Photocontrolled molecular assembler based on cucurbit[8]uril: [2+2]autophotocycloaddition of styryl dyes in the solid state and in water

Article abstract of DOI:10.1002/ejoc.200901324

Three styryl dyes of the 4-pyridine series that form syn-headto-tail dimeric pairs in polycrystalline films were synthesised. NMR and UV/Vis spectroscopic studies showed that this promotes stereospecific [2+2]-autophotocycloaddition (PCA) in the dimeric pairs to give rctt-isomers of cyclobutane derivatives. For the dye with an N-ammoniopropyl substituent, this transformation was accomplished according to the singlecrystal-to-single-crystal pattern. In aqueous solutions, the dyes and cucurbit[n]urils (CB[n], n = 7, 8) form complexes with a pseudorotaxane structure. CB[7] tends to form 1:1 complexes, and CB[8] forms 1:1 and 2:1 complexes. The structure of the termolecular complex formed by the betaine of the N-sulfonatopropyl styryl dye and CB[8] was determined by X-ray diffraction. The stability of the complexes was measured by 1H NMR titration in a D₂O/[D₃]MeCN (10:1) mixture (logK_1:1 ≥ 3.2, logK_2:1 ≥ 2.6). Free dyes and their complexes with CB[7] in water undergo only (E)/(Z) photoisomerisation. Termolecular complexes of all dyes with CB[8] were found to undergo effective stereospecific PCA reactions to give rctt isomers of cyclobutane derivatives. The 1:1 complexes of the obtained cyclobutanes with CB[8] (logK_cb = 3.2-4.8) are less stable than those of the starting dyes with the same stoichiometry. Thus, CB[8] can play the role of a photocontrolled molecular assembler, i.e., even in the presence of 5 mol-% of CB[8], complete conversion of styryl dyes into the corresponding cyclobutane derivatives takes place upon irradiation in solution.

Full text of DOI:10.1002/ejoc.200901324

FULL PAPER
DOI: 10.1002/ejoc.200901324
Photocontrolled Molecular Assembler Based on Cucurbit[8]uril: [2+2]-
Autophotocycloaddition of Styryl Dyes in the Solid State and in Water
Sergey P. Gromov,*[a] Artem I. Vedernikov,[a] Lyudmila G. Kuz’mina,[b]
Dmitry V. Kondratuk,[a] Sergey K. Sazonov,[a] Yuri A. Strelenko,[c] Michael V. Alfimov,[a] and
Judith A. K. Howard[d]
Keywords: Cavitands / Cycloaddition / Dyes/Pigments / Host–guest systems / Molecular devices / Photochemistry
Three styryl dyes of the 4-pyridine series that form syn-head-
to-tail dimeric pairs in polycrystalline films were synthesised.
NMR and UV/Vis spectroscopic studies showed that this pro-
motes stereospecific [2+2]-autophotocycloaddition (PCA) in
was measured by 1H NMR titration in a D2O/[D3]MeCN
(10:1) mixture (logK1:1 Ն 3.2, logK2:1 Ն 2.6). Free dyes and
their complexes with CB[7] in water undergo only (E)/(Z)
photoisomerisation. Termolecular complexes of all dyes with
the dimeric pairs to give rctt-isomers of cyclobutane deriva- CB[8] were found to undergo effective stereospecific PCA re-
tives. For the dye with an N-ammoniopropyl substituent, this
transformation was accomplished according to the single-
crystal-to-single-crystal pattern. In aqueous solutions, the
dyes and cucurbit[n]urils (CB[n], n = 7, 8) form complexes
with a pseudorotaxane structure. CB[7] tends to form 1:1
complexes, and CB[8] forms 1:1 and 2:1 complexes. The
structure of the termolecular complex formed by the betaine
actions to give rctt isomers of cyclobutane derivatives. The
1:1 complexes of the obtained cyclobutanes with CB[8]
(logKcb = 3.2–4.8) are less stable than those of the starting
dyes with the same stoichiometry. Thus, CB[8] can play the
role of a photocontrolled molecular assembler, i.e., even in
the presence of 5 mol-% of CB[8], complete conversion of
styryl dyes into the corresponding cyclobutane derivatives
of the N-sulfonatopropyl styryl dye and CB[8] was deter- takes place upon irradiation in solution.
mined by X-ray diffraction. The stability of the complexes
that constitute the CB[n] portals increases the stability of
Introduction
their adducts with positively charged ions. Owing to the
properties listed above, cucurbiturils tend to form rather
stable complexes with ammonium compounds[2] and qua-
ternary salts of nitrogen heterocycles[3] both in water and in
the solid phase.
Of particular interest for the study of the complexation
properties of cucurbiturils are guest molecules, in particular,
positively charged unsaturated compounds such as ammo-
nium stilbene derivatives and viologen vinylogs.[4] Owing to
the presence of a C=C double bond, these compounds are
able to undergo photoinduced changes in spatial structure
upon (E)/(Z) isomerisation and [2+2]-photocycloaddition
(PCA) reactions; i.e. they can mechanically move in the
CB[n] cavity with simultaneous changes in the stability of
complexes and, hence, these systems can be used to design
light-controlled molecular devices and machines.[5]
Molecular machines capable of directing chemical reac-
tions by positioning the molecules are called assemblers.[6]
Ribosome is an example of a natural assembler consisting
of ribonucleic acid and proteins that is capable of synthesis-
ing cell proteins from amino acids.[6b]
Presumably, cucurbiturils could function as molecular
assemblers in mechanosynthetic systems,[6c–6h] which selec-
tively bind a substrate and position it in the inner sphere in
a particular way, i.e., they pre-organise the substrate’s reac-
The complexation properties of a relatively new class of
cavitand molecules having the shape of a “barrel” with two
symmetric portals – the cucurbit[n]urils (CB[n]) – have been
vigorously studied over the last decade.[1] CB[n] have dif-
ferent sizes of the hydrophobic cavity depending on the
number of glycouril units (n = 5–8, or 10), which allows
them to encapsulate one or two organic molecules of appro-
priate size and shape. Cucurbiturils differ from other well-
known macrocyclic compounds having a 3D cavity (cyclo-
dextrins, calix[n]arenes) by enhanced structural rigidity;
therefore, they exhibit a higher selectivity in the formation
of inclusion complexes. The relatively high partial negative
charge on the donor oxygen atoms of the carbonyl groups
[a] Photochemistry Centre, Russian Academy of Sciences,
Novatorov str. 7A-1, Moscow 119421, Russian Federation
Fax: +7-495-936-12-55
E-mail: spgromov@mail.ru
[b] N. S. Kurnakov Institute of General and Inorganic Chemistry,
Russian Academy of Sciences,
Leninskiy prosp. 31, Moscow 119991, Russian Federation
[c] N. D. Zelinskiy Institute of Organic Chemistry,
Russian Academy of Sciences,
Leninskiy prosp. 47, Moscow 119991, Russian Federation
[d] Chemistry Department, Durham University,
South Road, Durham DH1 3LE, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901324.
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S. P. Gromov et al.
FULL PAPER
tive sites for the desired chemical reaction, provide for en- cyclic cavitands having rather large cavities. For example,
ergy supply and the mechanical migration of the substrate, the positively charged styryl dye cation seems a promising
allow chemical transformation to the products in the inner candidate for insertion into the electron-donating cucur-
sphere, and finally release the products to the outer medium bit[n]uril cavity to give complexes in which various pho-
due to the lower complementarity of the assembler and the toprocesses can occur selectively. However, although quite
products compared to the substrate. Several types of assem- a few cases of cucurbituril complexation with chromo-
blers have now been proposed; however, none have been (fluoro)phore compounds are known to date,[4d,10] almost
based on CB[n], and generally this field is relatively unex- no studies of complexes of CB[n] with styryl dyes have been
plored.
reported.[10l]
Recently, we showed[7] that bis(quaternary) salts of dipyr-
In this paper, we report a 1H NMR and UV/Vis spectro-
idylethylenes (E)-1a,b (Scheme 1) and CB[7] form stable 1:1 scopic study of the photochemical behaviour of a series of
pseudorotaxane complexes in water (logK1:1 = 5.1 and 3.5, related (4-pyridyl)styryl dyes (E)-2a–c differing in the struc-
respectively); CB[8], having a relatively larger cavity, was ture of the N-substituent (Scheme 2) and their complexes
capable[8] of forming highly stable complexes of different with CB[n] (n = 7 and 8). The complexation properties of
stoichiometry with N,NЈ-bis(ammoniopropyl) derivatives of cavitands are compared quantitatively as a function of their
dihetarylethylenes (E)-1c,d. An important role in these size and the structure of the N-substituents in the dyes and
complexes is the ability to form hydrogen bonds between the respective [2+2]-photocycloaddition products: 1,2,3,4-
the terminal ammonium groups of the guest and the oxygen tetrasubstituted cyclobutanes. The structures of dye (E)-2b,
atoms of CB[8] portals. On light irradiation of an aqueous the rctt isomer of the cyclobutane derivative obtained from
solution of a mixture of (E)-1d and CB[8], reversible (E)/ the dye by the single-crystal-to-single-crystal pattern, and
(Z) isomerisation of the unsaturated molecule took place to the termolecular complex {(E)-2c}2@CB[8] were deter-
give stable complex (Z)-1d@CB[8], which was characterised mined for the first time by X-ray diffraction.
by X-ray diffraction.
Scheme 2. Structure of styryl dyes 2a–c.
Scheme 1. Structure of viologen vinylogs 1a–d.
We found[9] that, unlike viologen vinylogs 1a–d, styryl
Results and Discussion
dyes with the general formula R–Het+–CH=CH–Ar X– do
not only undergo effective (E)/(Z) photoisomerisation reac-
tions, but also stereoselective [2+2]-PCA reactions, which
occur both in solution and in the solid phase. The optical
Synthesis
The synthesis of dyes (E)-2a,b was described previous-
characteristics of these dyes can be readily adjusted by vary- ly.[9e,11] Betaine dye 2c was prepared by two methods: either
ing the nature of the heterocyclic residue and substituents styrylpyridine (E)-3[12] was quaternised with 1,3-pro-
in the aryl group. The reversible PCA reaction of styryl dyes panesultone, or the betaine of heterocyclic salt 4 was con-
is of most interest for the design of photoswitchable molec- densed with veratraldehyde in the presence of pyrrolidine
ular devices, photocontrolled molecular machines, optical as the base (Scheme 3). Salt 4 is often used in the synthesis
molecular sensors, and reversible optical information re- of various dyes (see Hassner et al.[13] for an example); how-
cording systems. The resulting photoproducts – cyclobu- ever, it has been poorly described. We obtained this salt by
tane derivatives – are thermally stable, stable against photo- quaternisation of 4-picoline with 1,3-propanesultone and
degradation and do not fluoresce; the hypsochromic shift report for the first time its characteristics. According to the
of the long-wavelength absorption maximum reaches spin–spin coupling constants for the ethylene protons, dye
120 nm. For the PCA reaction to proceed in solution, the 2c was formed in the (E) configuration (3Jtrans-CH=CH
=
dye molecule must contain particular functional sites, such 16.3 Hz).
–
+
as a crown-ether fragment and a terminal SO3 or NH3
Previously, we showed[9c,9e,9f] that polycrystalline films of
group in the N-substituent. These are needed for self-as- (E)-2a and related styryl dyes containing electron-donating
sembly of molecules into dimeric complexes structurally alkoxy groups in the benzene ring, undergo stereospecific
pre-organised toward the PCA.[9a,9c] This considerably re- PCA reaction on exposure to visible light to give centro-
stricts the range of dyes and solvents that are suitable for symmetric rctt isomers of cyclobutane derivatives. This is
effective PCA.
caused by a structural pre-organisation of these dyes in the
The problem of styryl dye pre-organisation toward the solid phase, specifically in single-crystals, represented by a
PCA reactions in solutions can be solved by using macro- predominant stacking motif in the molecular packing. Most
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Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
rctt-5b,c were isolated from reaction mixtures in 85–86%
yields by fractional crystallisation.
The structures of all of the obtained compounds were
1
confirmed by H and 13C NMR spectroscopy, spectropho-
tometry, and by elemental analysis.
X-ray Diffraction Studies of Dye 2b and Cyclobutane 5b
Dye (E)-2b was prepared as single crystals by slow crys-
tallisation of the mother liquor formed after the exchange
of bromide anions with perchlorate anions on treatment of
the dibromide dye with perchloric acid.[11] The resulting
crystalline compound was a mixed salt containing an equal
ratio of bromide and perchlorate anions. Apparently, only
with this combination of anions can sufficiently large single
crystals of this dye, that are suitable for X-ray diffraction
analysis, be grown.
Scheme 3. Synthetic routes affording styryl dye 2c.
The structure of (E)-2b is shown in Figure 1. The unit
cell comprises two independent dye dications, two perchlo-
rate and two bromide anions, and a solvation water mole-
cule O(1W) with an occupation of 0.25. For more conve-
nient comparison of the geometric parameters of organic
cations, rather than following IUPAC rules, the same num-
bering of like atoms is used. The chromophore fragments
of both independent cations are nearly planar, which attests
to a high degree of π-conjugation. Indeed, the dihedral
angles between the pyridine and benzene ring planes are 6.3
and 14.8°. Both dye cations have (E) configuration of the
ethylene fragment. The ethylene bonds are substantially
localised; the bond lengths in the C(Py)–C=C–C(Ar) frag-
ments are distributed as follows: 1.468(7), 1.335(7), 1.466(7)
and 1.448(7), 1.340(7), 1.470(7) Å. The oxygen atoms O(1),
O(2), O(3) and O(4) are efficiently conjugated with the ben-
often, the stacks are composed of centrosymmetric dimeric
(stacking) pairs in which planar molecular cations are lo-
cated one above another according to the syn-head-to-tail
pattern. Undoubtedly, the structure of the dimeric pair is
dictated by minimisation of the Coulomb repulsion of like
charged fragments with the maximum secondary interac-
tion of the pz-orbitals of conjugated fragments. In the di-
meric pairs, the ethylene bonds are antiparallel and rather
closely spaced (up to 4.2 Å), which is favourable for a topo-
chemical PCA reaction, including the single-crystal-to-sin-
gle-crystal reaction, i.e., a reaction without crystal destruc-
tion.
The irradiation of polycrystalline films of dyes (E)-2a–c
yielded only centrosymmetric rctt isomers of cyclobutane
derivatives 5a–c (Scheme 4). This implies that syn-head-to-
tail dimeric pairs {(E)-2a–c}2, which precede the formation
of cyclobutanes with this stereochemistry, exist in the solid
phase. In the case of (E)-2a, photoreaction proceeds quanti-
tatively over a period of 110 h, whereas for (E)-2b,c this
process is much slower and does not reach completion even
after 230 h. Apparently, the presence of the long, bulky N-
substituent reduces the efficiency of the photoreaction,
which is in line with previous studies on PCA reactions of
styryl dye films.[9e] Yet another interpretation of the retar-
dation of PCA may be the fact that other molecular pack-
ing motifs that do not promote PCA reactions are also en-
countered in polycrystalline films of (E)-2b,c. Cyclobutanes
Scheme 4. Synthetic route to cyclobutanes rctt-5a–c in the solid
state.
Figure 1. Structure of dye (E)-2b. Thermal ellipsoids are drawn at
the 50% probability level.
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zene rings, as indicated by the values of bond angles at these trosymmetric rctt isomers of cyclobutane derivatives ob-
atoms [116.9(4)–117.7(4)°], which are close to the perfect tained from styryl dyes and their synthetic precursors,
value of 120° for the sp2-hybrid state.
namely, neutral styrylheterocycles. The dihedral angle be-
Highly skewed stacks composed of centrosymmetric di- tween the planes of the N(1)C5 pyridine ring and the cis-
meric pairs of the syn-head-to-tail type were found in the positioned benzene ring, and a similar angle between the
crystal for both independent cations (Figure 2); this is the N(3)C5 pyridine ring plane and cis-benzene ring, are 30.1
most commonly found packing motif of styryl dyes.[9e] The and 32.1°, respectively. Thus, in both cyclobutane tetracat-
ammonium groups in the dimeric pairs are positioned near ions, two cis substituents in the cyclobutane ring are proxi-
the methoxy groups of neighbouring cations in such a way mate in space, and the ammonium group of one of them
+
that one hydrogen atom of the NH3 group forms a bifur- forms a bifurcate hydrogen bond with oxygen atoms of the
cate hydrogen bond with two oxygen atoms. The N(2)– methoxy groups, which is similar to the situation in the pre-
H···O(1A), N(2)–H···O(2A), N(4)–H···O(3A) and N(4)– cursor dimeric pairs. Characteristics of the hydrogen bonds
H···O(4A) distances are in the range of 2.08–2.37 Å, the are as follows: the lengths, N(2)–H···O(1A), N(2)–
angles at the H atoms are 122–152°, which implies relatively H···O(2A), N(4)–H···O(3A) and N(4)–H···O(4A), occur in
weak hydrogen bonds. In the dimeric pairs, the chromo- the range of 2.19–2.34 Å, and the angles at the H atoms are
phore fragments occur in parallel planes at about 3.5 Å dis- 123–164°.
tances, their ethylene bonds being antiparallel and ap-
proaching each other to a distance of 4.00 Å [C(6)···C(7A)
and C(7)···C(6A)] and 3.68 Å [C(6Ј)···C(7ЈA) and C(7Ј)···
C(6ЈA)], whereas the distances between the ethylene bonds
of the dimeric pairs neighbouring in the stacks are in-
creased to 7.53 Å (both). Undoubtedly, this dye packing fa-
cilitates the solid-phase PCA reaction, giving the rctt isomer
of the cyclobutane derivative, as was shown previously[9c–9f]
for (E)-2a and the related styryl dyes.
Figure 3. Structure of cyclobutane rctt-5b. Thermal ellipsoids are
Figure 2. Structure of the dimeric pairs of independent cations of
dye (E)-2b. Most of the hydrogen atoms are omitted for clarity.
Hydrogen bonds and distances between ethylene bonds are drawn
drawn at the 50% probability level. Hydrogen bonds are depicted
with dashed lines. The additional letter “A” indicates that atoms
are at (1 – x, 1 – y, 1 – z) and (1 – x, 1 – y, 2 – z).
with dashed lines. The additional letter “A” indicates that atoms
are at (1 – x, 1 – y, 1 – z) and (1 – x, 1 – y, 2 – z).
Indeed, visible-light irradiation of crystals of (E)-2b for
20 h resulted in complete transformation of the dye into
1
UV/Vis and H NMR Spectroscopic Studies
centrosymmetric cyclobutane derivative rctt-5b according to
The ability of dyes (E)-2a–c to form inclusion complexes
the single-crystal-to-single-crystal type. The PCA reaction with CB[n] in water was studied by spectral methods. Free
took place in both independent dimeric pairs, and, hence, compounds (E)-2a, (E)-2b and (E)-2c in water have an in-
two independent cyclobutane tetracations were formed tense long-wavelength absorption band (LAB) with maxima
(Figure 3). The PCA was accompanied by release of crystal- at 385, 389 and 381 nm, respectively (ε = 29600, 30500 and
lisation water molecules and by only a 3.8% decrease in the 28300 –1 cm–1). Visible-light irradiation of dye solutions
crystal volume. The centres of the cyclobutane rings coin- with concentrations of ca. 5ϫ10–5  resulted in a gradual
cide with the symmetry centres of the crystal, which prede- decrease in the LAB intensity down to 76–83% of the initial
termines an ideally planar conformation of these rings. A value. Clearly, this reflects (E)/(Z) isomerisation of the dye
similar planar conformation of cyclobutane rings was ob- and relatively slow (over 1 h) development of the photo-
served in our previous study[9c,9f] for the crystals of all cen- stationary state. A similar behaviour was observed pre-
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Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
viously[9c] for a solution of a related crown-ether styryl dye
(E)-6 (see Scheme 5) in MeCN, where the photostationary
equilibrium was attained much faster (Ͻ10 min), other fac-
tors being the same, and resulted in a much more pro-
nounced decrease in LAB intensity (to 64% of the initial
value). Evidently, this difference in the behaviour of dyes
(E)-2a–c and (E)-6 is caused by the solvent nature, as also
indicated by the hypsochromic shift of the LAB maximum
of the dyes (E)-2a and (E)-6 (in MeCN, 397 and 399 nm,
respectively) and by a decrease in the extinction by ca. 25%
when changing the solvent from MeCN[9c,9e] to water.[14]
Figure 4. Absorption spectra in water at room temp.: (1) dye (E)-
2b (4.85ϫ10–5 , 1 cm quartz cell) and its mixtures with CB[7] in
(2) 1:1 and (3) 1:2 ratios.
Scheme 5. Structure of dye 6.
1
which points to fast exchange on the H NMR time scale.
The visible-light irradiation of ca. 1ϫ10–3  solutions of
dyes (E)-2a–c in a D2O/[D3]MeCN mixture (10:1) resulted,
after 2–5 h, in the appearance of second sets of signals in
Conversely, the spectrum of (E)-2c/CB[7] always exhibited
two sets of narrow proton signals for betaine (E)-2c and
two sets of signals for CB[7] (see Figure 5). This spectral
pattern attests to the formation of inclusion complex (E)-
2c@CB[7], which undergoes slow exchange with free com-
ponents. A similar spectral behaviour was observed pre-
viously[7] for the complexation of dibetaine (E)-1b with
CB[7]. Apparently, the presence of negatively charged bulky
sulfonate groups in the guest molecule hampers the decom-
position of the supramolecular complex (E)-2c@CB[7] to
the starting components and thus increases its kinetic sta-
bility. Note that the presence of two sets of signals for each
of the components contained in an equimolar ratio attests
to the relatively low stability constant of the 1:1 complex,
which was confirmed by investigating the quantitative char-
acteristics of (E)-2c complexation with CB[7] (see below).
The spectral behaviour of the system (E)-2b/CB[7] was
more complicated than that of systems based on dyes (E)-
1
the H NMR spectra, indicating the presence of (Z)-2a–c,
with typical spin–spin coupling constants for the ethylene
protons (3Jcis-CH=CH = 12.0–12.1 Hz). The relative amount
of (Z) isomers in the mixtures varied from 31 to 41%, as
indicated by comparison of the integral intensities of signals
of like protons of the two geometric isomers. Long-term
storage of the irradiated samples in the dark at room tem-
perature resulted in very slow decrease in the relative
amount of (Z) isomers (to 25–33% in 45 d), which is indica-
tive of a low rate of thermal (Z) Ǟ (E) isomerisation under
these conditions.
Cucurbit[n]urils do not contain long conjugated chromo-
phore fragments; therefore, even their saturated solutions
absorb above 250 nm only very slightly.[7,15] Mixing of (E)-
2a–c with either CB[7] or CB[8] leads to a considerable ba-
thochromic shift of the LAB maximum and to its broaden-
ing and decrease in intensity (for example, see Figure 4).
Apparently, this is due to the formation of inclusion com-
plexes of CB[n] with the dyes in which the local solvation
of the guest molecule differs from its solvation by water
molecules. Complexation with CB[7] induces much greater
shifts of the LAB maximum than with CB[8] (∆λmax up to
34 and 15 nm, respectively); this is attributable to tighter
arrangement of molecules (E)-2a–c in the smaller cavity
and, hence, their better shielding from the aqueous medium
by the cavitand walls. An increase in the cucurbituril con-
tent in (E)-2a–c/CB[n] mixtures with respect to the equi-
molar ratio results in only minor changes in the form and
position of the LAB (especially for CB[8]).
1H NMR spectroscopic studies of the complexation of
(E)-2a–c with CB[n] provided more information. The spec-
tral behaviour of the components differs substantially when
they are mixed in different ratios. For example, in the sys-
tem (E)-2a/CB[7], one set of rather narrow signals was pres-
Figure 5. The 1H NMR spectra (region of the aromatic protons) in
D2O/[D3]MeCN (10:1) at 30 °C: (a) dye (E)-2c (1ϫ10–3 ) and (b)
ent for each of the components at any component ratio, its 1:1 mixture with CB[7].
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2a,c. At a 1:2 component molar ratio of [(E)-2b]/(CB[7])
and at higher contents of CB[7], each system component
was responsible for one set of narrow signals, whereas an
increase in the relative content of (E)-2b resulted in pro-
nounced broadening of most of dye signals. This result
points indirectly to the formation of a more intricate com-
position of the supramolecular complexes and to their
higher stability with the dye containing an ammonium
group in the N-substituent compared to other styryl dyes.
In the case of mixtures of dyes (E)-2a–c with CB[8],
broadening of the proton signals of guest molecules was
more pronounced than for the CB[7] systems; this may be
indicative of a more complicated equilibrium, i.e., forma-
tion of complexes having a different composition for CB[8]
1
and relatively slow exchange on the H NMR time scale
between these complexes. Note that in the system (E)-2c/
CB[8], study of the complexation was complicated by low
solubility of the complexes, resulting in salting-out in the
presence of excess dye.
1
Figure 5 shows the changes in the positions of the H
NMR signals of the aromatic and ethylene protons of dye
(E)-2c following mixing with CB[7] in an equimolar ratio.
It can be readily seen that the signals of the new set con-
siderably differ in the direction and the magnitude of their
shift with respect to analogous signals of free (E)-2c. The
signals of both the pyridine residue and the ethylene bond
undergo upfield shifts (∆δH of up to –1.24 ppm), whereas
signals of the 2Ј-H and 6Ј-H protons of the benzene ring
are shifted downfield (∆δH up to 0.44 ppm). This means
that the CB[7] walls shield the protons of the CH=CHPy
fragment to the highest extent, and, hence, the cavitand is
predominantly arranged in the complex above the positively
charged region of the dye molecule. Following the mi-
gration away from the geometric centre of the CH=CHPy
fragment, the protons of molecule (E)-2c become less shi-
Scheme 6. Complex formation of dyes 2a–c with CB[n].
their concentrations for CB[7] systems was adequately de-
scribed by a model taking into account one equilibrium
[Equation (1)].
K1:1
–
elded, and the signals of the peripheral CH2SO3 group of
(E)-2a–c + CB[n] i (E)-2a–c@CB[n]
(1)
the N-substituent and the 2Ј-H and 6Ј-H protons show a
downfield shift, probably due to the deshielding action of
the carbonyl groups of the host molecule portals. The sig-
nals of the most remote protons – 5Ј-H of the benzene ring
and the methoxy protons – are relatively insensitive to com-
plex formation. This variation of the magnitude and direc-
tion of ∆δH attests to the formation of a pseudorotaxane
structure of complex (E)-2c@CB[7] where the guest mole-
cule runs through the macrocycle cavity, and its terminal
fragments are outside the cavity of CB[7] (Scheme 6). The
obtained NMR spectroscopic data lead to the same conclu-
sion concerning the structures of other supramolecular
complexes, although in the case of CB[8] complexes, in-
where K1:1 is the stability constant of complexes (E)-2a–
c@CB[n] [–1]. In the case of dye (E)-2b and CB[7], it was
necessary to take into account both Equations (1) and (2).
K1:2
(E)-2b@CB[7] + CB[7] i (E)-2b@{CB[7]}2
(2)
where K1:2 is the stability constant of complex (E)-
2b@{CB[7]}2 [–1]. For CB[8]-based systems, good results
were provided by simultaneously taking into account Equa-
tions (1) and (3).
K2:1
(E)-2a–c@CB[8] + (E)-2a–c i {(E)-2a–c}2@CB[8]
(3)
terpretation of the spectral changes is complicated by sub- where K2:1 is the stability constant of complexes {(E)-2a–
1
stantial broadening of the dye signals. Nevertheless, evi- c}2@CB[8] [–1]. In the case of slow exchange on the H
dence for this particular structure of complex {(E)- NMR time scale, averaged positions of like signals were cal-
2c}2@CB[8] was obtained by X-ray diffraction (see below). culated taking into account their integral intensities. The
Quantitative determination of the stability constants of stability constants thus found are summarised in Table 1.
the complexes of dyes (E)-2a–c with CB[n] was performed
It can be seen from Table 1 that CB[7] forms only 1:1
1
by H NMR titration in a D2O/[D3]MeCN mixture (10:1) complexes with monocationic and betaine styryl dyes (E)-
at 30 °C. The dependence of the variation of chemical shifts 2a,c. Evidently, the relatively small size of the cavity of this
(∆δH) of the dye and cucurbituril protons on the ratio of cavitand predetermines its ability to accommodate one
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Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
Table 1. Stability constants of complexes of CB[n] with dyes (E)-2a–c and cyclobutanes rctt-5a–c.[a]
Dye
CB[7]
CB[8]
logK2:1
Cyclobutane
[b]
[c]
[b]
[d]
[e]
logK1:1
logK1:2
Ͼ5
logK1:1
logKcb
(E)-2a
(E)-2b
(E)-2c
4.1
Ͼ5
3.2
4.9
4.1
4.4
2.6
4.3
4.8
3.2
rctt-5a
rctt-5b
rctt-5c
ca. 5.0
4.0
1
[a] H NMR titration in D2O/[D3]MeCN (10:1) at 30 °C. The formation constants are measured to within approximately Ϯ30%. [b] K1:1
= [(E)-2@CB[n]]/([(E)-2]·[CB[n]]) [–1] is the formation constant for a 1:1 complex. [c] K1:2 = [(E)-2@{CB[7]}2]/([CB[7]]·[(E)-2@CB[7]])
[–1] is the formation constant for a 1:2 (dye)/(CB[7]) complex. [d] K2:1 = [{(E)-2}2@CB[8]]/([(E)-2]·[(E)-2@CB[8]]) [–1] is the formation
constant for a 2:1 (dye)/(CB[8]) complex. [e] Kcb = [rctt-5@CB[8]]/([rctt-5]·[CB[8]]) [–1] is the formation constant for a 1:1 (cyclobutane)/
(CB[8]) complex.
guest molecule inside. The dicationic dye (E)-2b was also and O(1)···O(5A), being 9.37 and 10.45 Å, respectively. Cer-
able to form a termolecular complex (E)-2b@{CB[7]}2, in tainly, this distortion is a result of accommodating two dye
which two macrocyclic molecules are probably threaded molecules in the host cavity.
simultaneously onto a relatively long guest (Scheme 6). The
stability of the 1:1 complexes increases considerably in the
sequence (E)-2c Ͻ (E)-2a Ͻ (E)-2b, which correlates with
the increase in the effective positive charge of the dye mole-
cule on passing from the betaine to the dication structure.
In the case of (E)-2b, an additional contribution to the sta-
bility of the supramolecular complex comes from hydrogen
bonding between the terminal ammonium group of the dye
and the donor oxygen atoms of the CB[7] portals, as has
been found previously[8] for the complexes (E)-1c,d@CB[8].
Determining the stability constants of the complexes of (E)-
2b with CB[7] was precluded by their very high values,
1
which exceeded the upper limit of the H NMR titration
method (logK Ͼ 5). Cucurbit[8]uril forms two types of
complexes, 1:1 and 2:1, with all dyes; the stability sequences
for both types of complex as a function of dye structure are
similar to those of the CB[7] complexes. The 1:1 CB[8]-
based complexes proved to be somewhat more stable than
analogous complexes of CB[7] (∆logK1:1 up to 0.8) and
than the 2:1 complexes of CB[8] (∆logK1:1/2:1 = 0.6–1.4).
This can be attributed to (1) looser arrangement of the
guest in the larger cavity of CB[8] in 1:1 complexes, which
simultaneously reduces the free space needed to dispose the
second guest molecule in the 2:1 complex and (2) the Cou-
lomb repulsion of the molecular cations in the CB[8]-based
termolecular complexes. That is, by varying the terminal
functional group within the N-substituent of the dye mole-
cule, one can finely control the strength of its binding to
cavitands.
Complex {(E)-2c}2@CB[8] was obtained in the solid
Figure 6. Structure of independent components of crystal
state by precipitation upon mixing of aqueous solutions of
{2c}2@CB[8]·21.25H2O: (a) host molecule of CB[8] and (b) guest
the components in a 2:1 ratio; its stoichiometry was con-
firmed by elemental analysis (see Exp. Sect.).
molecule of dye (E)-2c, which is disordered over two s-trans confor-
mations. The minor conformer is drawn with hollow lines. Thermal
ellipsoids are drawn at the 40% probability level. The additional
letter “A” indicates that atoms are at (–x, 1 – y, –z).
X-ray Diffraction Study of Complex {(E)-2c}2@CB[8]
The chromophore fragment of (E)-2c exists in the (E)
We were able to prepare single crystals of the 2:1 complex configuration and is disordered over two positions corre-
of dye (E)-2c and cucurbit[8]uril. The structure of the inde- sponding to two s-trans conformers in a 0.78:0.22 ratio. As
pendent components of the complex is presented in Fig- in dye (E)-2b, the chromophore fragments of both s-con-
ure 6. The geometric centre of the molecule CB[8] coincides formers are nearly planar: the dihedral angles between the
with the centre of symmetry of the crystal. The CB[8] port- pyridine and benzene ring planes are 19.3 and 13.7°, respec-
als are distorted toward an oval: the shortest and longest tively, in the major and minor conformers. The ethylene
distances between the opposing oxygen atoms, O(3)···O(7A) bonds in the conformers are localised: the bond lengths in
Eur. J. Org. Chem. 2010, 2587–2599
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2593

S. P. Gromov et al.
FULL PAPER
the C(Py)–C=C–C(Ar) fragments are 1.461(13), 1.357(14), Photochemical Study of Complexes of the Styryl Dyes with
1.490(12) and 1.52(6), 1.34(6), 1.53(4) Å. The oxygen atoms CB[n]
O(4Ј) and O(5Ј) are effectively conjugated with the benzene
Visible-light irradiation of approximately 5ϫ10–5
aqueous solutions of equimolar mixtures of dyes (E)-2a–c
and CB[7], resulted in a relatively fast (over 10 min) de-
crease in the LAB intensity up to 47% of the initial value.
Subsequent irradiation did not result in changes in the spec-
tral characteristics of the mixtures, which proves that the
photostationary (E)/(Z) equilibrium had been attained.
This is the expected behaviour of CB[7]-based systems for
which the formation of only 1:1 and 1:2 complexes has been
observed (see above).
A different situation was observed on irradiation of solu-
tions of (E)-2a–c and CB[8] mixtures in 2:1 molar ratio. In
all cases, the LAB intensity decreased to nearly zero at
400 nm (e.g., Figure 8). This means that the chromophore
conjugation chain in dyes (E)-2a–c has been destroyed as a
result of effective PCA reaction taking place in termolecu-
lar complexes {(E)-2a–c}2@CB[8] to give complexes of cy-
clobutane derivatives rctt-5a–c@CB[8] (Scheme 7). Mea-
surement of the kinetics of disappearance of the long-wave-
length absorption showed equal reactivities for dyes (E)-
2a,c and somewhat slower consumption of dye (E)-2b, other

ring, as indicated by the values for the angles at these atoms,
115.0(6) and 119.1(5)°, which are typical of an sp2-hybrid
state.
Figure 7 shows the arrangement of the major compo-
nents of the complex {(E)-2c}2@CB[8]. A centrosymmetric
dimeric pair of dye molecules formed according to the syn-
head-to-tail pattern resides in the cucurbituril cavity. Only
the pyridine ring and the ethylene bond of each dye mole-
cule are located directly in the cavity; the sulfonatopropyl
and dimethoxyphenyl substituents protrude on both sides
of the torus-like cavitand. Apparently, this arrangement of
the parts of the dye with respect to the cucurbituril walls is
due to the favourable interaction of the electron-donating
CB[8] cavity, with the electron-withdrawing pyridine ring
bearing the greater part of the positive charge. Thus, this
complex is a pseudorotaxane sandwich structure. In the di-
meric pair, the chromophore fragments are located in paral-
lel planes about 3.7 Å apart. Their ethylene bonds are anti-
parallel; however, since the region of stacking interactions
covers only the vinylpyridine fragments of the dyes, the
C=C bonds are too remote from each other (the distance is
5.21 Å for both pairs of conformers) for solid-phase PCA
to occur. In solution, the mobility of the dye molecules in
2:1 complexes is clearly high enough, thus enabling the
PCA reaction to take place (see below).
Figure 8. Absorption spectra of mixtures of (E)-2c (4.88ϫ10–5 )
and CB[8] (2.44ϫ10–5 , 1-cm quartz cell) in water, after irradia-
tion for: (1) 0, (2) 200, (3) 500, (4) 1100, (5) 2300, and (6) 4700 s
(light from a 60 W incandescent lamp; distance from the light
source 10 cm).
Figure 7.
Arrangement
of
components
in
complex
{2c}2@CB[8]·21.25H2O. The additional letter “A” indicates that
atoms are at (–x, 1 – y, –z). Atoms of minor s-trans conformer of
(E)-2c, hydrogen atoms, and solvation water molecules are omitted
for clarity.
The unit cell was also found to contain 13 independent
solvation water molecules with either full or partial site oc-
cupations. The considerable disorder of the solvation shell
and the dye molecule decreases appreciably the quality of
the {(E)-2c}2@CB[8] crystal. Although the hydrogen atoms
of the water molecules could not be localised, the fact that
they are located approximately 2.5–2.9 Å from the oxygen
atoms of CB[8], sulfonate groups and from each other, indi-
cates unambiguously that the crystal contains a network of
numerous hydrogen bonds.
Scheme 7. Synthetic route to cyclobutanes rctt-5a–c in aqueous
solution.
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Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
factors being the same. In all cases, after exposure for
100 min, the subsequent spectral changes were negligible.
The structure of 5a–c obtained in solution was identical
to the structure of rctt isomers of cyclobutanes formed
upon irradiation of polycrystalline films of dyes (E)-2a–c;
1
this was confirmed by H NMR spectroscopic data. Quan-
titative determination of the stability constants of the com-
plexes formed by cyclobutanes rctt-5a–c and CB[8] was per-
formed by 1H NMR titration in a D2O/[D3]MeCN mixture
(10:1) at 30 °C. The change in the proton chemical shifts
of cyclobutane and cucurbituril following variation of their
concentration ratio was adequately described in this case by
a model including only one equilibrium [Equation (4)].
Kcb
rctt-5a–c + CB[8] i rctt-5a–c@CB[8]
(4)
Scheme 8. Working cycle of photocontrolled molecular assembler
giving cyclobutanes rctt-5a–c from styryl dyes 2a–c.
where Kcb is the stability constant of the complexes rctt-5a–
c@CB[8] [–1]. The stability constants found in this way are
summarised in Table 1.
Conclusions
The order of increasing stability of the complexes rctt-
5a–c@CB[8] is similar to the order of the starting dyes,
which confirms once again the conclusion that the most
stable complexes are formed by compounds bearing the
maximum possible positive charge and capable of hydrogen
bonding with the cavitand portals. It is noteworthy that the
stability of bimolecular complexes (E)-2a–c@CB[8] is much
higher than that of bimolecular complexes rctt-5a–c@CB[8]
(∆logK1:1/cb up to 0.8). This may be caused by the larger
size of the cyclobutane derivative compared with the pre-
ceding syn-head-to-tail dimeric pair of the styryl dye. Thus,
the competition between the dye and its photoproduct for
complexation with CB[8] in solution should result in the
predominant formation of dye complexes, in particular, the
termolecular complexes {(E)-2a–c}2@CB[8] pre-organised
toward PCA. This conclusion means that it is possible to
use catalytic amounts of CB[8] to perform the stereospecific
conversion of the styryl dye into rctt-cyclobutane in aque-
ous solution. Indeed, irradiation experiments with solutions
of (E)-2a–c in the presence of 5 mol-% of CB[8] demon-
strated complete transformation of the dye into rctt-5a–c
(NMR spectroscopic monitoring).
The stereospecific [2+2]-autophotocycloaddition of sty-
ryl dyes can be carried out both in their polycrystalline
films, in which the syn-head-to-tail organisation of dye mo-
lecules into dimeric pairs is controlled by the stacked molec-
ular packing, and in aqueous solution in the presence of
cucurbit[8]uril, whose cavity can accommodate a syn-head-
to-tail dimeric pair of the dye molecules to give a stable
pseudorotaxane complex. The stability of 1:1 complexes of
the cyclobutanes thus formed with CB[8] was found to be
lower than that of the complexes of the starting dyes of the
same stoichiometry. This was used to design the first light-
induced molecular assembler based on CB[8], which ensures
stereospecific transformation of styryl dyes into cyclobu-
tane derivatives in aqueous medium. This type of self-as-
sembly of styryl dyes can be used to produce photocon-
trolled molecular devices and machines, including photo-
controlled assemblers, and to design information recording
and storage systems at the molecular level.
Experimental Section
The whole functioning cycle of this photocontrolled mo-
lecular assembler, based on CB[8] in solution, is shown in
Scheme 8. In the presence of excess dye, complexes (E)-2a–
c@CB[8] are able to incorporate a second dye molecule, and
are assembled as dimeric pairs {(E)-2a–c}2@CB[8] in the
General: Melting points were measured with a Mel-Temp II appa-
ratus in capillaries. H and 13C NMR spectra were recorded with
1
a Bruker DRX500 instrument in [D6]DMSO and D2O/[D3]MeCN
(10:1) at 30 °C by using the solvent as internal reference (δH = 2.50
cavity as a result of pre-organisation. Upon light irradiation and 4.70 ppm, respectively; δC = 39.43 ppm for [D6]DMSO); 1H-
1H COSY and ROESY spectra and 1H-13C COSY (HSQC and
at the absorption maxima, the PCA reaction can be carried
HMBC) spectra were used to assign the proton and carbon signals
out in these pairs if necessary. The efficiency of binding
(see Schemes 2 and 4 for atom numbering). IR spectra were mea-
of the cyclobutane thus formed by the cavitand as rctt-5a–
c@CB[8] is considerably lower than that of the starting dyes
(E)-2a–c; this facilitates translocation of the reaction prod-
uct outside the CB[8] cavity. This release is followed by oc-
sured with a Bruker ISF-113V spectrometer. Absorption spectra
were recorded in distilled water (HPLC-grade, Aldrich) at room
temp. by using 1 cm quartz cells with a UV-3101PC spectropho-
tometer (Shimadzu) in the range of 200–600 nm, with an increment
cupation of the cavity by a new dye molecule. The subse-
of 0.5 nm. All solutions were prepared under red light and kept in
quent formation of further complexes (E)-2a–c@CB[8]
completes the functioning cycle of the photocontrolled mo-
lecular assembler and makes it ready for the next one.
the dark to avoid photoreactions. Elemental analyses were per-
formed at the microanalytical laboratory of the A. N. Nesmeyanov
Institute of Organoelement Compounds (Moscow, Russian Federa-
Eur. J. Org. Chem. 2010, 2587–2599
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2595

S. P. Gromov et al.
FULL PAPER
tion); the samples for elemental analyses were dried in vacuo at
3
3
4
7.07 (d, J = 8.2 Hz, 1 H, 5Ј-H), 7.29 (dd, J = 8.2, J = 1.8 Hz, 1
4
3
80 °C.
H, 6Ј-H), 7.39 (d, J = 1.8 Hz, 1 H, 2Ј-H), 7.40 (d, J = 16.3 Hz, 1
3
H, CH=CHPy), 7.95 (d, J = 16.3 Hz, 1 H, CH=CHPy), 8.15 (d,
Preparations: 4-Picoline, 1,3-propanesultone and veratraldehyde
were used as received (Aldrich). Styrylpyridine (E)-3 was obtained
according to a published procedure.[12]
Dye (E)-2a: Obtained according to the published procedure.[9e]
M.p. 224–226 °C (decomp.). 1H NMR (500 MHz, [D6]DMSO): δ
= 1.53 (t, 3J = 7.3 Hz, 3 H, CH3CH2), 3.83 (s, 3 H, 4Ј- CH3O),
3J = 6.8 Hz, 2 H, 3-H, 5-H), 8.90 (d, 3J = 6.8 Hz, 2 H, 2-H, 6-
H) ppm. 13C NMR (125 MHz, [D6]DMSO/D2O, 2:1): δ = 27.37
(CH2CH2N), 48.04 (CH2SO3), 56.58 (OCH3), 56.65 (OCH3), 59.45
(CH2N), 110.95 (2Ј-C), 112.71 (5Ј-C), 121.80 (CH=CHPy), 124.34
(6Ј-C), 124.52 (3-C, 5-C), 129.00 (1Ј-C), 142.10 (CH=CHPy),
144.53 (2-C, 6-C), 149.75 (3Ј-C), 151.86 (4Ј-C), 154.51 (4-C) ppm.
C18H21NO5S (363.43): calcd. C 59.49, H 5.82, N 3.85; found C
59.21, H 5.71, N 3.84.
3
3.85 (s, 3 H, 3Ј-CH3O), 4.51 (q, J = 7.3 Hz, 2 H, CH2), 7.08 (d,
3J = 8.3 Hz, 1 H, 5Ј-H), 7.30 (dd, J = 8.3, J = 1.8 Hz, 1 H, 6Ј-
3
4
H), 7.38 (br. s, 1 H, 2Ј-H), 7.40 (d, 3J = 16.5 Hz, 1 H, CH=CHPy),
3
3
Cyclobutane rctt-5a: A solution of dye (E)-2a (41.5 mg, 112 µmol)
in MeCN (1 mL) was kept in a Petri dish (d = 10 cm) for concentra-
tion to give a thin polycrystalline film of the compound. This film
was irradiated with light from a 60 W incandescent lamp (110 h;
distance from the light source 15 cm) to give rctt-5a (quantitative
yield) as a yellowish powder; m.p. 156–159 °C (ref.[9e] 155–158 °C).
7.96 (d, J = 16.5 Hz, 1 H, CH=CHPy), 8.16 (d, J = 6.7 Hz, 2 H,
3-H, 5-H), 8.90 (d, 3J = 6.7 Hz, 2 H, 2-H, 6-H) ppm. 13C NMR
(125 MHz, [D6]DMSO): δ = 15.90 (CH3CH2), 54.96 (CH2N), 55.48
(OCH3), 55.52 (OCH3), 109.95 (2Ј-C), 111.68 (5Ј-C), 120.67
(CH=CHPy), 122.98 (6Ј-C), 123.14 (3-C, 5-C), 127.88 (1Ј-C),
141.00 (CH=CHPy), 143.62 (2-C, 6-C), 148.99 (3Ј-C), 151.07 (4Ј-
C), 153.08 (4-C) ppm.
3
1H NMR (500 MHz, [D6]DMSO): δ = 1.42 (t, J = 7.3 Hz, 6 H, 2
CH3CH2), 3.66 (s, 6 H, 2 4Ј-CH3O), 3.68 (s, 6 H, 2 3Ј-CH3O), 4.50
Dye (E)-2b: Obtained according to the published procedure.[11]
3
3
3
(q, J = 7.3 Hz, 4 H, 2 CH2), 4.81 (dd, J = 9.8, J = 7.5 Hz, 2 H,
1
M.p. 224–226 °C. H NMR (500 MHz, [D6]DMSO): δ = 2.19 (m,
3
3
2 CHAr), 4.90 (dd, J = 9.8, J = 7.5 Hz, 2 H, 2 CHPy), 6.78 (s, 4
2 H, CH2CH2N), 2.86 (m, 2 H, CH2NH3), 3.84 (s, 3 H, 4Ј-CH3O),
3.86 (s, 3 H, 3Ј-CH3O), 4.55 (t, J = 7.0 Hz, 2 H, CH2N), 7.09 (d,
3
H, 2 5Ј-H, 2 6Ј-H), 6.80 (s, 2 H, 2 2Ј-H), 7.95 (d, J = 6.7 Hz, 4 H,
3
2 3-H, 2 5-H), 8.87 (d, J = 6.7 Hz, 4 H, 2 2-H, 2 6-H) ppm. 13C
3
3J = 8.4 Hz, 1 H, 5Ј-H), 7.31 (dd, J = 8.4, J = 1.6 Hz, 1 H, 6Ј-
H), 7.40 (d, 4J = 1.6 Hz, 1 H, 2Ј-H), 7.45 (d, 3J = 16.2 Hz, 1 H,
CH=CHPy), 7.78 (br. s, 3 H, NH3), 8.00 (d, 3J = 16.2 Hz, 1 H,
CH=CHPy), 8.21 (d, 3J = 6.8 Hz, 2 H, 3-H, 5-H), 8.89 (d, 3J =
6.8 Hz, 2 H, 2-H, 6-H) ppm. 13C NMR (125 MHz, [D6]DMSO): δ
= 28.35 (CH2CH2NH3), 35.64 (CH2NH3), 55.56 (2 OCH3), 56.48
3
4
NMR (125 MHz, [D6]DMSO): δ = 16.15 (2 CH3CH2), 45.00 (2
CHAr), 45.97 (2 CHPy), 55.30 (2 4Ј-OCH3), 55.46 (2 CH2N, 2 3Ј-
OCH3), 111.41 (2 5Ј-C), 112.04 (2 2Ј-C), 119.72 (2 6Ј-C), 126.97 (2
3-C, 2 5-C), 129.93 (2 1Ј-C), 143.18 (2 2-C, 2 6-C), 147.62 (2 4Ј-C),
148.42 (2 3Ј-C), 160.05 (2 4-C) ppm.
(CH2N), 110.02 (2Ј-C), 111.72 (5Ј-C), 120.70 (CH=CHPy), 123.15 Cyclobutane rctt-5b: A solution of dye (E)-2b (49.8 mg, 100 µmol)
(6Ј-C), 123.32 (3-C, 5-C), 127.89 (1Ј-C), 141.39 (CH=CHPy),
143.94 (2-C, 6-C), 149.02 (3Ј-C), 151.17 (4Ј-C), 153.48 (4-C) ppm.
in a mixture of MeCN (1 mL) and water (0.2 mL) was kept in a
Petri dish (d = 10 cm) for concentration to give a thin polycrystal-
line film of the compound. This film was irradiated with light from
a 60 W incandescent lamp (230 h; distance from the light source
15 cm). According to 1H NMR analysis, the dye/cyclobutane molar
ratio was 1.2:1 (conversion 64%) after 65 h and 1:4.3 (conversion
90%) after 230 h. The resulting substance was dissolved in a mix-
ture of MeCN (3 mL) and water (0.2 mL), and this solution was
slowly saturated with benzene and dioxane (1:1) at room temp. by
vapour diffusion methods for 2 weeks. The glassy precipitate
formed was decanted and dried in vacuo at 80 °C to give rctt-5b
(hydrate, 44.7 mg; 86%) as a dark-yellow powder; m.p. Ͼ175 °C
Betaine 4: A mixture of 4-picoline (1.36 mL, 14.0 mmol), 1,3-pro-
panesultone (2.60 g, 21.3 mmol) and benzene (7 mL) was heated at
reflux for 30 h. The precipitate formed was filtered, washed with
hot benzene, then with acetone, and recrystallized from EtOH to
give compound 4 (2.40 g, 80%) as a white powder; m.p. 205–
207 °C. 1H NMR (500 MHz, [D6]DMSO): δ = 2.20 (m, 2 H,
CH2CH2N), 2.40 (t, 3J = 7.3 Hz, 2 H, CH2SO3), 2.60 (s, 3 H, CH3),
3
3
4.66 (t, J = 6.7 Hz, 2 H, CH2N), 7.96 (d, J = 6.7 Hz, 2 H, 3-H,
5-H), 8.90 (d, 3J = 6.7 Hz, 2 H, 2-H, 6-H) ppm. C9H13NO3S
(215.27): calcd. C 50.21, H 6.09, N 6.51, S 14.90; found C 50.14,
H 6.10, N 6.54, S 15.13.
1
(decomp.). H NMR (500 MHz, [D6]DMSO): δ = 2.06 (m, 4 H, 2
CH2CH2N), 2.76 (m, 4 H, 2 CH2NH3), 3.65 (s, 6 H, 2 4Ј-CH3O),
3
Dye (E)-2c
3.68 (s, 6 H, 2 3Ј-CH3O), 4.52 (t, J = 7.3 Hz, 4 H, 2 CH2N), 4.82
3
3
3
3
(dd, J = 9.3, J = 7.7 Hz, 2 H, 2 CHAr), 4.90 (dd, J = 9.3, J =
7.7 Hz, 2 H, 2 CHPy), 6.77 (s, 4 H, 2 5Ј-H, 2 6Ј-H), 6.82 (s, 2 H,
Method 1: A mixture of compound (E)-3 (138 mg, 0.57 mmol), 1,3-
propanesultone (105 mg, 0.86 mmol) and anhydrous MeCN (3 mL)
was kept at room temp. in dark for 50 h. The precipitate formed
was filtered, washed with CH2Cl2 (3ϫ5 mL), and dried in air to
give dye (E)-2c (157 mg, 76%) as a yellow powder; m.p. 282–284 °C
(decomp.).
3
2 2Ј-H), 7.69 (br. s, 6 H, 2 NH3), 8.00 (d, J = 6.7 Hz, 4 H, 2 3-H,
2 5-H), 8.84 (d, J = 6.7 Hz, 4 H, 2 2-H, 2 6-H) ppm. 13C NMR
3
(125 MHz, [D6]DMSO): δ = 28.60 (2 CH2CH2NH3), 35.64 (2
CH2NH3), 45.13 (2 CHAr), 46.15 (2 CHPy), 55.38 (2 4Ј-OCH3),
55.54 (2 3Ј-OCH3), 57.05 (2 CH2N), 111.36 (2 5Ј-C), 112.01 (2 2Ј-
C), 119.79 (2 6Ј-C), 127.27 (2 3-C, 2 5-C), 129.93 (2 1Ј-C), 143.56
(2 2-C, 2 6-C), 147.67 (2 4Ј-C), 148.46 (2 3Ј-C), 160.61 (2 4-C) ppm.
C36H48Cl4N4O20·2.5H2O (1043.63): calcd. C 41.43, H 5.12, N 5.37;
found C 41.13, H 4.76, N 5.65.
Method 2: A mixture of compound 4 (0.65 g, 3.0 mmol), veratral-
dehyde (0.50 g, 3.0 mmol), pyrrolidine (1 drop) and abs. EtOH
(5 mL) was heated at reflux in the dark for 4 h. After cooling to
room temp., the precipitate formed was filtered, washed with abs.
EtOH, then with acetone, and dried in air to give dye (E)-2c
(0.25 g) as a yellow powder. The mother solution was cooled to
–10 °C, and the precipitate formed was filtered, washed with cold
abs. EtOH, and dried in air to give an additional amount of dye
Cyclobutane rctt-5c: A solution of dye (E)-2c (50.0 mg, 138 µmol)
in a mixture of MeCN (1 mL) and water (0.5 mL) was kept in a
Petri dish (d = 10 cm) for concentration to give a thin polycrystal-
line film of the compound. This film was irradiated with light from
a 60 W incandescent lamp (115 h; distance from the light source
1
(E)-2c (0.35 g, overall yield 55%); m.p. 284–287 °C (decomp.). H
3
NMR (500 MHz, [D6]DMSO): δ = 2.22 (quint, J = 7.0 Hz, 2 H,
3
CH2CH2N), 2.44 (t, J = 7.0 Hz, 2 H, CH2SO3), 3.83 (s, 3 H, 4Ј- 15 cm). According to 1H NMR analysis, the dye/cyclobutane molar
3
CH3O), 3.85 (s, 3 H, 3Ј-CH3O), 4.62 (t, J = 7.0 Hz, 2 H, CH2N), ratio was 1:2.1 (conversion 82%) after 50 h and 1:4.4 (conversion
2596
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2587–2599

Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
90%) after 115 h. The resulting substance was dissolved in a mix-
ture of MeCN (3 mL) and water (1 mL), and this solution was
slowly saturated with dioxane at room temp. by vapour diffusion
methods for 2 weeks. The glassy precipitate formed was decanted
and dried in vacuo at 80 °C to give rctt-5c (hydrate, 44.9 mg; 85%)
as a dark-yellow powder; m.p. Ͼ190 °C (decomp.). 1H NMR
ods in the dark. The crystals of the complex formed by 2c and
CB[8] were obtained as described above. Single crystals of all com-
pounds were coated with perfluorinated oil and mounted on a
Bruker SMART-CCD diffractometer (graphite-monochromatized
Mo-Kα radiation, λ = 0.71073 Å, ω-scan mode) under a stream of
cold nitrogen [T = 120.0(2) K]. All the calculations were performed
(500 MHz, [D6]DMSO): δ = 2.10 (m, 4 H, 2 CH2CH2N), 2.67 (t, by using the SHELXTL-Plus software.[17] CCDC-748331
3J = 7.4 Hz, 4 H, 2 CH2SO3), 3.66 (s, 6 H, 2 4Ј-CH3O), 3.69 (s, 6 (2b·0.125H2O), -748333 (rctt-5b), and -748332 ({2c}2@CB[8]·
3
3
H, 2 3Ј-CH3O), 4.60 (t, J = 6.7 Hz, 4 H, 2 CH2N), 4.81 (dd, J = 21.25H2O) contain the supplementary crystallographic data for this
3
3
3
10.3, J = 7.8 Hz, 2 H, 2 CHAr), 4.89 (dd, J = 10.3, J = 7.8 Hz,
2 H, 2 CHPy), 6.72 (dd, J = 8.4, J = 1.7 Hz, 2 H, 2 6Ј-H), 6.76
(d, J = 8.4 Hz, 2 H, 2 5Ј-H), 6.86 (d, J = 1.7 Hz, 2 H, 2 2Ј-H),
paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3
4
3
4
3
3
7.94 (d, J = 6.7 Hz, 4 H, 2 3-H, 2 5-H), 8.87 (d, J = 6.7 Hz, 4 H,
2 2-H, 2 6-H) ppm. 13C NMR (125 MHz, [D6]DMSO): δ = 27.21
(2 CH2CH2N), 44.98 (2 CHAr), 46.04 (2 CHPy), 46.55 (2
CH2SO3), 55.32 (2 4Ј-OCH3), 55.57 (2 3Ј-OCH3), 58.59 (2 CH2N),
111.38 (2 5Ј-C), 112.33 (2 2Ј-C), 119.69 (2 6Ј-C), 126.99 (2 3-C, 2
5-C), 129.89 (2 1Ј-C), 143.59 (2 2-C, 2 6-C), 147.66 (2 4Ј-C), 148.40
(2 3Ј-C), 160.22 (2 4-C) ppm. C36H42N2O10S2·2H2O (762.89): calcd.
C 56.68, H 6.08, N 3.67; found C 56.65, H 6.01, N 3.55.
Crystal Data for 2b·0.125H2O: A set of experimental reflections for
2b were measured by using a yellow single crystal of dimensions
0.26ϫ0.14ϫ0.06 mm. Absorption correction was applied by using
the SADABS method. The structure was solved by direct methods
and refined with anisotropic thermal parameters. All hydrogen
atoms were located in the difference Fourier synthesis but for fur-
ther refinement, their geometrically calculated positions were used.
All hydrogen atoms were refined with an isotropic approximation.
The hydrogen atoms of solvation water molecules were not located.
Complex between Dye (E)-2c and CB[8]: A mixture of dye (E)-2c
(5.8 mg, 16.0 µmol) and CB[8]·20H2O (12.1 mg, 7.2 µmol) in water
(15 mL) was heated at reflux in the dark for 1 h, then concentrated
to ca. 5 mL, and cooled to 5 °C. The crystals formed were decanted
and dried in vacuo at 80 °C to give {(E)-2c}2@CB[8] complex
(hydrate, 12.9 mg, 84%) as a yellow powder; m.p. Ͼ400 °C
¯
C18H24.25BrClN2O6.13, M = 482.00, triclinic, space group P1 (No.
2), a = 9.0420(13), b = 14.539(2), c = 16.857(2) Å, α = 71.242(3), β
= 87.881(3), γ = 84.445(3)°, V = 2088.5(5) Å3, Z = 4, µ =
2.133 mm–1 (min/max transmission = 0.3709/0.7544), ρcalcd.
=
1.533 gcm–3, 2θmax = 58.0°, 12607 reflections measured, 9719
unique (Rint = 0.0279), R1 = 0.0648 [6541 reflections with IϾ2σ(I)],
wR2 = 0.1559 (all data), goodness-of-fit on F2 = 1.046, 705 param-
eters, min/max residual electron density = –1.406/1.886 e– Å–3.
(decomp.). IR (KBr):
ν
˜
=
1736 (br., C=O) cm–1.
C48H48N32O16·2C18H21NO5S·5H2O (2146.04): calcd. C 47.01, H
4.70, N 22.19; found C 46.89, H 4.61, N 22.24.
1H NMR Titration: The titration experiments were performed in
D2O/[D3]MeCN (10:1) solutions at (30Ϯ1) °C. The concentration
of CB[7] was approximately 1ϫ10–3 , and the real concentrations
of CB[8] [(0.3–5.2)ϫ10–4 ] were calculated as described pre-
viously.[8] The concentration of 2 and 5 in the solution was grad-
ually increased starting from zero. The highest 2(5)/CB[n] real con-
centration ratios were ca. 3–90. The proton chemical shifts were
measured as a function of the 2(5)/CB[n] ratio. The ∆δH values
were measured with an accuracy of 0.001 ppm. In the case of slow
Crystal Data for rctt-5b: A single crystal of 2b was subjected to
irradiation with visible light from a standard incandescent lamp
(60 W, distance from the light source ca. 10 cm) over a period of
20 h to form rctt-5b. After irradiation, the single crystal became
light-yellow. A set of experimental reflections for rctt-5b was mea-
sured with the same diffractometer. Absorption correction was ap-
plied by using the SADABS method. The structure was solved and
refined as described above. The solvation water molecule was re-
leased during irradiation. C36H48Br2Cl2N4O12, M = 959.50, tri-
1
exchange on the H NMR time scale, the average chemical shifts
¯
clinic, space group P1 (No. 2), a = 8.4303(3), b = 14.7742(6), c =
were calculated taking into account the integral intensities of corre-
sponding signals, and the complex formation constants were then
calculated by using the HYPNMR program.[16]
16.9805(7) Å, α = 71.8470(10), β = 89.1700(10), γ = 88.3270(10)°,
V = 2008.78(14) Å3, Z = 2, µ = 2.217 mm–1 (min/max transmission
= 0.5964/0.8785), ρcalcd. = 1.586 gcm–3, 2θmax = 58.0°, 17722 reflec-
tions measured, 10510 unique (Rint = 0.0382), R1 = 0.0452 [7021
reflections with IϾ2σ(I)], wR2 = 0.1103 (all data), goodness-of-fit
on F2 = 0.951, 697 parameters, min/max residual electron density
= –0.587/1.337 e– Å–3.
Photolysis of Aqueous Solutions: The irradiation of aqueous solu-
tions of free dyes 2a–c (ca. 5ϫ10–5 , V = 3 mL, 1 cm quartz cell)
or their mixtures with CB[n] {approximately (5–10)ϫ10–5  for
CB[7] and (2.5–10)ϫ10–5  for CB[8]} was performed with light
from a 60 W incandescent lamp (distance from the light source
10 cm) for a period of 0–3 h. The course of photolysis was moni-
tored by spectrophotometric methods. For 1H NMR studies, the
D2O/[D3]MeCN (10:1) solutions of free dyes 2a–c (1ϫ10–3 , V =
0.55 mL, standard NMR tube) were irradiated with light from a
60 W incandescent lamp (distance from the light source 15 cm) for
Crystal Data for {2c}2@CB[8]·21.25H2O: Structure {2c}2@CB[8]
was solved by direct methods and refined in the anisotropic
approximation for all non-hydrogen atoms. The hydrogen atoms
were fixed at calculated positions and refined by using the riding
model. The strongest peaks in the residual-electron density map
were assigned to solvation water molecules with full or partial site
occupation factors. Hydrogen atoms of the water molecules were
not located. The difference Fourier map contained many electron
density peaks at distances from other atoms corresponding to
van der Waals contacts. However, structure refinement with ad-
ditional oxygen atoms attributed to these peaks gave unacceptable
values for their thermal parameters. C84H132.50N34O47.25S2, M =
2438.86, monoclinic, space group P21/c (No. 14), a = 14.3170(14),
b = 19.7222(18), c = 19.9897(18) Å, β = 105.533(2)°, V =
5438.2(9) Å3, Z = 2, µ = 0.159 mm–1 (no absorption correction
was applied), ρcalcd. = 1.489 gcm–3, 2θmax = 58.0°, 54587 reflections
1
2–5 h, and then the H NMR spectra were recorded. The aqueous
solutions of mixtures of dyes 2a–c (3.8ϫ10–4 , V = 10 mL, glass
bottle) and CB[n] (1 equiv. of CB[7] or 0.05–0.5 equiv. of CB[8])
were irradiated with light from a 60 W incandescent lamp (distance
from the light source 15 cm) with stirring for 20 h. After the irradi-
ation was finished, an aliquot (2–3 mL) of the solution was concen-
trated in vacuo at room temp., and the solid residue was dissolved
1
in [D6]DMSO to measure H NMR spectrum.
X-ray Crystallography: Crystals of 2b were obtained by slow satura-
tion of an MeCN solution with benzene by vapour diffusion meth-
Eur. J. Org. Chem. 2010, 2587–2599
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2597

S. P. Gromov et al.
FULL PAPER
M. T. Gandolfi, M. Venturi, Acc. Chem. Res. 2001, 34, 445–
455.
measured, 14447 unique (Rint = 0.1301), R1 = 0.1205 [6404 reflec-
tions with IϾ2σ(I)], wR2 = 0.3795 (all data), goodness-of-fit on F2
= 1.101, 850 parameters, min/max residual electron density =
–0.640/0.971 e– Å–3.
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Supporting Information (see footnote on the first page of this arti-
cle): Selected bond lengths and angles for 2b·0.125H2O, rctt-5b, and
{2c}2@CB[8]·21.25H2O (Tables S1–S3).
[7]
[8]
[9]
Acknowledgments
Support from the Russian Foundation for Basic Research, the Rus-
sian Academy of Sciences, the Royal Society (L. G. K.), and the
Engineering and Physical Sciences Research Council (EPSRC) for
a Senior Research Fellowship (J. A. K. H.) is gratefully acknowl-
edged. The authors thank Prof. Vladimir P. Fedin for providing
samples of cucurbit[n]urils and Mr. Pavel S. Loginov for his help
in synthesis.
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Eur. J. Org. Chem. 2010, 2587–2599

Photocontrolled Molecular Assembler Based on Cucurbit[8]uril
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Received: November 18, 2009
Published Online: March 23, 2010
Eur. J. Org. Chem. 2010, 2587–2599
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