Molecular interactions, proton exchange, and photoinduced processes prompted by an inclusion process and a [2]pseudorotaxane formation

Article abstract of DOI:10.1021/jo400752d

Appropriate design of the host and guest components allows formation of a novel [2]pseudorotaxane complex with an interrupted photoinduced electron transfer (PET)-coupled fluorescence resonance energy transfer (FRET) response. This is the first example of an inclusion complex with NO₆-based azacrown ether as the host unit (H). Different guest molecules (G1, G2, G3, and G4) with varying stopper size are used for the studies. Unlike G1, G2, and G3, G4 with a relatively bulkier stopper fails to form a [2]pseudorotaxane complex. Isothermal titration microcalorimetry measurements reveal a systematic increase in the association constant for H·G1, H·G2, and H·G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H·G1/H·G2/H·G3 is exclusively driven by a large positive entropic gain (TΔS = 19.69/26.80/21.81 kJ·mol^-1), while the enthalpy change is slightly negative for H·G1/H·G3 (-2.61/-1.97 kJ·mol^-1) and slightly positive for H·G2 (ΔH = 5.98 kJ·mol^-1). For these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is attributed to the subtle differences in acidity of the NH₂⁺ unit of the guest molecules and thus the proton exchange ability between the host and respective guest. This is substantiated by the results of the computational studies.

Full text of DOI:10.1021/jo400752d

Article
pubs.acs.org/joc
Molecular Interactions, Proton Exchange, and Photoinduced
Processes Prompted by an Inclusion Process and a
[
2]Pseudorotaxane Formation
†
†
†
§,∥,#
Amal Kumar Mandal, Moorthy Suresh, Manoj K. Kesharwani, Monalisa Gangopadhyay,
Manoj Agrawal, Vinod P. Boricha, Bishwajit Ganguly,* and Amitava Das*
†
†
,‡,†
,§,∥,#
†
CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat 364002, India
#
Organic Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Rd., Pune, Maharashtra 411008, India
‡
Academy of Scientific and Innovative Research, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat
3
64002, India
§
Academy of Scientific and Innovative Research, CSIR-National Chemical Laboratory, Pune, Maharashtra 411008, India
*
S Supporting Information
ABSTRACT: Appropriate design of the host and guest
components allows formation of a novel [2]pseudorotaxane
complex with an interrupted photoinduced electron transfer
(
(
PET)-coupled fluorescence resonance energy transfer
FRET) response. This is the first example of an inclusion
complex with NO -based azacrown ether as the host unit (H).
6
Different guest molecules (G1, G2, G3, and G4) with varying
stopper size are used for the studies. Unlike G1, G2, and G3,
G4 with a relatively bulkier stopper fails to form a
[
2]pseudorotaxane complex. Isothermal titration microcalorimetry measurements reveal a systematic increase in the association
constant for H·G1, H·G2, and H·G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H·G1/
H·G2/H·G3 is exclusively driven by a large positive entropic gain (TΔS = 19.69/26.80/21.81 kJ·mol ), while the enthalpy
change is slightly negative for H·G1/H·G3 (−2.61/−1.97 kJ·mol ) and slightly positive for H·G2 (ΔH = 5.98 kJ·mol ). For
these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is
attributed to the subtle differences in acidity of the NH2+ unit of the guest molecules and thus the proton exchange ability
between the host and respective guest. This is substantiated by the results of the computational studies.
−1
−1
−1
INTRODUCTION
induced electron transfer (PET) and a fluorescence on
response, which in turn initiates a FRET process. Here the
choice of the azacrown moiety, used as a guest, is separated
■
It has long been known that crown ethers are capable of
forming hydrogen-bonded adducts with organic ammonium
1
from the photoactive donor unit by a −CH − spacer, which
ions. Researchers have exploited this binding motif and have
2
shown that a range of wire-type secondary ammonium ions
allows the unshared pair of electrons of the tertiary Ncrown to
+
2
(
R NH ) could be used to thread through the cavities of
participate effectively in the PET process and thereby to
2
9
appropriately sized crown ether derivatives to afford interwoven
complexes. This act of supramolecular recognition has very
recently led to the development of new classes of molecular
participate in the switch-on/off-type luminescence response.
Though this scheme has been successfully utilized for designing
9
sensors for metal ion recognition, to date no literature report
2
3
4
level devices, such as molecular switches, motors, rotors,
states that such a concept has been utilized for the generation
of a threaded inclusion complex with an interrupted response.
The appropriate choice of the donor (pyrene) and acceptor
5
6
7
shuttles, muscles, extension cables, etc. In this regard, the
most studied crown ether is dibenzo-24-crown-8 (DB24C8) or
1
e,8
its derivatives.
Balzani et al. have also demonstrated the
(
anthracene) units, which possess the fitting spectral properties
fluorescence resonance energy transfer (FRET)-based plug in
socket function at a molecular level using inclusion complexes
for a probable FRET process, is also crucial in the present
study. To the best of our knowledge, there is no example of a
relatively simple supramolecular assembly available in the
literature that is capable of exhibiting a FRET process, which is
1c
of a crown ether, derived from binapthol. Such an idea can be
further extended to achieve a more complex system, where one
can have additional control on the input signal and the
consequential modified output response. To demonstrate such
a process, we have utilized a supramolecular assembly where
the threading phenomena result in an interrupted photo-
Received: April 12, 2013
Published: August 16, 2013
©
2013 American Chemical Society
9004
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
initiated by the luminescence on-effect due to an interrupted
PET process involving the donor fluorophore.
desired hexafluorophosphate salts were isolated as insoluble
solids by anion exchange in aqueous medium. The synthetic
procedure and all relevant characterization details of these host
and guest molecules are provided in the Supporting
Information (SI).
In this paper, we report the formation of a
2]pseudorotaxane assembly from an azacrown-based host
[
unit (H) and different secondary ammonium ion as the
threaded guest (Figure 1). Importantly, interwoven complex
Complexation of H with G1, G2, G3, and G4. The
complexation of azacrown-based host H with various guest
molecules (G1, G2, and G3) in CDCl /CD CN (4:1, v/v)
3
3
1
solution was first investigated in detail using H NMR
spectroscopic studies by systematically varying the concen-
tration of the guest fragment. Let us first discuss the results of
1
1
the H NMR spectral studies involving H and G1. Partial H
NMR spectra of H, G1, and a mixture of H and G1 are shown
in Figure 3.
Figure 1. Molecular structure of the host and guest molecules.
formation leads to rare examples of the interrupted PET-
coupled FRET process. To ensure the formation of the
threaded complex involving NO -based azacrown ether as the
6
host and the secondary ammonium ion as the guest
component, we have also synthesized the hexafluorophosphate
salt of different guest molecules (G1, G2, G3, and G4) with
varying stopper size (Figure 1) and studied the complex
formation process with the host molecule H using different
spectroscopic techniques.
1
Figure 3. Partial H NMR spectra (500 MHz, 298 K) recorded in
RESULTS AND DISCUSSION
■
CDCl /CD CN (4:1, v/v) for (a) 7.3 mM H, (b) 7.3 mM H with 3.6
mM G1, (c) 7.3 mM H with 7.3 mM G1, (d) 7.3 mM H with 15.6
mM G1, and (e) 7.3 mM G1.
3
3
Synthesis. The methodology that was adopted for the
synthesis of the azacrown derivative H is shown in Figure 2.
Alkylation of 1,2-dihydroxybenzene was achieved with reason-
able yield by reaction with 2-[2-(2-chloroethoxy)ethoxy]-
ethanol in a suspension of K CO in DMF as the solvent.
1
Only one set of peaks were observed in the H NMR
spectrum of the mixed solution of H and G1, which implied
that the equilibrium kinetics were fast within the H NMR time
scale. Respective δ values for H and H of each −CH − group
of G1 were found to be shifted from 5.01 and 4.35 to 4.74 and
4.06, respectively, for 1 equiv of added G1. Signals for most of
the protons, which belonged to the anthracene/phenyl ring of
G1, were found to be upfield shifted relative to those signals for
the free individual components (Figure 3). Thus, the observed
results suggested that these aromatic protons of G1 resided
under the shielding influence of the aromatic rings of the host
2
3
1
Chromatographic purification yielded the bishydroxy inter-
mediate 1, which was further converted to the corresponding
bistosylate derivative 2. The intermediate product 2 was
allowed to react with pyren-2-ylmethanamine hydrochloride to
give the desired host molecule H. The various guest molecules
with different stopper sizes were synthesized by reducing the
product of the Schiff base reaction between appropriate amine
and aldehyde derivatives (Figure 2). These secondary amine
derivatives were protonated and eventually isolated, and the
6
7
2
Figure 2. Methodology adopted for the synthesis of host and guest molecules.
9
005
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
molecule H during the binding process. Conversely, the nature
of the shift was not uniform for the pyrene protons in host H.
In contrast, the hexafluorophosphate salt of G4, which was
substituted with relatively bulkier 3,5-di-tert-butyl groups,
showed no apparent shift in the signals in its H NMR
1
Appreciable upfield shifts in the signals for H protons (Δδ =
n
−
0.21 ppm) was observed, while a downfield shift was observed
spectrum when mixed with the crown ether-based host H
under identical experimental conditions. Literature reports
clearly suggest that the 3,5-di-tert-butylphenyl groups, being too
big, fail to penetrate through the even bigger crown ether
for H proton (Δδ = −0.13 ppm). The phenyl protons (H and
l
a
H ) of the host molecule H were upfield shifted (Δδ = −0.16
b
ppm) and split into two sets of signals during binding to the
guest molecule G1. The difference in the shift pattern of the
aromatic protons of host molecule H was mainly due to the
difference in the extent of shielding of the protons due to the
anisotropy of the ring current effect.
10
(
DB24C8) cavity. Thus, on the basis of the observations
discussed above for G4, it is not unreasonable to conclude that,
for the NO -based azacrown moiety, the pseudorotaxane
6
formation depends on the relative size and shape of the
stopper unit, and the guest molecule G4 with two bulky 3,5-di-
tert-butyl groups failed to form an interwoven or pseudorotax-
ane complex with H.
1
The H NMR spectroscopic titration of H, with varying
concentration of another two guest compounds, G2 and G3,
also suggested the formation of host−guest complexes H·G2
and H·G3 (Figure 4 and SI Figures 2 and 3). In both cases the
The respective binding stoichiometry (1:1) for the formation
of H·G1, H·G2, and H·G3 was established on the basis of the
1
inflection point in the mole ratio plots of the H NMR spectral
studies (Figure 5). Electrospray ionization (ESI) mass
spectrometry also revealed the 1:1 complex formation between
H with three secondary ammonium salts (G1, G2, and G3) in
the gas phase. In the case of G1, the peak was observed at m/z
8
64.77 for H + G1, which corroborated the formation of 1:1
complex H·G1 (SI Figure 4). The peaks at m/z 981.15 for H +
+
+
G2 + PF ¯ + H and m/z 1091.95 for H + G3 + PF ¯ + Na
6
6
also supported the formation of 1:1 complexes H·G2 and H·G3
(
SI Figures 4 and 5).
Association Constant and Thermodynamics. The
complexation processes and associated changes in thermody-
namic parameters for the complex formation between the
azacrown-based host H and different guest molecules G1−G4
were investigated in CHCl /CH CN (4:1, v/v) medium by
1
Figure 4. Partial H NMR spectra (500 MHz, 298 K) recorded in
3
3
CDCl /CD CN (4:1, v/v) for (a) 6.7 mM H, (b) 6.7 mM H with 3.3
mM G2, (c) 6.7 mM H with 6.7 mM G2, (d) 6.7 mM H with 13.4
mM G2, and (e) 6.7 mM G2.
3
3
isothermal titration microcalorimetry (ITC) measurements. A
good fit of the titration curve to a 1:1 binding model was also
observed when analogous measurements were carried out in
CDCl /CH CN (4:1, v/v) solution, a conclusion that was again
3
3
1
supported by mole ratio plot analyses in the case of the H
NMR studies (Figure 5). The corresponding titration curves for
the ITC measurements and their corresponding thermody-
namic parameters (inset data) are shown in Figure 6. The
obtained “N” data, which refer to the binding sites for the
complexation of three sets of complexes (N = 1.06 ± 0.0416
sites for G1, N = 0.97 ± 0.0434 sites for G2, and N = 0.98 ±
0.00412 sites for G3) were also consistent with a 1:1 binding
model and corroborated our observations with H NMR
spectral studies.
The thermodynamic parameters obtained from the ITC
titration studies are listed in Table 1. An important parameter
for ITC experiments with low-affinity systems is the so-called
nature of the spectral shifts was found to be similar to that
observed for the formation of the complex H·G1. Quite
substantial complexation-induced shifts (Δδ = 0.47 and 0.31
ppm, respectively, for H and H ) of the methylene protons
6
7
were observed in complexation of H with G2 relative to free
G2. In contrast, these shifts for H and H for G1 in H·G1 were
6
7
only 0.27 and 0.29 ppm, respectively. These significant
differences in the shift values for H·G2 could be attributed to
the more polarized methylene groups next to the cationic
ammonium center in G2, which resulted a much stronger C−
H···O hydrogen bond with the crown ether oxygen. Shifts of
1
1
the H NMR spectra for H·G3 were analogous to those
observed for H·G1.
Figure 5. Mole ratio plot in CDCl /CD CN (4:1, v/v) for the complexation between H and (a) G1, (b) G2, and (c) G3.
3
3
9
006
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
Figure 6. ITC profiles at 25 °C in CHCl /CH CN (4:1, v/v) for the binding of host H (5 mM) with (a) guest G1 (50 mM), (b) guest G2 (50 mM),
3
3
and (c) guest G3 (50 mM). Top: raw data for the sequential 2 μL injection of respective guests into H. Bottom: heat evolved (kcal) per mole of
guest added, corrected for the heat of guest dilution, against the molar ratio of the guest to H. The data (filled circle) were fitted to a single set
binding model, and the solid line represents the best fit.
Table 1. Thermodynamic Data and Association Constant
Obtained from the ITC Measurements with
Pseudorotaxanes Formed from Host H and Guests G1−G4
A previous report revealed that crown ether-based
pseudorotaxane complexes were mainly stabilized by hydrogen
a
+
bonding (N −H···O and C−H···O) and π−π interactions in a
1d
nonpolar solvent. The literature report also revealed that a
change in guest molecule from secondary dibenzylammonium
host−guest
association constant,
ΔG (kJ·
ΔH (kJ·
TΔS (kJ·
−1
1
−1
−1
complex
Ka (M−
)
mol
)
mol
)
mol )
hexafluorophosphate (360 M− in acetone-d6)− to the
1
12
3
3
4
H·G1
H·G2
H·G3
H·G4
(8.1 ± 1.7) × 10
(4.47 ± 1.0) × 10
(1.45 ± 0.4) × 10
−22.30
−20.82
−23.78
−2.61
5.98
19.69
26.80
21.81
1
anthracenyl methyl-substituted analogue (496 M in ace-
1
3
tone-d6) improved the affinity of the respective guest
molecule for interwoven complex formation with DB24C8.
This enhanced affinity was mainly attributed to a more efficient
π−π interaction involving the anthracene π-system. Analo-
gously, for the present study stronger binding of H with G1 and
G3 compared to G2 was mainly due to the presence of the
phenyl unit, which stabilized the adducts through an additional
π-interaction. However, the higher stability of H·G3 compared
to H·G1 could perhaps also reflect the presence of a bulkier 4-
tert-butyl group, which presumably helped in forming a
relatively more rigid adduct.
−1.97
no binding was observed in the ITC experiment
a
ITC measurements were performed in CHCl /CH CN (4:1, v/v) at
3
3
25 °C.
Wiseman “c” value, which is the product of the total host
11
concentration and the binding constant Ka. For c < 10, ITC
experiments become challenging. For our studies, the respective
value evaluated for c in each case is found to be larger than 10,
and this confirms that data obtained from the ITC measure-
ments are reliable.
The obtained thermodynamic data clearly indicate that the
complexation of azacrown-based host H with guests G1 and G3
in CHCl /CH CN (4:1, v/v) is exclusively driven by a large
As can be seen from Table 1, the association constants (Ka)
for the complexation of host H with three different guest
molecules (G1−G3) were obtained from the ITC titration
profile. The corresponding binding constants for H·G1, H·G2,
3
3
−1
positive entropic gain (TΔS = 19.69−21.81 kJ·mol ) and is
accompanied by small negative enthalpy changes (−ΔH =
−1
3
3
2.61−1.97 kJ.mol ), as shown in Table 1. In contrast, the
and H·G3 are (8.1 ± 1.7) × 10 , (4.47 ± 1.0) × 10 , and (1.45
4
−1
complexation of H with G2 is driven by a large positive
±
0.4) × 10 M , respectively. A comparison of the observed
−1
entropic gain (TΔS = 26.80 kJ·mol ) along with a small
data revealed that the value for K for the formation of H·G3 is
a
−1
positive change in enthalpy (ΔH = 5.98 kJ·mol ).
3
.2 and 1.8 times higher than those for H·G1 and H·G2,
It is generally accepted that the association process arising
from conformational freedom and the desolvation effect is
respectively.
A systematic increase in the values of the association constant
is observed on changing the stopper from butyl to 4-tert-
butylphenyl in the guest molecules. This indicates that the size
of the substituents on the guest molecules plays an important
role in the binding affinity and also in the binding mode during
the complexation process. However, no binding was observed
for the complexation of H with G4 in the ITC experiment. The
presence of relatively bulky stopper units such as the 3,5-di-tert-
butylphenyl moiety prevented threading of the G4 moiety
14
entropically favored (TΔS > 0). It is also known that the
negative enthalpy contributions (ΔH < 0) arise mainly from the
electrostatic, hydrogen-bonding, π−π, and van der Waals
14
interactions upon complexation of the host with a guest. In
the present case, both the host and all guest molecules (G1, G2,
and G3) have the same charge number and binding units. Thus,
the size and nature of the different stopper units (e.g., phenyl
for G1, butyl for G2, and 4-tert-butylphenyl for G3) must play a
crucial role in dictating the small but realistic change in
thermodynamic data. The obtained data clearly indicate that
the entire complexation process is exclusively driven by a large
positive entropic gain. Complexation with the guest molecule
through the cavity of the NO -based azacrown ether unit and
6
thus the formation of any threaded or inclusion complex. This
1
also agrees well with the results of the H NMR studies
described earlier (vide infra).
9
007
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
Figure 7. (a) UV−vis spectra for H ([H] = 1.11 × 10−5 M), G1 ([G1] = 3.24 × 10−6 M), and the adduct H·G1 (1:1) and (b) spectral overlap
between donor (host H) emission and acceptor (guest G1) absorption in CH Cl /CH CN (99:1, v/v). λ = 314 nm was used for recording the
2
2
3
ext
emission spectra for H.
Figure 8. Fluorescence titration in CH Cl /CH CN (99:1, v/v) medium (λ = 314 nm) for H ([H] = 1.12 × 10− M) with [G1] varying (a) from 0
5
2
2
3
ext
−4
−5
−5
to 3.90 × 10 M, (b) from 0 to 1.16 × 10 M, while pyrene-based fluorescence was enhanced until [G1] = 1.16 × 10 M, and (c) from 1.16 ×
−
4
−4
10
to 3.90 × 10 M, while a gradual decrease in pyrene-based emission with a concomitant increase in anthracene-based emission was observed.
G2, which has a more conformationally flexible n-butyl stopper
unit, is driven by a comparatively larger positive entropic gain
than that with G3 and G1. Enthalphy changes due to
complexation are relatively small but decisive enough to reflect
differences due to structural variations. The presence of a
phenyl stopper in the case of G1 and G3 is mainly responsible
for the negative enthalpy change during the adduct formation,
which helps to stabilize adducts through H-bonding in addition
to π−π interaction. In the case of G2, the stability arises only
from H-bonding, which is accountable for the positive enthalpy
change. The more negative enthalpy change for G1 (−ΔH =
initial addition of G1 (∼1 mol equiv with respect to [H]), only
an enhancement in the pyrene-based emission at 378 nm was
observed (Figure 8a,b). This observation tends to suggest that,
during initial addition of G1, the concentration of the H-
bonded adduct H·G1, involving the lone pair of electrons on
+
Ncrown/Ocrown through [N −H] ···OH/[C−H] ···OH inter-
G1
G1
actions, increases and accounts for the interruption of the PET
process. This interrupted PET process could be attributed to
9
the observed enhancement of the pyrene-based emission. On
further addition of G1 ([G1]/[H] > 1) to this solution, the
pyrene-based emission at 378 nm was found to decrease with a
concomitant increase in the anthracene-based emission at 425
and 450 nm (Figure 8a,c).
Figure 7a clearly reveals that the anthracene moiety in G1
does not absorb at 314 nm, and thus, the observed
enhancement in anthracene-based emission on excitation of
the pyrene fragment at 314 nm in the hydrogen-bonded adduct
H·G1 implies an efficient FRET-based process involving the
donor pyrene fragment and the acceptor anthracene unit in the
[2]pseudorotaxane. A possible FRET-based process is further
corroborated by the fact that there exists a significant spectral
−1
2
.61 kJ·mol ), compared to that for G3 (−ΔH = 1.97 kJ·
−1
mol ), could be accounted for if one considers the more acidic
nature of the hydrogen atoms of the NH2+ unit of G1, which
helps in forming stronger H-bonds with the crown ether
moiety.
Photophysical Study. The absorption spectrum recorded
for azacrown-based host H was dominated by the absorption
maxima at 314, 328, and 344 nm, which are characteristic for
the pyrene moiety (Figure 7a). For G1, the absorption
spectrum was dominated by the absorption band of the
anthracene moiety with absorption maxima at 350, 370, and
overlap between the emission spectra of the donor pyrene and
H
390 nm. Analogous absorption spectra were also observed for
the acceptor anthraceneG1 centers (Figure 7b), which thus
G2 and G3. The host molecule H showed a very weak emission
at 378 nm on excitation at any one of these three (314, 328,
and 344 nm) wavelengths. The weak pyrene-based emission is
explained on the basis of the PET process involving the
constitute an appropriate pair for fluorescence resonance
15
energy transfer. To further support this phenomenon, we
have also recorded the emission spectra of the same molar
solution of G1 in the presence and absence of H at the same
excitation wavelength of 314 nm. Thus, a comparison of the
results of the steady-state emission studies for H·G1 with those
for G1 alone strongly suggests that an efficient FRET process is
operational between pyrene as the donor and anthracene
acceptor units in the hydrogen-bonded adduct. The energy
transfer (ET) quantum yield for the H·G1 complex was
unshared pair of electrons of the tertiary −N
and the
azacrown
9
HOMO of the photoexcited pyrene moiety. To check the
complexation-induced change between H with the guest
molecule G1, fluorescence spectra were recorded for a solution
pyr
of H with increasing [G1] in CH Cl using 314 nm (λ ) as
2
2
ext
the excitation wavelength (Figure 8). Interestingly, during the
9
008
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
Figure 9. Fluorescence titration in CH Cl /CH CN (99:1, v/v) medium (λ = 314 nm) for H ([H] = 1.54 × 10− M) with varying (a) [G2] from 0
to 5.39 × 10 M and (b) [G3] from 0 to 6.31 × 10 M.
6
2
2
3
ext
−5
−4
1
6
calculated to be 22.8%. The ET rate was evaluated by using a
the integral equation formalism polarizable continuum model
(IEF-PCM) of solvation. The calculated results show that, for
7
−1 16
19
standard equation and was found to be 1.51 × 10 s . These
data also enable us to calculate the Forster distance of 48.4 Å
R ) by using a standard equation reported previously (SI p
̈
the interwoven complex H·G1, head to head interaction
(
between anthraceneG1 and pyrene was energetically preferred
0
H
1
7
−1
9).
over the head to tail orientation by 12.5 kJ·mol in CH Cl
medium (Figure 10). A conformation with head to head
2
2
We also recorded the emission spectra of H in the presence
of three other guest molecules (G2, G3, and G4) to study the
complexation process in CH Cl /CH CN (99:1, v/v) medium
2
2
3
following excitation at 314 nm. The trend in the changes in the
spectral pattern for H observed on formation of the complex
with G2 and G3 was similar to that found for the complexation
with G1 (Figure 9). During the initial stages of the addition of
G2 or G3 (until [G2]/[H] or [G3]/[H] < 1 equiv) to a
solution of H, the pyrene-based emission at 378 nm was found
to increase due to the interruption of the PET process.
However, this enhancement in emission intensity at 378 nm
(
3.4-fold for G2 and 1.3-fold for G3) was much lowered
Figure 10. B3LYP/6-31+G**(DCM)//B3LYP/6-31G*-calculated
−1
compared to that of the complexation with G1 (37.5-fold). This
clearly revealed that the interruption of the PET process was
most efficient in the case of H·G1. These observations perhaps
tend to suggest that the subtle differences in the acidity of the
relative energy (kJ·mol ) for (a) head to head and (b) head to tail
alignment of an interwoven thread complex of H and G1 using the
PCM (the H molecule is represented in tube form, and the G1
molecule is represented in ball and stick form).
hydrogen atoms in the NH2+
moiety of the respective guest
guest
molecule must play a crucial role either in establishing an
effective H-bond involving the unshared pair of electrons
residing on the N-atom of the NHH moiety (of the host
orientation between the anthraceneG1 moiety and the pyreneH+
moiety could possibly be better suited for the transfer of a H
+
+
+
component) or in a possible H transfer from the NH2 unit of
from {−(H)NHR } to {−(N)H } and eventually results in
G1
2 H
the guest molecule to the NH moiety during the adduct (H·
H
a more efficient FRET process with pyrene as the donor moiety
and anthracene as the acceptor moiety. Furthermore, to
examine the feasibility of proton transfer from various guest
molecules (G1, G2, and G3) to the host molecule H, the
proton affinities of the host and respective amine of the guest
molecules have been calculated using the B3LYP/6-31+G**-
(DCM)//B3LYP/6-31G* level of theory (SI Figure 6). The
calculated proton affinity (PA) for host molecule H in DCM
Gx; x being 1 or 2 or 3) formation, as either or both of these
processes in combination could be responsible for this observed
pyrene-based emission enhancement. Thus, as we have
assumed that the NH2+ units of G1 are more acidic in nature
compared to those of G2 and G3, G1 shows more emission
enhancement (37.5-fold) during the complexation process with
H. This result was further supported by the calculated proton
affinity of the N-atom of the NHH moiety in the azacrown
ether-based host molecule and the respective amine fragment
−1
medium has been found to be 1178.3 kJ·mol , which is ∼5 kJ·
−1
mol higher than that of the respective amine of the guest
−
1
(
(
−NH ) of the guest molecules through detailed DFT studies
molecule G1 (PA = 1173.7 kJ·mol ) (SI Figure 6).
Furthermore, the calculated proton affinity for the amine of
the respective guest molecule G3 has been found to be 1176.7
2
vide infra). Conversely, no complexation-induced change in
the emission spectrum of H was observed in the presence of the
guest molecule G4. This further nullifies the possibility of
formation of any type of adduct due to the presence of a
relatively bulky stopper unit.
−1
kJ.mol , which is also lower than the proton affinity of H (SI
Figure 6). These results suggest that there is a possibility of
more effective proton transfer from the respective NH2+ unit of
the guest molecule to the N-atom of the NH fragment of the
Computational Study. The complexation between H and
guest molecule G1 was also examined using density functional
theory calculations. All geometries were optimized using the
NO -based host molecule H. This also suggests that the larger
6
difference in proton affinity values between H and G1 was
mainly responsible for the large pyrene-based emission
enhancement during the complexation between H and G1,
compared to the complexation between H and G3.
18
B3LYP/6-31G* level of theory in the gas phase. Furthermore,
energy calculations have been performed in DCM medium with
the B3LYP/6-31+G**//B3LYP/6-31G* level of theory using
9
009
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
Interestingly, the calculated proton affinity of the respective
amine of the guest molecule G2 (PA = 1178.7 kJ· mol ) was
found to be very close to that of the host molecule H (SI Figure
the complexation process were also observed in the emission
spectral studies. In all cases different degrees of emission
enhancement due to interruption of the PET process were
observed on initial addition of the guest molecules, which
initiates a FRET process during complexation. Finally, the
computational studies revealed that there was a possibility of
proton transfer from the guest unit to the host during the+
complexation process, and the difference in acidity of the NH2
unit of the guest molecules was mainly responsible for the
different degrees of emission enhancement.
−1
6
). This tends to suggest that there is a lesser possibility of any
proton transfer from the guest molecule G2 to the host H
during the complexation process or the H-bonded adduct
formation. Thus, the observed small enhancement (Figure 9) in
pyrene-based emission intensity is probably due to an effective
C−H···N hydrogen bond formation involving hydrogen atoms
of the polarized methylene groups (−CH −) next to the
2
cationic ammonium center and the unshared pair of electrons
of the NH moiety of the host molecule H. This is supported
H
EXPERIMENTAL SECTION
■
by the observed substantial complexation-induced shifts (Δδ =
Catechol, 2-[2-(2-chloroethoxy)ethoxy]ethanol, p-toluenesulfonyl
chloride, pyren-2-ylmethanamine hydrochloride, benzylamine, 4-tert-
butylbenzylamine, n-butylamine, 3,5-di-tert-butylbenzyl bromide,
hexamethylenetetramine, and anthracene-9-carbaldehyde were ob-
tained commercially and were used as received without any further
0
.47 and 0.31 ppm, respectively, for H and H ) of these
6 7
methylene protons in H·G2 relative to free G2 (Figure 4). In
contrast, these shifts for H and H for G1 in H·G1 were only
6
7
0
.27 and 0.29 ppm, respectively (SI Figures 1 and 2), which
indicated a relatively weaker H-bond formation.
purification. [NH ]PF6 was recrystallized from ethanolic solution
4
Furthermore, appropriate orientation of protons of the NH2+
fragment of the respective guest molecule with respect to that
of the N-atom of the NH unit in the host molecules is also
expected to influence the efficiency of the proton transfer
process. We have performed molecular dynamic calculations
with host−guest complexes to check the frequency of closeness
between the host nitrogen and guest amine hydrogens. The
molecular dynamic simulations were performed for the
complexes of host molecule H with guests G1 and G2 for 5
ns time period with 2 fs time steps using the Merck molecular
force field (MMFF) method. A total of 1000 geometries were
examined to check the proton−nitrogen distance (after every 5
ps). In the case of the G1 molecule as the guest, the proton−
nitrogen distances were below 2.2 Å a total of 394 times,
whereas, in the case of the G2 molecule as the guest, this
happened 350 times. These results again supported the
possibility of more facile proton transfer from G1 to the H
molecule, which is in support of the experimental observations.
before use, and all solvents were dried and distilled prior to use
following standard procedures.
1
H NMR spectra were recorded on a 500 MHz FT NMR
spectrometer at room temperature (rt). The chemical shift (δ) data
and coupling constant (J) values are given in parts per million and
hertz, respectively, throughout this paper unless mentioned otherwise.
Synthesis of 1. 1,2-Dihydroxybenzene (3.00 g, 27.27 mmol) was
dissolved in 70 mL of freshly dried DMF in a two-neck round-bottom
flask. To this solution was added K CO powder (11.30 g, 81.81
2
3
mmol). Then the reaction mixture turned from brown to violet in
color, and KI (13.60 g, 81.81 mmol) was added. This mixture was
allowed to stir for 15 min, and 2-[2-(2-chloroethoxy)ethoxy]ethanol
20
(
9.10 g, 54.54 mmol) was added via a syringe at 60 °C. Then the
temperature was raised to 80 °C and the mixture allowed to stir for 5
days. The solvent was removed under reduced pressure and the
residue extracted three times with CHCl and water. Organic layers
3
were combined and dried over anhydrous sodium sulfate. Solvent was
removed under reduced pressure to give a crude product which was
purified on a silica gel column using methanol/dichloromethane (2:98,
v/v) as the eluent to yield 1 (5.40 g, 53.3%) as a sticky brown
1
semisolid. H NMR (500 MHz, CDCl , δ, ppm): 3.58 (4H, t, J = 4.5),
3
CONCLUSION
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). Anal. Calcd for C H O : C, 57.74; H,
In summary, we have demonstrated how appropriate design of
the host and guest components helps to develop a supra-
molecular assembly where the threading phenomenon results in
an interrupted PET and a fluorescence on response, which in
turn initiates a FRET process. We have also investigated,
through different spectroscopic studies, which stopper size is
18 30 8
8
3
.08. Found: C, 57.67; H, 8.01. ESI-MS: m/z calcd for C H O Na
18 30 8
97.19, found 397.41 [M + Na] .
Synthesis of 2. Compound 1 (5.40 g, 14.56 mmol) was dissolved
+
in THF (40 mL), and 5 mL of NaOH solution (10 M) was added to it
at 0 °C. p-Toluenesulfonyl chloride (9.70 g, 50.96 mmol) 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 the
appropriate for the threading of the cavity of the NO crown
6
ether moiety to form a [2]pseudorotaxane complex. Detailed
1
residue extracted three times with CHCl and water. The organic
H NMR spectroscopic studies revealed that the guest
3
layers were combined and dried over anhydrous sodium sulfate.
Solvent was removed under reduced pressure to give a crude product.
This was purified on a silica gel column using CH OH/CH Cl (2:98,
molecules G1, G2, and G3 are able to thread through the
cavity of the host unit to form the 1:1 complex. However, for
G4, which was substituted with relatively bulkier 3,5-di-tert-
butyl groups, no complexes with the host unit were formed.
The association constants for adducts H·G1, H·G2, and H·G3
evaluated from the ITC measurements showed a systematic
increase in values on changing the stopper from butyl to 4-tert-
butylphenyl in the guest molecules. The obtained thermody-
namic data indicate that the complexation process is also
influenced by the nature of the stopper units. That is, the
complexation of H with guests G1 and G3 is exclusively driven
by a large positive entropic gain and is accompanied by a small
negative enthalpy change. In contrast, the complexation of H
with G2 is driven by a large positive entropic gain along with a
small positive change in enthalpy. The subtle difference in the
nature of the stopper units of the guest molecules influencing
3
2
2
1
v/v) as the eluent to yield 2 (7.75 g, 78.0%) as a sticky brown mass. H
NMR (500 MHz, CDCl , δ, ppm): 2.41 (6H, s), 3.59 (4H, t, J = 4.0),
3
3
.69−3.63 (8H, m), 3.82 (4H, t, J = 5.0), 4.13 (4H, t, J = 5.0), 6.90
13
(4H, s), 7.31 (4H, d, J = 8.0), 7.79 (4H, d, J = 8.5). C NMR (δ,
ppm): 150.7, 147.0, 134.8, 131.8, 129.8, 128.0, 123.4, 116.2, 72.5, 71.5,
70.5, 23.3. Anal. Calcd for C32
H O S : C, 56.29; H, 6.20; S, 9.39.
42 12 2
Found: C, 56.18; H, 6.14; S, 9.31. ESI-MS: m/z calcd for C H O S
32 43 12
2
+
6
5
83.21, found 683.40 [M + H] .
Synthesis of H. Compound 2 (1.00 g, 1.46 mmol) was dissolved in
mL of freshly distilled CH CN in a two-neck round-bottom flask.
3
Pyren-2ylmethanamine hydrochloride (0.43 g, 1.60 mmol) was added
followed by five drops of triethylamine to get a clear solution. To this
stirred solution were added K CO (2.20 g, 16.00 mmol), KI (0.40 mg,
2
3
2.40 mmol), and 30 mL of solvent. The reaction mixture was refluxed
for 18 h. Solvent was removed under reduced pressure and the residue
9
010
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
extracted three times with CHCl . The combined organic layers were
dried over anhydrous sodium sulfate. The crude product was purified
at room temperature. A white precipitate appeared after 24 h and was
filtered through a crucible and dried. It was further dissolved in 5 mL
3
by being passed through an alumina column using hexane/CHCl3
of CHCl . To this mixture was added 25 mL of methanol, and the
3
(
2:8, v/v) as the eluent to yield H (0.49 g, 60.0%) as a sticky brown
reaction mixture was cooled to 0 °C. NaBH (0.50 g) was added
4
1
mass. H NMR (500 MHz, CD Cl , δ, ppm): 2.86 (4H, t, J = 5.5),
portionwise to the stirred cooled reaction mixture, which was stirred
2
2
3
.60−3.58 (8H, m), 3.66 (4H, t, J = 5.0), 3.81 (4H, t, J = 4.5), 4.10
for another 1 h at 0 °C. The solvent was removed under reduced
(
4H, t, J = 4.5), 4.34 (2H, s), 6.91 (4H, s), 7.98 (2H, d, J = 7.5), 8.04
2H, s), 8.11 (2H, d, J = 7.5), 8.17 (2H, d, J = 7.5), 8.65 (1H, d, J = 9).
pressure, the residue was extracted three times with CHCl and water,
3
(
and the organic layers were combined and dried over anhydrous
sodium sulfate. The solvent was removed under reduced pressure to
give the compound as a sticky brown solid. A solution of HCl
(concentrated HCl (0.5 mL) dissolved in acetone (2 mL)) was added
dropwise to the sticky solid dissolved in acetone (20 mL) and the
resulting mixture stirred for 2 h. A white solid was formed, which was
1
3
C NMR (125 MHz, CDCl , δ, ppm): 150.6, 134.8, 132.9, 132.5,
3
1
1
32.3, 131.5, 129.8, 129.1, 128.6, 127.4, 126.6, 126.5, 126.4, 126.0,
23.2, 116.1, 72.6, 72.2, 71.5, 71.3, 70.8, 60.0, 55.8. Anal. Calcd for
C H NO : C, 73.79; H, 6.90; N, 2.46. Found: C, 73.61; H, 6.82; N,
35
39
6
2
H] .
.39. ESI-MS: m/z calcd for C H NO 570.28, found 570.69 [M +
35 40 6
+
isolated by filtration and air-dried. Finally, anion exchange in water
−
Synthesis of 3. 3,5-Di-tert-butylbenzyl bromide (0.50 g, 1.76
using NH
4
PF
60.0%. H NMR (500 MHz, CDCl
(1H, s), 8.11 (2H, d, J = 7.5), 7.96 (2H, d, J = 8.0), 7.58−7.55 (6H,
6
gave the desired PF
6
salt of G3 with a yield of 0.45 g,
1
mmol) was dissolved in a CHCl /EtOH (12:2 v/v), solvent mixture.
3
/CD
3
CN (4:1, v/v), δ, ppm): 8.65
3
To this solution was added hexamethylenetetramine (0.25 g, 1.76
mmol), and the reaction mixture was refluxed for 7 h. A white
precipitate appeared and was filtered through a crucible and dried.
Again the white precipitate was dissolved in 20 mL of EtOH and 5 mL
of concd HCl solvent mixture. Then the reaction mixture was refluxed
for 10 h. A white precipitate appeared and was filtered through a
crucible, dissolved in 100 mL of water, and neutralized with NaHCO3.
Then the mixture was extracted three times with CHCl . The organic
layers were combined and dried over anhydrous sodium sulfate.
Solvent was removed under reduced pressure to yield 3 (0.23 g,
1
3
m), 7.51 (2H, m), 5.12 (2H, s), 4.37 (2H, s), 1.38 (9H, s). C NMR
(125 MHz, CD CN, δ, ppm): 153.4, 131.5, 131.0, 130.9, 130.5, 129.7,
127.8, 127.6, 126.3, 125.8, 123.3, 121.4, 51.7, 42.9, 34.7, 30.7. Anal.
Calcd for C26 : C, 62.52; H, 5.65; N, 2.80. Found: C, 62.42;
H, 5.60; N, 2.72. ESI-MS: m/z calcd for C26 28N 354.22, found
3
H
28NPF
6
H
−
+
3
54.27 [M − PF ] .
6
−
Synthesis of G4. The desired PF6 salt of G4 was obtained by
3
following an experimental procedure similar to that described for G3
1
as a white solid (yield 0.47 g, 57.0%). H NMR (500 MHz, CDCl /
3
1
CD CN (4:1, v/v), δ, ppm): 8.38 (1H, s), 8.20 (2H, d, J = 8.5), 7.99
6
7
0.0%) as a sticky brown solid. H NMR (500 MHz, CD Cl , δ, ppm):
3
2
2
(
(
2H, d, J = 8.5), 7.48−7.42 (4H, m), 7.39 (1H, s), 7.29 (2H, s), 4.67
.30 (1H, s), 7.15 (2H, s), 3.80 (2H, s), 1.31 (18H, s). Anal. Calcd for
2H, s), 4.05 (2H, s), 1.36 (18H, s). 13C NMR (125 MHz, CD CN, δ,
C H N: C, 82.13; H, 11.49; N, 6.39. Found: C, 82.07; H, 11.43; N,
3
15
25
ppm): 151.1, 139.3, 135.1, 134.5, 131.7, 130.5, 129.1, 127.4, 126.2,
25.3, 124.7, 122.9, 121.4, 54.1, 44.3, 34.7, 31.0. Anal. Calcd for
C H NPF : C, 64.20; H, 6.50; N, 2.58. Found: C, 64.18; H, 6.46; N,
6
.31. ESI-MS: m/z calcd for C H N 219.20, found 219.02.
15 25
1
Synthesis of G1. Benzylamine (0.50 g, 5.20 mmol) was added to
anthracene-9-carbaldehyde (1.07 g, 5.20 mmol) dissolved in dry
methanol (25 mL), and the reaction mixture was stirred vigorously at
room temperature. After 24 h, the reaction mixture was cooled to 0
29 35
6
2
.56. ESI-MS: m/z calcd for C H N 410.28, found 410.35 for [M −
6
30 36
− +
PF ] .
°
C. NaBH (0.50 g) was added portionwise to the stirred cooled
4
reaction mixture, which was stirred for another 1 h at 0 °C. The
reaction mixture was allowed to reach room temperature and stirred
for a further 2 h. The solvent was removed under reduced pressure, the
ASSOCIATED CONTENT
* Supporting Information
Determination of the binding constant, computational method,
B3LYP/6-31G*-optimized coordinates, and some spectro-
scopic results. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
residue was extracted three times with CHCl and water, and the
organic layers were combined and dried over anhydrous sodium
sulfate. The solvent was removed under reduced pressure to give the
3
crude product, which was purified on silica gel with CH OH/CHCl3
3
(
4:96, v/v) as the eluent. The desired compound was isolated as a
sticky brown solid. A solution of HCl (concentrated HCl (0.5 mL)
dissolved in acetone (2 mL)) was added dropwise to the sticky solid
dissolved in acetone (20 mL) and the resulting solution stirred for 2 h.
A white solid was formed, which was isolated by filtration and air-
dried. Finally anion exchange in water using NH PF gave the desired
AUTHOR INFORMATION
Corresponding Authors
E-mail: ganguly@csmcri.org.
E-mail: a.das@ncl.res.in.
Notes
■
*
*
4
6
−
1
PF6 salt of G1 with a yield of 0.92 g, 40.0%. H NMR (500 MHz,
CD Cl /CD CN (4:1, v/v), δ, ppm): 8.63 (1H, s), 8.12 (2H, d, J =
The authors declare no competing financial interest.
Previous Affiliation for M.G. and A.D.: CSIR-Central Salt and
Marine Chemicals Research Institute, Bhavnagar, Gujarat
364002, India.
2
2
3
∥
8
7
.0), 8.03 (2H, d, J = 8.5), 7.61 (2H, t, J = 7.5), 7.56 (2H, t, J = 7.5),
.51 (5H, s), 5.10 (2H, s), 4.35 (2H, s). 13C NMR (125 MHz,
CD CN, δ, ppm): 131.3, 130.8, 130.5, 130.3, 129.9, 129.5, 129.2,
3
1
27.8, 125.6, 123.1, 121.0, 52.0, 43.1. Anal. Calcd for C H NPF : C,
22 20 6
5
9.60; H, 4.55; N, 3.16. Found: C, 59.50; H, 4.51; N, 3.11. ESI-MS:
ACKNOWLEDGMENTS
−
+
■
m/z calcd for C H N 298.16, found 298.12 [M − PF ] .
2
2
20
6
−
A.D. thanks the Department of Science and Technology
(DST), New Delhi, India, for financial support. A.D. and B.G.
thank the Council of Scientific and Industrial Research (CSIR)
(Network Projects M2D and MSM-CSC-0129) for support.
A.K.M. and M.S. thank the CSIR (India) for Research
Fellowship. We thank the anonymous reviewers for their
suggestions and comments, which have helped us to improve
the paper.
Synthesis of G2. The desired PF6 salt of G2 was obtained by
following an experimental procedure similar to that described for G1
as a brown solid (yield 0.56 g, 55.0%). H NMR (500 MHz, CDCl /
CD CN (4:1, v/v), δ, ppm): 8.70 (1H, s), 8.27 (2H, d, J = 9.0), 8.16
1
3
3
(
2H, d, J = 8.0), 7.72 (2H, t, J = 7.7), 7.60 (2H, t, J = 6.5), 5.22 (2H,
s), 3.21 (2H, t, J = 8.0), 1.70−1.65 (2H, m), 1.41−1.36 (2H, m), 0.96
3H, m). 13C NMR (125 MHz, CD CN, δ, ppm): 131.3, 130.8, 129.5,
(
1
3
27.6, 125.7, 123.3, 121.1, 118.1, 117.3, 48.8, 44.0, 27.4, 19.3, 12.7.
Anal. Calcd for C H NPF : C, 55.75; H, 5.42; N, 3.42. Found: C,
19
22
6
5
2
5.68; H, 5.37; N, 3.38. ESI-MS: m/z calcd for C H N 264.17, found
19 22
−
+
REFERENCES
64.14 [M − PF ] .
■
6
Synthesis of G3. 4-tert-Butylbenzylamine (0.25 g, 1.53 mmol) was
(1) (a) Sutherland, I. O. Chem. Soc. Rev. 1986, 15, 63. (b) Stoddart, J.
E. Top. Stereochem. 1988, I7, 205. (c) Ishow, E.; Credi, A.; Balzani, V.;
Sapdola, F.; Mandolini, L. Chem.Eur. J. 1999, 5, 984. (d) Cantrill, S.
added to anthracene-9-carbaldehyde (0.31g, 1.53 mmol) dissolved in
dry methanol (25 mL), and the reaction mixture was stirred vigorously
9
011
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012

The Journal of Organic Chemistry
Article
J.; Pease, A. R.; Stoddart, J. F. J. Chem. Soc., Dalton Trans. 2000, 3715.
Rissanen, K.; Kirchner, B.; Schalley, C. A. Org. Biomol. Chem. 2012, 10,
5954.
(
e) Meilion, J. C.; Voyer, N.; Biron, E.; Sanschagrin, F.; Stoddart, J. F.
Angew. Chem., Int. Ed. 2000, 39, 143. (f) Dichtel, W. R.; Miljanic, O. S.;
́
(12) (a) Ashton, P. R.; Chrystal, E. J. T.; Glink, P.; Menzer, S.;
Schiavo, C.; Spencer, N.; Stoddart, J. F.; Tasker, P. A.; White, A. J. P.;
Williams, D. J. Chem.Eur. J. 1996, 2, 709.
Zhang, W.; Spruell, J. M.; Patel, K.; Aprahamian, I.; Heath, J. R.;
Stoddart, J. F. Acc. Chem. Res. 2008, 41, 1750. (g) Niu, Z.; Gibson, H.
W. Chem. Rev. 2009, 109, 6024. (h) Suresh, M.; Mandal, A. K.; Suresh,
(13) (a) Jiang, W.; Winkler, H. D. F.; Schalley, C. A. J. Am. Chem. Soc.
2
(
008, 130, 13852.
̈
14) (a) Bonal, C.; Israeli, Y.; Morel, J. P.; Morel-Desrosiers, N. J.
E.; Das, A. Chem. Sci. 2013, 4, 2380. (i) Spat
Org. Chem. 2010, 6, 32.
2) (a) Bossi, M.; Belov, V.; Polyakova, S.; Hell, W. S. Angew. Chem.,
̈ ̈
h, A.; Konig, B. Beilstein J.
Chem. Soc., Perkin Trans. 2001, 2, 1075. (b) Liu, Y.; Guo, D. S.; Zhang,
H. Y.; Ma, Y. H.; Yang, E. C. J. Phys. Chem. B 2006, 110, 3428. (c) Liu,
Y.; Ma, Y. H.; Chen, Y.; Guo, D. S.; Li, Q. J. Org. Chem. 2006, 71,
(
Int. Ed. 2006, 45, 7462. (b) Yen, M. L.; Li, W. S.; Lai, C. C.; Chao, I.;
Chiu, S. H. Org. Lett. 2006, 8, 3223. (c) Cooke, G.; Woisel, P.; Bria,
M.; Delattre, F.; Garety, J. F.; Hewage, S. G.; Robani, G.; Rosair, G. M.
Org. Lett. 2006, 8, 1423. (d) Olson, A. M.; Braunschweig, A. B.; Fang,
L.; Ikeda, T.; Klajn, M. R.; Trabolsi, A.; Wesson, J. P.; Benilez, D.;
Mirkin, C. A.; Grzybowski, B. A.; Stodart, J. F. Angew. Chem., Int. Ed.
6
9
468. (d) Chen, L.; Zhang, Y. M.; Liu, Y. J. Phys. Chem. B 2012, 116,
500. (e) Chen, L.; Zhang, H. Y.; Liu, Y. J. Org. Chem. 2012, 77, 9766.
(
15) (a) Lakowicz, J. R. Principles of Fluorescence Sspectroscopy, 3rd
ed.; Springer: New York, 2006.
16) (a) Mandal, A. K.; Suresh, M.; Das, P.; Das, A. Chem.Eur. J.
012, 18, 3906.
17) (a) Watrob, H. M.; Pan, C. P.; Barkley, M. D. J. Am. Chem. Soc.
003, 125, 7336.
18) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
b) Hehre, W. J.; Radom, L.; Schleyer, P. V. R.; Pople, J. A. Ab Initio
(
2
(
2
2
009, 48, 1. (e) Lohmann, F.; Ackermann, D.; Famulok, M. J. Am.
Chem. Soc. 2012, 134, 11884.
3) (a) Kelly, T. R. Acc. Chem. Res. 2001, 34, 514. (b) Schalley, C. A.;
Beizai, K.; Vogtle, F. Acc. Chem. Res. 2001, 34, 465. (c) Makita, Y.;
Kihara, N.; Takata, T. J. Org. Chem. 2008, 73, 9245.
4) (a) Barrell, M. J.; Leigh, D. A.; Lusby, P. J.; Slawin, A. M. Z.
(
̈
(
(
(
Molecular Orbital Theory; Wiley: New York, 1988. (c) Becke, A. D. J.
Chem. Phys. 1993, 98, 5648.
Angew. Chem., Int. Ed. 2008, 47, 8036. (b) Yang, C. H.; Prabhakar, C.;
Huang, S. L.; Lin, Y. C.; Tan, W. S.; Misra, N. C.; Sun, W. T.; Yang, J.
S. Org. Lett. 2011, 13, 5632. (c) Dial, B. E.; Pellechia, P. J.; Smith, M.
D.; Shimizu, K. D. J. Am. Chem. Soc. 2012, 134, 3675.
(
̀
19) (a) Cances, E.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997,
1
5
3
4
2
07, 3032. (b) Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997, 106,
151. (c) Barone, V.; Cossi, M.; Tomasi, J. J. Chem. Phys. 1997, 107,
210. (d) Barone, V.; Cossi, M.; Tomasi, J. J. Comput. Chem. 1998, 19,
(
5) (a) Keaveney, C. M.; Leigh, D. A. Angew. Chem., Int. Ed. 2004, 43,
222. (b) Saha, S.; Flood, A. H.; Stoddart, J. F.; Impellizzeni, S.; Silvi,
S.; Venturi, M.; Credi, A. J. Am. Chem. Soc. 2007, 129, 12159.
c) Yamauchi, A.; Miyawaki, A.; Takashima, Y.; Yamaguchi, H.;
1
04. (e) Tomasi, J.; Mennucci, B.; Cances
11.
20) (a) Halgren, T. J. Comput. Chem. 1996, 17, 490. (b) Halgren, T.
J. Comput. Chem. 1996, 17, 520. (c) Halgren, T. J. Comput. Chem.
996, 17, 553.
̀
, E. J. Mol. Struct. 1999, 464,
(
(
Harada, A. J. Org. Chem. 2010, 75, 1040. (d) Fahrenbach, A. C.; Bruns,
C. J.; Cao, D.; Stoddart, J. F. Acc. Chem. Res. 2012, 45, 1581.
1
(
1
e) Zhang, Z. J.; Han, M.; Zhang, H. Y.; Liu, Y. Org. Lett. 2013, 15,
698.
6) (a) Okamoto, A.; Tanaka, K.; Saito, I. J. Am. Chem. Soc. 2004,
26, 9458. (b) van Noort, D.; Landweber, L. F. Nat. Comput. 2005, 4,
63. (c) Romuald, C.; Busseron, E.; Coutrot, F. J. Org. Chem. 2010, 75,
516. (d) Horie, M.; Suzaki, Y.; Hashizume, D.; Abe, T.; Wu, T.;
(
1
1
6
Sassa, T.; Hosokai, T.; Osakada, K. J. Am. Chem. Soc. 2012, 134, 17932.
e) Suresh, M.; Mandal, A. K.; Kesharwani, M. K.; Adarsh, N. N.;
Ganguly, B.; Kanaparthi, R. K.; Samanta, A.; Das, A. J. Org. Chem.
(
2
011, 76, 138. (f) Mandal, A. K.; Suresh, M.; Das, P.; Das, A. Chem.
Eur. J. 2012, 18, 3906. (g) Mandal, A. K.; Suresh, M.; Das, A. Org.
Biomol. Chem. 2011, 9, 4811.
(
7) (a) Balllardini, R.; Balzani, V.; Leon, M. C.; Credi, A.; Gandolfi,
M. T.; Ishow, E.; Perkins, J.; Stoddart, J. F.; Tseng, H. R.; Wenger, S. J.
Am. Chem. Soc. 2002, 124, 12786. (b) Leong, W. L.; Vittal, J. J. Chem.
Rev. 2011, 111, 688.
(
8) (a) Kolchinski, A. G.; Busch, D. H.; Alcock, N. W. Chem.
Commun. 1995, 1289. (b) Jones, J. W.; Gibson, H. W. J. Am. Chem.
Soc. 2003, 125, 7001.
(
9) (a) deSilva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Nature
1
993, 364, 42. (b) deSilva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson,
T.; Huxley, A. J. M.; MeCoy, C. P.; Rademacher, J. T.; Rice, T. E.
Chem. Rev. 1997, 97, 1515. (c) Ghosh, P.; Bharadwaj, P. K.; Roy, J.;
Ghosh, S. J. Am. Chem. Soc. 1997, 119, 11903. (d) Chen, X.; Pradhan,
T.; Wang, F.; Kim, J. S.; Yoon, J. Chem. Rev. 2012, 112, 1910. (e) Bull,
S. D.; Davidson, M. G.; van den Elsen, J. M. H.; Fossey, J. S.; Jenkins,
A. T. A.; Jiang, Y.; Kubo, Y.; Marken, F.; Sakurai, K.; Zhao, J.; James,
T. D. Acc. Chem. Res. 2013, 46, 312.
(
10) (a) Cantrill, S. J.; Fulton, D. A.; Heiss, A. M.; Pease, A. R.;
Stoddart, J. F.; White, A. J. P.; Williams, D. J. Chem.Eur. J. 2000, 6,
274. (b) Zhang, C.; Li, S.; Zhang, J.; Zhu, K.; Li, N.; Huang, F. Org.
2
Lett. 2007, 9, 5553. (c) Jiang, W.; Winkler, H. D. F.; Schalley, C. A. J.
Am. Chem. Soc. 2008, 130, 13852. (d) Turnbull, W. B.; Daranas, A. H.
J. Am. Chem. Soc. 2003, 125, 14859.
(
11) (a) Wiseman, T.; Williston, S.; Brandts, J. F.; Lin, L.-N. Anal.
Biochem. 1989, 179, 131. (b) Kaufmann, L.; Dzyuba, E. V.; Malberg,
F.; Low, N. L.; Groschke, M.; Brusilowskij, B.; Huuskonen, J.;
̈
9
012
dx.doi.org/10.1021/jo400752d | J. Org. Chem. 2013, 78, 9004−9012