Studies on [3]pseudorotaxane formation from a bis-azacrown derivative as host and imidazolium ion-derivatives as guest

Article abstract of DOI:10.1039/c0ob01106a

A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest molecules in non-polar solvents through hydrogen-bonded adduct f

Full text of DOI:10.1039/c0ob01106a

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PAPER
Studies on [3]pseudorotaxane formation from a bis-azacrown derivative as
host and imidazolium ion-derivatives as guest†
Amal Kumar Mandal, Moorthy Suresh and Amitava Das*
Received 2nd December 2010, Accepted 1st March 2011
DOI: 10.1039/c0ob01106a
A new host molecule, having two azacrown derivatives bridged by luminescent naphthalene diimide
functionality, is found to form a [3]pseudorotaxane derivative with imidazolim ion-based guest
molecules in non-polar solvents through hydrogen-bonded adduct formation. Depending upon the
length of the covalent linker that links the imidazolium ion and the luminescent naphthalene fragment
in the guests, the [3]pseudorotaxane adducts adopt different conformation or orientation with varying
p–p/donor–acceptor interaction. The mechanism for the naphthalene-based luminescence quenching
by NDI fragment on adduct formation was found to be a combination of static, as well as dynamic with
static quenching as the dominant one.
Studies on the influences that different structural parameters
and nonbonding interactions play in achieving a supramolec-
ular assembly comprises one of the most fascinating areas of
contemporary research.1 The consequence of such studies has
more significance when it is possible to probe the effect of
the variation(s) in structure of the host or guest fragment in
adopting or stabilizing a specific conformation in the host–guest
noncovalent complex.2c Such studies using tailor-made host and
guest molecules with predicted spatial orientation or topology
are key in developing a deeper insight into understanding more
complicated supramolecular structures where individual molecu-
lar components are held by various non-bonded interactions.2 The
importance of such noncovalent interactions in supramolecular
assemblies in biological systems and bioinspired material is also
well documented. Any change in molecular conformation or
orientation of the individual component in such an assembly
is known to influence greatly the activity or property of such
a noncovalent complex.3 Thus, orientation–activity correlation
in designed supramolecular assemblies is expected to help in
understanding the change in activity pattern of bioactive frag-
ments like peptides, proteins etc. with conformational change(s)
in various natural/biological assemblies; where relative stability
of different conformations is the manifestation of the change(s)
in any or a combination of these non-bonded interactions.4
For such purpose-build supramolecular assemblies, the design
aspect involves various non-covalent interactions, like ion–dipole
interaction,5 hydrogen bonding,6 p-stacking,7 and charge transfer
interaction.8 More importantly, appropriate derivatization of the
host and guest fragments with a judiciously chosen photoactive
donor or acceptor fragment allows the desired handle to probe
the supramolecular complex formation. However, such examples
are not very common in the literature.9,10 Recently Rebek et al.
have shown that intermolecular resonance energy transfer (RET)
between pyrene and perylene moieties occur when monofunction-
alized pyragallol or resorcinol arene moieties form self assembled
hexameric capsule like architecture. It has been shown that the
formation of such self-assembled structures is a random process
and one out of many conformers and assemblies could show
the RET process.9a,9b In one of our recent reports we have
demonstrated that for a donor–acceptor assembly, the resonance
energy transfer process and thereby the new optical response
can further be used to probe the folding–unfolding movement
in a definite self-assembled system; where p-stacking interaction
plays an important role.10 Iverson has shown that a p-stacking
interaction can be utilized in achieving a folded conformation in
solution for a certain aedamer,11 where the efficiency of the p-
stacking interactions and the consequential optical responses are
dependent on the length and flexibility of the spacer linking the
two aromatic fragments involved in the p-stacking interaction.
Wilson et al. recently identified the specific p-stacking pair among
the nine combination of donors and acceptors grafted on a
macromolecular backbone. More importantly, they have shown
that the efficiency of the p-stacked assembly could be probed based
on the studies of static and dynamic quenching.8b
We could demonstrate through static and dynamic quenching
studies that the p-stacking interaction efficiency and thus the
donor (naphthalene)–acceptor (NDI) is dependant on the spacer
that links the imidizolium ion and the naphthalene unit in
the guest moiety. The acceptor property of the NDI-fragment
was ascertained from its relatively lower reduction potential as
compared to the naphthalene moiety.13,11b The complex formation,
i.e., the [3]pseudorotaxane formation between H and G1 or G2
Central Salt & Marine Chemicals Research Institute (CSIR), Bhavna-
gar: 364002, Gujarat, India. E-mail: amitava@csmcri.org; Fax: +91 278
2567562; Tel: +91 278 2567760 [672]
† Electronic supplementary information (ESI) available: 1H NMR, 13C
NMR, and ESI-MS characterization. See DOI: 10.1039/c0ob01106a
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and ESI-MS. Analytical and spectroscopic data matched well to
ascertain the structure proposed for the respective intermediate
and final host (H)/guest (G) compounds, as well as the desired
purity.
As mentioned earlier, 1,3-disubstituted imidazolium salts are
known to form an inclusion complex with DB24C8 or its
derivatives through intermolecular hydrogen-bond formation as
demonstrated by different research groups.12 In 1,3-disubstituted
imidazolium salts, all protons on the imidazolium ring are quite
acidic, as the positive charge is delocalized over the entire
imidazolium ring. The acidic hydrogen atoms participate in
hydrogen-bond formation with the lone pair of electrons of the
oxygen/nitrogen atoms on the azacrown moiety and this accounts
for the stability of the adduct formed. A mass spectrometry study
confirmed the formation of such a hydrogen bonded complex.
Electrospray ionisation mass spectroscopy (ESI-Ms) is used to
“fish” loosely bonded supramolecular complexes, obtained by
mixing one equivalent of the host molecule (H) with 2.5 mole
equivalent of the respective guest molecule (G1 or G2) in CH2Cl2
solution. The ESI-mass spectra in the positive ion mode showed
m/z peaks at 1785.11 and 1735.80, respectively for use of G1 and
G2 as the guest fragment. m/z peaks at 1785.11 corresponds to
[H.2G1 + Na+] and thus confirms the formation of a 1 : 2 complex
between H and G1; while for m/z peaks at 1735.80 correspond to a
similar 1 : 2 complexation and confirmed formation of the adduct
Fig. 1 Structures of host and guest components.
1
(Fig. 1), was characterised by H-NMR, ESI-Ms, electronic and
fluorescence spectroscopic studies.
The methodology that was adopted for the synthesis of the
azacrown derivative (H) is shown in Scheme 1. Alkylation of 1,2-
dihydroxy benzene was achieved with reasonable yield by reaction
with 2-[2-(2-chloroethoxy)-ethoxy]-ethanol in a suspension of
K2CO3 in DMF (dry) as solvent.
[H.2G2 - PF6 ]+.
-
The complexation of H with G1 or G2 was studied in detail
by 1H-NMR spectra in CD2Cl2 at 25 ◦C. Hydrogen bonded
adduct formation between H and G1 or G2 is expected to be
more efficient in a relatively less polar solvent. For solvents with
higher polarity, the efficient solvation of the cationic imidizolium
ion could compete with the H-bonded adduct formation between
the cationic guest (G1 or G2) and the azacrown ether-based host
molecule. Experimental studies also revealed that the host (H) and
guest component (G1 or G2) in the hydrogen-bonded adduct H.2G1
or H.2G2 dethreads in the presence of polar solvents like methanol
Scheme 1 Synthesis of H. Reagents and conditions: (a) Cl(CH2O)3H,
K2CO3, KI, DMF, 90 ◦C (b) TsCl, NaOH, THF/H2O, 0 ◦C - RT. (c)
K2CO3, KI, H2N(CH2)2NHBoc, CH3CN, 81 ◦C. (d) HCl, Et2O-DCM,
1
or CD3OD. We recorded H-NMR spectra for H in the absence
RT. (e) 1,4,5,8-Naphthalene dianhydride, CH3CN, 81 ◦
C
and the presence of G1 (Fig. 2A) and G2 (Fig. 2B) in CD2Cl2.
Previous reports on inclusion complex formation between
crown ether derivatives and imidizolium ion suggest three possible
modes of interaction. The most prominent one is the hydrogen
bonding interaction between OCrown and acidic C–H proton of
imidazolium ion ({C–H}Imidazolium) for [{C–H}Imidazolium ◊ ◊ ◊ OCrown]-
interaction. p–p stacking interactions between the electron poor
imidazolium ring and aryl groups of the crown ether-based
host is the second one which is expected to contribute to the
stability of the adduct formation. The possibility of such an
interaction for an analogous system was reported earlier.12a,d Apart
from H-bonding and p–p stacking interactions, induced dipole–
dipole interaction between imidizolium ion and OCrown having
-d charge could also contribute to the overall stability of the
adduct formation; such a proposition was made independently by
Schmitzer et al. and Pursiainen et al.12a,d,15 However, this induced
dipole–dipole interaction is expected to be weaker as compared
to two previous modes of interaction discussed. All these reports
have unambiguously shown that an interwoven complex formation
takes place between the crown ether-based host molecule and
imidizolium ion derivative(s) as guest through detailed 1H-NMR
studies.
Chromatographic purification yielded the bis hydroxy interme-
diate (yield: 53.3%), which was further converted to the corre-
sponding bis tosylate derivative (1; yield: 78%). The intermediate
product (1) was allowed to react with N-Boc-ethyldiamine to
give the desired compound 2.14 Purification of 2 was achieved
by gravity chromatography and the pure protected form of the
aza-macrocycle was isolated in 57.64% yield. Finally deprotection
of the N-Boc-derivative resulted in the desired amine derivative
3, which on treatment with 1,4,5,8-naphthalenedianhydride in
acetonitrile afforded the final product H in 40% yield after the
necessary purification by column chromatography.
The preparation of imidazolium cationic salts G1 and G2 was
done mainly in two steps. The reaction of the 1-methylimidazole
with the respective bromoalkyl derivative (2-bromomethyl naph-
thalene for G1 and 2-(4-bromobutoxy)naphthalene for G2) in
toluene resulted in the bromide salt of G1 and G2; while the desired
-
and corresponding PF6 salt was isolated by anion exchange in
aqueous medium.
All compounds have been characterised by elemental analysis
and various spectroscopic methods like, 1H-NMR, 13C-NMR
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In the case of using G2 as the guest fragment the pattern
of shifts for the individual hydrogen atoms of the H and G2
fragments on adduct formation (H.2G2) was much different. An
appreciable downfield shift for the signal of H15 was observed;
while little upfield shift for other imidazolium protons (H12, H13)
was observed. This presumably suggests a orientation for the
imadazolium ring that allows a relatively stronger H-bonding for
H15 as compared to H12 and H13, as well as a weak p–p interaction
involving H12 and H13 and the phenyl ring of H. Thus two opposing
influences operational for H12 and H13, namely H-bonding and p–
p interaction, are perhaps responsible for small but distinct upfield
shifts for these two protons. For NDI hydrogen atoms (Hh), as well
as other protons (barring H6) of the two naphthalene moieties
of G2, distinct upfield shifts were observed. These suggest a p–
p stacking interaction involving an NDI fragment and GNaphthalene
moieties. Little downfield shift for H6 suggests that it oriented in
the deshielding zone of the NDI fragment. Such an observation
is reported by Iverson et al. based on 1H NMR, as well as
detailed electrostatic surface potential studies.11a,c Based on the
differences in the observed chemicals shifts for the two adducts,
H.2G1 and H.2G2, and the associated modes of interaction, two
different interaction schemes may be proposed and schematic
representation of such interactions are shown in Fig. 3 and 4,
respectively. In both cases, i.e. for H.2G1 and H.2G2, down field
shifts for -N–CH3 protons of the imidazolium unit (Hxi for G1
and H14 for G2) were observed, when compared with free guest
molecules.†
Fig. 2 (A) Partial H-NMR spectra recorded in CD2Cl2 at 25 ◦C of (a)
1
5.43 mM H; (b) in presence of 10.89 mM G1 and (c) in the presence of
10.89 mM of G1 and 5.43 mM H. (B) Partial 1H-NMR spectra recorded
in CD2Cl2 at 25 ◦C of (a) 4.68 mM H; (b) in presence of 9.38 mM G2 and
(c) in the presence of 9.38 mM G2 and 4.68 mM H.
The nature of the shifts in the 1H-NMR spectra for the
two major modes of interaction, namely H-bonding and p–p
stacking interactions are expected to be quite different. One would
expect a down field shift for hydrogen atom(s) involved in H-
bonding interaction(s). For p–p stacking/arene donor–acceptor
interactions, upfield or down field shifts for hydrogen atoms of
aromatic/arene moiety(ies) could be observed depending upon
the nature and degree of shielding influence(s) that it experience(s)
due to its specific orientation with respect to the other interacting
p-system.11
Fig. 3 Schematic presentation of the probable orientation of the H and
G1 in the [3]pseudorotaxane H.2G1 in CH2Cl2.
1
In the present study, we have recorded the H-NMR spectra
for host molecule (H) in the absence and presence of two mole
equivalent of the respective guest molecule (G1 or G2) (Fig. 2A and
2B) – a condition that allows formation of the 1 : 2 adduct between
H and G1 or G2, i.e., H.2G1 or H.2G2 and this was evident from
the mass spectral results.†
1
A comparison of the H-NMR spectra for H.2G1 (Fig. 2A)
with those of free H and G1 fragments revealed that the signals for
hydrogen atoms of the arene units of the crown ether moiety were
upfield shifted; while those for three imidazolium ion (Hix, Hx and
Hxii) were downfield shifted. Though small, distinct upfield shifts
for the naphthalene protons were observed on adduct formation.
Downfield shifts for the imidazolium ion supports adduct
formation (H.2G1) through H-bond formation involving the [{C–
H}Imidazolium ◊ ◊ ◊ O/NCrown]-interaction. Upfield shifts for the protons
of the naphthyl moiety of G1 and two phenyl rings of H, suggests
a p–p interaction; observed dH for H was 8.689 ppm; while that
in the hydrogen bonded adduct (i.e. for H.2G1) was 8.679 ppm.
However, this upfield shift for the protons of the NDI unit is not
very significant and this suggests a weak p–p stacking interaction.
Fig. 4 Schematic presentation of the probable orientation of the H and
G2 in the [3]pseudorotaxane H.2G2 in CH2Cl2.
However, it is worth mentioning here that the extent of shifts
for the p–p interactions are much smaller than those are usually
observed for strongly interacting p–p donor–acceptor systems in
highly polar solvents.8b,c,9 This is understandable as the present
study was carried out in a weakly polar solvent medium like
CH2Cl2 to favour the interwoven complex formation. Further sup-
port for the weaker p–p stacking interaction came from the results
of the 2D-NOESY spectra for H.2G1 and H.2G2.† For H.2G2
cross peaks were observed for imidazolium protons (H12,13,15) and
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crown ether protons (Hc, Hf). Analogously, for H.2G1 cross peaks
were observed for imidazolium protons (HIX, X, XII) and crown ether
protons (Hc, Hf). These confirm the hydrogen bond interaction
through space coupling. However, no cross peaks were observed
between naphthalene and naphthalenediimide which indicates that
˚
these two units are too far away (>5 A) for any significant p–
p stacking interaction. This result also supports our results on
steady-state absorption spectral data where no charge transfer
band was observed.
Thus, the above results revealed that two different linkers that
bind the imidazolium ring to the naphthyl moiety in G1 and
G2 play an important role in the binding process and thus the
relative conformation adopted by the two guests in the respective
adducts, i.e. H.2G1 and H.2G2, respectively. More importantly, 1H
NMR studies revealed an apparent perpendicular orientation of
the imidazolium moiety of G1 in the azacrown cavity of H.2G1;
while this seemed to be different for G2 in H.2G2. The possibility
of such an orientation for the imidizolium ion is confirmed
by Rissianen and Pursiainen for analogous inclusion complex
formation between imidazolium ion and dibenzo 18-crown-6.12a
The absorption and fluorescence spectra of G1 and G2 were
recorded in CH2Cl2 at room temperature. The absorption spec-
trum of G1 is dominated by the characteristic absorption band of
the naphthalene moiety at 276 nm and a more intense band at
shorter wavelength. On excitation at 276 nm, an emission band
appeared at 336 nm. For G2, absorption and emission bands
appeared at 273 and 348 nm, respectively.
Fig. 5 (a) Absorption (solid line) and fluorescence (dashed line) spectra
of G1 (red) and H (blue); (b) Absorption (solid line) and fluorescence
(dashed line) spectra of G2 (red) and H (blue) in CH2Cl2 at 25 ◦C.
A strong absorption band for H was observed at 380 nm along
with a weaker band at 360 nm. The absorption band at 380 nm
was attributed to the S0–S1 and/or S0–S2 transition associated with
the NDI unit. The absorption and emission characteristics of the
three molecules are shown in Table 1 and normalized spectra for
these units are shown in Fig. 5. Electronic spectra for H and H
in the presence of varying Gx (x = 1 or 2) were recorded. Even in
the presence of 2.25 mole equivalent of Gx in CH2Cl2 (a condition
where H.2Gx adducts exist predominantly), neither any shift of the
respective absorption band of the individual component, nor any
new absorption band was observed. This nullifies the possibility of
the formation of any donor–acceptor type charge transfer complex
between acceptor NDI-based host and donor naphthalene-based
guest fragments. This agrees well with the results of the 1H-NMR
spectra, which predicted a weaker p–p interaction between the two
chromophores.
Fig. 6 Luminescence quenching of (a) G1 (6.76 ¥10-6 M) and (b) G2
(6.96 ¥ 10-6 M) observed with increasing [H]. The arrow highlights the
effect of increasing concentration of H.
G2) were plotted against [H]. The values for I0/I with varying [H]
were plotted using the standard Stern–Volmer relationship, which
is shown in expression 1.
⎛
⎜
⎜
⎞
⎟
⎟
⎟
⎟
⎠
kq
I0
I
⎡
⎤
⎡
⎤
=1+
C
=1+ KD CQ
(1)
Q
⎢
⎥
⎢
⎥
⎦
⎜
⎜
⎝
⎣
⎦
⎣
K + k
e
d
Where Kq, Ke and Kd are the rate of quenching, emission
and deactivation respectively. KD is the Stern–Volmer quenching
constant for collisional deactivation and CQ is the concentration
of quencher. Plots of I0/I against varying quencher (H) concen-
tration were not linear.† An independent plot of I0/I for G1
and G2, respectively, against increasing [H] showed an upward
curvature. This tends to suggest that both static and dynamic
quenching were operational at the same time. The occurrence of
dynamic quenching can also be recognised by measurement of the
fluorescence life time of G1 and G2 with increasing concentration
of H.16a
Steady state fluorescence spectra recorded for G1 or G2 with
increasing [H] revealed a steady decrease of emission intensity
of the respective molecules (Fig 6). The quenching ratio I0/I,
(where I0 and I are the emission intensity in the absence and in the
presence of H respectively) for respective guest molecules (G1 or
Table 1 Absorption and fluorescence spectral details observed for H, G1
The values of static quenching constants for the two respective
systems were determined from the initial linear segment of the
Stern–Volmer plot for the lowest concentration of the quencher
(H) and are shown in Table 2. The contribution to quenching
through a dynamic (collisional) mechanism was determined from
and G2 in CH2Cl2 at 25 ◦
C
Electronic spectral
parameters
Fluorescence spectral
parameters
lmax
emax/dm3 mol-1 cm-1
lmax
t/ns
x
x
x
x
the plot of t0 /t (where t0 and t are the life time of Gx (x is 1
or 2) in the absence and presence of H, respectively) against [H]
(Fig. 7) and quenching constants for the respective guest molecules
were evaluated and are shown in Table 2.
H
G1
G2
380
276
273
16352
5938
3747
412
336
348
5.37
10.43
5.11
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Table 2 Static and dynamic quenching constant values for H.2G1 and
H.2G2, along with the formation constant of the ground state host–guest
complexes
Table 3 Values of static quenching constants for different excitation
wavelengths for H.2G1 and H.2G2
l (nm)
Static quenching constants
R2
Dynamic quenching
process
Formation
constant
H.2G1
H.2G2
274
290
314
274
290
314
2.3 ¥ 104
1.86 ¥ 104
1.79 ¥ 104
6.81 ¥ 104
6.27 ¥ 104
5.1 ¥ 104
0.99
0.97
0.99
0.99
0.98
0.97
Static quenching process
Static quenching
constant/M-1
Dynamic quenching
constant/M-1
R2
R2
Kf/M-1
H.2G1 2.3 ¥ 104
H.2G2 6.81 ¥ 104
0.99 1.97 ¥ 102
0.99 3.56 ¥ 103
0.95 1.07 ¥ 104
0.93 1.09 ¥ 105
the absorption spectra in the presence and absence of quencher
may therefore be due to very similar extinction coefficients (e) of
the fluorophore and fluorophore-quencher complex.18
Conclusions
Two imidazolium ion-based molecules (G1 and G2), with different
lengths of covalent linker that links the imidazolium unit to
the fluorescence active naphthalene moiety, have been used for
Fig. 7 Linear trend of Stern–Volmer plot for both emission quenching
and fluorescence lifetime decrease for (a) H.2G1 system and (b) H.2G2
system at low concentration of H addition.
1
studying the interwoven complex formation. Detailed H-NMR
spectral studies revealed that hydrogen bonding interactions ([{C–
H}Imidazolium ◊ ◊ ◊ O/NCrown]), apart from the weaker p–p/arene–arene
donor–acceptor interactions resulted in moderately strong (Kf =
1.07 ¥ 104 for H.2G1, Kf = 1.09 ¥ 105 for H.2G2) inclusion
complex formation in less polar solvents like CH2Cl2. Results
of the electronic and fluorescence spectral studies also suggest
the formation of a ground state complex. Quenching of the
luminescence of the naphthalene moiety of the guest molecules (G1
and G2) by the NDI moiety of H was found to be predominantly
static in nature.
Similar procedure was adopted by many researchers for evalu-
ation of the static and dynamic quenching constants and are well
documented in the literature.8b,16
The formation constant (Kf) for the hydrogen bonded adduct
(H.2G1 and H.2G2) was determined from the systematic fluores-
cence titration17 and the values for respective complexes are also
shown in Table 2. Comparison of the Kf values for H.2G1 and
H.2G2 suggest that one of the two imidazolium-ion based guests
(G2), forms a more stable inclusion complex with the same host
molecule, H. This certainly reflects the higher flexibility of the
linker in G2 as the favorable factor for aligning the donor in a more
symmetric fashion for more effective p–p stacking. However, one
cannot completely ignore the influence of the different electronic
nature of the two different donor units towards the observed
difference in binding constants.8b,c,11a
To verify the formation of a ground state hydrogen bonded
complex, quenching experiments were performed at different
excitation wavelengths for both H.2G1 and H.2G2 systems (Fig. 8).
The data are summarised in Table 3. The value of the static
quenching constant appears to decrease with increasing excitation
wavelength. This decrease is small but regular for both the H.2G1
and H.2G2 systems. This strongly suggests the formation of a
ground state complex. The reason for no discernable change of
Experimental procedures
1H-NMR spectra were recorded either on a Bruker 200 MHz
FT NMR (model: Advance-DPX 200) or on a Bruker 500 MHz
FT NMR (model: Advance-DPX 500) spectrometer at room
temperature (RT, 25 ◦C). The chemical shift (d) data and
coupling constant (J) values are given in parts per million and
Hertz, respectively, throughout this manuscript unless mentioned
otherwise. ESI-MS measurements were carried out on a Waters
QTof-Micro instrument. UV-Vis spectra were obtained by using
either a Shimadzu UV-3101 PC or a Cary 500 Scan UV-Vis-NIR
spectrometer. Steady state emission spectra at room-temperature
were obtained using a Fluorolog Horiba Jovin Yvon luminescence
spectrofluorimeter. Time resolved emission studies were carried
out using Time Correlated Single Proton Counting (TCSPC)
technique were carried out using Edinburgh Instruments F900.
Materials and methods
Catechol, 2-[2-(2-chloro-ethoxy)-ethoxy]-ethanol, p-toluenesul-
fonyl chloride, di-tert-butyl dicarbonate were obtained from
Sigma-Aldrich Chem. Co. and were used as received without any
further purification. [NH4]+PF6- was recrystallised from ethanolic
solution before use. All solvents were of reagent grade and were
procured from S.D. Fine Chemicals (India) and all solvents were
dried and distilled prior to use following standard procedures.
Fig. 8 Linear trend of Stern–Volmer Plot of I0/I against concentration
of H at different excitation wavelength (a) for H.2G1 system (b) for H.2G2
system.
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Synthesis
3: Compound 2 (1.82 g, 3.64 mmole) was dissolved in 20 ml
of dichloromethane and then treated with 15 ml of HCl-
saturated ether solution. The reaction mixture was stirred for
24 h at room temperature. The solvents were removed under
vacuum conditions. The mixture was extracted three times using
dichloromethane and water, during extraction the pH of the
mixture was adjusted to 12 using NH4OH. The organic layers
were combined and dried over anhydrous sodium sulfate. Solvent
was removed under reduced pressure to give crude product. This
crude product was loaded on an alumina column and eluted by
chloroform : methanol (92 : 8) to give compound 3 as a sticky
brown solid with the yield of 1.16 g, 80.0%. 1H-NMR (500 MHz,
CDCl3, d (ppm)): 6.87 (4H, s), 4.10 (4H, t, J = 4), 3.86 (4H, t, J =
4), 3.68 (4H, t, J = 4), 3.61 (4H, t, J = 4), 3.45 (4H, t, J = 4.75), 2.76
(4H, t, J = 4.5), 2.74–2.69 (4H, m). 13C-NMR (500 MHz, CDCl3,
d (ppm)): 149.3, 124.1, 115.3, 72.3, 72.2, 71.5, 70.2, 57.3, 53.2,
40.4. Elemental analysis: Calculated for C20H34N2O6: C 60.22, H
8.60, N 7.03; found: C 60.10, H 8.50, N 7.00. ESI-MS: Calc. for
C20H34N2O6: 398.49, found: 399.65 [M + 1]+.
A: 1,2-Dihydroxy benzene (3 g, 27.27 mmole) was dissolved in
70 ml of freshly dried DMF in two neck round bottom flask. To
this solution K2CO3 powder (11.28 g, 81.81 mmole) was added.
Then the reaction mixture turned from brown to violet colour,
KI (13.58 g, 81.81 mmole) was added. This mixture was allowed
to stir for 15 min, and 2-[2-(2-chloro-ethoxy)-ethoxy]-ethanol
(9.16 g, 54.54 mmole) was added via a syringe at 60 ◦C. Then the
temperature was raised up to 80 ◦C and allowed to stir for 5 days.
The solvent was removed under reduced pressure and extracted
three times with CHCl3 and water. Organic layers were combined
and dried over anhydrous sodium sulfate. Solvent was removed
under reduced pressure to give crude product which was purified
on a silica-gel column, using methanol : dichloromethane (2 : 98
v/v) as an eluent with the yield of (A) 5.44 g, 53.3%, as a sticky
1
brown semisolid. H-NMR (500 MHz, CDCl3, d (ppm)): 3.58
(4H, t, J = 4.5), 3.66 (4H, t, J = 4.5); 3.74–3.70 (8H, m), 3.86
(4H, t, J = 4.5), 4.15 (4H, t, J = 4), 6.89 (4H, s). Elemental
analysis: Calculated for C18H30O8: C 57.74, H 8.08; found: C,
57.50; H, 8.10. (ESI-MS) calcd for C18H30O8: 374.19, found: 397.41
[M + Na]+.
H: In a 100 ml two neck round bottom flask, compound 3
(0.489 g, 1.22 mmole) was added to a suspension of 1,8:4,5-
naphthalene dianhydride (0.15 g, 0.55 mmole) in 50 ml of
acetonitrile. The reaction mixture was refluxed for 3 days. The
hot reaction mixture was filtered. All the solvents were evaporated
and loaded on an alumina column using chloroform : methanol
(98 : 2) as an eluent to yield the final compound H with the yield
1: Compound [A] (5.44 g, 14.56 mmole) was dissolved in THF
(40 ml) and 5 ml NaOH solution (10 M) was added to it at
0 ◦C. p-Toluenesulfonyl chloride (9.71 g, 50.96 mmole) in 15 ml of
THF was added dropwise over a period of 30 min to the reaction
mixture at 0 ◦C with vigorous stirring. The reaction was stopped
after 5 days. The solvent was removed under reduced pressure and
extracted three times with CHCl3 and water. The organic layers
were combined and dried over anhydrous sodium sulfate. Solvent
was removed under reduced pressure to give crude product. This
was purified on a silica-gel column, using CH3OH : CH2Cl2 (2 : 98
v/v) as an eluent with the yield of (1) 7.75 g, 78.0%, as a sticky
brown mass. 1H-NMR (500 MHz, CDCl3, d (ppm)): 2.41 (6H, s),
3.59 (4H, t, J = 4), 3.69–3.63 (8H, m), 3.82 (4H, t, J = 5), 4.13 (4H,
t, J = 5), 6.90 (4H, s), 7.31 (4H, d, J = 8), 7.79 (4H, d, J = 8.5). 13C-
NMR: 150.7, 147.0, 134.8, 131.8, 129.8, 128.0, 123.4, 116.2, 72.5,
71.5, 70.5, 23.3. Elemental analysis: Calculated for C32H42O12S2:
C 56.29, H 6.20; found: C 56.10, H 6.10. (ESI-MS): Calcd. for
C32H42O12S2: 682.21, found: 683.40 [M + 1]+.
2: Compound 1 (2.0 g, 2.92 mmole) and N-Boc ethylene diamine
(0.468 g, 2.92 mmole) were dissolved in 15 ml of dry acetonitrile. To
this solution K2CO3 powder (4.04 g, 29.28 mmole) and KI (728 mg,
4.39 mmole) were added. The whole reaction mixture was allowed
to reflux for 24 h under complete nitrogen atmosphere. After
filtration of the cooled reaction mixture, solvent was removed from
the filtrate under reduced pressure and extracted three times with
CHCl3 and water. Organic layers were combined and dried over
anhydrous sodium sulfate. Solvent was removed under reduced
pressure to give crude product. This was purified on a silica-gel
column using chloroform : methanol (92 : 8) as an eluent with yield
1
of 0.23 g, 40.0%. H-NMR (500 MHz, CD2Cl2, d (ppm)): 8.69
(4H, s), 6.80 (4H, d, J = 10), 6.79 (4H, d, J = 9.5), 4.25 (4H, t,
J = 7.25), 4.05 (8H, t, J = 4.75), 3.80 (8H, t, J = 4.5), 3.63–3.62
(12H, m), 3.56–3.54 (16H, m), 2.85 (8H, s). 13C-NMR (500 MHz,
CDCl3, d (ppm)): 162.8, 148.9, 130.8, 126.6, 121.4, 114.5, 70.9,
70.7, 70.1, 69.9, 69.2, 54.3, 52.3. ESI-MS (HRMS): Calculated for
HH+ (C54H69N4O16):1029.47; Experimentally found: 1029.47. mp:
152 ◦C.
G1: (0.5 g, 2.26 mmole) of bromomethyl naphthalene and
(0.185 g, 2.26 mmole) of 1-methyl imidazole was dissolved in 20 ml
of dry toluene and refluxed for 24 h under N2 atmosphere. Then the
reaction mixture was cooled and kept in a freezer overnight. The
white sticky solid which was settled in the bottom was separated
out and washed several times with toluene to give the bromide
salt. finally anion exchange in water using NH4PF6 gave the desired
PF6- salt of G1 with the yield of 0.50 g, 60.0%. 1H-NMR (500 MHz,
CD2Cl2, d (ppm)): 8.94 (1H, s), 7.92–7.87 (4H, m), 7.57–7.55
(2H, d, J = 9), 7.40 (1H, d, J = 8.5), 7.23 (2H, s), 5.49 (2H,
s), 3.93 (3H, s). 13C-NMR (200 MHz, CD3CN, d (ppm)): 136.3,
133.2, 131.3, 129.1, 128.0, 127.0, 125.6, 124.0, 122.4, 117.4, 52.9,
35.9. Elemental analysis: Calculated for C15H15N2PF6: C 48.92, H
4.11, N 7.61; found: C 49.00, H 4.10, N 7.50. ESI-MS: Calc. for
◦
-
C15H15N2PF6: 368.29, found: 223.12 [M - PF6 ]+. mp: 86 C.
G2: (0.4 g, 1.43 mmole) of bromobutyl naphthalene and (0.118 g,
1.43 mmole) of 1-methyl imidazole were dissolved in 20 ml of dry
toluene and refluxed for 24 h under N2 atmosphere. Then the
reaction mixture was cooled and kept in a freezer overnight. The
white sticky solid which was settled in the bottom was separated
out and washed several times with toluene to give the bromide salt.
Finally anion exchange in water using NH4PF6 gave the desired
PF6- salt of G2 with the yield of 0.30 g, 50.0%. 1H-NMR (500 MHz,
CD2Cl2, d (ppm)): 8.56 (1H, s), 7.78–7.74 (3H, m), 7.45 (1H, t, J =
7.5), 7.34 (1H, t, J = 7.5), 7.31 (1H, s), 7.23 (1H, s), 7.16 (1H, s),
1
of 0.84 g, 57.6% of the desired product 2. H-NMR (200 MHz,
CD2Cl2, d (ppm)): 6.89 (4H, s), 4.11 (4H, s), 3.85 (4H, s), 3.72
(4H, s), 3.63 (4H, s), 3.53 (4H, s), 3.10 (2H, s), 2.72 (4H, s), 2.58
(2H, s), 1.40 (9H, s). 13C-NMR (500 MHz, CD2Cl2, d (ppm)):
155.4, 148.4, 120.8, 113.7, 77.8, 70.3, 69.9, 69.2, 68.4, 68.0, 53.8,
52.7, 38.1, 27.6. Elemental analysis: Calculated for C25H42N2O8: C
60.22, H 8.49, N 5.62; found: C 60.30, H 8.40, N 5.60. ESI-MS:
Calc. for C25H42N2O8: 498.60, found: 499.56 [M + 1]+.
4816 | Org. Biomol. Chem., 2011, 9, 4811–4817
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7.14 (1H, d, J = 9), 4.30 (2H, t, J = 7.5), 4.15 (2H, t, J = 5.75),
3.90 (3H, s), 2.19–2.13 (2H, m), 1.94–1.89 (2H, m). 13C-NMR
(200 MHz, CD3CN, d (ppm)): 135.9, 129.3, 127.5, 126.5, 123.7,
122.3, 118.7, 117.3, 106.7, 67.0, 49.3, 35.8, 26.7, 25.4. Elemental
analysis: Calculated for C18H21N2OPF6: C 50.71, H 4.96, N 6.57;
Sijbesma and E. W. Meijer, Curr. Opin. Colloid Interface Sci., 1999,
4, 24; (g) G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford
University Press, New York, 1997; (h) J.-B. Guo, Y. Jiang and C.-F.
Chen, Org. Lett., 2010, 12, 5764–5767; (i) J.-B. Guo, J.-F Xiang and
C.-F. Chen, Eur. J. Org. Chem., 2010, 5056; (j) J.-M. Zhao, Q.-S. Zong,
T. Han, J.-F. Xiang and C.-F. Chen, J. Org. Chem., 2008, 73, 6800–6806.
7 (a) C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990,
112, 5525–5534; (b) G. B. McGaughey, M. Gagne and A. K. Rappe,
J. Biol. Chem., 1998, 273(25), 15458–15463; (c) C. G. Claessens and
J. F. Stoddart, J. Phys. Org. Chem., 1997, 10, 254; (d) J. C. Nelson,
J. G. Saven, J. S. Moore and P. G. Wolynes, Science, 1997, 277, 1793;
(e) C. A. Hunter, Angew. Chem., Int. Ed. Engl., 1993, 32, 1584–1586;
(f) C. A. Hunter, Chem. Soc. Rev., 1994, 23, 101; (g) S. J. Cantrill, A. R.
Pease and J. F. Stoddart, J. Chem. Soc., Dalton Trans., 2000, 3715–3734;
(h) A. D. Hamilton and D. V. Engen, J. Am. Chem. Soc., 1987, 109,
5035–5036; (i) M. Nishio and M. Hirota, Tetrahedron, 1989, 45, 7201.
8 (a) V. F. Traven, Frontier Orbitals and Properties of Organic Molecules,
Ellis Horwood, London, 1992, p. 67; (b) N. S. S. Kumar, M. D. Gujrati
and J. N. Wilson, Chem. Commun., 2010, 46, 5464–5466; (c) S. I. Kato,
T. Matsumoto, K. Ideta, T. Shimasaki, K. Goto and T. Shinmyozu,
J. Org. Chem., 2006, 45, 3643–3647; (d) Q. Jiang, H. Y. Zhang, M. Han,
Z. J. Ding and Y. Liu, Org. Lett., 2010, 12, 1728–1731.
9 (a) E. Barrett, T. J. Dale and J. J. Rebek, J. Am. Chem. Soc., 2008, 130,
2344–2350; (b) E. S. Barrett, T. J. Dale and J. J. Rebek, Chem. Commun.,
2007, 4224–4226; (c) E. Ishow, A. Credi, V. Balzani, F. Spadola and
L. Mandolini, Chem.–Eur. J., 1999, 5, 984–989; (d) R. Ballardini, V.
Balzani, A. Credi, M. T. Gandolfi and M. Venturi, Acc. Chem. Res.,
2001, 34, 445–455 and references therein.
10 (a) M. Suresh, A. K. Mandal, M. K. Kesharwani, N. N. Adarsh, B.
Ganguly, R. K. Kanaparthi, A. Samanta and A. Das, J. Org. Chem.,
2011, 76, 138–144.
11 (a) A. J. Zych and B. L. Iverson, J. Am. Chem. Soc., 2000, 122, 8898–
8909; (b) G. J. Gabriel, S. Sorey and B. L. Iverson, J. Am. Chem. Soc.,
2005, 127, 2637–2640; (c) M. S. Cubberley and B. L. Iverson, J. Am.
Chem. Soc., 2001, 123, 7560–7563.
12 (a) S. Kiviniemi, A. Sillanpaa, M. Nissinen, K. Rissanen, M. T. Lamsa
and J. Pursiainen, Chem. Commun., 1999, 897–898; (b) S. Kiviniemi,
M. Nissinen, M. T. Lamsa, J. Jalonen, K. Rissanen and J. Pursiainen,
New J. Chem., 2000, 24, 47–52; (c) M. Lee, Z. Niu, D. V. Schoonover,
C. Slebodnick and H. W. Gibson, Tetrahedron, 2010, 66, 7077–7082;
(d) N. Noujeim, L. Leclercq and A. R. Schmitzer, J. Org. Chem., 2008,
73, 3784–3790.
13 (a) J. J. Reczek and B. L. Iverson, Macromolecules, 2006, 39, 5601;
(b) Z. M. Al-Badri and G. N. Tew, Macromolecules, 2008, 41, 4173.
14 (a) C. P. Mandl and B. Ko¨nig, J. Org. Chem., 2005, 70, 670–674.
15 (a) M. Lamsa, J. Huuskonen, K. Rissanen and J. Pursiainen, Chem.–
Eur. J., 1998, 4, 84–92; (b) M. Lamsa, T. Suorsa, J. Pursiainen, J.
Huuskonen and K. Rissanen, Chem. Commun., 1996, 1443–144; (c) M.
Lamsa, J. Pursiainen, K. Rissanen and J. Huuskonen, Acta Chem.
Scand., 1998, 52, 563.
16 (a) P. L. Gentili, F. Ortica and G. Favaro, J. Phys. Chem. B, 2008, 112,
16793–16801; (b) P. P. H. Cheng, D. Silvester, G. Wang, G. Kalyuzhny,
A. Douglas and R. W. Murray, J. Phys. Chem. B, 2006, 110, 4637–4644.
17 A. C. Tedesco, D. M. Oliveira, Z. G. M. Lacava, R. B. Azevedo, E. C. D.
Lima and P. C. Morais, J. Magn. Magn. Mater., 2004, 2404–2405.
18 P. K. Behera, T. Mukherjee and A. K. Mishra, J. Lumin., 1995, 65,
131.
found: C 50.80, H 5.01, N 6.50. ESI-MS: Calc. for C18H21N2OPF6:
◦
426.37, found: 281.36 [M - PF6 ]+. mp: 78 C.
-
Acknowledgements
The authors wish to acknowledge DST and CSIR for financial
support. A. D thanks P. K. Ghosh for his keen interest in this work.
A. K. M and M. S acknowledge CSIR for a research fellowship.
References
1 (a) S. Sivakova and S. J. Rowan, Chem. Soc. Rev., 2005, 34, 9; (b) G.
Cooke and V. M. Rotello, Chem. Soc. Rev., 2002, 31, 275; (c) J.-
M. Lehn, Supramolecular chemistry: Concepts and Perspectives, Wiley
VCH, Weinheim, 1995; (d) O. Takahashi, Y. Kohno and M. Nishio,
Chem. Rev., 2010, 110, 6049–6076; (e) C. Zhang, S. Li, J. Zhang, K.
Zhu, N. Li and F. Huang, Org. Lett., 2007, 9, 5553–5556; (f) M. Zhang,
K. Zhu and F. Huang, Chem. Commun., 2010, 46, 8131–8141; (g) C.
Zhang, K. Zhu, S. Li, J. Zhang, F. Wang, M. Liu, N. Li and F. Huang,
Tetrahedron Lett., 2008, 49, 6917–6920.
2 (a) C. A. Royer, Chem. Rev., 2006, 106, 1769–1784; (b) S. P. Fletcher,
F. Dumur, M. M. Pollard and B. L. Feringa, Science, 2005, 310, 80–
82; (c) L. Hedstrom, Chem. Rev., 2002, 102, 4501–4524; (d) J. Wang
and M. A. El-Sayed, Biophys. J., 2000, 78, 2031; (e) W. A. Loughlin,
J. D. A. Tyndall, M. P. Glenn and D. P. Fairlie, Chem. Rev., 2004, 104,
6085–6118; (f) F. Zeng and S. C. Zimmerman, Chem. Rev., 1997, 97,
1681–1712.
3 (a) I. G. Denisov, T. M. Makris, S. G. Sligar and I. Schlichting, Chem.
Rev., 2005, 105, 2253–2278; (b) R. P. Cheng, S. H. Gellman and W. F.
DeGrado, Chem. Rev., 2001, 101, 3219–3232; (c) P. G. Vasudev, S.
Chatterjee, N. Shamala and P. Balaram, Chem. Rev., 2011, 111, 657–
687; (d) S. L. Cravens, A. C. Navapanich, B. H. Geierstanger, D. C.
Tahmassebi and T. J. Dwyer, J. Am. Chem. Soc., 2010, 132, 17588–
17598.
4 (a) C. A. Hunter, K. R. Lawson, J. Perkins and C. J. Urch, J. Chem.
Soc., Perkin Trans. 2, 2001, 651–669; (b) E. A. Meyer, R. K. Castellano
and F. Diederich, Angew. Chem., Int. Ed., 2003, 42, 1210–1250; (c) F. G.
Klarner and B. Kahlert, Acc. Chem. Res., 2003, 36, 919–932.
5 (a) L. Sobczyk, S. J. Grabowski and T. M. Krygowski, Chem. Rev., 2005,
105, 3513–3560; (b) M. Mautner, Chem. Rev., 2005, 105, 213–284; (c) M.
Lamsa, J. Huuskonen, K. Rissanen and J. Pursiainen, Chem.–Eur. J.,
1998, 4, 84–92.
6 (a) G. W. Gokel, W. M. Leevy and M. E. Weber, Chem. Rev., 2004, 104,
2723–2750; (b) M. M. Conn and J. Jr. Rebek, Chem. Rev., 1997, 97,
1647–1668; (c) L. M. Greig and D. Philip, Chem. Soc. Rev., 2001, 30,
287–302; (d) L. J. Prins, D. N. Reinhoudt and P. Timmerman, Angew.
Chem., Int. Ed., 2001, 40, 2382–2426; (e) M. Kotera, J. M. Lehn and
J. P. Vigneron, J. Chem. Soc., Chem. Commun., 1994, 197; (f) R. P.
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