular movement to an ap-
preciable nanometer scale.[9] Diederich et al. have reported
a molecular muscle, a resorcinarene-based device which can
perform movement over a distance of 70 Š. This process
relies on the expansion and contraction of the flexible, acet-
ylene-expanded cavity of a resorcinarene system.[10] Like-
wise, the group of Weiss has prepared different pincer-type
Within the field of calixarene-based supramolecular sys-
tems,[1] the prospect of having deep cavitands has gained in-
[a] Dr. G. Hennrich, Dr. M. T. Murillo, Prof. Dr. P. Prados
Departamento de Química Orgµnica, C-I
Universidad Autonoma de Madrid, Cantoblanco
28049 Madrid (Spain)
Fax : (+34)914973966
E-mail: gunther.hennrich@uam.es
[b] H. Al-Saraierh, A. El-Dali, Dr. D. W. Thompson, J. Collins,
Prof. Dr. P. E. Georghiou
Department of Chemistry, Memorial University of Newfoundland
St. Johnꢀs, Newfoundland and Labrador
A1B 3X7 (Canada)
Fax : (+1)7373702
E-mail: parisg@mun.ca
[c] A. Teshome, Dr. I. Asselberghs, Prof. Dr. K. Clays
Department of Chemistry, University of Leuven
Celestijnenlaan, 200D, 3001 Leuven (Belgium)
Fax : (+32)16327982
E-mail: koen.clays@fys.kuleuven.be
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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ligands based on a bisalkynylcalix[4]arene platform in which
the terminal porphyrin receptor moieties can adjust their in-
termolecular distance to the steric demands of the respec-
tive bifunctional guest molecules.[11] In these types of tweez-
er molecules, molecular motion can be stimulated by an
electrochemical input.[12] Again, the principle of molecular
movement is based on the flexibility of the calixarene plat-
form. In both examples, the extension of the cavitand by
triple-bond substitution guarantees a controlled, one-dimen-
sional orientation of the molecular movement. In contrast to
vinylic or diazo systems, which can undergo cis–trans isomer-
isation, rigid, linear acetylene systems do not possess such
additional complications to their conformational freedom.
Another facet of calixarenes of continuing relevance is
their application as nonlinear optical chromophores.[13]
Guided by the pioneering work of Reinhoudt and Per-
soons,[14] we have also recently focused our research on or-
ganic molecules for second-order nonlinear optics, that is,
on the use of alkynyl-substituted calixarenes. In the case of
alkynyl-substituted calixarenes, these systems can be consid-
ered as an ensemble of independent, dipolar tolane subchro-
mophores held together in a defined, pseudo-rigid confor-
mation. In the case of nonlinear optically-active calixarenes,
as well as in the examples outlined above, the determination
of the relative orientation of the subunits to each other is a
crucial issue. The dipolar and octopolar components that
contribute to the overall hyperpolarizability of donor–ac-
ceptor (D–A)-substituted calix[4]arenes in their different
conformations (cone, partial cone, 1,2-alternate, and 1,3-al-
ternate) have been investigated experimentally and by com-
putational methods.[15] The variation of the interdipolar
angle between the aromatic subunits has been assessed em-
ploying theoretical calculations.[16] In solution, this important
parameter, the opening angle of the calixarene cavity, could
only be measured qualitatively by dipolometry and,[17] tradi-
tionally, NMR spectroscopy. Depending on the chemical
shifts of the methylene bridge 13C NMR signals, the calixar-
ene is described as more or less conical.[18] In a first commu-
nication, we have shown that hyper-Rayleigh scattering is a
useful tool to determine the interdipolar angle in tetraalkyn-
yl calix[4]arenes in solution.[19] Although X-ray crystallogra-
phy is an invaluable technique for static structure determi-
nation in the solid phase, it is obvious that a reliable solu-
tion-based analytical method for the average structure of
these highly dynamic systems, the
Figure 1. Schematic depiction of different D–A-substituted bis- and tet-
raalkynylcalix[4]arenes.
The introduction of D–A end groups into the tolane subu-
nits should give rise to a high NLO activity (NLO=nonlin-
ear optical). The different types of calixarenes were chosen
to vary the flexibility of the molecular scaffold and, there-
fore, a variation of the interdipolar angle is expected. Fur-
thermore, this angle, that is, the opening of the calixarene
cavity, and also the second-order NLO properties can be de-
termined by hyper-Rayleigh scattering (HRS). The confor-
mation analysis in solution is accompanied by, where possi-
ble, a single crystal X-ray structure determination or by mo-
lecular modeling calculations.
Results and Discussion
Synthesis: The synthesis of the upper-rim alkynylated com-
pounds A1–A3 was achieved in good yields by fourfold So-
nogashira coupling of the tetraiodo precursor 1[20] with dif-
ferent arylethynyls, analogous to the reported procedure
(Scheme 1).[19]
To our surprise, the synthesis of the 5,17-bisarylalkynylca-
lix[4]arenes B1–B3 was initially complicated by the difficult
accessibility of the diiodo precursor 2b. Even though this
compound has been mentioned in several synthetic proce-
dures as the starting material, it has not to our knowledge
actually been described and characterized properly. Some of
the previous papers cite the diiodo starting material 2a er-
ratically as the bismethoxy derivative. Compound 2[21] is io-
dinated in two repetitive steps by using excess benzyltrime-
thylammonium dichloroiodate (BTMA·ICl2) in a dichloro-
methane/methanol mixture.[22] The extremely low solubility
of 2a hampered its purification and characterization signifi-
cantly necessitating the complete characterization at the
stage of the synthesis of tetrapropylated 2b. The final cou-
typical medium of study of which
is the liquid phase (extraction,
self-assembly, molecular recogni-
tion, etc.), is highly desirable. In
continuation of our previous work,
we have designed an elaborate
series of second-order NLO-
active, expanded calix[4]arenes in
which the calixarene platform is
substituted on both the upper- or
lower-rim by two or four aryl-
ethynyl moieties (Figure 1).
Scheme 1. Synthesis of the tetraalkynylcalix[4]arenes A1–A3.
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Alkynyl Expanded Donor–Acceptor Calixarenes
FULL PAPER
pling step proceeded smoothly to give compounds B1–B3 in
acceptable yields (Scheme 2). In the 13C NMR spectrum, the
methylene bridge carbons appear at d=30.9 and 30.8 ppm
for the type A and B calixarenes, respectively, which is indi-
cative for the cone-conformation of these compounds in so-
lution.
Type C calixarenes C1–C3 were synthesized in the same
manner as previously described.[23] The bistriflate 3[24,25] was
used as the starting compound and the Sonogashira reac-
tions afforded the narrow-rim substituted intermediate com-
pounds 3a–3c in acceptable yields. To directly compare with
the wide-rim substituted alkynyl-substituted calixarenes B1–
B3, compounds 3a–3c were converted into their corre-
sponding O-propylated derivatives C1–C3, respectively
(Scheme 3).
electronic communication between the subunits, the spectro-
scopic properties of the type A–C calixarenes were com-
pared with the respective D–A-tolanes 4–9 which were pre-
pared separately.
The absorption spectra of A1–A3 and B1–B3 confirmed
this hypothesis. The spectral positions and the band charac-
teristics can be interpreted as an additive composition of the
Linear spectroscopy: In accordance with the concept of
treating the calixarenes as a covalent ensemble of dipolar
subunits containing nonzero interdipolar angles and with no
Scheme 2. Synthesis of the bisalkynylcalix[4]arenes B1–B3. Pr-I=1-Iodopropane.
Scheme 3. Synthesis of the narrow-rimmed functionalized bisalkynylcalix[4]arenes C1–C3. DBU=1,8-Diazabicyclo[5.4.0]undec-7-ene.
G
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G. Hennrich, P. E. Georghiou, K. Clays et al.
respective tolane absorptions. A broad, unstructured charge-
transfer (CT) band, in particular, for each of the NO2 deriv-
atives (A1, B1, C1, 4, 7) reveals the pronounced CT charac-
ter of these D–p–A systems. This behavior is observed to a
lesser extent in the CF3-substituted derivatives (A2, B2, C2,
5, 8) for which the absorption maxima are bathochromically
shifted with respect to the phenylacetylenes (A3, B3, C3, 6,
9). As with the latter ones, they also display vibronic struc-
turing of the low-energy absorption band (Figure 2). If one
views these calixarenes as multichromophore assemblies, an
important aspect to contemplate is the possibility of intra-
molecular dipole interactions, which can be conveniently as-
sessed by UV/visible absorption spectroscopy.[26] The spec-
tral shifts between the calixarenes and the corresponding
tolane derivatives are small enough that the assumption of
independent chromophores without electronic communica-
tion within the calixarene molecule can be considered valid.
Nevertheless, in the type C subseries (C1–C3) it is notable
that the differences between the absorption maxima of the
calixarene C1–C3 and the tolane reference compounds 7–9
increases with increasing acceptor strength of the terminal
phenyl substituent from 6 (C3 versus 9) to 12 nm (C2 versus
8) and finally 19 nm (C1 versus 7). This result can be inter-
preted as an indication of some weak interaction between
two adjacent subunits, especially when the individual solva-
tion spheres are taken into consideration and the fact that
the terminal phenylethynyl groups are kept in close proximi-
ty by the lower-rim substituted calixarene scaffold.[27]
Apart from these spectroscopic details, a more important
observation is the scaling of the absorptive properties with
the number of tolane subunits. With the difference in vi-
bronic structure for the different compounds, the value for
the extinction coefficient at the wavelength of maximal ab-
sorption might not be the best quantitative parameter to
use, but the general trend is clearly observed, especially
with the smooth spectra for the nitro compounds. When
comparing the type C calixarene C1 with the reference com-
pound 7, the ratio of the extinction coefficient is 2.0, while
comparing the tetrasubstituted calixarene C1 with the type
B calixarene B1, this ratio is also 2.0. For the other com-
pounds, the ratios may not be as perfect as expected, due to
the effect of vibronic structure on the spectrum, but the
same tendency is clearly observed, corroborating the as-
sumption of electronic independent tolane subunits.
For the nitro-derivatives A1, B1, C1, 4, and 7, no fluores-
cence was observed either in the linear optical experiments
(no one-photon excited emission spectra) or in the second-
order nonlinear experiments for which no demodulation or
phase shifts were observed in the HRS experiments). For
the other compounds, weak emission was observed, with the
concomitant red shift in the emission spectra for the CF3-
substituted A2, B2, C2, 5, and 8 versus the unsubstituted
A3, B3, C3, 6, and 9. Based on the absorption and fluores-
cence spectroscopic data, the transition dipole moments
have been calculated. As can be seen in the Supporting In-
formation, these results are in line with the experimental
findings.
Figure 2. Absorption spectra of calixarenes A1–A3, B1–B3, C1–C3, and
tolanes 4–9 measured in CH2Cl2, c=10ꢀ6 molLꢀ1
.
Second-order nonlinear optical properties: The second-
order nonlinear polarizability, or first hyperpolarizability, b,
of a single chromophore can be derived from the classic
two-level formulation of b [Eq. (1)].[28]
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Alkynyl Expanded Donor–Acceptor Calixarenes
FULL PAPER
2
2
6ðPgeÞn ðDmgeÞnðEopÞn
tributing to the NLO response or to another cause of the
depolarization. The lowest value for 1 that can be achieved
from off-diagonal contributions is 1.5 for purely octopolar
molecular geometries. For the fluorescent tolane references,
the even lower depolarization ratios (as low as 1.11) are
clearly caused by fluorescence depolarization and do not
convey information about hyperpolarizability tensor compo-
nents.
0
ð1Þ
bn
¼
2
2
2
2
½ðEopÞn ꢀð2EincÞ ꢁ½ðEopÞn ꢀEinc
ꢁ
in which Eop is the energy of the optical (charge transfer)
transition of interest and Pge and Dmge are the transition
strength and ground-to-excited state dipole moment change
associated with the charge-transfer absorption, respectively.
A strong transition, with a large difference in dipole
moment between ground and excited state, as encountered
in charge-transfer chromophores, results in a substantial
nonlinearity. The wavelength dependence is more intricate:
A lower energy transition favors a larger b, yet the closeness
of the transition wavelength to the measurement wavelength
determines the degree of resonance enhancement. This two-
level formalism also allows extracting the inherent static,
wavelength-independent bo from the dynamic, wavelength-
dependent b.[29]
For the tolane reference compounds 4–9, the b and bo
values can be rationalized in terms of the degree of charge
transfer as a function of substituent (H, CF3, or NO2). The
stronger the electron-withdrawing effect, increasing in the
order H<CF3 <NO2, the lower the energy of the transition,
the stronger the red-shift of the absorption, and the larger
the value for b.[30] We also observed the effect of the lower
electron-donor strength in the tolanes 7–9 with respect to
the tolanes 4–6 in both the wavelength of the charge-trans-
fer transition and the value of b. The depolarization ratio
gives a good indication about the validity of the assumption
that a single major hyperpolarizability tensor component
dominates the NLO response. For dipolar CT molecules
with the unique dipolar axis along the z dimension, bzzz is
dominant. When this is the case, the depolarization ratio 1
is larger than 2.5 and in the limiting case 5. This is clearly
observed for the nonfluorescent compounds A1, B1, C1, 4,
and 7, with a strikingly high value of 4.96 for the tetrasubsti-
tuted calixarene A1. Lower values for the depolarization
ratio can point to off-diagonal tensor contributions in which
there are additional hyperpolarizability tensor elements con-
Congruent with the analysis of the linear optical proper-
ties as originating from the appropriate number of noninter-
acting chromophores in the calixarenes, we can express the
bzzz in the calixarenes as resulting from the vector additions
of the individual bmono as bzzz =n
(cosq)3bmono, with q the
A
opening angle between the chromophoric tolane subunits
and n=4 for the tetra- and n=2 for the disubstituted calix-
arenes. This then results in a value for the opening angle q.
Please note that these values are essentially identical when
using the static bzzz,o values, as the resonance enhancement
factors within a series of model compound, di- and tetrasub-
stituted calixarenes, are very similar. The values for the
opening angle q for the di- and tetrasubstituted calixarenes
as derived from HRS experiments are given in the last
column of Table 1.
X-ray structure analysis: Single crystals suitable for X-ray
structural determination were obtained for A3 and C3, re-
spectively (Figures 3and 4). This allows a reliable compari-
son between the type A and C calixarenes in terms of the
electronic situation of the tolane subunits, which have a sim-
ilar D–A substitution.
For A3, the two opposite tolane subchromophores are
held in an angle of 127 and 178, respectively. Note that all
four triple bonds permit both rotational and bending mo-
tions, such that none of the opposing acetylenic phenyl ter-
mini are in relative orientations indicative of attractive (p-
stacking) interactions.
In the case of calixarene C3, the opening angle as sub-
tended by the two opposite tolane subunits is approximately
four degrees, while the planes of the two terminal phenyl
Table 1. Spectroscopic data for A1–A3, B1–B3, C1–C3, and 4–9 measured in CH2Cl2.
lmax
(abs) [nm]
emax [cm2 molꢀ1
]
lmax(em)[a] [nm]
f[b]
t [ns]
1
bzzz,800 [10ꢀ30esu]
bzzz,0 [10ꢀ30esu]
q [8]
A1
A2
A3
B1
B2
B3
C1
C2
C3
4
353
317
309
358
315
309
362
321
309
357
318
309
343
309
303
76799
54870
88221
38250
40299
42184
43669
48745
42814
27200
24170
25819
21543
28102
31877
–
<0.01
0.03
0.01
<0.01
0.03
0.01
<0.01
0.18
0.36
<0.01
0.01
<0.01
<0.01
0.02
–
4.96ꢂ0.09
1.36ꢂ0.08
1.11ꢂ0.01
3.0ꢂ0.1
ꢂ0.1
530ꢂ20
100ꢂ20
80ꢂ10
480ꢂ20
60ꢂ10
60ꢂ10
670ꢂ130
46ꢂ6
94ꢂ4
43ꢂ2
23ꢂ7
ꢂ6
ꢂ5
ꢂ10
ꢂ10
16ꢂ10
0ꢂ10
0ꢂ10
–
382
368
–
388
369
–
363
343
–
370
349
–
1.1ꢂ0.2
3.0ꢂ0.1
–
0.6ꢂ0.32.3
1.0ꢂ0.2
–
1.5ꢂ0.5
0.7ꢂ0.1
–
31ꢂ25
3
27ꢂ33
76ꢂ327
19ꢂ312
21ꢂ316
96ꢂ19
14ꢂ2
1.6ꢂ0.1
2.91ꢂ0.05
1.8ꢂ0.1
2.4ꢂ0.1
4.02ꢂ0.09
1.8ꢂ0.1
1.5ꢂ0.1
2.50ꢂ0.05
ꢂ0.1
59ꢂ4
20ꢂ1
340ꢂ40
32ꢂ5
55ꢂ6
5
6
7
8
–
10ꢂ2
–
–
–
–
4ꢂ6
34ꢂ5
12ꢂ2
–
380ꢂ40
22ꢂ2
82ꢂ9
337
324
1.8ꢂ0.32.3
7.6ꢂ0.7
ꢂ1
9
<0.01
1.8ꢂ0.31.5
ꢂ0.1
28ꢂ310
–
[a] Excitation wavelength l(ex)=300 nm; the nitro compounds A1, B1, C1, 4, and 9 are practically nonfluorescent. [b] Fluorescent quantum yields, F,
were determined by using quinine sulphate in 0.1n H2SO4 as standard.
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G. Hennrich, P. E. Georghiou, K. Clays et al.
tool for the structural determination of calixarenes in solu-
tion. Being aware of the limitations of treating the nonlinear
optically-active calixarenes as an ensemble of isolated D–A
chromophores,[31] this simplified model can be considered
valid and useful for most of the (supramolecular) chemical
issues addressed when working with calixarenes. Neverthe-
less, the consistently larger opening angles for the NO2-sub-
stituted calixarenes observed point in this direction: The
close proximity of strongly polar/polarizable subunits is
avoided by larger opening angles. As a result of the steric
conditions in each calixarene scaffold, consistently larger
opening angles are found for the upper rim disubstituted
type B calixarenes than for the lower rim, type C, disubsti-
tuted ones, while this angle is the largest for the tetrasubsti-
tuted, type A calixarenes. When comparing an average of a
dynamic opening angle as obtained from HRS measure-
ments in solution with the values observed in the solid state,
good agreement is found for the lower-rim substituted C3.
A very clear parallel arrangement of the two phenyl-
Figure 3. Structural diagram of calixarene A1 (ORTEP, 50% probability
ellipsoids). Hydrogen atoms have been omitted for clarity.
A
with the findings in the X-ray structure. Despite the fact
that for the type A calixarene A1, the discrepancy between
the angles determined in solution and in the solid state is
still within the error margin,[19] for compound A3 the value
of 338 in solution stands out against a value of 728 in the
crystal. We attribute this difference to the crystal packing,
for which the molecules of A3 form columns of cone stacks.
However, this case demonstrates once again the necessity of
having a reliable analytical tool in hand to asses the structur-
al features of the highly dynamic calixarene analytes in solu-
tion.
Experimental Section
Figure 4. Structural diagram of calixarene C1 (ORTEP, 50% probability
ellipsoids). Hydrogen atoms have been omitted for clarity.
General: All solvents and reagents were used as purchased. Ethynylaryls
were purchased from Aldrich and used without further purification. TLC
was performed on Alugram SilG/UV254-coated aluminum sheets (Ma-
cherey–Nagel) with UV detection at 254/365 nm. Melting points were de-
termined on a Gallenkamp melting point apparatus and are uncorrected.
1H and 13C NMR spectra were recorded on a Bruker AC-300 spectrome-
ter at 300 and 75 MHz, respectively, in deuterated chloroform (deutera-
tion grade >99.80%) with the solvent signal serving as the internal stan-
dard. MS were recorded on a HP1100MSD spectrometer. MALDI-TOF
MS spectra were recorded on an Applied Biosystems DE-RP equipment.
API-MS spectra were recorded with an Agilent 1100 series LC/MSD
chromatographic system. Preparative thin-layer chromatography (PLC)
was carried out using TLC high-purity silica as supplied by Aldrich with
gypsum binder added. Elemental analyses were performed on a LECO
CHNS 932 microanalyzer. Spectroscopic measurements were performed
by using HPLC-quality solvents and are solvent corrected. UV/visible
spectra were measured on a HP8453(Hewlett–Packard) spectrophotom-
eter. A Perkin–Elmer LS50B luminescence spectrometer was employed
for the fluorescence studies, in a four-sided quartz cell at RT in a right
angle geometry and are corrected for the spectral response for the detec-
tion system.
rings are not parallel to each other, but are titled inwards to
each other by an angle of 188. It is also evident that the
triple bonds of the arylalkynyl moieties in 9 are bent with
an average dihedral angle of 268. The lower-rim O-propoxy
groups contribute a considerable amount of steric bulk, sup-
posedly obstructing a rapid “breathing” of the calixarene
cavity.
Conclusion
A number of acetylene expanded calixarene-based deep-
cavitands have been synthesized by Sonogashira-coupling,
displaying elevated second-order nonlinearities. The impor-
tant conclusion to be drawn from the spectroscopic investi-
gations is that it is possible to derive a value for the opening
angle q from the hyperpolarizability values for the type A–
C calixarenes, hence, HRS can be employed as an analytical
Materials: The synthesis of A1, A3, 3c, and 4 has been reported previ-
ously.[19,23]
5,17-Diiodo-bis-25,27-(n-propoxy)-26,28-dihydroxycalix[4]arene
(2a):
CaCO3 (1.0 g) was added to a solution of 2 (509 mg, 1.0 mmol) and ben-
zyltriammonium dichloroiodate (1.38 g, 4.0 mmol) in CH2Cl2/MeOH 5:3
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Alkynyl Expanded Donor–Acceptor Calixarenes
FULL PAPER
(80 mL). After stirring at 258C for 24 h, the reaction was quenched by
addition of HCl (conc, 2 mL). A solution of NaHSO3 (10%, 20 mL) was
added, the organic layer was separated, washed with water (3”20 mL),
dried (Na2SO4), and then concentrated in vacuo. The resulting crude
product was reacted again with benzyltriammonium dichloroiodate
(1.38 g, 4.0 mmol) in the presence of CaCO3 (1.0 mg) in CH2Cl2/MeOH
5:3(80 mL) for 72 h at 25 8C. Following the workup described above, 2a
was produced as a crude product (479 mg) which was sufficiently pure to
be employed in the next step. 1H NMR: d=8.40 (s, 2H), 7.34 (s, 4H),
6.94–6.78 (m, 6H), 4.22 (d, J=13.3 Hz, 4H), 3.95 (t, J=7.8 Hz, 4H), 3.31
(d, J=13.4 Hz, 4H), 2.08–2.01. (m, J=8.0 Hz, 8H), 0.85 ppm (t, J=
7.5 Hz, 6H).
129.2, 128.1, 125.1, 122.4, 115.7, 92.6, 86.7, 77.0, 76.9, 30.9, 23.4, 23.2, 10.5,
10.1 ppm; MALDI-TOF MS: m/z: 928 [M+]; elemental analysis calcd
(%) for C58H54F6O4: C 74.98, H 5.86; found: C 74.83, H 5.86.
5,17-Bis[(phenyl)ethynyl)]-25,26,27,28-tetra(n-propoxy)calix[4]arene
A
(B3): Column chromatography (hexanes/EtOAc 20:1) and final recrystal-
lization from EtOH gave pure B3 as colorless crystals. Yield: 105 mg,
1
53%; m.p. 188–199 8C; H NMR: d=7.54 (dAB, J=8.7 Hz, 4H), 7.50 (dAB
,
J=8.7 Hz, 4H), 7.13(s, 4H), 6.49 (brs, 6H), 4.47 (d, J=13.4 Hz, 4H),
3.99 (t, J=7.7 Hz, 4H), 3.80 (t, J=7.2 Hz, 4H), 3.20 (d, J=13.4 Hz, 4H),
2.02–1.87 (m, 8H), 1.07 (t, J=7.5 Hz, 6H), 0.98 ppm (t, J=7.4 Hz, 6H);
13C NMR: d=158.3, 155.8, 136.4, 133.6, 132.1, 131.5, 129.6, 129.2, 128.1,
125.1, 122.4, 115.7, 92.6, 86.7, 77.0, 76.9, 30.9, 23.4, 23.2, 10.5, 10.1 ppm;
MALDI-TOF MS: m/z: 792 [M+]; elemental analysis: calcd (%) for
C56H54O4·1/2H2O: C 83.86, H 7.16; found: C 83.82, H 7.14.
5,17-Diiodo-25,26,27,28-tetra-(n-propoxy)calix[4]arene
(2b):
NaH
(200 mg, 5.0 mmol, 60% suspension in mineral oil) was added to a stirred
solution of 2a (380 mg, 0.5 mmol) in dry DMF (20 mL) and, after 45 min,
n-propyliodide (488mL, 5.0 mmol) was also added. The reaction mixture
was stirred at 808C for 24 h before it was quenched with HCl (1m,
10 mL). The aqueous phase was extracted with CH2Cl2 and the separated
organic layer was washed with 1m HCl (10 mL), a sodium hydrogen sul-
phite solution (10%, 10 mL), water, and brine. The organic phase was
dried (MgSO4) and concentrated in vacuo. The remaining solid was re-
crystallized from CH2Cl2/MeOH 10:1 to give pure 2b as a colorless solid.
Yield: 295 mg, 68%; Rf =0.13(hexanes); m.p. 204–209 8C; 1H NMR: d=
7.12 (s, 4H), 6.54–6.47 (m, 6H), 4.36 (d, J=13.3 Hz, 4H), 3.86 (t, J=
7.8 Hz, 4H), 3.77 (t, J=7.4 Hz, 4H), 3.09 (d, J=13.4 Hz, 4H), 1.92–1.86
(m, 8H), 1.00 (t, J=7.5 Hz, 6H), 1.00 ppm (t, J=7.4 Hz, 6H); 13C NMR:
d=157.0, 155.9, 138.3, 137.1, 133.8, 128.2, 122.5, 85.5, 76.8, 76.3, 30.2,
23.3, 23.1, 10.4, 10.2 ppm; MALDI-TOF HRMS: m/z: calcd for
C40H46O4Na: 867.1386; found: 867.1378.
5,11,17,23-Tetra(tert-butyl)-26,28-bis(p-nitrophenylethynyl)calix[4]arene
(3a): A solution of DBU (66.9 mg, 0.44 mmol) and 1-ethynyl-4-nitroben-
zene (35.3 mg, 0.24 mmol) in dry toluene (3 mL) were added to a stirred
mixture
of
(p-tert-butylcalix[4]arene-1,3-bistriflate)
(100.0 mg,
0.11 mmol), [PdCl2
AHCTREUNG
0.005 mmol) in dry toluene (10 mL) at reflux temperature. The resulting
mixture was stirred for 24 h at the reflux temperature, cooled, and then
poured into saturated aqueous ammonium chloride (20 mL) and washed
with H2O (20 mL). The organic layer was dried (MgSO4), filtered, and
evaporated in vacuo. The residue was purified by PLC (EtOAc/hexanes
1:99) to give 3a (53mg, 27%); m.p. 145–147 8C; 1H NMR: d=7.89 (dAB
,
J=8.0 Hz, 4H), 7.54 (dAB, J=8.0 Hz, 4H), 7.18 (s, 4H), 6.79 (s, 4H), 5.29
(s, 2H), 4.56 (d, J=14.0 Hz, 4H), 3.65 (d, J=14.0 Hz, 4H), 1.33 (s, 18H),
0.91 ppm (s, 18H); 13C NMR: d=152.4, 152.2, 151.3, 147.0, 143.1, 142.1,
132.0, 130.2, 128.5, 125.8, 124.7, 123.6, 117.8, 95.6, 93.2, 37.1, 34.6, 34.2,
31.9, 30.8 ppm; MS (APCI+): m/z: calcd for C60H62N2O6: 907.16 [M+];
found: 907.50.
General procedure for the Sonogashira couplings yielding A1–A3, B1–
B3, and 5–6: The respective iodoarene (0.25 or 0.5 mmol) was stirred to-
gether with [Pd(PPh3)2Cl2] (5 mol% per iodo group) and CuI (5 mol%
A
5,11,17,23-Tetra(tert-butyl)-25,27-dipropoxy-26,28-bis(p-nitrophenylethy-
nyl)calix[4]arene (C1): NaH (6.4 mg, 0.265 mmol) was added to a solu-
tion of 3a (60 mg, 0.066 mmol) in anhydrous DMF (1 mL) and THF
(10 mL), followed by the addition of n-propyliodide (45.1 mg,
0.265 mmol). The resulting mixture was heated at reflux temperature for
6 h. After this time, the mixture was cooled to RT and the THF was
evaporated in vacuo. The residue was then added to H2O (10 mL) to give
a yellow precipitate which was purified by PLC (60% CH2Cl2 in petrole-
um ether) to give C1. Yield: 55.6 mg, 85%; m.p. >3308C; 1H NMR: d=
8.20 (dAB, J=8.0 Hz, 4H), 7.61 (dAB, J=8.0 Hz, 4H), 7.27 (s, 4H), 6.56 (s,
4H), 4.68 (d, J=12.5 Hz, 4H), 4.08–4.05 (m, 4H), 3.49 (d, J=12.5 Hz,
4H), 2.13–1.86 (m, 4H), 1.39 (s, 18H), 0.86 (s, 18H), 0.51–0.48 ppm (m,
6H); 13C NMR: d=154.0, 150.8, 146.6, 146.0, 142.6, 135.6, 132.0, 131.6,
126.3, 123.9, 123.7, 118.3, 97.8, 97.5, 92.3, 75.5, 36.6, 34.4, 32.0, 31.0, 23.0,
9.9 ppm; MS (APCI+): m/z: calcd for C66H74N2O6: 991.3[ M+]; found:
991.5.
per iodo group) in degassed diisopropylamine (10 mL) for 30 min at RT
before the acetylene compound (1.5 molequiv per iodo group) was
added. The mixture was heated at 808C for the time specified. After this
time, the solvent was removed and the remaining residue was suspended
in water (50 mL) and extracted with EtOAc (3”20 mL). The combined
organic layers were dried (MgSO4) and concentrated in vacuo. The crude
products were purified as described.
5,11,17,23-Tetrakis{[(4-trifluoromethyl)phenyl]ethynyl}-25,26,27,28-
tetra(n-propoxy)calix[4]arene (A2): Reaction time: 48 h. The remaining
solid was purified by column chromatography (hexanes/EtOAc 10:1) to
give pure A2 as pale-yellow plates. Yield: 189 mg, 60%; m.p. 163–1658C.
1H NMR: d=7.47 (dAB, J=8.6 Hz, 8H), 7.40 (dAB, J=8.6 Hz, 8H), 6.96
(s, 8H), 4.46 (d, J=13.5 Hz, 4H), 3.90 (t, J=7.5 Hz, 8H), 3.20 (d, J=
13.5 Hz, 4H), 1.94 (m, 8H), 1.01 ppm (t, J=7.0 Hz, 12H); 13C NMR: d=
157.4, 155.5, 134.9, 132.0, 131.5, 127.3, 125.0, 116.3, 92.3, 87.0, 77.2, 30.8,
23.2, 10.3 ppm; MALDI-TOF MS: m/z: 1264 [M+]; elemental analysis:
calcd (%) for C76H60O4F12: C 72.15, H 4.78; found: C 71.67, H 4.91.
5,11,17,23-Tetra(tert-butyl)-26,28-bis[p-(trifluoromethyl)phenylethynyl]-
calix[4]arene (3b): A solution of DBU (66.9 mg, 0.44 mmol) and 4-ethyn-
yl-a,a,a-trifluorotoluene (40.8 mg, 0.24 mmol) in dry toluene (3mL)
were added to a stirred mixture of p-tert-butylcalix[4]arene-1,3-bistriflate
5,17-Bis[(4-nitrophenyl)ethynyl]-25,26,27,28-tetra(n-propoxy)calix[4]ar-
ene (B1): Column chromatography (hexanes/EtOAc 20:1) and final re-
crystallization from EtOH/toluene 1:1 gave pure B1 as yellow crystals.
Yield: 116 mg; 53%; Rf =0.46 (hexanes/EtOAc 20:1); m.p. 245–2478C;
1H NMR: d=8.08 (dAB, J=8.1 Hz, 4H), 7.52 (dAB, J=8.1 Hz, 4H), 7.09
(s, 4H), 6.49 (brs, 6H), 4.46 (d, J=13.4 Hz, 4H), 3.97 (t, J=7.0 Hz, 4H),
3.80 (t, J=7.0 Hz, 4H), 3.18 (d, J=12.9 Hz, 4H), 1.93(m, 8H), 1.08–
0.97 ppm (m, 12H); 13C NMR: d=158.7, 155.9, 146.5, 136.4, 133.7, 132.2,
131.9, 130.8, 128.1, 123.4, 122.3, 115.3, 95.9, 86.5, 76.9, 76.8, 30.9, 23.3,
23.2, 10.5, 10.1 ppm; MALDI-TOF HRMS: m/z: calcd for C56H54O8N2:
882.3875; found: 882.3839.
(100 mg, 0.11 mmol), [PdCl2(PPh3)2] (5.0 mg, 0.007 mmol), and CuI
A
(1 mg, 0.005 mmol) in dry toluene (10 mL) at reflux temperature. The re-
sulting mixture was stirred for 24 h at the reflux temperature, cooled, and
then poured into saturated aqueous ammonium chloride (20 mL) and
washed with H2O (20 mL). The organic layer was dried (MgSO4), fil-
tered, and evaporated in vacuo. The residue was purified by PLC
(CH2Cl2/petroleum ether 3:7) to give 3b. Yield: 24.1 mg, 23%; m.p. 271–
2738C; 1H NMR: d=7.53(d AB, J=8.5 Hz, 4H), 7.33 (dAB, J=8.5 Hz,
4H), 7.16 (s, 4H), 6.78 (s, 4H), 5.33 (s, 2H), 4.58 (d, J=14.0 Hz, 4H),
3.63 (d, J=14.0 Hz, 4H), 1.31 (s, 18H), 0.91 ppm (s, 18H); 13C NMR: d=
151.7, 151.2, 142.8, 142.0, 131.8, 130.4, 128.5, 127.2, 125.8, 125.4, 124.6,
122.9, 118.3, 95.9, 89.9, 37.1, 34.5, 34.2, 31.9, 30.9 ppm; MS (APCI+):
m/z: calcd (%) for C62H62F6O2: 953.16 [M+]; found: 953.50.
5,17-Bis{[(4-trifluoromethyl)phenyl]ethynyl}-25,26,27,28-tetra(n-propox-
y)calix[4]arene (B2): Column chromatography (hexanes/EtOAc 20:1)
and final recrystallization from EtOH gave pure B2 as colorless crystals.
Yield: 128 mg, 55%; m.p. 2378C; 1H NMR: d=7.54 (dAB, J=8.7 Hz, 4H),
7.50 (dAB, J=8.7 Hz, 4H), 7.13(s, 4H), 6.49 (brs, 6H), 4.47 (d, J=
13.4 Hz, 4H), 3.99 (t, J=7.7 Hz, 4H), 3.80 (t, J=7.2 Hz, 4H), 3.20 (d, J=
13.4 Hz, 4H), 2.02–1.87 (m, 8H), 1.07 (t, J=7.5 Hz, 6H), 0.98 ppm (t, J=
7.4 Hz, 6H); 13C NMR: d=158.3, 155.8, 136.4, 133.6, 132.1, 131.5, 129.6,
5,11,17,23-Tetra(tert-butyl)-25,27-dipropoxy-26,28-bis(p-trifluoromethyl-
phenylethynyl)calix[4]arene (C2): NaH (4.8 mg, 0.20 mmol) was added to
a solution of 3b (50 mg, 0.05 mmol) in anhydrous DMF (1 mL) and THF
(10 mL), followed by the addition of n-propyliodide (34.0 mg,
Chem. Eur. J. 2007, 13, 7753– 7761
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7759

G. Hennrich, P. E. Georghiou, K. Clays et al.
0.20 mmol). The reaction was then conducted as with 7, giving a pale-
white precipitate, which was purified by PLC (CH2Cl2/petroleum ether
1:3) to give C2. Yield: 48.2 mg, 93%; m.p. >3008C; 1H NMR: d=7.58–
7.57 (m, 8H), 7.19 (s, 4H), 6.54 (s, 4H), 4.71 (d, J=12.5 Hz, 4H), 4.10–
4.07 (m, 4H), 3.45 (d, J=12.5 Hz, 4H), 2.01–1.93(m, 4H), 1.37 (s, 18H),
0.85 (s, 18H), 0.48–0.44 ppm (m, 6H); 13C NMR: d=154.1, 150.1, 145.8,
142.3, 135.9, 131.4, 126.2, 125.4, 123.6, 123.1, 118.7, 99.8, 94.3, 92.1, 76.5,
36.7, 34.4, 34.3, 32.0, 31.0, 22.8, 9.7 ppm (one missing carbon resonance in
the aromatic region); MS (APCI+): m/z: calcd for C60H62N2O6: 1037.3
[M+]; found: 1037.7.
4-[(4-tert-Butylphenyl)ethynyl]benzene (9): Tetrabutylammonium fluo-
ride (784.4 mg, 3.00 mmol) and H2O (54 mg, 3.00 mmol) were added to a
stirred mixture of 1-bromo-4-tert-butylbenzene (213.0 mg, 1.00 mmol),
phenylacetylene (122.4 mg, 1.20 mmol), and [PdCl2(PPh3)2] (21.0 mg,
N
0.03mmol) under argon at RT. The resulting mixture was stirred for 1.5 h
at 808C and was then cooled. H2O (10 mL) was added and then extracted
with Et2O (2”10 mL). The organic layer was dried (MgSO4), filtered,
and evaporated in vacuo. The residue was purified by PLC (hexanes/
EtOAc 20:1) to give 9. Yield: 70.0 mg, 30%; m.p. 62–638C; 1H NMR:
d=7.53–7.46 (m, 5H), 7.38–7.31 (m, 4H), 1.33 ppm (s, 9H); 13C NMR:
d=151.8, 131.8, 131.6, 128.5, 128.3, 125.6, 123.8, 120.5, 89.8, 88.9, 35.0,
31.4 ppm; GCMS: m/z: calcd for C18H18: 234.1 [M+]; found: 234.2.
5,11,17,23-Tetra(tert-butyl)-25,27-dipropoxy-26,28-bis(phenylethynyl)ca-
lix[4]arene (C3): NaH (5.8 mg, 0.24 mmol) was added to a solution of 3c
(50 mg, 0.06 mmol) in anhydrous DMF (1 mL) and THF (10 mL), fol-
lowed by the addition of n-propyliodide (40.8 mg, 0.24 mmol). The reac-
tion was then conducted as for 7, giving a pale-yellow precipitate, which
was purified by PLC (hexanes/EtOAc 10:1) to give C3. Yield: 51.9 mg,
96%; m.p. >3008C; 1H NMR: d=7.53(d AB, J=7.5 Hz, 4H), 7.32–7.28
(m, 6H), 7.18 (s, 4H), 6.53(s, 4H), 4.77 (d, J=12.5 Hz, 4H), 4.16–4.13
(m, 4H), 3.44 (d, J=12.5 Hz, 4H), 2.02–1.97 (m, 4H), 1.38 (s, 18H), 0.86
(s, 18H), 0.47–0.44 ppm (m, 6H); 13C NMR: d=154.2, 149.3, 145.6, 142.1,
136.3, 131.4, 128.2, 127.5, 126.0, 125.2, 123.4, 119.5, 93.3, 91.5, 76.5, 36.7,
34.4, 34.2, 32.0, 31.0, 22.7, 9.6 ppm; MS (APCI+): m/z: calcd for
C66H76O2: 901.3[ M+]; found: 901.5.
X-ray crystallographic analysis
Summary for A1: Colorless prisms were obtained from toluene; space
group=P21/n; Z=4 in
33.194(4), c=14.7531(18) Š; a=90.00, b=116.842(3), g=90.008; V=
5915.6(12) Š3; 1calcd =1.138 gcmꢀ3; m=0.069 mmꢀ1; F
(000)=2152. A total
a cell of dimensions: a=13.5384(16), b=
AHCTREUNG
of 28568 reflections were measured, 17877 unique, by using graphite
monochromatized MoKa radiation (l=0.71073Š) at 100 K. The structure
was refined on F2 to Rw =0.1520 with a goodness-of-fit=1.018 for 764 re-
fined.
Summary for C1: Colorless platelet crystals were obtained from CHCl3/
MeOH; monoclinic; space group=P21/n; Z=4 in a cell of dimensions:
a=13.002(3), b=24.016(5), c=17.003(4) Š; a=90.00, b 118.442(6), g=
4-[(4-Propoxyphenyl)ethynyl]trifluoromethylbenzene (5): Column chro-
matography (hexanes/EtOAc 20:1) and final recrystallization from EtOH
90.008; V=5441(2) Š3; 1calcd =1.225 gcmꢀ3
;
m=0.064 mmꢀ1
;
F(000)=
A
gave pure
5 as yellow needles. Yield: 117 mg, 77%; m.p. 1058C;
1952. A total of 4821 reflections were measured, 4402 unique, by using
graphite monochromatized MoKa radiation (l=0.71073Š) at 113K. The
structure was refined on F2 to Rw =0.3323 with a goodness-of-fit=1.117
for 596 refined parameters.
1H NMR: d=7.63–7.59 (m, 4H), 7.48 (dAB, J=8.9 Hz, 2H), 6.89 (dAB, J=
8.9 Hz, 2H), 3.94 (t, J=6.5 Hz, 2H), 1.84 (m, 2H), 1.05 ppm (t, J=
7.4 Hz, 3H); 13C NMR: d=159.7, 133.2, 132.8, 131.6, 125.5, 125.3, 125.2,
114.6, 114.3, 92.1, 86.8, 69.6, 22.5, 10.5 ppm; HRMS (EI+): m/z: calcd for
C18H15OF3: 304.1075; found: 304.1079.
CCDC-641917 and -643528 contain the supplementary crystallographic
data for these compounds, respectively. These data can be obtained free
of charge from The Cambridge Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[(4-Propoxyphenyl)ethynyl]benzene (6): Column chromatography (hex-
anes/EtOAc 20:1) and final recrystallization from EtOH gave pure 6 as
pale-yellow plates. Yield: 96 mg, 81%; m.p. 648C; 1H NMR: d=7.63–
7.59 (m, 4H), 7.48 (dAB, J=8.4 Hz, 2H), 6.89 (dAB, J=8.4 Hz, 2H), 3.94
(t, J=6.6 Hz, 2H), 1.84 (sex., J=7.2 Hz, 2H), 1.07 ppm (t, J=7.4 Hz,
3H); 13C NMR: d=159.2, 133.0, 131.4, 128.3, 127.8, 123.6, 115.1, 114.5,
89.5, 87.9, 69.5, 22.5, 10.5 ppm; MS (EI+): m/z: 236 (53) [M+]; elemental
analysis: calcd (%) for C17H16O: C 86.40, H 6.82; found: C 85.89, H 6.75.
Second-order nonlinear optical (HRS) measurements: The second-order
nonlinear optical polarizability, or first hyperpolarizability of potentially
fluorescent chromophores has to be measured by frequency-resolved
femtosecond HRS.[32] If no attention is devoted to the potential multipho-
ton fluorescence contribution to the HRS signal, a systematic overestima-
tion of b can result.[33] This systematic error can be avoided by making
the distinction between immediate scattering and time-delayed fluores-
cence in the spectral domain (spectrally broad fluorescence versus sharp
scattering at the second-harmonic of the laser line only), in the time
domain (a nanosecond fluorescence tail following the femtosecond laser
pulse excitation),[34] or in the frequency domain. In the latter approach,
the fluorescence is demodulated (diminished in amplitude) and acquires
a phase shift with respect to scattering only. We have implemented this
frequency-domain technique and determined the high-frequency limit of
the HRS signal. This signal was then free of fluorescence and was used
to retrieve an accurate, fluorescence-free b value.[35] As the reference
compound to determine hyperpolarizability values at 800 nm, crystal
4-[(4-tert-Butylphenyl)ethynyl]nitrobenzene (7): A mixture of 1-bromo-
4-tert-butylbenzene (106.5 mg, 0.5 mmol), 1-ethynyl-4-nitrobenzene
(87.2 mg, 0.60 mmol), and [PdCl2(PPh3)2] (17.6 mg, 0.025 mmol) in dry
G
degassed triethylamine (5 mL) was stirred at RT for 20 min, after which
time, CuI (3.8 mg, 0.02 mmol) was added. The resulting mixture was
stirred at reflux for 1 h and, after cooling, the solvent was evaporated in
vacuo. The residue was then dissolved in EtOAc (10 mL) and washed
with H2O (15 mL). The organic layer was dried (MgSO4), filtered, and
the residue was purified by PLC (CH2Cl2/petroleum ether 1:1) to give 7.
1
Yield: 83.0 mg, 60%; m.p. 145–1468C; H NMR: d=8.22 (dAB, J=8.5 Hz,
2H), 7.66 (dAB, J=8.5 Hz, 2H), 7.50 (dAB, J=8.0 Hz, 2H), 7.41 (dAB, J=
8.0 Hz, 2H), 1.35 ppm (s, 9H); 13C NMR: d=153.0, 147.2, 132.4, 131.9,
130.9, 125.8, 123.9, 119.3, 95.3, 87.3, 35.2, 31.4 ppm; GCMS: m/z: calcd
for C18H17NO2: 279.3[ M+]; found: 279.0.
violet in methanol was used (bxxx,
800 =338”10ꢀ30 esu). In the analysis, the
difference between the octopolar symmetry of crystal violet and the dipo-
lar symmetry of the compounds A1–A3, B1–B3, C1–C3, and 4–9, as well
as the different solvents were taken into account. An additional experi-
mental parameter that can be determined by HRS is the nonlinear depo-
larization ratio, that is, the ratio between the HRS intensity for parallel
(vertical) and perpendicular (horizontal) polarization in the detection
(vertical polarization for the excitation).[36] This ratio is 5 in the limit of a
single major (dipolar) hyperpolarizability tensor component (diagonal
bzzz tensor element along the dipolar molecular z axis) and infinitely
small numerical aperture. This ratio can be as low as 1.5 for purely octo-
polar structures and in the case the off-diagonal component bzxx is just as
large as the diagonal bzzz. Multiphoton fluorescence has a much more
pronounced effect on the value of the depolarization ratio. As the emis-
sion is occurring nanoseconds after the excitation, the fluorescence con-
tribution to the HRS signal can be strongly depolarized, resulting in a
ratio as low as 1.[37]
4-[(4-tert-Butylphenyl)ethynyl]trifluoromethylbenzene (8): Tetrabutylam-
monium fluoride (392.2 mg, 1.50 mmol) and H2O (27.5 mg, 1.50 mmol)
were added to
(106.5 mg, 0.5 mmol),
0.60 mmol), and [PdCl2(PPh3)2] (10.5 mg, 0.015 mmol) under argon at
a
stirred mixture of 1-bromo-4-tert-butylbenzene
4-ethynyl-a,a,a-trifluorotoluene (102.1 mg,
ACHTREUNG
RT. The resulting mixture was stirred for 3h at 80 8C, then cooled, dis-
solved in H2O (10 mL), and extracted with EtOAc (2”10 mL). The or-
ganic layer was dried (MgSO4), filtered, and evaporated in vacuo. The
residue was purified by PLC (hexanes/EtOAc 20:1) to give 8. Yield:
59.0 mg, 39%; m.p. 121–1238C; 1H NMR: d=7.62 (dAB, J=8.5 Hz, 2H),
7.59 (dAB, J=8.5 Hz, 2H), 7.48 (dAB, J=8.5 Hz, 2H), 7.39 (dAB, J=8.5 Hz,
2H), 1.33 ppm (s, 9H); 13C NMR: d=152.6, 132.0, 131.7, 130.1, 127.6,
125.7, 125.5, 123.1, 119.8, 92.2, 87.6, 35.1, 31.4 ppm; GCMS: m/z: calcd
for C19H17F3: 302.33 [M+]; found: 302.0.
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Chem. Eur. J. 2007, 13, 7753– 7761

Alkynyl Expanded Donor–Acceptor Calixarenes
FULL PAPER
K. Clays, A. Persoons, D. N. Reinhoudt, Adv. Mater. 1993, 5, 925–
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This work was supported by the Ministerio de Educación y Ciencia
(Spain; CTQ2004–02865/BQU and a Ramón y Cajal contract for G.H),
the Natural Sciences and Research Council of Canada (NSERC), the De-
partment of Chemistry, Memorial University of Newfoundland, the Uni-
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Received: April 23, 2007
Published online: July 3, 2007
Chem. Eur. J. 2007, 13, 7753– 7761
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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