Pseudorotaxane complexes between viologen vinylogues and cucurbit[7]uril: New prototype of photocontrolled molecular machine

Article abstract of DOI:10.1016/j.molstruc.2011.01.013

Dibetaines of unsaturated viologen analogues that form supramolecular complexes with cucurbit[7]uril were synthesized. The pseudorotaxane structure and stability of the complexes were established by UV/Vis and ¹H NMR spectroscopy and by X-ray d

Full text of DOI:10.1016/j.molstruc.2011.01.013

Journal of Molecular Structure 989 (2011) 114–121
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Pseudorotaxane complexes between viologen vinylogues and cucurbit[7]uril:
New prototype of photocontrolled molecular machine
Artem I. Vedernikov a, Natalia A. Lobova a, Lyudmila G. Kuz’mina b, Judith A.K. Howard c, Yuri A. Strelenko d,
Michael V. Alfimov a, Sergey P. Gromov a,
⇑
a Photochemistry Centre, Russian Academy of Sciences, ul. Novatorov 7A-1, Moscow 119421, Russian Federation
b N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskiy prosp. 31, Moscow 119991, Russian Federation
c Chemistry Department, Durham University, South Road, Durham DH1 3LE, UK
d N.D. Zelinskiy Institute of Organic Chemistry, Russian Academy of Sciences, Leninskiy prosp. 47, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Dibetaines of unsaturated viologen analogues that form supramolecular complexes with cucurbit[7]uril
were synthesized. The pseudorotaxane structure and stability of the complexes were established by UV/
Vis and 1H NMR spectroscopy and by X-ray diffraction analysis. Complexes of this structure are proto-
types of a light-controlled molecular machine.
Received 22 October 2010
Received in revised form 11 January 2011
Accepted 11 January 2011
Available online 22 January 2011
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Viologen vinylogues
Cucurbit[7]uril
Host–guest complexes
X-ray structures
Light-operated molecular machines
1. Introduction
On exposure of an aqueous solution of a (E)-1b and CB[8] mixture
to light, the reversible E–Z isomerization of the unsaturated guest
The complexing properties of a new class of cavitand molecules,
cucurbit[n]urils (CB[n], n = 5–8, 10), have been intensively studied
in recent years [1–6]. Remarkable is the ability of CB[n] to form sta-
ble complexes in aqueous solutions with positively charged organ-
ic molecules such as ammonium compounds and quaternary salts
of nitrogen-containing heterocycles. Among the potential guest
molecules, of particular interest are positively charged unsaturated
compounds, ammonium derivatives of stilbene and viologen viny-
logues [7–9]. Owing to their ability to undergo photoinduced
changes of the spatial structure in E–Z isomerization and [2 + 2]
photocycloaddition reactions, these molecules can mechanically
move in the CB[n] cavity with simultaneous change in the stability
of complexes; hence, such systems can be used for the design of
light-controlled molecular machines [10–16]. However, this area
still remains poorly explored.
molecule was found to occur to give stable complex (Z)-
1b@CB[8] (Scheme 1), which was characterized by 1H NMR spec-
troscopy and an X-ray diffraction analysis.
The cavity of the smaller CB[7] is better suited for the formation of
1:1 complexes with the E isomers of unsaturated viologen analogues
[3,4,8]. We have also established [18] that structurally related 4-
pyridine-derived styryl dyes (E)-2a–c form pseudorotaxane com-
plexes with CB[7] and CB[8] of different stoichiometry (Scheme 2).
The stability of these complexes is determined by the nature of the
N-substituent on the dye.
This communication describes the synthesis of unsaturated dib-
etaines (E)-3a–d, related to 1, and UV/Vis and 1H NMR spectro-
scopic studies of their complexation with CB[7]. The structures of
supramolecular complexes (E)-3a,b,d@CB[7] were studied by
X-ray diffraction analysis. N,N0-Diethyl-(E)-di(4-pyridinioyl)ethylene
diperchlorate ((E)-4) [19] was used as the model compound to
study the complexation with CB[7].
Recently, we have shown [17] that CB[8] with a relatively large
cavity is able to form stable complexes of different stoichiometry
with diammoniopropyl dipyridylethylene and diquinolylethylene
derivatives 1a,b, in which hydrogen bonds between the guest
ammonium groups and oxygen atoms of the CB[8] portals form.
2. Experimental
2.1. General
⇑
The melting points (uncorrected) were measured in capillaries
on a Mel-Temp II instrument. 1H NMR spectra were recorded on
Corresponding author. Tel.: +7 495 9350116; fax: +7 495 9361255.
E-mail address: spgromov@mail.ru (S.P. Gromov).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.01.013

A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
115
O
N
N
N
N
_
+
+
4 ClO4
NH3
NH3
R
R
+
8
NH3
O
+
+
+
N
N
_
N
+
4 ClO4
N
+
hν
H3N
(for 1b)
R
R
(E)-1: R = H (a), R + R = C4H4 (b)
(Z)-1b@CB[8]
Scheme 1.
O
N
N
N
N
7
O
OMe
OMe
OMe
+
+
R
N
R
N
logK > 3.2 [M-1]
OMe
(E)-2: R = Et + ClO4- (a),
(CH2)3NH3+ + 2 ClO4- (b),
(CH2)3SO3- (c)
(E)-2a-c@CB[7]
Scheme 2.
a Bruker DRX500 spectrometer (500.13 MHz) in D2O and DMSO-d6
at 30 °C using the signal from the solvents as the internal standards
(dH 4.70 and 2.50, respectively). The chemical shifts were measured
with an accuracy of 0.01 ppm and the spin–spin coupling constants
were determined with an accuracy of 0.1 Hz. Absorption spectra
were recorded on a Shimadzu UV–3101PC spectrophotometer in
the range of 200–500 nm (water, HPLC grade, Aldrich), C3,4 = 2 ꢀ
10ꢁ5 M, CCB[7] = 1 ꢀ 10ꢁ3 M, 1-cm quartz cell, room temperature)
with an increment of 1 nm. Emission spectra were measured on
a Shimadzu RF-5301PC spectrofluorimeter in the range of 325–
600 nm (water, C3,4 = 2 ꢀ 10ꢁ5 M, CCB[7] = 1 ꢀ 10ꢁ3 M, 1-cm quartz
cell, room temperature; excitation at 320 nm) with an increment
of 1 nm. Elemental analyses were performed at the Laboratory of
Microanalysis of the A.N. Nesmeyanov Institute of Organoelement
Compounds of the Russian Academy of Sciences (Moscow).
J = 6.9 Hz) ppm. UV/Vis kmax
(
e
/cmꢁ1 Mꢁ1): 322 nm (40.3 ꢀ 103).
Fluorescence kmax: 360 nm. Calcd. for C16H18N2O6S2ꢂ0.5EtOH: C
48.44, H 5.02, N 6.65; found: C 48.72, H 4.65, N 6.69.
2.3. 3,30-[(E)-Ethene-1,2-diylbis(pyridinio-4,1-diyl)]dipropane-1-
sulfonate ((E)-3b)
A mixture of (E)-1,2-di(4-pyridyl)ethylene (91 mg, 0.5 mmol)
and 1,3-propanesultone (183 mg, 1.5 mmol) (Aldrich) was heated
at 140 °C (oil bath) for 40 h. The resulting mass was refluxed with
benzene (ꢃ10 mL) for 2 h, filtered, washed with benzene and ace-
tone, and re-crystallized from water–EtOH (2.7:1 (v/v), 2.8 mL) to
yield 167 mg (78%) of (E)-3b as a pinkish powder; m.p. 359–
360 °C (decomp.). 1H NMR (DMSO-d6) d: 2.56 (m, 4 H, 2 CH2CH2N),
2.94 (m, 4 H, 2 CH2SO3), 4.72 (m, 4 H, 2 CH2N), 7.76 (s, 2 H,
CH = CH), 8.14 (d, 4 H, 2 H(3), 2 H(5), J = 6.7 Hz), 8.76 (d, 4 H, 2
H(2), 2 H(6), J = 6.7 Hz) ppm. UV/Vis kmax
(e
/cmꢁ1 Mꢁ1): 321 nm
363 nm. Calcd. for
2.2. 2,20-[(E)-Ethene-1,2-diylbis(pyridinio-4,1-diyl)]diethanesulfonate
((E)-3a)
(36.1 ꢀ 103).
Fluorescence
kmax:
C
18H22N2O6S2ꢂ1.5H2O: C 47.67, H 5.56, N 6.18; found: C 47.71, H
5.61, N 5.94.
A mixture of (E)-1,2-di(4-pyridyl)ethylene (91 mg, 0.5 mmol)
and sodium 2-bromoethanesulfonate (317 mg, 1.5 mmol) (Aldrich)
in abs. EtOH (3 mL) was refluxed with stirring for 50 h. The insol-
uble substance was filtered, washed with benzene, MeOH, and ace-
tone, and re-crystallized from water–EtOH (2.8:1 (v/v), 2.7 mL) to
yield 128 mg (64%) of (E)-3a as a pinkish powder; m.p. 295–
296 °C (decomp.). 1H NMR (D2O–MeCN-d3 (10:1)) d: 3.64 (m, 4
H, 2 CH2SO3), 5.03 (m, 4 H, 2 CH2N), 7.94 (s, 2 H, CH@CH), 8.30
(d, 4 H, 2 H(3), 2 H(5), J = 6.9 Hz), 8.94 (d, 4 H, H(2), H(6),
2.4. 4,40-[(E)-Ethene-1,2-diylbis(pyridinio-4,1-diyl)]dibutane-1-
sulfonate ((E)-3c)
A mixture of (E)-1,2-di(4-pyridyl)ethylene (91 mg, 0.5 mmol)
and 1,4-butanesultone (204 mg, 1.5 mmol) (Aldrich) was heated
at 140 °C (oil bath) for 40 h. The resulting mass was refluxed with
benzene (ꢃ15 mL) for 2 h, filtered, washed with benzene and

116
A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
acetone, and re-crystallized from water–EtOH (2.5:1 (v/v), 1.4 mL)
to yield 184 mg (81%) (E)-3c as a white powder; m.p. 358–359 °C
(decomp.). 1H NMR (D2O) d: 1.68 (m, 4 H, 2 CH2CH2SO3), 2.04 (m,
4 H, 2 CH2CH2N), 2.85 (m, 4 H, 2 CH2SO3), 4.43 (m, 4 H, 2 CH2N),
7.76 (s, 2 H, CH@CH), 8.14 (d, 4 H, 2 H(3), 2 H(5), J = 6.7 Hz), 8.76
2.6.1. Complex (E)-3a@CB[7] (hydrate)
Complex (E)-3a@CB[7] (hydrate) was obtained as a white pow-
der (yield 53%); m.p. > 350 °C (decomp.). Calcd. for C16H18N2O6-
S2ꢂC42H42N28O14ꢂ11H2O: C 39.59, H 4.70, N 23.88; found: C 39.37,
H 4.12, N 23.66.
(d, 4 H, 2 H(2), 2 H(6), J = 6.7 Hz) ppm. UV/Vis kmax
(
e
/cmꢁ1 Mꢁ1):
: 362 nm. Calcd. for
320 nm (35.6 ꢀ 103). Fluorescence kmax
C20H26N2O6S2ꢂ0.5EtOHꢂH2O: C 50.89, H 6.31, N 5.65; found: C
2.6.2. Complex (E)-3b@CB[7] (hydrate)
50.74, H 6.12, N 5.15.
Complex (E)-3b@CB[7] (hydrate) was obtained as a white pow-
der (yield 52%); m.p. > 355 °C (decomp.). Calcd. for C18H22N2O6-
S2ꢂC42H42N28O14ꢂ12H2O: C 39.91, H 4.91, N 23.27; found: C 39.98,
H 4.14, N 23.29.
2.5. 2,20-[(E)-Ethene-1,2-diylbis(pyridinio-4,1-
diylmethylene)]dibenzenesulfonate ((E)-3d)
A mixture of (E)-1,2-di(4-pyridyl)ethylene (91 mg, 0.5 mmol)
and 3H-2,1-benzoxathiole 1,1-dioxide [20] (255 mg, 1.5 mmol)
was heated at 140 °C (oil bath) for 70 h. After addition of the sec-
ond portion of sultone (85 mg, 0.5 mmol) and toluene (3 mL), the
resulting mixture was refluxed for 100 h. The solvent was evapo-
rated in vacuo and the residue was refluxed with benzene
(ꢃ20 mL) for 0.5 h, filtered, and washed with benzene and acetone
to give a hardly separable mixture of mono- and bisquaternized
products (in ꢃ1.4:1 M ratio, 184 mg) as a yellow-pinkish powder.
(E)-3d: 1H NMR (D2O) d: 6.13 (s, 4 H, 2 CH2), 7.59 (d, 2 H, 2
H(50), J = 7.4 Hz), 7.68 (m, 4 H, 2 H(30), 2 H(40)), 7.81 (s, 2 H,
CH@CH), 8.02 (d, 2 H, 2 H(20), J = 7.3 Hz), 8.15 (d, 4 H, 2 H(3), 2
H(5), J = 6.4 Hz), 8.75 (d, 4 H, 2 H(2), 2 H(6), J = 6.4 Hz).
2.6.3. Complex (E)-3c@CB[7] (hydrate)
Complex (E)-3c@CB[7] (hydrate) was obtained as a white
powder (yield 45%); m.p. > 350 °C (decomp.). Calcd. for C20H26
-
N2O6S2ꢂC42H42N28O14ꢂ14H2O: C 39.83, H 5.18, N 22.47; found: C
39.48, H 4.08, N 22.61.
2.6.4. 1H NMR titration
1H NMR titrations were performed on a Bruker DRX500 spec-
trometer in D2O–MeCN-d3 (10:1, v/v) at 30 °C. In the course of
titration, the concentration of CB[7] was maintained at about
1 ꢀ 10ꢁ3 M and the concentration of (E)-3a–c (or (E)-4) was varied
from 0 to 3 ꢀ 10ꢁ3 M. The variation of the proton chemical shifts of
3a–c (or 4) and CB[7] depending on the 3a–c/CB[7] (or 4/CB[7])
molar ratio was monitored. Because of slow exchange on the 1H
NMR time scale in systems 3a-c/CB[7], the average proton chemi-
cal shifts were calculated taking into account the integral intensi-
ties of the corresponding signals. Some titration curves for systems
3a–c(4)/CB[7] are given in Supplementary data (Fig. S1). The stabil-
ity constants of complexes (E)-3a–c@CB[7] and (E)-4@CB[7] were
calculated using HYPNMR program [21].
2.6. Preparation of complexes between (E)-3a–c and CB[7] (general
procedure)
A solution of (E)-3a–c (8.0
l
mol) and CB[7]ꢂ10H2O (10.6 mg,
7.9
lmol) in water (ꢃ3 mL) was slowly saturated with MeCN by
the vapour diffusion method at room temperature in the dark until
a crystalline precipitate was formed (ꢃ2 weeks). The precipitate
was decanted and dried at 80 °C in vacuo.
Table 1
Summary of crystal data and structure refinement for (E)-3a@CB[7]ꢂ0.5MeCNꢂ0.75MeOHꢂ7H2O, (E)-3b@CB[7]ꢂ8.06H2O, and (E)-3d@CB[7]ꢂ12.5H2O.
Structure
(E)-3a@CB[7]ꢂ0.5MeCNꢂ0.75MeOHꢂ7H2O
59.75H78.5N30.5O27.75S2
1732.15
Colourless; block
120.0(2)
(E)-3b@CB[7]ꢂ8.06H2O
C60H80.13N30O28.06S2
1734.83
Colourless; plate
120.0(2)
Monoclinic
P21/c
(E)-3d@CB[7]ꢂ12.5H2O
C68H89N30O32.5S2
1910.81
Colourless; block
120.0(2)
Monoclinic
P21/c
Empirical formula
Formula weight (g molꢁ1
Colour; shape
Measured temperature (K)
Crystal system
C
)
Monoclinic
P21/n
Space group
Unit cell dimensions (Å, °)
a = 13.6012(7)
b = 33.0413(16)
c = 17.1321(9)
b = 90.944(3)
7698.1(7)
a = 13.7380(19)
b = 22.251(3)
c = 27.184(4)
b = 98.503(3)
8218.6(19)
4
a = 26.882(2)
b = 13.2626(10)
c = 25.650(2)
b = 110.939(3)
8541.0(11)
4
Volume (Å3)
Z
4
Dx (g cmꢁ3
)
1.495
0.171
1.402
0.161
1.486
0.166
l
(mmꢁ1
)
Absorption correction
F(0 0 0)
Not applied
3618
Not applied
3627
Not applied
3996
h range (°)
Completeness to h (%)
2.86–29.00
98.3
1.76–27.00
99.7
1.60–29.00
99.0
h, k, l
ꢁ18 6 h 6 18
ꢁ45 6 k 6 45
ꢁ22 6 l 6 23
64,975
20,109 [R(int) = 0.1655]
7352
–17 6 h 6 13
–21 6 k 6 28
–34 6 l 6 33
40,219
17,914 [R(int) = 0.1244]
5476
–36 6 h 6 32
–18 6 k 6 16
–34 6 l 6 34
70,261
22,479 [R(int) = 0.1714]
8683
Reflections collected
Reflections unique
Unique reflections with I P 2
Number of parameters
Goodness-of-fit on F2
r(I)
1271
0.985
1135
0.934
1225
1.147
Final R indices [I P 2
r
(I)]
R1 = 0.1119, wR2 = 0.2755
R1 = 0.2642, wR2 = 0.3125
1.253, ꢁ0.867
R1 = 0.1255, wR2 = 0.3292
R1 = 0.2946, wR2 = 0.3912
1.112, ꢁ0.559
R1 = 0.1887, wR2 = 0.3963
R1 = 0.3342, wR2 = 0.4492
1.984, ꢁ0.856
R indices (all data)
Residual highest peak and deepest hole (e Åꢁ3
)

A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
117
2.7. X-ray crystallography
3. Results and discussion
Colourless crystals of complexes (E)-3@CB[7] were grown by
slow saturation of an aqueous solution of the equimolar mixture
of dibetaine (E)-3a,b,d (a ꢃ 1.4:1 mixture of mono- and bisquat-
ernized salts in the case of 3d) and cucurbit[7]uril with a mixture
of MeCN and MeOH (ꢃ5:1, v/v) by the vapour diffusion method at
room temperature in the dark. Single crystals of each of the com-
plexes was coated with perfluorinated oil and mounted on a Bruker
3.1. Synthesis
Dibetaine (E)-3a was synthesized by quaternization of (E)-di(4-
pyridyl)ethylene on treatment with sodium bromoethanesulfo-
nate (Scheme 3). Dibetaines (E)-3b,c were obtained by heating
(E)-di(4-pyridyl)ethylene with alkanesultones at 140 °C. During
quaternization, the introduction of one sulfonatoalkyl substituent
considerably hampers the introduction of the second one; there-
fore, the products with extended N-substituents were obtained un-
der rigorous conditions by fusing the reactants together. Dibetaine
(E)-3d was prepared similarly to dibetaines (E)-3b,c; however, the
preparation process of (E)-3d was accompanied by partial sublima-
tion of the sultone; therefore, subsequently the process was carried
out in a high-boiling organic solvent (toluene). The final product
was obtained as a mixture of (E)-3d and the monosubstituted
product (in ꢃ1:1.4 ratio).
SMART CCD diffractometer (graphite monochromatized Mo-K
a
radiation, k = 0.71073 Å,
x-scan mode) under a stream of cooled
nitrogen.
All the structures were solved by direct methods and refined
with full-matrix least-squares on F2 in anisotropic approximation
for all non-hydrogen atoms (except for atoms of disordered frag-
ments of dibetaine molecule in structure (E)-3b@CB[7]ꢂ8.06H2O,
which were refined isotropically). MeCN, MeOH, and/or water sol-
vate molecules were found in the unit cells. The positions of hydro-
gen atoms at carbon atoms were calculated geometrically and then
refined using a riding model. The hydrogen atoms of solvate water
molecules and OH groups of MeOH molecules were not located.
In all the residual electron density maps, many peaks around
the main components, host and guest molecules, were found. The
strongest peaks were assigned to the solvate molecules with whole
or partial site occupation factors. The difference Fourier maps also
contained many weaker electron density peaks at distances from
other atoms corresponding to van der Waals contacts. However,
structure refinement with additional oxygen atoms attributed to
these peaks did not result in any improvement of the refinement
parameters and gave unacceptable values for their thermal param-
eters. Undoubtedly, such high disorder of the solvation shells and
the guest molecules reduced substantially the accuracy of the
resulting parameters.
3.2. UV/Vis and 1H NMR spectroscopy studies
The ability of dibetaine compounds (E)-3a–c and model
compound (E)-4 to form inclusion complexes with CB[7] in
water was studied by spectroscopy. Free 3a–c and 4 show
intensive long-wavelength absorption with kmax = 318–322 nm
(e
= (31.4–40.3) ꢀ 103 cmꢁ1 Mꢁ1
) and slight fluorescence with
kmax = 360–363 nm (e.g., Fig. 1 and 2, curves 1, 3; see also Figs.
S2, S3 in Supplementary data). CB[7] does not contain chromo-
phore groups; therefore, even its concentrated solution
(C = 1 ꢀ 10ꢁ3 M) absorbs weakly above 250 nm and demonstrates
a low-intensity structureless fluorescence at about 330–530 nm,
possibly due to the presence of impurities [18]. Upon mixing 3a–
c, 4 with excess CB[7], the intensity of the long-wavelength
absorption decreases (e.g., Fig. 1 and 2, curves 2), probably as a re-
sult of violation of the co-planarity of their chromophores in the
complex (see also Section 3.3.). The changes that take place in
The calculations of the structures were performed using the
SHELXTL–Plus software package [22]. Crystal data and data collec-
tions and refinement details are summarized in Table 1.
_
2
6
3
5
+
O3S
N
BrCH2CH2SO3Na
EtOH
_
+
N
SO3
(E)-3a
O
n
O
S
_
O3S
O
+
N
+
N
N
_
n
n
N
SO3
(E)-3b (n = 1),
(E)-3c (n = 2)
O
O
S
O
_
+
N
SO3
_
+
O3S
N
(E)-3d
N
_
+
+
O3S
N
Scheme 3.

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A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
fluorescence is somewhat built-up (Fig. 2, curve 4). This difference
in the behaviours of dibetaines and the model compound may be
attributed to the effect of the closely spaced anionic groups in
the excited state of molecules (E)-3a–c.
The 1H NMR study of the complexation of (E)-3a–c and (E)-4
with CB[7] provided more information. Mixing components in
equimolar amounts gave rise to a second set of proton signals from
both dibetaines 3a–c and CB[7], most of the new signals being
shifted upfield as compared with the proton signals of the starting
compounds (e.g., Fig. 3; see also Figs. S4, S5 in Supplementary
data). This spectral pattern indicates the formation of inclusion
complexes (E)-3a–c@CB[7], which undergo exchange slow on the
1H NMR (500 MHz) time scale with the free components. The
presence of signals from free components in the equimolar mixture
implies a lower stability constant of the bimolecular complexes
3a–c@CB[7] compared to the complexes of compounds 1a,b
with CB[8] (log K1:1 P 4.6 [Mꢁ1]) [17]. Among the signals in
the aromatic region, the most pronounced upfield shift
Fig. 1. (1, 2) Absorption and (3, 4) fluorescence spectra of (1, 3) (E)-3b
(C = 2 ꢀ 10ꢁ5 M) and (2, 4) its mixture with CB[7] (C = 1 ꢀ 10ꢁ3 M) in water (1-cm
quartz cell, room temperature).
(DdH = 0.90–1.03 ppm) was found for the ethylene protons of 3a–
c. This means that the walls of CB[7] shield these protons to the
greatest extent; hence, in the complexes, the cavitand is arranged
mainly above the central area of the dibetaine molecule. As the dis-
tance from the centre of molecule 3a–c increases, the protons of its
conjugated fragment become successively less shielded, so that the
signals of peripheral CH2SOꢁ groups of N-substituents show a
3
downfield shift of 0.16–0.20 ppm with respect to free (E)-3a–c,
apparently due to the deshielding effect of the carbonyl groups
of the host molecule portals. This order of variation of the
DdH
magnitude and sign attests to a pseudorotaxane structure of com-
plexes 3a–c@CB[7], in which the guest molecule runs through the
macrocycle cavity, its terminal fragments being outside the CB[7]
cavity (Scheme 4). Particularly this structure of the inclusion com-
plexes was obtained by X-ray diffraction analysis (see Section 3.3).
According to 1H NMR data, the model compound (E)-4 and
CB[7] also form an inclusion complex having a pseudorotaxane
structure (Scheme 3). Unlike systems 3a–c/CB[7], the system 4/
CB[7] exhibited one set of signals for each component present at
any ratio (Fig. 4), indicating fast exchange on the 1H NMR time
scale. Apparently, the presence of negatively charged sulfonate
groups in 3a–c hampers the decomposition of supramolecular
complexes 3a–c@CB[7] into the starting components, thus increas-
ing their kinetic stability.
Fig. 2. (1, 2) Absorption and (3, 4) fluorescence spectra of (1, 3) (E)-4
(C = 2 ꢀ 10ꢁ5 M) and (2, 4) its mixture with CB[7] (C = 1 ꢀ 10ꢁ3 M) in water (1-cm
quartz cell, room temperature).
the fluorescence spectra of 3a–c and 4 upon mixing with CB[7] are
different. Fluorescence of 3a–c and CB[7] mixtures somewhat de-
creases compared to the fluorescence of free dibetaines (e.g.,
Fig. 1, curve 4), which is also indicative of violation of the conjuga-
tion in the chromophore fragment of these compounds upon the
formation of complexes. Conversely, on mixing 4 and CB[7],
Fig. 3. Fragments of 1H NMR spectra (500 MHz) of (a) (E)-3b, (b) CB[7] (C = 1 ꢀ 10ꢁ3 M) and (c) their 1:1 mixture in D2O–MeCN-d3 (10:1, v/v), 30 °C.

A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
119
_
_
O3S
O3S
+
CB[7]
+
N
N
+
+
N
_
n
N
_
n
logK = 2.6-3.5 [M-1]
(slow)
n
SO3
n
SO3
(E)-3a-c (n = 0-2)
(E)-3a-c@CB[7]
_
2 ClO4
_
2 ClO4
+
Me
N
CB[7]
+
+
N
Me
Me
N
+
N
Me
logK = 5.1 [M-1]
(fast)
(E)-4
(E)-4@CB[7]
Scheme 4.
The stability constants of the complexes formed by dibetaines
(E)-3a–c with CB[7] and also by model compound (E)-4 with
CB[7] were determined by 1H NMR titration. The obtained depen-
dences of the variation of proton chemical shifts of 3a–c (or 4) and
the low-field signals of CB[7] most sensitive to complexation on
the change in the component ratio corresponded in all cases to
1:1 stoichiometry of complexation (Scheme 4). The determined
stability constants for the complexes 3a@CB[7], 3b@CB[7], and
3c@CB[7] were log K = 3.5 0.2, 2.6 0.2, and 2.7 0.2 [Mꢁ1],
respectively. Thus, a change from sulfonatoethyl to longer N-sub-
stituent results in a decrease in the stability of inclusion com-
plexes. This may be a consequence of decrease in the effective
positive charge on the dipyridylethylene fragment of molecule
3b,c caused by spatial proximity of covalently bound anionic
groups, which weakens the ion–dipole interaction of the dipyridyl-
ethylene fragment of guest molecule with the electron-donating
Fig. 4. Fragments of 1H NMR spectra (500 MHz) of (a) (E)-4, (b) CB[7] (C = 1 ꢀ 10ꢁ3 M) and their (c) 2:1 and (d) 1:1 mixtures in D2O–MeCN-d3 (10:1, v/v), 30 °C.

120
A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
cavity of the host molecule. Note that the betaine styryl dye (E)-2c
forms a 1:1 complex with CB[7] having a comparable stability
(log K = 3.2 [Mꢁ1]) [18].
log K ꢄ 5–6 [Mꢁ1], see, for example, [23–28]). That is, by varying
the N-substituent length and the nature of its terminal functional
group, one can tune the binding strength of the guest molecule
with the cavitand.
Complexes (E)-3a–c@CB[7] were obtained as solids by precipi-
tation from an aqueous solution of an equimolar mixture of the
components, and their stoichiometry was confirmed by elemental
analysis data.
The stability of complex (E)-4@CB[7], log K = 5.1 0.2 [Mꢁ1],
was more than an order of magnitude higher than those of the
complexes of dibetaines (E)-3a–c and comparable with the stabil-
ities of analogous complexes (E)-1a,b@CB[8] [17] or most com-
plexes of viologen derivatives with CB[7] (in aqueous solutions,
(a)
(b)
(c)
Fig. 5. Structures of (a) (E)-3a@CB[7]ꢂ0.5MeCNꢂ0.75MeOHꢂ7H2O, (b) (E)-3b@CB[7]ꢂ8.06H2O, and (c) (E)-3d@CB[7]ꢂ12.5H2O. All non-hydrogen atoms of guest molecules and
oxygen atoms of CB[7] are shown at 30% probability of their thermal anisotropic displacement parameters (except for most atoms of 3b). Molecules 3a and 3b are disordered
over two positions; the minor conformers are drawn with hollow lines. Hydrogen atoms and solvate molecules are not shown for clarity.

A.I. Vedernikov et al. / Journal of Molecular Structure 989 (2011) 114–121
121
3.3. X-ray diffraction studies
substituents. The use of the anionic groups provided generally
electrically neutral guest species, which promoted the formation
of the pseudorotaxane structure of their complexes with CB[7] as
a result of repulsion of anionic groups and carbonyl oxygen atoms
of the host molecular portals bearing a partial negative charge. The
spatial structure of the supramolecular cucurbituril complexes
with viologen vinylogues was established for the first time, and
the pseudorotaxane structures were confirmed. The self-assembly
features found for the unsaturated viologen analogues and cucurb-
iturils can be used for the design of photocontrolled molecular
machines.
The structures of complexes (E)-3a,b,d@CB[7] were determined
by an X-ray diffraction analysis; Fig. 5 shows the structures of their
main components. The relatively poor accuracy of the resultant
geometric parameters caused by the pronounced disorder of the
solvation shell and guest molecules only allows us to consider gen-
eral conformational characteristics of the components and their
mutual arrangement in the complex.
All complexes have 1:1 stoichiometry and the structure with
the dibetaine molecule running through CB[7]. For this arrange-
ment of the components, only the ethylene group and one pyridine
residue of molecule 3 are located inside the host cavity. The other
fragments of 3 are located on both sides of the CB[7] portals thus
forming a non-symmetrical pseudorotaxane structure. The portals
of the CB[7] molecule are distorted toward ovals where the longest
diagonal distances between the oxygen atoms, O(1),. . .,O(7),
O(8),. . .,O(14), vary in the range of 7.25(1)–8.99(1) Å, respectively.
Apparently, this shape of the portals provides a better fit of the
guest molecule to the CB[7] cavity. In the crystals, the methanol
and water solvate molecules are located near the oxygen atoms
of the CB[7] portals and the sulfonate groups of 3, being apparently
multiply hydrogen bonded to them.
The conjugated fragment and one sulfonatoethyl substituent of
molecule (E)-3a are disordered over two positions with the ratio of
occupancies 0.70:0.30. In both conformers, the dipyridylethylene
fragment of 3a has a considerable deviation from the ideal planar
structure: the dihedral angles between the pyridine rings in the
major and minor conformers are 43° and 23°, respectively. This
geometry of the conjugated fragment of the guest molecule may
result from steric interactions of the disordered pyridine atoms
with the O(1),. . .,O(7) oxygen atoms of the host molecule portal.
The CH2CH2S(1)O3 substituent at the pyridine N(10)C5 residue
shielded by the CB[7] portals and walls has a transoid conforma-
tion and, hence, forms a solvent-separated ion pair with the pyrid-
inium cation (the S(1). . .N(10) distance is 4.04(1) Å). Conversely,
the sulfonate group of the second, disordered N-substituent is
located closely to the pyridine residue and forms a contact ion pair,
the S(2). . .N(20) and S(3). . .N(200) distances being 3.28(1) and
3.23(3) Å.
Acknowledgements
Support from the Russian Foundation for Basic Research, the
Russian Academy of Sciences, the Royal Society (L.G.K.), and the
EPSRC for a Senior Research Fellowship (J.A.K.H.) is gratefully
acknowledged. Authors thank Prof. V.P. Fedin for providing sample
of cucurbit[7]uril.
Appendix A. Supplementary material
CCDC-640892 ((E)-3a@CB[7]ꢂ0.5MeCNꢂ0.75MeOHꢂ7H2O), ꢁ796959
((E)-3b@CB[7]ꢂ8.06H2O), and -796960 ((E)-3d@CB[7]ꢂ12.5H2O) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax:+44 1223 336033).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2011.01.013.
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4. Conclusions
Thus, we demonstrated the preparation of inclusion complexes,
stable in solution and in the solid phase, between cucurbit[7]uril
and viologen vinylogue dibetaines containing N-sulfonatoalkyl