Macrocycles consisting of flexible and rigid segments: Enforced folding and host-guest inclusion exciplex formation

Article abstract of DOI:10.1016/j.tet.2013.07.020

Macrocycles consisting of two tris(phenylene ethynylene) (or tri-PE) units connected via two flexible linkers adopt an 'unfolded' conformation that is converted into a folded conformation upon introducing intramolecular hydrogen bonding interaction. These foldable macrocycles are capable of forming inclusion charge transfer (CT) complex with electron-deficient small aromatics.

Full text of DOI:10.1016/j.tet.2013.07.020

Tetrahedron 69 (2013) 8487e8493
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Macrocycles consisting of flexible and rigid segments: enforced
folding and host-guest inclusion exciplex formation
,
a
a
a
a
,
,
*
Xiaomei Tang a , Li Lin , Futao Liu , Xiangjun Yue , Bing Gong c, Minfeng Li a
,
*
,b,
Lan He a
*
a College of Chemistry, Beijing Normal University, Beijing 100875, PR China
b National Institutes for Food and Drug Control, Beijing 100050, PR China
c Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 May 2013
Received in revised form 1 July 2013
Accepted 8 July 2013
Available online 23 July 2013
Macrocycles consisting of two tris(phenylene ethynylene) (or tri-PE) units connected via two flexible
linkers adopt an ‘unfolded’ conformation that is converted into a folded conformation upon introducing
intramolecular hydrogen bonding interaction. These foldable macrocycles are capable of forming in-
clusion charge transfer (CT) complex with electron-deficient small aromatics.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Macrocycles
Folding
Hydrogen binding
Inclusion complex
Charge transfer complex
1. Introduction
benzene units that flank their central meta-linked residue were
prepared.
Well-defined molecular and supramolecular structures are
generated by restricting the relative rotational and translational
motion of two or more structural components using multi-point
interactions.1 The formation of supramolecular assemblies with
defined shapes relies on multi-point intermolecular interactions
that act cooperatively.2,3 Folded molecular structures of both nat-
ural4 and unnatural5,6 origins are examples of intramolecular self-
assemblies in which the corresponding sub-structural compo-
nents are connected via both covalent and non-covalent forces. The
relative motion of covalently linked structural units of a folded
structure leads to conformational change that plays a critical role in
various binding and catalytic events. We recently described double-
decked molecular crescents based on macrocycles that consist of
flexible covalent tethers and two para-linked phenylene ethynylene
(PE) halves with a persistent shape.7 To further explore the gen-
erality of the observed folding behavior, we set out to investigate
the effects of structural variations on the conformational transi-
tions of these molecules. Macrocycles 1 (Scheme 1) with two
2. Results and discussion
1H NMR dilution studies in CDCl3 revealed that there were no
appreciable changes of chemical shifts from 1 mM to 10 mM for
macrocycle 1a, which suggested that 1a did not engage in signif-
icant intermolecular aggregation within this concentration range.
In comparison to the aromatic protons of 2a, which can be
regarded as being half of 1a, the aromatic protons of 1a show
small upfield shifts (from 0.01 ppm to 0.11 ppm). In contrast, the
aromatic protons of fully folded macrocycle consisting of two
stacked halves, were found to undergo much larger upfield shifts
(up to 0.23 ppm) as compared to its untethered tri-PE ‘half’.7 These
results suggested that, compared to those of 1, the two tri-PE
halves of 1a have a low propensity for stacking interaction,
which implies that 1a may adopt a conformation that is different
from the fully folded ones.7
The crystal structure of 1a (obtained from CHCl3/CH3OH by slow
evaporation of solvent) (Fig. 1) reveals that the two halves of 1a
only partially overlap, with the disulfide-tethered benzene residues
sitting on top of the ethynyl moieties, leading to a ‘partially folded’
conformation in which the concave edges of the two tri-PE units
roughly face each other and the two meta-linked benzene rings
* Corresponding authors. E-mail addresses: minfeng_li@bnu.edu.cn (M. Li),
helan1961@yahoo.com.cn (L. He).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.020

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X. Tang et al. / Tetrahedron 69 (2013) 8487e8493
X
O
R
1
X
O
6
R
2
5
4
1
3
I2
6
S
S
S
S
2
O
O
O
O
O
O
O
O
5
4
1
CH2Cl2
3
Ph3CS
SCPh3
O
O
O
O
2
a: X=O, R= -(CH2CH2O)2CH3
b: X=O, R= -(CH2CH2O)3CH3
c: X=NH, R= -CH2CH2CH2CH3
R
O
X
Scheme 1. Synthesis and structures of macrocycles 1.
presence of two different C2eHs caused by the folding of 1c, which
leads to two different distances and thus different NOE contacts
between C2eHs and C1eHs. Specifically, due to the folding of 1c,
the one C2eH that shares on the same benzene ring with C1eH, is
different distance-wise from the other C2eH that is on the other
benzene ring. However, both C2eHs are close to C1eH as indicated
by the observed NOEs. This result supports the folded conformation
of 1c.
Similar phenomenon was observed when C10eH was satu-
rated. The signal of CONH now splits into a doublet. It is likely
that the doublet indicates that the two of CONH protons, one
from the CONH on the same side chain and the other from the
side chain on the other half of the molecule, are all placed into
close proximity to the C10eH. This also supports the folding
of 1c.
Intrinsic fluorescence has been widely applied to study the
conformational states and transitions of protein8 and synthetic
foldamers such as oligo(phenylene ethynylenes) in solution.9
Fig. 3a summarizes the absorption and emission spectra of 1b, 1c
Fig. 1. The solid-state structure of macrocycle 1a. Hydrogen atoms are omitted for
clarity.
were apart from each other by pointing to nearly opposite di-
rections. The crystal structure of 1a has provided an explanation on
why the observed upfield shifts of the aromatic protons of 1a were
smaller than expected. The crystal structure also suggests that
a subtle structural change, i.e., from para- to meta-substitution,
leads to dramatic changes in folding behavior.
(3.0 mM, excitation 285 nm), and H1c (6.0 mM, excitation 285 nm)
It was expected that, if additional forces were introduced via
structural modification, the conformation of the resultant de-
rivative may be tuned accordingly. To probe whether enhancing the
strength and directionality of non-covalent interaction between the
two tri-PE halves could enforce a folded conformation, the ester
groups of 1a or 1b were replaced with a secondary amide group to
give macrocycle 1c. With its two amide side chains capable of
forming an intramolecular H-bond, macrocycle 1c may adopt
a folded conformation similar to those observed for fully folded
ones. Examining 1c with 1H NMR revealed that, in contrast to the
small shifts exhibited by the aromatic protons of 1b, those of
macrocycle 1c showed noticeable upfield shifts (up to 0.21 ppm)
relative to the protons of 2c (see Supplementary data). Besides, the
amide proton signal of 1c showed a large (0.90 to w1.00 ppm)
downfield shift relative to that of 2c. The observed downfield shift
of the amide proton of 1c was essentially independent of concen-
trations (from 2 mM to 8 mM, see Supplementary data), which
demonstrates the presence of intramolecular H-bonds and suggests
that intermolecular aggregation is negligible. The 1H NMR data of
1c confirmed our expectation that, due to the presence of an
intramolecular H-bond between its two amide groups, compound
1c adopts a folded conformation reminiscent of those fully folded
ones.7 Meanwhile, data from the NOE difference spectra of 1c in
deuterated chloroform also confirmed that compound 1c adopts
a folded conformation (Fig. 2).
measured in methanol. H1c can be regarded as half of 1c. The ab-
sorption and emission spectra of the three compounds are very
similar. The absorption peaks of 1b are at 285 and 302 nm, 1c at 284
and 304 nm, and H1c at 280 and 303 nm, respectively. The emission
maximum of 1b, 1c, and H1c is at 365 nm, 355 nm, and 355 nm,
respectively. These results are not surprising since all three struc-
tures share the same chromophore. Apparently, the nature of side
chains (ester or amide) does not have any effect on the photo-
physical characteristics of these molecules. However, the emission
intensity of 1c is significantly lower than those of the other two
compounds (1b and H1c), with the order of maximum intensity of
both absorbance and emission being H1c>1b>1c. Furthermore, no
significant difference was observed in the excited state dynamics of
1b and H1c. Both display a similar fluorescence lifetime of 4.1 ns
(Fig. 3b and Supplementary data). However, the excited state of 1c
shows an increased lifetime of 5.1 ns, which strongly suggests the
existence of intramolecular interactions between the two PE halves
of 1c. Taken together, the fluorescence decrease observed for 1c is
most likely due to quenching caused by its folded conformation in
which the two tri-PE units are brought into close proximity, most
likely in a superposed fashion. It is apparent that the observed
strong fluorescence of 1b and H1c also arises from their confor-
mations in solution. Significant interaction between two tri-PE
units of 1b like that of 1a is not likely because of its partially fol-
ded conformation. Compound H1c, being molecularly dissolved in
solution, should not engage in any meaningful intermolecular ag-
gregation. The nearly identical emission intensities of 1b and H1c,
which are much stronger than that of 1c, provide experimental
When the signal of C1eH was saturated by irradiation, it is
apparent that the signals of C2eH and CONH show NOE noticeable
changes. Two peaks, one upward and the other downward, are
observed for C2eH. This observation may be explained by the

X. Tang et al. / Tetrahedron 69 (2013) 8487e8493
8489
Fig. 2. From top to bottom the signals of the protons of 1c that are irradiated are C10eH, CONH, C1eH and C3eH.
H
N
O
O
O O
O
O
H
N
O
S
S
S
S
S
S
S
S
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
1c
H1c
1b
HS
SH
O
O
O
O
O
O
O
O
O
O
N
H
a.600
b.
4
H1c
1b
1c
1c
1b
H1c
400
3
2
1
0
200
0
200
250
300
350
Wavelength, nm
400
450
500
60
70
80
t / ns
Fig. 3. (a) Excitation (dashed lines) and emission spectra (solid lines) of macrocycle 1b (red), 1c (blue), and half ring H1c (black) in methanol. (b) Fluorescence decay traces of
macrocycle 1b, 1c, and half ring H1c in methanol (lex¼285 nm).

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X. Tang et al. / Tetrahedron 69 (2013) 8487e8493
evidence supporting that the fluorescence quenching observed for
1c is the result of the folded conformation of this molecule. Given
the observed difference in the emission intensities of 1b and 1c, the
critical role played by intramolecular H-bonding in ‘locking’ the
folded conformation of 1c is obvious. Results from fluorescence
studies are consistent with NMR data of 1b and 1c, and with the
crystal structure of 1b.
The fluorescence spectra of 1c and H1c also indicate that, be-
sides intramolecular H-bonding, the two covalent tethers of 1c are
also crucial for the two PE halves to superpose in the folded con-
character in the interaction between 1c and HFB. It is notable that,
in the fluorescence excitation spectra (Fig. 4b), the original ab-
sorption in the blue region of 1c at 235 nm has red-shifted to
355 nm, along with the significant fluorescence enhancement of 1c
in the presence of HFB. In contrast, compounds 1b (Fig. 4c and d)
and H1c (data not shown) do not display appreciable hyper-
chromism or fluorescence enhancement in the present of HFB.
Considering the different conformations adopted by 1c and 1b in
solution and the electrostatic complementarity between the
electron-deficient HFB and the relatively electron-rich tri-PE units
of 1c, it can be concluded that HFB and 1c in its folded conformation
form a hosteguest inclusion complex,1ceHFB, with charge transfer
characters. A discrete CT transition of 1c although a red shift of
absorption is displayed. One possible reason for this might be that
excitation leading to the CT states occurs directly via a local tran-
sition of donor (1c).10
formation. To verify this, compound 1c (3.0 mM in methanol) was
treated with glutathione (GSH), a reducing reagent that can effi-
ciently cleave disulfide bonds, to break the macrocycle into two
identical halves. It is found that the shapes of the absorption and
emission spectra of the solution of GSH-treated 1c remain similar to
those of 1c and H1c (see Supplementary data, Fig. s5). However, the
fluorescence intensity of GSH-treated 1c (3.0
that of 1c (3.0 M) and is in fact nearly identical to that of H1c at the
same concentration of tri-PE units (6.0 M in methanol). The result
confirms that covalent tethers play an indispensable role in the
folding of 1c, which accounts for its observed fluorescence
quenching.
The folding of 1c may form a cavity that may interact with other
aromatics, especially those with complementary electronic prop-
erties. The interaction between 1 and electron-deficient aromatic
molecules was thus investigated. As shown in Fig. 4a, UV spectra of
1c and hexafluorobenzene (HFB) (1:3) in methanol show a dra-
matic hyperchromism. The mixture exhibits an over ten-fold in-
crease in UV absorbance as compared to that of 1c or HFB alone
under the same conditions. The observation of hyperchromism for
the mixture of 1c and HFB clearly indicates the charge transfer (CT)
m
M) is higher than
Another piece of evidence supporting the formation of inclusion
exciplex is provided by examining the kinetics of the excited states.
The emission lifetime of 1c increased from 5.10 ns to 5.46 ns upon
adding HFB (Fig. 5a and see Supplementary data), which is a strong
indication for the formation of inclusion complex.11 The observed
fluorescence enhancement of 1c in the complex may arise from
structural rigidification of the chromophore units induced by
complex formation, which leads to a decrease of rotational and
vibrational degree of freedom and reduction of the probability of
non-radiative decay relaxation.12 The stoichiometry of the 1ceHFB
complex was determined based on continuous variation (Job’s plot)
method, which suggested that stoichiometry of the 1ceHFB com-
plex was 1:3 (see Supplementary data, Fig. s6), which was con-
firmed by the observation of a peak corresponding to the complex
[1cþ3HFB] in the MALDI-TOF mass spectra (Fig. 5b).
m
m
Fig. 4. Representative (a) UV (the inset shows details of 1c’s absorbance) and (b) excitation and emission spectra of 1c in the absence (red) and presence (black) of HFB; (c) UV and
(d) excitation and emission spectra of 1b in the absence (red) and in the presence (black) of HFB. The concentration of 1b and 1c is 2.5
lem¼350 nm.
m
M in methanol and HFB 7.5
mM. lex¼285 nm,

X. Tang et al. / Tetrahedron 69 (2013) 8487e8493
8491
Fig. 5. (a) Fluorescence decay traces of 1c and 1ceHFB mixture (1:3, mole ratio) in methanol (lex¼285 nm); (b) MALDI-TOF mass spectra of 1ceHFB mixture (1:3, mole ratio),
dithranol as matrix.
3. Conclusions
4.2.1. Compound 2a.
O
O
O
O
O
In summary, macrocycles 1a and 1b, consisting of two rigid tri-
PE halves connected via two flexible disulfide-containing covalent
tethers, were found to adopt an unfolded (or partially folded)
conformation. Introducing of intramolecular H-bonding led to
macrocycle 1c that was found to adopt a folded and, most likely,
face-to-face ‘stacking’ conformation. It is demonstrated that 1c in
a folded conformation is capable of forming inclusion charge
transfer complex with hexafluorobenzenes, either by insertion or
intercalating into the folded macrocycles, which results in signifi-
cant hyperchromism in UV absorption and fluorescence enhance-
ment. This work revealed that this class of foldable macrocycles
may serve as basis for developing of novel host molecules in the
design of molecular sensor and controlled delivery vehicles.
SCPh3
Ph3CS
O
O
O
2a
Compound 2awas obtained in 50% yield as a yellow solid.1H NMR
(400 MHz, CDCl3):
d
8.20 (d, J¼1.4 Hz, 4H), 8.01 (d, J¼7.9 Hz, 2H), 7.89
(s, 1H), 7.71 (d, J¼7.7 Hz, 2H), 7.45 (d, J¼7.3 Hz, 14H), 7.29 (t, J¼7.5 Hz,
12H), 7.21 (t, J¼7.2 Hz, 6H), 4.58e4.49 (m, 2H), 4.13 (t, J¼6.5 Hz, 4H),
3.91e3.83(m, 2H), 3.76e3.67 (m, 2H), 3.63e3.54 (m, 2H), 3.39 (s, 3H),
4. Experimental section
4.1. General
2.63 (t, J¼6.5 Hz, 4H); 13C NMR (100 MHz, CDCl3):
d 165.38, 165.14,
144.62, 138.42, 135.88, 132.87, 132.56, 131.05, 130.45, 129.83, 129.61,
128.62,128.13,126.84,123.88,123.10, 89.92, 88.44, 71.98, 70.61, 69.16,
66.98, 64.54, 63.49, 59.10; MS: m/z (MALDI-TOF): 1139.5 [MþNa]þ.
Chemicals were purchased from commercial sources and used
as received. Reactions requiring an inert gas were all under nitro-
gen. Silica gel for analytical thin layer chromatography (TLC) and
column chromatography (200w300 mesh) were purchased from
Qingdao Haiyang Chemical Co., Ltd & Spegial Silica Gel Factory. The
1H NMR spectra were recorded at 400 MHz and 13C NMR spectra
were measured at 100 MHz on a Bruker AV400 spectrometer at
ambient temperature using CDCl3 as solvent (purchased from Bei-
jing Chongxi High-Tech Incubator Co., Ltd). Chemical shifts are re-
ported in parts per million (ppm) downfield from TMS
(tetramethylsilane). Coupling constant in 1H NMR are expressed in
hertz (Hz). Mass spectra (MALDI-TOF) were obtained on a Bruker
autoflex-III spectrometer. Fluorescent spectra were recorded on an
Agilent Technologies FL1109M011 fluorescent spectrometer. Fluo-
rescent lifetime spectra were recorded on a HORIB-Tempro-01
spectrometer. The sparkling lamp-house (ns) was HORIB-IBH-
NanoLED-280. UVevis spectra were recorded on a VARIAN 50
Conc spectrometer. Data from the NOE difference spectra of 1c in
deuterated chloroform were obtained on a VNS-600. Mixing time
was 0.6 s, and relaxation time was 1.2 s.
4.2.2. Compound 1a.
O
O
O
O
S
S
S
S
O
O
O
O
O
O
O
O
O
O
O
O
1a
Compound 1a was obtained in 44% yield as a white solid. 1H
NMR (400 MHz, CDCl3):
d
8.15 (t, J¼1.4 Hz, 4H), 8.12 (d, J¼1.6 Hz,
4H), 8.05e7.96 (m, 4H), 7.79 (t, J¼1.5 Hz, 2H), 7.70e7.60 (m, 4H),
7.41 (t, J¼7.8 Hz, 4H), 4.62 (t, J¼6.5 Hz, 8H), 4.56e4.47 (m, 4H),
3.93e3.82 (m, 4H), 3.71 (dd, J¼5.6 Hz, 3.6 Hz, 4H), 3.39 (s, 6H), 3.13
4.2. General procedure for synthesis of compounds 1aec and
2aec
(t, J¼6.5 Hz, 8H); 13C NMR (100 MHz, CDCl3):
d 165.43, 165.02,
Compounds 2aec and 1aec were synthesized based on the
same procedure we described before.7
138.35,135.90,132.84,132.42,130.88,130.23,129.72,128.60,123.74,

8492
X. Tang et al. / Tetrahedron 69 (2013) 8487e8493
123.11, 89.83, 88.46, 71.93, 70.56, 69.12, 64.48, 63.02, 59.04, 37.56;
Compound 2c was obtained in 71% yield as a yellow solid. 1H NMR
(400 MHz, CDCl3):
MS: m/z (MALDI-TOF): 1283.1 [MþNa]þ.
d
8.19 (s, 2H), 8.01 (d, J¼7.9 Hz, 2H), 7.89 (s, 2H),
7.83 (s, 1H), 7.71 (d, J¼7.7 Hz, 24H), 7.46 (m, 14H), 7.30 (t, J¼7.6 Hz,
12H), 7.22 (t, J¼7.2 Hz, 6H), 6.13 (t, J¼5.4 Hz, 1H), 4.12 (t, J¼6.5 Hz,
4H), 3.47 (dd, J¼13.0 Hz, 7.0 Hz, 2H), 2.62 (t, J¼6.5 Hz, 4H),1.65e1.58
(m, 2H), 1.48e1.38 (m, 2H), 0.97 (t, J¼7.3 Hz, 3H); 13C NMR
4.2.3. Compound 2b.
(100 MHz, CDCl3):
d 165.85, 165.39, 144.57, 136.84, 135.86, 135.64,
132.87,130.45,129.83,129.58,128.64,128.01,126.84,123.92,123.05,
89.88, 88.54, 66.94, 63.48, 39.99, 31.62, 30.98, 20.16, 13.79; MS: m/z
(MALDI-TOF): 1092.7 [MþNa]þ.
4.2.6. Compound 1c.
H
N
O
Compound 2b was obtained in 59% yield as a yellow wax. 1H
NMR (400 MHz, CDCl3):
d
8.11 (s, 4H), 7.93 (d, J¼7.9 Hz, 2H), 7.81 (s,
1H), 7.64 (d, J¼7.8 Hz, 2H), 7.60e7.56 (m, 2H), 7.38 (t, J¼7.9 Hz,16H),
7.23e7.15 (m, 22H), 4.44 (t, J¼4.9 Hz, 2H), 4.07 (t, J¼6.5 Hz, 4H), 3.79
(dd, J¼4.9, 6.6 Hz, 2H), 3.66e3.63 (m, 2H), 3.61e3.59 (m, 2H),
3.58e3.56 (m, 2H), 3.46 (t, J¼5.0 Hz, 2H), 3.26 (s, 3H), 2.99 (q,
J¼7.3 Hz, 2H), 2.57 (t, J¼6.6 Hz, 4H); 13C NMR (100 MHz, CDCl3):
S
S
S
S
O
O
O
O
O
O
O
O
d
164.35, 164.10, 143.59, 137.41, 134.87, 131.84, 131.50, 131.14, 131.04,
130.95, 130.93, 130.02, 129.48, 128.81, 128.57, 127.60, 127.55, 127.43,
126.98, 123.88, 122.85, 122.05, 89.91, 87.40, 76.35, 70.03, 69.70,
69.64, 69.61, 68.09, 65.95, 63.54, 62.46, 57.97, 44.50, 29.97; MS: m/z
(MALDI-TOF): 1183.3 [MþNa]þ.
O
N
H
4.2.4. Compound 1b.
1c
O
O
O
O
O
Compound 1c was obtained in 35% yield as a white solid. 1H
NMR (400 MHz, CDCl3):
d
8.02 (s, 4H), 7.96 (d, J¼7.9 Hz, 4H), 7.78 (d,
J¼1.3 Hz, 4H), 7.61 (s, 2H), 7.57 (d, J¼7.7 Hz, 4H), 7.37 (d, J¼7.8 Hz,
4H), 7.01 (t, J¼5.7 Hz, 2H), 4.63 (t, J¼6.4 Hz, 8H), 3.54 (dd, J¼12.9 Hz,
7.0 Hz, 4H), 3.15 (t, J¼6.4 Hz, 8H), 1.74e1.70 (m, 5H), 1.49e1.44 (m,
S
S
S
S
O
O
O
O
O
O
O
O
4H), 1.00 (t, J¼7.3 Hz, 6H); 13C NMR (100 MHz, CDCl3):
d 166.23,
165.64, 136.56, 135.96, 135.47, 132.82, 130.13, 130.10, 129.62, 128.62,
123.64, 123.19, 89.64, 88.80, 63.08, 40.14, 37.71, 31.69, 20.27, 13.84;
MS: m/z (MALDI-TOF): 1189.4 [MþNa]þ.
Acknowledgements
O
O
O
O
O
1b
This work was supported by the Cultivation Fund of the Key
Scientific and Technical Innovation Project, Ministry of Education of
China Grant 706009 (to B.G.), the NSFC Grant 20070027038 (to L.H.)
and 91027034 (to Y.J.O.), the Training Program of the Major Research
Plan of the NSFC Grant 91227109 (to B.G.), the Special Fund for Agro-
scientific Research in the Public Interest Grant 201103027 and Sig-
nificant New Drugs Creation-special Science and Technology Major
Grant 2011ZX09307-002-01 (to L.H.), and the US National Science
Foundation Grants CBET-1066947 and CHE-1306326 (to B.G.).
Compound 1b was obtained in 41% yield as a straw yellow, viscous
solid. 1H NMR (400 MHz, CDCl3):
d
8.15 (s, 4H), 8.12 (d, J¼1.2 Hz, 4H),
8.01 (d, J¼7.9 Hz, 4H), 7.79 (s, 2H), 7.67 (d, J¼7.8 Hz, 4H), 7.44 (t,
J¼7.8 Hz, 4H), 3.87 (t, J¼4.8 Hz, 4H), 3.73e3.72 (m, 4H), 3.69e3.67 (m,
4H), 3.66e3.64 (m, 4H), 3.54 (t, J¼4.3 Hz, 4H), 3.34 (s, 6H), 3.15 (t,
J¼6.4 Hz, 8H); 13C NMR (100 MHz, CDCl3):
d 164.46, 164.05, 137.40,
134.94, 131.87, 131.42, 129.90, 129.24, 128.76, 127.63, 122.77, 122.12,
88.86, 87.47, 76.34, 76.02, 75.70, 70.94, 69.69, 69.65, 69.61, 68.11, 63.53,
62.04, 57.97, 36.56, 28.68; MS: m/z (MALDI-TOF): 1371.4 [MþNa]þ.
Supplementary data
4.2.5. Compound 2c.
NMR spectra; mass spectra; fluorescence lifetime measure-
ment; experiment procedure of H1c and Job’s plot. Supplementary
data associated with this article can be found in the online version,
at http://dx.doi.org/10.1016/j.tet.2013.07.020.
H
N
O
References and notes
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