A chromogenic molecular capsule attributable to dipolar amide resonance structure

Article abstract of DOI:10.1039/c4cc10412a

A new chromogenic, self-assembled molecular capsule G@2₂ is developed by introducing four (N,N-dimethyl-4-aminophenyl) azobenzyl moieties on the upper rim of a resorcin[4]arene-based amidoimino-cavitand. The tuning of conjugation between amido and (N,N-dimethyl-4-aminophenyl)azobenzyl groups by acid-base titration allows naked-eye detection of molecular capsule formation.

Full text of DOI:10.1039/c4cc10412a

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. Paek, Y. S. Park
and J. Park, Chem. Commun., 2015, DOI: 10.1039/C4CC10412A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/chemcomm

Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/C4CC10412A
ChemComm
RSCPublishing
COMMUNICATION
A chromogenic molecular capsule attributable to
dipolar amide resonance structure
Yeon Sil Park, Juwan Park and Kyungsoo Paek*
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2014,
Accepted 00th January 2014
DOI: 10.1039/x0xx00000x
www.rsc.org/
A new chromogenic, self-assembled molecular capsule G@22 is
developed by introducing four (N,N-dimethyl-4-aminophenyl)
azobenzyl moieties on the upper rim of a resorcin[4]arene-based
amidoimino-cavitand. The tuning of conjugation between amido
and (N,N-dimethyl-4-aminophenyl)azobenzyl groups by acid-
base titration allows naked-eye detection of molecular capsule
formation.
If a protonated N,Nꢀdisubstituted azobenzene dye combines with
an amide group, dipolar resonance structure D could extend its
conjugation up to the protonated N,Nꢀdisubstituted azobenzene dye
(Fig. 1(c) tautomer E).
a)
N
N
N
H+
N+
H
N
N
N
N
N
N+
H
Interests in developing new selfꢀassembled molecular capsules
have been unabated for more than a decade. In the presence of
suitable guest molecules selfꢀassembled molecular capsules are
spontaneously formed in solution by multiple hydrogen bonds,1
metalꢀligand interactions,2 hydrophobic interactions,3 and hybrid
noncovalent interactions.4 The characteristics of their nanoꢀsized
cavities as molecular receptor, sensor, reactor, storage, and delivery
systems are widely reported.5
Although various molecular capsules with distinctive properties
are wellꢀstudied, ‘naked eye’ detection of monomerꢀtoꢀdimeric
capsule and vice versa is not reported yet due to the difficulty in
designing a sensitive capsular chromogenic system.
tautomer A
λ
max = 320 nm
tautomer B
N
H
N+
λ
max = 516 nm
-O
O
b)
c)
N+
N
H
H
resonance C
resonance D
H
H
N+
N+
H
N
N
N
N+
H
N
N+
-O
-O
tautomer F
tautomer E
Fig. 1 a) Two tautomers (
resonance structures (
combinations of tautomer
A
and
and
or
B
) of N,N-disubstituted azobenzene dye, b) two
) of amide group, c) tautomers and : the
and resonance structure
C
D
E
F
N,NꢀDisubstituted azobenzene dyes exist in acidic solution as an
equilibrium mixture of two tautomers ꢀ ammonium form A (yellow)
and quinoid form B (reddish purple).6 (Fig. 2(a)) The ammonium
form A is favorable in high pH, but the tautomeric equilibrium
gradually shifts to favor B as pH decreases.7 This tautomeric
equilibrium in acidic solution was confirmed by Raman spectra8(a)ꢀ(b)
A
B
D.
We have recently demonstrated that iminoꢀcavitand 1 containing
four benzamido moieties on its upper rim efficiently selfꢀassembles
into thermally inert molecular capsule G@12 in the presence of
complimentary guests such as toluene or 1,4ꢀdimethoxy benzene via
eight intermolecular amide N–H···O=C hydrogen bonds. (Fig.
1(a))1(k)
When a N,Nꢀdisubstituted azobenzene dye is coupled to cavitand
1, the extent of conjugation between amide group and a N,Nꢀ
disubstituted azobenzene dye (tautomer E) may depend on the stable
hydrogen bond of amide group and acid concentration. In this paper,
as well as 15N and 13C NMR8(c)
.
Amide group exists as two resonance structures9 ꢀ neutral
structure C and dipolar structure D, and neutral structure C is
favourable than dipolar structures in neutral pH. For instance,
Kemnitz et al. reported that the relative concentrations of neutral
structure C and dipolar structure D in acetamide are 60% and 25%,
respectively.9(b) When an amide group hydrogen bonds, the dipolar
structure D becomes favorable.10
This journal is © The Royal Society of Chemistry 2014
Chem. Commun., 2014, 00, 1-3 | 1

ChemComm
Page 2 of 4
View Article Online
COMMUNICATION
ChemComm
DOI: 10.1039/C4CC10412A
we report the first nakedꢀeye detection of the assembly and temperature. The structure of cavitand 2 was fully characterized by
disassembly of a chromogenic, selfꢀassembled molecular capsule.
1H NMR, 13CꢀNMR spectroscopy, highꢀresolution MALDIꢀTOF
mass spectrometry, and elemental analysis.
N
Cavitand 2 forms a stable molecular capsule, tolueneꢀd8@22, in
tolueneꢀd8, whose structure was confirmed using H NMR and 2Dꢀ
NOESY experiments (Fig. S3, ESI).
To examine whether hydrogenꢀbondꢀinduced dipolar amide
(resonance structure D) forms a significant electronical conjugation
with protonated N,Nꢀdimethylamino group as shown Fig. 2 (b), UVꢀ
Vis absorption shift of molecular capsule toluene@22 was
investigated through CH3SO3H titration in toluene (Fig. 3).
N
N
1
N
a)
N
N
N
N
O
N
N
N
N
N
N
N
O
O
O
O
O
H
H
H
H
N
N
N
N
O
N
O
N
N
N
N
N
N
N
N
N
H
H
N
H
N
H
H
N
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
H3CO
OCH3
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
H
N+
H
N+
H
N+
H
N+
N
N
N
N
1
2
3
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
b)
c)
H
N
N
H
N
N
N
N
N
N
N
N
O
O
O
O
OO
N
O
N
O
O
O
O
O
O
O
O
O
N
N
N
O
N
O
N
N
N
N
N
N
N
N
N
N
C7H15
N
T
N
T
H
H
o
N
H
O
o
N
H
O
4
CH3SO3
H
H
H
H
H
O
O
l
l
O
O
O
O
u
u
O
O
e
e
H
H
N
n
n
H
O
N
H
O
N
H
N
H
N
N
N
N
e
e
base
N
N
N
N
N
N
O
N
O
O
N
N
N
N
N
O
N
N
O
N
N
N
N
N
O
O
N
O
N
O
O
O
O
N
N
N
O
O
O
O
N
N
O
N+
H
H
N
C7H15
C7H15
C7H15
N
N+
H
C7H15
C7H15
C7H15
C7H15
N+
H
N
N
O
N+
H
N
C7H15
H
H
N
O
toluene@22⋅8H+
N
toluene@22
N
O
O
N
O
O
N
4
4
C7H15
C7H15
N
H
dominant structure of 2 4H+
⋅
dominant structure of 22 8H+
⋅
Fig. 2 a) Benzamido-iminocavitand
and model compound
capsule 22·8H+, c) protonated cavitand
1
and 2 for self-assembled molecular capsule,
3
b) suggested structures of chromogenic molecular
·4H+.
2
O
1) NaNO2, HCl, THF, 0 o
C
O
N
H2N
OEt
N
N
2) N,N-dimethyl aniline
OEt
45%
4
5
O
HN2NH2⋅H2
O
N
N
×
10-6 M in
NHNH2
Fig. 3 Changes in UV-Vis absorption spectra of toluene@22 (4.7
toluene) upon addition of CH3SO3H.
N
EtOH, 80 o
56%
C
6
N
N
N
N
Upon addition of 8.0 equiv. of CH3SO3H, the protonated capsule
H
g
toluene@22·8H+ shows a distinct hyperchromic effect with 1.7ꢀfold
H
N
N
e
N
N
N
N
N
N
enhancement of
ε at λmax = 440 nm compared to that of capsule
H
O
O
H
O
O
H
H
H
d
toluene@22 (yellow solution). As more acid was added up to 40.0
equiv., this band (λ max = 440 nm) shifted to 506 nm (ꢀλ = 66 nm)
H
O
O
O
O
O
O
O
6
O
O
O
N
b
O
H
H
a
N
N
MgSO4, DMF, rt
85%
O
N
N
N
N
H
with isosbestic point at 471 nm (red solution). Also a band at λ max
=
N
H
H
h
C7H15
C7H15
C7H15
H
c
H
j
C7H15
O
564 nm (from quinoid tautomer F) increased gradually. This process
can be reversed by addition of organic bases such as pyridine,
triethylamine, and DBU. These phenomena indicate that the strong
intermolecular hydrogenꢀbondꢀinduced dipolar amide resonance of
molecular capsule toluene@22·8H+ (Fig. 2(b)) becomes more
predominant upon addition of acid. And the heavily extended
conjugation explains the color change as well as hyperchromic effect.
In order to prove that the strong hydrogen bondꢀassisted dipolar
amide resonance structure D as shown Fig. 2 (b) is important for the
bathochromic shift, acid titration experiments of cavitand 2 and
model compound 3 were performed (Fig. 4). Cavitand 2 in 8%
methanol/toluene cannot form molecular capsule (Fig. 6(c)) and
neutral amide resonance C is favorable in this condition (Fig. 2(c)).
When CH3SO3H was added to a solution of cavitand 2 in 8%
methanol/toluene, no bathochromic shift was observed. Only slight
equilibrium shift to quinoid tautomer B was gradually observed as
the acid concentration increased (Fig. 4(a)). Similar result was
observed for model compound 3 in toluene (1.4 × 10ꢀ4 M) (Fig. 4(b)).
O
O
O
O
O
O
O
7
H
i
H
f
C7H15
C7H15
C7H15
C7H15
2
Scheme 1. Synthesis of cavitand 2.
In order to introduce azobenzene moiety on the upper rim of
iminocavitand 1, diazoꢀbenzoic hydrazide derivative was
synthesized in two steps from ethyl 4ꢀaminobenzoate 4. The
diazonium salt obtained from the reaction of ethyl 4ꢀaminobenzoate
4 with NaNO2 in the presence of HCl at 0 C was in situ added to a
THF solution of N,Nꢀdimethyl aniline to give diazoꢀcompound 5 as a
red solid in 45% yield. Diazoꢀbenzoic hydrazide 6 was prepared in
56% yield from the reaction of 5 with excess hydrazine. C4ꢀ
symmetric iminocavitand 2 was obtained in 85% yield from the
condensation reaction between tetraformyl cavitand 711 and
hydrazide 6 in a mixture of MgSO4 and dry DMF at room
6
o
2 | Chem. Commun., 2014, 00, 1-3
This journal is © The Royal Society of Chemistry 2014

Page 3 of 4
ChemComm
ChemComm
View Article Online
COMMUNICATION
DOI: 10.1039/C4CC10412A
These tautomeric equilibrium shift is characteristic for N,Nꢀ the this molecular capsule solution broke intermolecular amide N–
disubstituted azobenzene dyes in acidic solution.6ꢀ8
H···O=C hydrogen bonds due to the competitive hydrogenꢀbonding
These results prove that strong hydrogen bondꢀassisted dipolar ability of CD3OD, and the conversion from molecular capsule to
amide group of molecular capsule toluene@22·8H+ (Fig. 2(b)) is the cavitand can be observed by 1H NMR spectrum. The 1H NMR
key to its chromogenic phenomena.
spectrum in the presence of 2% CD3OD (Fig. 6(b)) showed both
signals of dimeric capsule 22·8H+ (black) and dissociated cavitand
2·4H+ (green). Capsule 22⋅8H+ and cavitand 2·4H+ exist as an
equilibrium mixture in a 62:38 ratio, which is inferred from
comparing 1H NMR integration ratios.
Fig. 4 a) Changes in UV-Vis absorption spectra upon addition of CH3SO3H: a)
2 (4.7 × 3 (1.4 ×
10-6 M in 8% methanol/toluene), b) model compound
cavitand
10-4 M in toluene).
Fig. 5 shows the UVꢀVis absorption shift of the protonated
molecular capsule, toluene@22·8H+ by addition of methanol. As
methanol increases, the band with λ max = 506 nm disappears and a
new blueꢀshifted (ꢀλ = ꢀ72nm) absorption band with λ max = 434 nm
appears with isosbestic point at 458 nm. This blue shift implies that
the protonated molecular capsule, toluene@22·8H+ dissociates to
cavitand 2·4H+ upon methanol addition, losing electrical conjugation.
As a result, the red color of molecular capsule, 22·8H+ turned yellow.
Fig. 6 1H NMR spectra (400 MHz) in toluene-d8 at 298 K of: a) toluene-d8@22
b) after the addition of 2% CD3OD, c) after the addition of 8% CD3OD. [22] = 5
mM. The signals of capsule 22 black and cavitand green are
8H+ 4H+
highlighted. The residual peaks of solvents are marked “*”.
⋅
8H+
H
N+
H
N+
H
N+
H
N+
H
N+
H
H
N+
H
N+
N+
C7H15
C7H15
C7H15
⋅
(
)
2
⋅
(
)
C7H15
N
O
N
N
N
N
N
O
OO
N
N
O
O
N
O
O
N
N
O
N
N
N
N
N
N
N
N
N
N
polar solvent
H
N
H
H
H
O
O
O
O
2
O
O
H
N
O
O
H
H
H
O
N
N
O
H
N
N
N
N
N
N
H
N
N
N
N
N
H
N
N
N
N
N
N
O
O
O
O
O
N
O
O
O
O
N
O
O
O
O
O
O
N+
H
C7H15
C7H15
N+
C7H15
C7H15
C7H15
C7H15
N+
H
N+
H
C7H15
C7H15
H
8H+
+
toluene@22
⋅
⋅
2
4H
Fig. 7 Energy minimized structures (Semi-Empirical PM3 level, Spartan06 V112)
of: a) capsule 22·8H+, b) cavitand ·4H+.
2
Broken intermolecular hydrogenꢀbonding of the dissociated
cavitand 2·4H+ caused an upfield shift (ꢀδ = ꢀ0.93 ppm) of the
amide NꢀH protons and relatively fast deuterium exchange compared
to those of dimeric capsules. Notably, the methine protons (Hi) are
observed at 5.50 ppm, which shows that cavitand 2·4H+ exists as
more C4vꢀsymmetric vase confomer than dimeric capsule 22⋅8H+.12
The energyꢀminimized structure of cavitand 2·4H+ shows that it
prefers a C4vꢀsymmetric vase conformer and four azobenzene
moieties are arranged perpendicular to each other (Fig 7). When
cavitand 2·4H+ selfꢀassembles to molecular capsule 22·8H+, two
vaseꢀshaped cavitands should partially open to kiteꢀshaped cavitands
to embrace each other, forming strong eight intermolecular
hydrogenꢀbonds and resulting in a downfield shift (ꢀδ = 0.62 ppm)
of Hi in cavitand 2·4H+.13 For the same reason, the signals of inner
(Hh) and outer (Hj) protons of the dioxymethylene bridge in
dissociated cavitand 2·4H+ were shifted downfield by 0.32 and 0.71
ppm, respectively. The aromatic protons (Hb and Hd) in the
Fig. 5 Changes in UV-Vis absorption spectra of toluene@22·8H+ (4.7
toluene) upon addition of methanol.
×
10-6 M in
The conversion from capsule to cavitand was also observed in
1H NMR. 1H NMR spectrum of molecular capsule 22⋅8H+ in tolueneꢀ
d8 shows sharp and highly symmetrical proton signals (Fig. 6(a)).
The intermolecular hydrogenꢀbonding amide NꢀH protons of
molecular capsule appear as a singlet at 12.74 ppm, and the signals
of inner (Hh) and outer (Hj) protons of the dioxymethylene bridge
and methine protons (Hi) appear at 4.35, 6.40, and 4.88 ppm as a pair
of doublets and a triplet, respectively. And the methyl protons of
heptyl feet are observed at 0.84 ppm as a triplet. Adding CD3OD to
This journal is © The Royal Society of Chemistry 2014
Chem. Commun., 2014, 00, 1-3 | 3

ChemComm
Page 4 of 4
View Article Online
COMMUNICATION
ChemComm
DOI: 10.1039/C4CC10412A
dissociated cavitand 2·4H+ showed an upfield shift (ꢀδ = ꢀ1.00 and ꢀ
0.28 ppm) because these protons are located inside the magnetic
shielding zone of adjacent azobenzene units. Interestingly, the peaks
of heptyl feet in dimeric capsules 22·8H+ are shifted to upfield
relative to those of cavitand 2·4H+ due to the aromatic shielding
effect of the long azobenzene pendants of a counter cavitand. The
addition of > 8% CD3OD completely dissociated capsule 22·8H+ to
cavitand 2·4H+ (Fig. 6(c)), and the peak of amide NꢀH disappeared
due to the fast deuteriumꢀexchange with CD3OD. These changes by
methanol addition are consistent with UVꢀVis experiment and the
dissociation process can be observed visually via color change.
and K. Paek, Org. Lett., 2004,
6
, 4431; (g) M. Yamanaka, K. Ishii, Y.
Yamada and K. Kobayashi, J. Org. Chem., 2006, 71, 8800; (h) D.
Ajami and J. Rebek, Jr. Angew. Chem. Int. Ed., 2007, 46, 9283; (i) Y.
S. Park and K. Paek, Org. Lett., 2008, 10, 4867; (j) S. Harthong, B.
Dubessy, J. Vachon, C. Aronica, J.ꢀC. Mulatier and J.ꢀP. Dutasta, J.
Am. Chem. Soc., 2010, 132, 15637; (k) Y. S. Park, J. Park and K.
Paek, Chem. Commun., 2013, 49, 6316.
2. (a) P. Jacopozzi and E. Dalcanale, Angew. Chem. Int. Ed., 1997, 36
,
613; (b) O. D. Fox, N. K. Dalley and R. G. Harrison, J. Am. Chem.
Soc., 1998, 120, 7111; (c) O. D. Fox, M. G. B. Drew and P. D. Beer,
Angew. Chem. Int. Ed., 2000, 39, 135; (d) R. Pinalli, V. Cristini, V.
Sottili, S. Geremia, M. Campagnolo, A. Caneschi and E. Dalcanale,
J. Am. Chem. Soc., 2004, 126, 6516; (e) K. Kobayashi, Y. Yamada,
M. Yamanaka, Y. Sei and K. Yamaguchi, J. Am. Chem. Soc., 2004,
126, 13896; (f) S. J. Park, D. M. Shin, S. Sakamoto, K. Yamaguchi,
Y. K. Chung, M. S. Lah and J.ꢀI. Hong, Chem.-Eur. J., 2005, 11, 235;
(g) T. Haino, M. Kobayashi, M. Chikaraishi and Y. Fukazawa, Chem.
Commun., 2005, 2321; (h) O. Ugono, J. P. Moran and K. T. Holman,
Chem. Commun., 2008, 1404.
H
N+
H
N+
H
N+
H
N+
N
C7H15
N
N
N
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
N
N
N
N
O
N
N
N
O
N
N
OO
N
O
O
O
O
O
O
O
N
O
O
O
N
O
O
N
O
N
O
N
N
N
N
N
N
N
N
N
N
N
T
N
T
CH3SO3
H
H
N
H
O
o
H
N
H
H
o
H
H
O
H
l
O
O
O
l
u
O
O
u
O
O
e
e
H
N
H
N
n
O
H
O
N
n
H
H
O
N
base
N
N
H
N
e
N
e
N
N
N
N
N
N
O
N
N
N
O
N
N
N
N
N
N
N
O
O
N
O
O
N
O
O
N
O
O
O
O
N
O
O
N+
H
N
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
N
N+
H
N
N+
H
N+
H
N
C7H15
toluene@22
⋅
8H+
toluene@22
λ
max = 440 nm
λ
max = 506 nm
polar solvent
polar solvent
3. (a) C. L. D. Gibb and B. C. Gibb, J. Am. Chem. Soc., 2004, 126
,
H
N+
H
N+
N
H
N+
N
H
N+
N
11408; (b) L. S. Kaanumalle, C. L. D. Gibb, B. C. Gibb and V.
Ramamurthy, J. Am. Chem. Soc., 2004, 126, 14366.
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
4. (a) M. Yamanaka, N. Toyoda and K. Kobayashi, J. Am. Chem. Soc.,
2009, 131, 9880; (b) M. Yamanaka, M. Kawaharada, Y. Nito, H.
Takaya and K. Kobayashi, J. Am. Chem. Soc., 2011, 133,16650.
5. (a) F. Hof, S. L. Craig, C. Nuckolls and J. Rebek, Jr. Angew. Chem.
Int. Ed., 2002, 41, 1488; (b) L. C. Palmer and J. Rebek, Jr. J. Org.
O
2
O
O
2
O
O
H
H
N
N
O
N
O
N
N
H
H
N
N
N
O
N
N
N
N
N
N
H
N
H
H
N
H
O
O
O
O
O
O
O
O
O
O
O
O
O O
O
O
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
C7H15
2
⋅
4H+
λmax = 434 nm
2
λ
max = 440 nm
Biomol. Chem., 2004, 2, 3051; (c) T. S. Koblenz, J. Wassenaar and J.
Fig. 8 The assembly and disassembly of a chromogenic molecular capsule.
N. H. Reek, Chem. Soc. Rev., 2008, 37, 247; (d) J. Rebek, Jr. Acc.
Chem. Res., 2009, 42, 1660; (e) M. Yoshizawa, J. K. Klosterman and
M. Fujita, Angew. Chem. Int. Ed., 2009, 48, 3418; (f) M. J. Wiester, P.
A. Ulmann and C. A. Mirkin, Angew. Chem. Int. Ed., 2011, 50, 114;
(g) D. Ajami and J. Rebek, Jr. Acc. Chem. Res., 2012, 46, 990.
6. (a) G. M. Badger, R. G. Buttery and G. E. Lewis, J. Chem. Soc., 1954,
1888; (b) I. M. Klotz, H. A. Fiess, J. Y. Chen Ho and M. Mellody, J.
Am. Chem. Soc., 1954, 76, 5136; (c) G. Cilento, E. C. Miller and J. A.
Miller, J. Am. Chem. Soc., 1956, 78, 1718.
In summary, a new chromogenic, selfꢀassembled molecular
capsule 22 based on amidoiminoꢀcavitand containing four (N,Nꢀ
dimethylꢀ4ꢀaminophenyl)azobenzyl moieties is characterized.
Nakedꢀeye detection of assembly and disassembly of a molecular
capsule by tuning the conjugation of amido group with (N,Nꢀ
dimethylꢀ4ꢀaminophenyl)azobenzyl group is expected to promote the
research on chromogenic molecular capsules.
This research was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded 7. (a) E. Sawicki, J. Org. Chem., 1956, 21, 605; (b) E. Sawicki, J. Org.
by the Ministry of Education, Science and Technology (NRFꢀ
2012R1A1A3005152 and 2012R1A1A2039112).
Chem., 1957, 22, 365; (c) E. Sawicki, J. Org. Chem., 1957, 22, 621;
(d) E. Sawicki, J. Org. Chem., 1957, 22, 1084; (d) E. Sawicki, J. Org.
Chem., 1958, 23, 532.
Notes and references
Department of Chemistry, Soongsil University, Seoul 156-743, Korea.
8. (a) K. Machlda, B.ꢀK. Kim, Y. Saito, K. Igarashi and T. Uno, Bull.
Chem. Soc. Jpn., 1974, 47, 78; (b) T. Uno, B.ꢀK. Kim, Y. Saito and K.
Machlda, Spectrochim. Acta, Part A, 1976, 32, 1179; (c)Y. Kuroda,
H. Lee and A. Kuwae, J. Phys. Chem., 1980, 84, 3417.
E-mail: kpaek@ssu.ac.kr; Fax: +82-2-822-2362; Tel: +82-2-820-0435
†
Electronic Supplementary Information (ESI) available: Synthetic
procedures, characterization data for all the compounds, results of various
NMR spectra, UVꢀ and data. See DOI: 10.1039/c000000x/
9. (a) J. I. Mujika, J. M. Matxain, L. A. Eriksson and X. Lopez, Chem.
Eur. J., 2006, 12, 7215; (b) C. R. Kemnitz and M. J. Loewen, J. Am.
Chem. Soc., 2007, 129, 2521.
1
(a) R. G. Chapman and J. C. Sherman, J. Am. Chem. Soc., 1995, 117,
10. (a) H. Guo and M. Karplus, J. phys. Chem., 1992, 96, 7273; (b) R.
9081; (b) T. Heinz, D. M. Rudkevich and J. Rebek, Jr. Nature, 1998,
394, 467; (c) A. Lützen, A. R. Renslo, C. A. Schalley, B. M. O’Leary
and J. Rebek, Jr. J. Am. Chem. Soc., 1999, 121, 7455; (d) K.
Kobayashi, T. Shirasaka, K. S. Yamaguchi, E. Sakamoto, N. Horn,
Furukawa, Chem. Commun., 2000, 41; (e) K. Kobayashi, K. Ishii, S.
Sakamoto, T. Shirasaka and K. Yamaguchi, J. Am. Chem. Soc., 2003,
125, 10615; (f) H.ꢀJ. Choi, Y. S. Park, C. S. Cho, K. Koh, S.ꢀH. Kim
Ludwig, F. Weinhold and T. C. Farrar, J. phys. Chem.,
A
1997, 101
,
8861; (c) T. Hayashi, W. Zhuang and S. Mukamel, J. phys. Chem.,
A
2005, 109, 9747; (d) N. S. Myshakina, Z. Ahmed and S. A. Asher, J.
phys. Chem., 2008, 112, 11873.
B
11. M. L. C. Quan and D. J. Cram, J. Am. Chem. Soc., 1991, 113, 2754.
12. J. R. Moran, J. L. Ericson, E. Dalcanale, J. A. Bryant, C. B. Knobler
and D. J. Cram, J. Am. Chem. Soc., 1991, 113, 5707.
4 | Chem. Commun., 2014, 00, 1-3
This journal is © The Royal Society of Chemistry 2014