Light-harvesting in multichromophoric rotaxanes

Article abstract of DOI:10.1002/chem.201102981

Two rotaxanes with benzyl ether axles and tetralactam wheels were synthesized through an anion template effect. They carry naphthalene chromophores attached to the stopper groups and a pyrene chromophore attached to the wheel. The difference between the t

Full text of DOI:10.1002/chem.201102981

DOI: 10.1002/chem.201102981
Light-Harvesting in Multichromophoric Rotaxanes
Maria E. Gallina,[a] Bilge Baytekin,[b, c] Christoph Schalley,*[b] and Paola Ceroni*[a]
Abstract: Two rotaxanes with benzyl
ether axles and tetralactam wheels
were synthesized through an anion
template effect. They carry naphtha-
lene chromophores attached to the
stopper groups and a pyrene chromo-
phore attached to the wheel. The dif-
ference between the two rotaxanes is
represented by the connecting unit of
the naphthyl chromophore to the ro-
taxane axle: a triazole or an alkynyl
group. Both rotaxanes exhibit excellent
light-harvesting properties: excitation
of the naphthalene chromophores is
followed by energy transfer to the
pyrene unit with efficiency higher than
90% in both cases. This represents an
example of light-harvesting function
among chromophores belonging to me-
chanically interlocked components,
that is, the axle and the wheel of the
rotaxanes.
Keywords: energy transfer · molec-
ular antenna
· photochemistry ·
photophysics · rotaxanes
Introduction
ane working as a light-harvesting antenna, a possible strat-
egy is to place several donor chromophores on dendritic
stoppers and the acceptor one on the wheel of the rotaxane.
This construction enabled us to investigate the energy trans-
fer process between mechanically bonded functional units.
By proper design of this kind of supramolecular structures,
future developments along this research line can result in
light-activated molecular shuttles in which the light ab-
sorbed by the antenna is used to promote a molecular
movement. This will increase the efficiency of light absorp-
tion.
Rotaxanes, catenanes, and other interlocked molecules[1]
have been extensively studied for the development of me-
chanically bonded molecular machines,[2] such as shuttles,
switches, and even muscles. On the other hand, only few ex-
amples have been reported on rotaxanes containing multiple
chromophoric units either in the axle or in the wheel com-
ponent, in which energy transfer processes take place upon
light excitation.[3] In this view, we would like to couple the
concept of light-harvesting antennae and rotaxanes.
An antenna for light harvesting is an organized multicom-
ponent system in which many chromophoric molecular units
absorb the incident light and then channel the excitation
energy to a common acceptor component.[4] Most of the ar-
tificial light-harvesting antennae are based on dendrimers,[5]
well-defined tree-like macromolecules that are characterized
by a high degree of order and the possibility to contain se-
lected chemical units in predetermined sites of their struc-
ture.[6] Examples of rotaxanes containing dendritic wedges
in the axle and/or in the wheel,[7] as well as dendrimers
based on rotaxanes[8] or pseudo-rotaxanes[9] branching units
are present in the literature, but none of them has been de-
signed to perform as a molecular antenna. To make a rotax-
In the present paper, the two rotaxanes investigated (R1
and R2 in Scheme 1) consist of six naphthyl units in the
stoppers and a pyrene chromophore appended to the
wheel.[10,11] The difference between the two rotaxanes is rep-
resented by the connecting unit of the naphthyl chromo-
phore to the rotaxane axle, a triazole or an alkynyl group in
the rotaxanes R1 and R2, respectively. The stoppers S1 and
S2, axle A1, macrocycles W and W-Py, methylnaphthalene
and methylpyrene (Scheme 1) serve as model compounds
and were investigated for comparison purposes. The results
obtained evidence a highly efficient energy transfer from
the naphthalene chromophores of the stoppers to the
pyrene chromophore bound to the wheel.
Results and Discussion
[a] Dr. M. E. Gallina, Prof. Dr. P. Ceroni
Department of Chemistry “G. Ciamician”, Via Selmi 2
40126 Bologna (Italy)
Syntheses: Scheme 1 shows the two rotaxanes R1 and R2 to-
gether with their syntheses. Starting with parafuchsine (1),
the trityl stopper 5 carrying three acetylene groups can be
synthesized as the key intermediate through a sequence of
diazotation and iodination providing compound 2, Friedel–
Crafts alkylation yielding the tris-iodotritylphenol 3 fol-
lowed by Sonogashira coupling to give compound 4, and de-
protection of the acetylenes.[12] Intermediate 5 can then
either be coupled to naphthalene through a second Sonoga-
E-mail: paola.ceroni@unibo.it
[b] Dr. B. Baytekin, Prof. Dr. C. Schalley
Institut fꢀr Chemie und Biochemie der Freien Universitꢁt
Takustr. 3, 14195 Berlin (Germany)
E-mail: christoph@schalley-lab.de
[c] Dr. B. Baytekin
Present address: Non-equilibrium Energy Research Center
Northwestern University, 2145 Sheridan Rd.
Evanston, IL 60208 (USA)
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Chem. Eur. J. 2012, 18, 1528 – 1535

FULL PAPER
Scheme 1. Synthesis of the photoactive rotaxanes R1 and R2. a) 1) NaNO2, 08C, 1 H; H2O; 2) KI, 808C, 2 H; H2O, 82%. b) H2SO4 (cat.), 808C, 4 H;
76%. c) [PdACHTUNGTRENNUNG(PPh3)2Cl2] (cat.), PPh3, CuI, TMS–acetylene, 408C, 4 H; NEt3, DMF, 40%. d) KOH, RT, MeOH/H2O (1:1), 85%. e) [PdACHTUNGTRENN(NGU PPh3)2Cl2] (cat.),
CuI, RT, 21 H; NEt3, DMF, 56%. f) CuSO4·H2O, Na-ascorbate, RT, 2 d, H2O/THF (1:1), 88%. g) dibenzo[18]crown-6, K2CO3, 1,4-di-(bromomethyl)ben-
zene, CH2Cl2, RT, 6 d, R1: 82%, R2: 85%. Methylpyrene (Py), (1-methyl)naphthalene (Naph), and the axle A1 of rotaxane R1 were used as control
compounds.
shira–Hagihara coupling reaction[13] to yield stopper S1 or it
can be converted to the tris-triazole stopper S2 with the cor-
responding azide through click chemistry.[14] With these two
stoppers in hand, the two rotaxanes R1 and R2 are prepared
with quite high yields of >80% through the Vçgtle anion
template effect.[15]
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1529

P. Ceroni, C. Schalley et al.
Photophysical properties: All experiments were performed
in dichloromethane/acetonitrile (1:1, v/v) at 298 K and in di-
chloromethane/chloroform (1:1, v/v) at 77 K to get a trans-
parent matrix. The most relevant photophysical properties
of the rotaxanes R1 and R2, and of their model compounds
are reported in Table 1.
Table 1. Photophysical properties of the rotaxanes R1 and R2, and their
model compounds in air-equilibrated dichloromethane/acetonitrile (1:1,
(v/v) at 298 K and in dichloromethane/chloroform (1:1, v/v) rigid matrix
at 77 K.
298 K
77 K
absorption
fluorescence
Fem
phosphorescence
[b]
lmax
e
lmax
t
lmax
t
[nm][a] [mꢀ1 cmꢀ1
]
[nm]
[ns] [nm]
[ms]
R1
R2
328
346
152300
25200
24800
41200
136000
68000
4900
411
411
407
378
371
371
336
336
0.20
0.23
0.24
0.01
0.58
0.54
0.08
0.04
4.6 610
5.0 610
5.7 610
16.3 602
1.3 550
1.5 550
10 475
14 475
250
300
250
250
310
210
1320
–
Figure 1. Absorption (left axis) and emission spectra (right axis) of W-Py
(black solid lines) and Py (black dashed lines), as well as absorption spec-
trum of W (gray solid line) in air-equilibrated acetonitrile/dichlorome-
thane (1:1, v/v) at 298 K. Emission spectra are normalized at their maxi-
mum. lex =320 nm.
W-Py 346
Py
A1
S1
343
328
328
Naph 276
S2 265
[c]
27200
[a] Lowest energy absorption band. [b] Excitation was performed in the
lowest energy absorption band. [c] The phosphorescence intensity is too
weak to measure the excited state lifetime.
to the fact that in this spectral region, light is absorbed not
only by the pyrene unit but also by the tetralactam macrocy-
cle (see W for comparison), which is not effective to popu-
late the luminescent excited state of the pyrene chromo-
phore. This is confirmed by the excitation spectrum per-
formed at lem =420 nm: it shows an intensity ratio of the
bands at l=280 and 346 nm lower than that observed in the
absorption spectrum.
Let us consider at first the wheel and the axle components
separately, as well as their model compounds, to better un-
derstand the more complex behavior of the two rotaxanes.
The wheel component: Compound W-Py (Scheme 1) was in-
vestigated in comparison to Py, and the macrocycle with no
appended functionality (W in Scheme 1).
At 77 K in dichloromethane/chloroform rigid matrix, W-
Py presents a phosphorescence band with a maximum at l=
610 nm, similar to that of Py (lmax =602 nm). The lifetime of
the phosphorescent state is 250 ms for both compounds.
The macrocycle W-Py shows two intense absorption
bands with maxima at l=280 and 346 nm (black solid line
in Figure 1). These spectral features are reminiscent of those
observed for Py (dashed line in Figure 1), but they are char-
acterized by a lower intensity, a less-resolved vibrational
structure, and a slight red-shift. The absorption spectrum of
the unfunctionalized macrocycle W (gray line in Figure 1) is
a tail-like band below l=320 nm. From these data it is evi-
dent that the main chromophoric unit of W-Py is the pyrene
component. Its photophysical properties are affected by the
delocalization of the p electrons extended to the directly
linked aromatic group of the macrocycle.
As to the emission properties, W is not luminescent,
whereas W-Py and Py exhibit an emission band with
maxima at l=407 and 377 nm, respectively. The differences
between the two molecules are not only the red-shift and
less-resolved vibrational structure of the W-Py emission
band, but also the much higher emission quantum yield
(Fem =24% and 1% for W-Py and Py, respectively) and the
lower excited-state lifetime (t=5.7 and 16.3 ns for W-Py
and Py, respectively). In the case of W-Py, the fluorescence
quantum yield is sensitive to the excitation wavelength: it is
24% upon excitation at the lowest energy absorption band
and it decreases upon excitation at l<300 nm. This is due
The two axle components: The axle of rotaxane R1, here-
after called A1, has been examined in comparison with the
corresponding stopper S1.
The absorption spectra of A1 and S1 (black solid line in
Figure 2) have identical shape. Due to the limited amount of
sample available for A1, its molar absorption coefficient
was not measured, but it can be assumed to be the double
of that of S1. This hypothesis, based on the expected similar
photophysical properties of the two compounds, is corrobo-
rated by the strong analogy found also in their luminescent
properties. Their emission spectra are superimposed (for S1,
see the black solid line in Figure 2), the corresponding fluo-
rescence quantum yields are very close (54 and 58% for S1
and A1, respectively) and the luminescent excited-state life-
times (Table 1) are identical within the experimental error.
Phosphorescence was observed in dichloromethane/chloro-
form at 77 K for both A1 and S1 with maxima located at l=
550 nm with a slightly longer lifetime of the phosphorescent
excited state in the case of A1 (Table 1).
The photophysical properties of A1 and S1 are significant-
ly different from those of Naph (dashed lines in Figure 2),
which exhibits a strongly blue-shifted absorption with lower
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Light-Harvesting in Rotaxanes
FULL PAPER
Indeed, the lowest singlet excited state of the naphthyl chro-
mophore in the stopper has one more deactivation pathway,
that is, the excimer formation.
A weak phosphorescence was observed in rigid matrix at
77 K for S2, very similar in shape and position to that of
naphthalene, further confirming the similarity between the
photophysical properties of the two species.
Rotaxanes: Rotaxane R1 presents an intense and structured
absorption band in the UV region with maximum at l=
328 nm (black lines in Figure 3) and its absorption spectrum
Figure 2. Absorption (left axis) and emission spectra (right axis) of S1
(black solid lines), S2 (gray lines), and Naph (black dashed lines) in air-
equilibrated acetonitrile/dichloromethane (1:1, v/v) at 298 K. Note that
the molar absorption coefficient of Naph is multiplied by three for com-
parison purposes. Emission spectra are normalized at their maximum.
lex =320 nm for S1 and lex =275 nm for S2 and Naph.
intensity, even if we take into account the number of naph-
thyl units in the stopper component S1. Also the fluores-
cence band is blue shifted and characterized by a lower
emission quantum yield (Table 1). As a result, we can con-
clude that the spectroscopic features of the naphthyl units
present in A1 and S1 are strongly modified by the presence
of the phenyl–acetylene group, which participates strongly
to the delocalization of p electrons. This is confirmed by the
appreciable shift of the absorption spectrum towards higher
wavelengths that was reported in the literature[16] in going
from naphthalene to 1-ethinyl-naphtalene in dimethylsulfox-
ide solution. The discrepancy between the properties of
naphthalene and those of A1 and S1 can be found in the
analysis of the triplet excited states as well: the phosphores-
cence of Naph is strongly blue-shifted (the emission maxi-
mum is located at l=475 nm) and characterized by a much
longer lifetime (Table 1).
In the case of the rotaxane R2, the axle component was
not available and only the stopper unit S2 was investigated.
In contrast to S1, the absorption and emission spectra of
S2 (gray lines in Figure 2) are very similar to that of Naph.
This result points out that the functionalization with a tria-
zole group through a methylene spacer does not significantly
affect the photophysical properties of the naphthalene chro-
mophore.
Figure 3. Absorption (left axis) and emission spectra (right axis) of rotax-
ane R1 (black solid lines), A1 (gray solid lines), and W-Py (gray dashed
lines) in air-equilibrated acetonitrile/dichloromethane (1:1, v/v) at 298 K.
Emission spectra are normalized at their maximum value. lex =328 nm.
is superimposed to the sum of the absorption spectra of the
axle A1[18] (gray line in Figure 3) and the wheel W-Py
(dotted line in Figure 3), demonstrating that there is no
ground-state interaction between the two mechanically in-
terlocked components of the rotaxane.
Upon excitation at l=324 nm, where light is absorbed by
both the naphthalene units of the axle (91%) and the
pyrene group of the wheel (9%), R1 presents an emission
spectrum very similar to that of W-Py. The emission maxi-
mum is slightly red-shifted and the corresponding excited-
state lifetime is slightly lower (Table 1). This result demon-
strates a small effect of the close axle component on the ex-
cited-state properties of the pyrenyl chromophore. A very
small band is observed in the spectral region where the
naphthyl chromophores of A1 emit. The corresponding life-
time is below 0.5 ns, that is, the equipment time resolution,
evidencing that the axle emission is strongly quenched and
the pyrene emission is sensitized.
To get more quantitative data, the emission quantum
yield of R1 was measured also upon excitation at l=342 nm
where 17% of the light are absorbed by the pyrenyl chro-
mophore of the wheel. The value of Fem obtained upon exci-
tation at l=324 nm was the same (0.20) within experimental
error. Moreover, a close match of the absorption and excita-
The molar absorption coefficient of S2 is somewhat
higher than that expected for three naphthyl units, particu-
larly in the l=250–280 nm region. This can be partly ex-
plained by the contribution of the other chromophoric units
of the stopper. The emission spectrum of S2 shows a tail
above l=350 nm, which can be related to naphthalene exci-
mers, as commonly observed for supramolecular systems
containing multiple naphthyl units linked by flexible
spacers.[17] This hypothesis is supported by the lower emis-
sion quantum yield observed for S2 compared to Naph.
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1531

P. Ceroni, C. Schalley et al.
tion spectrum performed at lem =450 nm suggests an almost
quantitative energy transfer efficiency (hET >90%).
The phosphorescence spectrum of R1 in rigid matrix at
77 K is superimposed to that of W-Py upon excitation at l=
328 nm, where both A1 and W-Py absorb. No phosphores-
cence of the naphthyl chromophore was observed in agree-
ment with an efficient energy transfer process, which deacti-
vates its lowest singlet excited state, thus preventing inter-
system crossing to populate the lower lying triplet excited
state.
Rotaxane R2 has a strong absorption with the lowest
energy band at l=346 nm perfectly coincident in shape and
intensity with that of the wheel W-Py. The absorption spec-
trum of R2 is similar to the sum of two stopper components
S2 (the axle component is not available) and a wheel com-
ponent W-Py.
From the value of the shorter lifetime, we can estimate
the efficiency of the quenching process (hq) by the following
Equation (1):
hq ¼ 1ꢀt=t0
ð1Þ
where t and t0 are the lifetime in the presence and in the
absence of the wheel component.
In the present case, the value of hq is 94%. Therefore,
also in this case a very efficient energy transfer takes place
from the stopper chromophores to the wheel unit.
The phosphorescence of R2 observed in rigid matrix at
77 K with lex =348 nm is very similar to that observed for
W-Py.
Upon excitation at l=348 nm, where only the wheel ab-
sorbs light, the emission spectrum of R2 presents a maxi-
mum at l=411 nm, very similar to that of W-Py with a
slight red-shift and an identical emission quantum yield
(Table 1) within the experimental error. Upon excitation at
l=267 nm, where approximately 55% of the light are ab-
sorbed by the axle component, a strong emission at l=
411 nm and an emission band with a maximum at l=
335 nm, typical of the naphthyl chromophores of the axle is
observed (Figure 4). The excited-state lifetime measured at
Conclusion
The investigated rotaxanes consist of a multichromophoric
axle containing six naphthyl units in the two stoppers and a
pyrenyl unit appended to the wheel. In the case of the rotax-
ane R1, the naphthyl chromophores are strongly perturbed
by the alkynyl bridge, so that their absorption and emission
bands occur at lower energy, with molar absorption coeffi-
cient and emission quantum yield higher than those of (1-
methyl)naphthalene. On the other hand, for the rotaxane
R2, the naphthyl chromophores are linked by a methylene
spacer to a triazole group: the photophysical properties are
very similar to those of the model compound. For both ro-
taxanes, no ground-state interaction was evidenced between
the wheel and the axle, but strong interactions take place in
the excited states. Indeed, upon excitation of the naphthyl
chromophores of the axle, a very efficient energy transfer to
the pyrenyl unit of the wheel occurs.
R1 and R2 couple the function of mechanically inter-
locked molecules to that of light-harvesting antennae. To
the best of our knowledge, it is the first time in which
energy transfer processes have been reported between mul-
tiple donor chromophores placed on the axle and an accept-
or one on the wheel. This study can have future develop-
ments in the field of molecular machines. Up to now, light-
powered molecular machines are based on the absorption of
light by a single chromophore, followed, for example, by an
electron transfer reaction which drives the molecular move-
ment.[1] Properly designed dendritic light-harvesting stoppers
would offer the advantage to absorb a larger fraction of the
incident light and to extend the spectral window useful to
drive the mechanical movement.
Figure 4. Emission spectra of rotaxane R2 (black solid line), S2 (gray
solid line), and W-Py (dashed gray line) in air-equilibrated acetonitrile/di-
chloromethane (1:1, v/v) at 298 K. The emission spectra of R2 and W-Py
are normalized at their maximum for comparison purposes. lex =267 nm.
lem =411 nm is very close to that observed for W-Py, where-
as the emission intensity decay measured at l=335 nm is
biexponential: t1 around 0.8 ns and t2 =14 ns. The first com-
ponent can be assigned to the quenched emission of the
naphthyl chromophore. The second component (t2) is identi-
cal to the fluorescent excited-state lifetime measured for S2,
suggesting that an impurity of axle not threaded into the
wheel is present.
Experimental Section
General methods: Reagents were purchased from Aldrich, ACROS, or
Fluka and used without further purification. The macrocycles W and W-
Py were synthesized according to literature procedures.[8,19] CH2Cl2,
MeOH, EtOAc, and toluene were dried and distilled prior to use by
usual laboratory methods, whereas all other solvents were used from
commercial sources. Thin-layer chromatography (TLC) was performed
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Light-Harvesting in Rotaxanes
FULL PAPER
on pre-coated silica gel 60/F254 plates (Merck KGaA). Silica gel (0.04–
0.063 mm), (0.63–0.100 mm), Merck KGaA, and Al2O3 (neutral) (Riedel
de Haꢃn) were used for column chromatography.
(62.5 MHz, CDCl3): d=0.00, 64.2, 94.6, 104.8, 114.6, 121.0, 130.8, 131.3,
132.2, 137.8, 146.7, 153.9 ppm; MS (EI) (2208C) m/z (%): 624.3 (100)
+
C
[M]
.
1H and 13C NMR spectra were recorded with Bruker AC 250 and AM
400 instruments. All chemical shifts are reported in ppm with solvent sig-
nals taken as internal standards; coupling constants are in Hertz. Electro-
spray mass spectra (ESI-MS) were recorded on an Agilent 6210 ESI-
TOF, Agilent Technologies, Santa Clara, CA, USA and Varian/Ionspec
FTICR mass spectrometers. The solvent flow rate was adjusted to
4 mLminꢀ1, the spray voltage set to 4 kV. Drying gas flow rate was set to
15 psi (1 bar). All other parameters were adjusted for a maximum abun-
dance of the desired ions. Electron ionization mass spectra (EI-MS) were
measured on a MAT 711 spectrometer, Varian MAT, Bremen. The elec-
tron energy was set to 80 eV. Elemental analyses of the macrocyclic com-
pounds reported here almost always fail due to solvent molecules that
are encapsulated inside the macrocyclesꢄ cavities. These solvents cannot
be removed by high vacuum, not even, when the substances are heated.
They appear in the NMR spectra and are also visible in the crystal struc-
tures with quite some disorder. Therefore, elemental compositions were
assessed by isotope pattern analysis of the corresponding ions observed
in the mass spectra.
4-[Tris(4-ethynylphenyl)methyl]phenol (5): Compound
4
(154 mg,
0.245 mmol) and KOH (138 mg, 2.46 mmol) were stirred in a mixture of
methanol and water (1:1, 10 mL) overnight. The mixture was neutralized
by a few drops of HCl (conc.) and the desired compound was extracted
into dichloromethane, dried over MgSO4, filtered, and the solvent was
evaporated. When necessary, a short silica column was employed to fur-
ther purify the compound, by eluting with dichloromethane to give the
1
desired product (85.4 mg, 85%). H NMR (250 MHz, CDCl3): d=3.05 (s,
3H), 6.64 (d, J=9 Hz, 2H; PhHphenol), 6.85 (d, J=9 Hz, 2H; PhHphenol),
7.04 (d, J=8.3 Hz, 2H; PhH), 7.28 ppm (d, J=8.3 Hz, 2H; PhH);
13C NMR (100 MHz, CDCl3) d=64.24, 83.39, 99.98, 114.75, 120.07,
130.87, 131.58, 132. 19, 137.64, 147.02, 154.09 ppm; MS (ESI-FTICR) m/z
(%): 407.15 (100) [MꢀH]ꢀ, 815.30 (5) [2MꢀH]ꢀ.
4-{Tris[4-(naphthalen-1-ylethynyl)phenyl]methyl}phenol (S1): Dry NEt3
(10 mL) was added to compound 5 (98 mg, 0.24 mmol), 1-iodonaphtha-
lene (198 mg, 0.78 mmol), CuI (28.5 mg), and [PdACHTUNGTRNEG(UN PPh3)2Cl2] (35 mg) in
DMF (10 mL) and the reaction mixture stirred under an argon atmos-
phere for 21 h. The solvents were evaporated in vacuo and the residue
was purified on a silica column by eluting with dichloromethane. The
product was obtained after excess iodonaphthalene (first band) as the
second band from the column (105.7 mg, 56%). Rf =0.7; 1H NMR
(250 MHz, CDCl3): d=6.77 (d, 2H; J=8.3 Hz, PhHphenol), 7.12 (d, J=
8.3 Hz, 2H; PhHphenol), 7.30 (d, J=9 Hz, 6H; PhH), 7.42–7.62 (m, 9H;
Arnaph), 7.74–7.88 (m, 9H; Arnaph), 8.43 ppm (d, J=7.7 Hz, 3H; PhH);
13C NMR (100 MHz, CDCl3): d=64.44, 87.92, 94.16, 114.84, 120.95,
121.35, 125.39, 126.30, 126.54, 126.90, 128.42, 128.89, 130.49, 131.09,
2-(Azidomethyl)naphthalene:
2-(Bromomethyl)naphthalene
(1.1 g,
5 mmol) and sodium azide (2.6 g, 40 mmol) were heated in dry DMSO
under an argon atmosphere at 458C for 17 h. After cooling to RT water
(200 mL) was added and the product was extracted with dichloromethane
(3ꢅ100 mL). The combined organic phases were dried with MgSO4, fil-
tered, and the solvent evaporated. The desired compound was obtained
1
as a solid (0.89 g, 97%). M.p. 46–498C; H NMR (250 MHz, CDCl3): d=
4.46 (s, 2H; CH2), 7.45- 7.53 (m, 3H; Ar), 7.81–7.86 ppm (m, 4H; Ar);
13C NMR (100 MHz, CDCl3): d=55.06, 125.98, 126.46, 126.58, 127.27,
131.15, 132.30, 133.29, 133.36, 137.90, 146.84, 154.20 ppm; MS (EI)
+
127.86, 128.06, 128.85, 128.86, 125.87, 132.93, 133.17, 133.34 ppm; MS
C
(3008C) m/z (%): 786.3 (32) [M]
.
+
(EI) (308C) m/z (%): 183.2 (66.6) [M] , 141.2 (100) [MꢀN3] +, 154.2
C
C
4-(Tris{4-[1-(naphthalen-2-ylmethyl)-1H-1,2,3-triazol-4-yl]phenyl}meth-
AHCTUNGERTGyNNUN l)phenol (S2): 2-(Azidomethyl)naphthalene (143 mg, 0.78 mmol), com-
+
C
(47.8) [MꢀN2]
.
Tris-(4-iodophenyl)methanol (2): Concentrated sulfuric acid (4 mL) was
added to parafuchsin hydrochloride (1.77 g, 5.46 mmol) in water (10 mL)
and the mixture was cooled to 08C. A solution of sodium nitrite (1.24 g,
18 mmol) in water (4 mL) was added to the solution dropwise and the
stirring was continued for 1 h. Potassium iodide (10 g, 60 mmol) dissolved
in water (10 mL) was then added and the reaction was first let to room
temperature and then kept at 808C for 2 h. The dark purple precipitate
formed was filtered, washed with water, and dried. Column chromatogra-
phy on silica gel by eluting with dichloromethane yielded the pure prod-
uct (2.80 g, 82%); Rf =0.8; 1H NMR (250 MHz, CDCl3): d=6.88 (d, J=
8.7 Hz, 6H), 7.54 ppm (d, J=8.7 Hz, 6H); 13C NMR (62.5 MHz, CDCl3):
d=81.6, 94.0, 129.9, 137.6, 145.8 ppm.
pound 5 (100 mg, 0.245 mmol), CuSO4·5H2O (1.84 mg, 7.35 mmol), and
sodium ascorbate (7.28 mg, 36.8 mmmol) were stirred in THF/H2O (1:1,
10 mL) at RT for 2 d, by which time the reaction mixture became clearer
and the dispersed product mixture separated from the aqueous phase as
a yellow liquid after stirring was terminated. The product was extracted
into dichloromethane (3ꢅ20 mL), washed thoroughly with water (2ꢅ
50 mL), dried with MgSO4, filtered, and the solvent was evaporated. The
yellow residue was purified on a silica column and eluted first with pure
dichloromethane to remove low-polarity impurities. Then, the eluent was
changed to CH2Cl2/MeOH (1:1) to obtain the desired product (206.4 mg,
88%). 1H NMR (250 MHz, CDCl3): d=5.60 (s, 6H; CH2), 6.55 (d, 2H;
J=9 Hz, PhHphenol), 6.87 (d, J=9 Hz, 2H; PhHphenol), 7.11 (d, J=8.3 Hz,
6H; PhH), 7.24 (d, 3H; Arnaph), 7.37–7.43 (m, 6H; Arnaph), 7.48 (d, J=
8.3 Hz, 6H; PhH), 7.63 (s, 3H; CH), 7.65 (s, 3H; Arnaph), 7.68–7.74 ppm
(m, 9H; Arnaph); 13C NMR (62.5 MHz, CDCl3): d=54.40, 63.9, 120.26,
124.86, 125.16, 126.71, 127.32, 127.72, 127.89, 129.13, 131.38, 131.86,
131.96, 133.16, 133.19, 137.03, 147.04, 147.81 ppm; MS (ESI-TOF) m/z=
958.41 [M+H]+, 980.39 [M+Na]+.
4-[Tris(4-iodophenyl)methyl]phenol (3): Sulfuric acid (ten drops) was
added to compound 2 (5 g, 7.84 mmol) and phenol (4 g, 43 mmol) and
the mixture was stirred under argon for 4 h at 808C. The melting phenol
served as the solvent; no other solvent was added. After cooling down to
room temperature, an aqueous solution of NaOH (10%, 50 mL) was
added and the precipitate formed was filtered off. Column chromatogra-
phy on silica gel by eluting with petroleum ether/ethyl acetate (5:1) yield-
[2]-{1,4-Bis[(4-ACTHNUGRTNEUNG{tris[4-(naphthalen-1-ylethynyl)phenyl]methyl}phenyloxy)-
1
ed the pure product (4.25 g, 76%). Rf =0.7; H NMR (250 MHz, CDCl3):
methyl]benzene}{10’-tert-butyl-29’-pyrenyl-5’,17’,23’,35’,38’,40’,43’,45’-
octamethyldispiro[cyclohexane-1,2’-7’,15’,25’,33’-tetraazaheptacyclo-
d=6.61 (d, J=8.8 Hz, 2H), 6.82 (d, J=8.8 Hz, 2H), 6.86 (d, J=8.6 Hz,
6H), 7.60 ppm (d, J=8.6 Hz, 6H); 13C NMR (62.5 MHz, CDCl3): d=
62.9, 91.6, 114.3, 130.9, 132.2, 134.8, 136.1, 145.6, 155.3 ppm; MS (EI)
[32.2.2.23’,6’.216’,19’.221’,24’.19’,13’.127’,31’]hexatetraconta-3’,5’,9’,11’,13’
ACHTUNGTRENNUNG
18’,21’,23’,27’,29’,31’ACHTGNUTRENNUNG
+
+
C
C
(2208C) m/z (%): 714.3 [M] (74), 511.2 [MꢀPhI]
.
hexane]-8’,14’,26’,32’-tetraon}rotaxane (R1): Dibenzo[18]crown-6 (3.9 mg,
0.011 mmol), pyrene macrocycle W-Py (20.0 mg, 0.017 mmol), K2CO3
(59 mg, 0.43 mmol), 1,4-dibromomethylbenzene (11.0 mg, 0.043 mmol),
and compound S2 (27.2 mg, 0.034 mmol) were stirred in dry dichlorome-
thane (10 mL) for a week. The solvent was then evaporated and the resi-
due was purified on a silica column with dichloromethane. The second
band was collected as the pure rotaxane (39.6 mg, 82%). 1H NMR
(250 MHz, CDCl3): d=1.32 (s, 9H; CCH3), 1.45–1.70 (brs, 12H; Cy=cy-
lohexyl), 1.93 (s, 12H; PhCH3), 1.96 (s, 12H; PhCH3), 2.32 (brs, 8H; Cy),
4.44 (s, 4H; OCH2), 5.93 (s, 4H; PhHaxle), 6.52 (d, J=8.3 Hz, 4H;
PhHstopper), 7.05 (s, 8H; PhH), 7.10 (d, J=8.3 Hz, 4H; PhHstopper), 7.19–
8.17 (m, 93H; ArH), 8.38 ppm (d, 12H; 2-Naph); 13C NMR (62.5 MHz,
4-(Tris{4-[(trimethylsilyl)ethynyl]phenyl}methyl)phenol (4): Compound 3
(2.3 g, 3.22 mmol), trimethylsilylacetylene (2.75 mL, 19.5 mmol), bis(tri-
phenylphosphine) palladium(II)dichloride (371 mg, 0.53 mmol), and tri-
phenylphosphine (338 mg, 1.29 mmol) were dissolved in dry DMF
(20 mL) and dry triethylamine (90 mL). The reaction mixture was kept at
408C for 4 h. After all the solvent was evaporated in vacuo the residue
was purified by column chromatography on a silica column by eluting
with petroleum ether/ethyl acetate (5:1) to give the desired product
(0.8 g, 40%). Rf =0.6; 1H NMR (250 MHz, CDCl3): d=0.00 (s, 27H;
CH3), 4.77 (brs, 1H; OH), 6.46 (d, J=8.8 Hz, 2H), 6.71 (d, J=8.8 Hz,
2H), 6.83 (d, J=8.6 Hz, 6H), 7.10 ppm (d, J=8.6 Hz, 6H); 13C NMR
Chem. Eur. J. 2012, 18, 1528 – 1535
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1533

P. Ceroni, C. Schalley et al.
CDCl3): d=14.19, 18.82, 22.77, 23.10, 26.38, 29.43, 29.74, 31.22, 31.99,
35.41, 35.78, 45.49, 64.38, 71.07, 88.23, 93.87, 113.84, 120. 81, 121.71,
124.86, 125.35, 126.22, 126.53, 126.90, 127.02, 127.07, 127.84, 127.86,
128.10, 128.25, 128.35, 128.40, 128.46, 128.96, 129.29, 130.54, 130.60,
130.95, 131.10, 131.24, 131.34, 131.59, 132.65, 133.28, 133.32, 133.97,
134.71, 135.01, 135.15, 135.18, 135.68, 140.14, 146.23, 156.23, 165.37,
We are also grateful to the Deutsche Forschungsgemeinschaft for finan-
cial support (SFB 765 “Multivalency”).
[1] For reviews, see: a) S. Bonnet, J.-P. Collin, Chem. Soc. Rev. 2008, 37,
1207–1217; b) B. Champin, P. Mobian, J.-P. Sauvage, Chem. Soc.
Rev. 2007, 36, 358–366; c) C. A. Schalley, T. Weilandt, J. Brꢀgge-
mann, F. Vçgtle, Top. Curr. Chem. 2004, 248, 141–200; d) M.
Blanco, M. Consuelo Jimꢆnez, J.-C. Chambron, V. Heitz, M. Linke,
J.-P. Sauvage, Chem. Soc. Rev. 1999, 28, 293–305; e) F. M. Raymo,
J. F. Stoddart, Chem. Rev. 1999, 99, 1643–1663; f) J.-P. Sauvage, Acc.
Chem. Res. 1998, 31, 611–619; g) S. A. Nepogodiev, J. F. Stoddart,
Chem. Rev. 1998, 98, 1959–1976; h) R. Jꢁger, F. Vçgtle, Angew.
Chem. 1997, 109, 966–980; Angew. Chem. Int. Ed. Engl. 1997, 36,
930–944; i) R. Hoss, F. Vçgtle, Angew. Chem. 1994, 106, 389–398;
Angew. Chem. Int. Ed. Engl. 1994, 33, 375–384; j) S. Anderson,
H. L. Anderson, J. K. M. Sanders, Acc. Chem. Res. 1993, 26, 469–
475; k) J.-P. Sauvage, Acc. Chem. Res. 1990, 23, 319–327; l) C. O.
Dietrich-Buchecker, J.-P. Sauvage, Chem. Rev. 1987, 87, 795–810.
[2] a) P. Ceroni, A. Credi, M. Venturi, V. Balzani, Photochem. Photo-
biol. Sci. 2010, 9, 1561–1573; b) S. Durot, F. Reviriego, J.-P. Sauvage,
Dalton Trans. 2010, 39, 10557–10570; c) P. Bodis, M. R. Panman,
B. H. Bakker, A. Mateo-Alonso, M. Prato, W. J. Buma, A. M.
Brouwer, E. R. Kay, D. A. Leigh, S. Woutersen, Acc. Chem. Res.
2009, 42, 1462–1469; d) S. Silvi, M. Venturi, A. Credi, J. Mater.
Chem. 2009, 19, 2279–2294; e) V. Balzani, A. Credi, M. Venturi,
Molecular Devices and Machines—Concepts and Perspectives for the
Nanoworld, Wiley-VCH, Weinheim, 2008; f) E. R. Kay, D. A. Leigh,
F. Zerbetto, Angew. Chem. 2007, 119, 72–196; Angew. Chem. Int.
Ed. 2007, 46, 72–191; g) A. Mateo-Alonso, D. M. Guldi, F. Paolucci,
M. Prato, Angew. Chem. 2007, 119, 8266–8272; Angew. Chem. Int.
Ed. 2007, 46, 8120–8126; h) A. Credi, Angew. Chem. 2007, 119,
5568–5572; Angew. Chem. Int. Ed. 2007, 46, 5472–5475; i) V. Balza-
ni, A. Credi, S. Silvi, M. Venturi, Chem. Soc. Rev. 2006, 35, 1135–
1149; j) M. Clemente-Leꢇn, A. Credi, M.-V. Martꢈnez-Dꢈaz, C. Min-
gotaud, J. F. Stoddart, Adv. Mater. 2006, 18, 1291–1296; k) S.
Bonnet, J.-P. Collin, M. Koizumi, P. Mobian, J.-P. Sauvage, Adv.
Mater. 2006, 18, 1239–1250; l) W. R. Browne, B. L. Feringa, Nat.
Nanotechnol. 2006, 1, 25–35; m) A. R. Pease, J. O. Jeppesen, J. F.
Stoddart, Y. Luo, C. P. Collier, J. R. Heath, Acc. Chem. Res. 2001,
34, 433–444; n) R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi,
M. Venturi, Acc. Chem. Res. 2001, 34, 445–455; o) A. Harada, Acc.
Chem. Res. 2001, 34, 456–464; p) C. A. Schalley, K. Beizai, F.
Vçgtle, Acc. Chem. Res. 2001, 34, 465–476; q) J.-P. Collin, C. Die-
trich-Buchecker, P. GaviÇa, M. Consuelo Jimenez-Molero, J.-P.
Sauvage, Acc. Chem. Res. 2001, 34, 477–487; r) V. Balzani, A. Credi,
F. M. Raymo, J. F. Stoddart, Angew. Chem. 2000, 112, 3484–3530;
Angew. Chem. Int. Ed. 2000, 39, 3348–3391.
165.85 ppm; MS (ESI-FTICR) m/z (%): 1520.75 (22) [M+2HNEt3]2+
2939.34 (18) [M+HNEt3]+.
,
1,4-Bis{[4-ACHTUNGTRENNUNG(tris{4-[1-(naphthalen-2-ylmethyl)-1H-1,2,3-triazol-4-yl]phe-
nyl}methyl)phenoxy]methyl}benzene (A1): The axle was obtained as a
byproduct (5%) of the rotaxane synthesis. Due to the low available
amount, it was characterized only by 1H NMR spectroscopy. Rf =0.9;
1H NMR (250 MHz, CDCl3): d=4.96 (s, 4H; CH2), 6.81 (d, J=7.0 Hz,
2H; PhH), 7.06 (d, J=7.0 Hz, 2H; PhH), 7.18 (d, J=6.8 Hz, 6H; PhH),
7.46 (d, J=6.8 Hz, 6H; PhH), 7.31–7.74 (m, 36H; Naph), 8.31 ppm (d,
J=6.5 Hz, 6H; 2-Naph).
[2]-(1,4-Bis{[4-ACHTUNGTRENNUNG(tris{4-[1-(naphthalen-2-ylmethyl)-1H-1,2,3-triazol-4-yl]-
phenyl}methyl)phenoxy]methyl}benzene)-{10’-tert-butyl-29’-pyrenyl-
5’,17’,23’,35’,38’,40’,43’,45’-octamethyldispiro[cyclohexane-1,2’-7’,15’,
25’,33’-tetraazaheptacyclo[32.2.2.23’,6’.216’,19’.221’,24’.19’,13’.127’,31’]hexatetra-
A
ACHTUNGTRENNUNG(44’),16’,18’,21’,23’,27’,29’,31’ACHTUNGTNER(NUGN 39’),34’,36’,37’,40’,42’,45’-
ACHTUNGTRENNUNG
zo[18]crown-6 (3.9 mg, 0.011 mmol), pyrene macrocycle W-Py (50 mg,
0.043 mmol), K2CO3 (59 mg, 0.43 mmol), 1,4-dibromomethylbenzene
(11.0 mg, 0.043 mmol), and compound S2 (82 mg, 0.086 mmol) were
stirred in dry dichloromethane (10 mL) for one week. The solvent was
then evaporated and the residue was purified on a silica column with di-
chloromethane/methanol (20:1). The first band was collected as the pure
rotaxane (116.2 mg, 85%). 1H NMR (250 MHz, CDCl3/CD3OD=5:1):
d=1.11 (s, 9H; CCH3), 1.40–1.52 (brs, 12H; Cy), 1.77 (s, 24H; PhCH3),
2.11 (brs, 8H; Cy), 4.20 (s, 4H; OCH2), 5.57 (s, 12H; CH2), 5.91 (s, 4H;
PhHaxle), 6.34 (d, J=8.3 Hz, 4H; PhHstopper), 6.96 (s, 8H; PhH), 7.00 (d,
J=8.3 Hz, 4H; PhHstopper), 7.11–8.02 (m, 99H; ArH), 7.92 (s, 2H; 4,6-
isophth), 8.11 ppm (s, 1H; 2-isophth); 13C NMR (62.5 MHz, CDCl3) d=
14.04, 18.65, 22.66, 22.93, 29.33, 29.65, 30.95, 31.91, 35.15, 45.30, 53.47,
54.42, 63.93, 70.43, 113.67, 120.09, 124.73, 124.97, 125.06, 125.13, 125.17,
125.19, 126.73, 127.31, 127.34, 127.74, 127.76, 127.83, 127.89, 127.91,
127.95, 128.18, 128.23, 129.02, 129.17, 131.02, 131.10, 131.28, 131.33,
131.38, 131.83, 131.89, 132.39, 133.17, 133.19, 133.21, 134.23, 134.87,
135.06, 135.77, 140.22, 146.35, 146.82, 147.67, 147.86, 166.35, 167.07 ppm;
MS (ESI-FTICR) m/z (%): 1691.71 (100) [M+2HNEt3]2+
.
Photophysical experiments: The photophysical experiments were per-
formed in dichloromethane/acetonitrile (1:1, v/v) under air-equilibrated
conditions at 298 K and in a dichloromethane/chloroform (1:1, v/v) rigid
matrix at 77 K. UV/Vis absorption spectra were recorded with a Perkin–
Elmer l40 spectrophotometer. Fluorescence spectra were obtained with
a Perkin–Elmer LS-50 spectrofluorimeter, equipped with a Hamamatsu
R928 phototube for the UV/Vis range, the same instrument was used to
record phosphorescence lifetimes. The emission quantum yields of W-Py,
Py, A1, S1, R1, and R2 were determined by the method of Demas and
Crosby by using anthracene in ethanol as a reference.[20] In the case of
Naph and S2 naphthalene in cyclohexane[20] was used as a standard to de-
termine the emission quantum yield. Fluorescence lifetime measurements
were performed by using an Edinburgh FLS920 spectrofluorimeter
equipped with a TCC900 card for data acquisition in time-correlated
single-photon counting experiments (0.5 ns time resolution) with a D2
lamp.
[3] a) J.-Y. Wang, J.-M. Han, J. Yan, Y. Ma, J. Pei, Chem. Eur. J. 2009,
15, 3585–3594; b) H. Onagi, J. Rebek, Jr., Chem. Commun. 2005,
4604–4606.
[4] For reviews, see for example: a) V. Balzani, P. Ceroni, M. Maestri,
V. Vicinelli Curr. Opin. Chem. Biol. 2003, 7, 657; b) F. Wꢀrthner,
T. E. Kaiser, C. R. Saha-Mçller, Angew. Chem. Int. Ed. 2011, 50,
3376; c) S. V. Eliseevaa, J.-C. G. Bꢀnzli, Chem. Soc. Rev. 2010, 39,
189–227; d) M. R. Wasielewski, Acc. Chem. Res. 2009, 42, 1910–
1921; e) N. Aratani, D. Kim, A. Osuka, Acc. Chem. Res. 2009, 42,
1922–1934; f) F. Scandola, C. Chiorboli, A. Prodi, E. Iengo, E. Ales-
sio, Coord. Chem. Rev. 2006, 250, 1471–1496.
The estimated experimental errors are: 2 nm on the band maximum, 5%
on the molar absorption coefficient, on the emission quantum yield and
the lifetimes.
[5] For some recent examples, see for example: a) A. Uetomo, M.
Kozaki, S. Suzuki, K. Yamanaka, O. Ito, K. Okada, J. Am. Chem.
Soc. 2011, 133, 13276–13279; b) B. Branchi, G. Bergamini, L. Fian-
dro, P. Ceroni, F. Vçgtle, F.-G. Klꢁrner, Chem. Commun. 2010, 46,
3571–3573; c) D. G. Kuroda, C. P. Singh, Z. Peng, V. D. Kleiman,
Science 2009, 326, 263–267; d) C. Giansante, P. Ceroni, V. Balzani,
F. Vçgtle, Angew. Chem. 2008, 120, 5502–5505; Angew. Chem. Int.
Ed. 2008, 47, 5422–5425; e) J.-L. Wang, J. Yan, Z.-M. Tang, Q. Xiao,
Y. Ma, J. Pei, J. Am. Chem. Soc. 2008, 130, 9952–9962.
Acknowledgements
This work has been supported in Italy by Fondazione Carisbo (“Disposi-
tivi nanometrici basati su dendrimeri e nanoparticelle”), bilateral project
Italy–China 2011 (MAE DGPCC), and MIUR (PRIN 20085ZXFEE).
1534
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 1528 – 1535

Light-Harvesting in Rotaxanes
FULL PAPER
[6] a) V. Balzani, G. Bergamini, P. Ceroni, E. Marchi, New J. Chem.
2011, 35, 1944; b) A.-M. Caminade, A. Hameau, J.-P. Majoral,
Chem. Eur. J. 2009, 15, 9270–9285.
[7] a) D. A. Tramontozzi, N. D. Suhan, S. H. Eichhorn, S. J. Loeb, Chem.
Eur. J. 2010, 16, 4466–4476; b) A. M. Elizarov, T. Chang, S.-H. Chiu,
J. F. Stoddart, Org. Lett. 2002, 4, 3565–3568.
[8] A. M. Elizarov, S.-H. Chiu, P. T. Glink, J. F. Stoddart, Org. Lett.
2002, 4, 679–682.
[9] a) Y. Zeng, Y. Li, M. Li, G. Yang, Y. Li, J. Am. Chem. Soc. 2009,
131, 9100–9106; b) S.-Y. Kim, Y. H. Ko, J. W. Lee, S. Sakamoto, K.
Yamaguchi, K. Kim, Chem. Asian J. 2007, 2, 747–754.
[15] a) G. M. Hꢀbner, J. Glꢁser, C. Seel, F. Vçgtle, Angew. Chem. 1999,
111, 395–398; Angew. Chem. Int. Ed. 1999, 38, 383–386; b) G. M.
Hꢀbner, G. Nachtsheim, Q. Y. Li, C. Seel, F. Vçgtle, Angew. Chem.
2000, 112, 1315–1318; Angew. Chem. Int. Ed. 2000, 39, 1269–1272.
Also, see: c) P. Ghosh, G. Federwisch, M. Kogej, C. A. Schalley, D.
Haase, W. Saak, A. Lꢀtzen, R. A. Gschwind, Org. Biomol. Chem.
2005, 3, 2691–2700; d) P. Ghosh, O. Mermagen, C. A. Schalley,
Chem. Commun. 2002, 2628–2629; e) A. Affeld, G. M. Hꢀbner, C.
Seel, C. A. Schalley, Eur. J. Org. Chem. 2001, 2877–2890.
[16] N. D. Marsh, C. J. Mikolajczak, M. J. Wornat, Spectrochim. Acta Part
A 2000, 56, 1499–1511.
[10] a) C. A. Hunter, J. Chem. Soc. Chem. Commun. 1991, 749–751;
b) C. A. Hunter, J. Am. Chem. Soc. 1992, 114, 5303–5311; c) F.
Vçgtle, S. Meier, R. Hoss, Angew. Chem. 1992, 104, 1628–1631;
Angew. Chem. Int. Ed. Engl. 1992, 31, 1619–1622; d) S. Ottens-Hil-
debrandt, S. Meier, W. Schmidt, F. Vçgtle, Angew. Chem. 1994, 106,
1818–1821; Angew. Chem. Int. Ed. Engl. 1994, 33, 1767–1770.
[11] B. Baytekin, S. S. Zhu, B. Brusilowskij, J. Illigen, J. Ranta, J. Husko-
nen, L. Russo, K. Rissanen, L Kauffman, C. A. Schalley, Chem. Eur.
J. 2008, 14, 10012–10028.
[12] S. Sengupta, S. K. Sadhukhan, S. Muhuri, Synlett 2003, 2329–2332.
[13] a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 1975,
16, 4467–4470; b) R. Chinchilla, C. Najera, Chem. Rev. 2007, 107,
874–922.
[17] See, for example: a) L. Rodrꢈguez, E. Delgado-Pinar, A. Sornosa-
Ten, J. Alarcon, E. Garcia-Espana, M. Cano, J. C. Lima, F. Pina, J.
Phys. Chem. B 2009, 113, 15455–15459; b) C. Saudan, V. Balzani, P.
Ceroni, M. Gorka, M. Maestri, V. Vicinelli, F. Vçgtle, Tetrahedron
2003, 59, 3845–3852.
[18] As previously discussed, the molar absorption coefficient of A1 was
assumed to be double of that of S1.
[19] a) H. Meyer, Monatsh. Chem. 1901, 22, 415–442; b) R. Jꢁger, T.
Schmidt, D. Karbach, F. Vçgtle, Synlett 1996, 723–725; c) R. Jꢁger,
Ph.D. Thesis, Universitꢁt Bonn (Germany), 1997.
[20] M. Montalti, A. Credi, L. Prodi, M. T. Gandolfi, Handbook of Pho-
tochemistry, 3rd ed., CRC Press, Boca Raton, 2006, Chapter 7.
[14] a) H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001, 113,
2056–2075; Angew. Chem. Int. Ed. 2001, 40, 2004–2021; b) C. W.
Torne, C. Christensen, M. Meldal, J. Org. Chem. 2002, 67, 3057–
3064.
Received: September 22, 2011
Published online: December 28, 2011
Chem. Eur. J. 2012, 18, 1528 – 1535
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1535