Synthesis, structure, fullerene-binding and resolution of C 3-symmetric cavitands with rigid and deep cavities

Article abstract of DOI:10.1039/c1ob06465g

An efficient palladium-catalyzed Suzuki-Miyaura coupling method involving the reaction between CTV-Br₃ and a variety of aryl and heteroaryl boronic acids in the presence of indolyl phosphane ligands has been developed. This reaction procedure p

Full text of DOI:10.1039/c1ob06465g

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PAPER
Synthesis, structure, fullerene-binding and resolution of C3-symmetric
cavitands with rigid and deep cavities†
Jin-Tao Yu, Zhi-Tang Huang and Qi-Yu Zheng*
Received 26th August 2011, Accepted 8th November 2011
DOI: 10.1039/c1ob06465g
An efficient palladium-catalyzed Suzuki–Miyaura coupling method involving the reaction between
CTV-Br3 and a variety of aryl and heteroaryl boronic acids in the presence of indolyl phosphane
ligands has been developed. This reaction procedure provided a series of C3-symmetric aryl-extended
rigid cavitands for the first time. X-ray crystal structure analysis revealed that the phenyl substituted
cavitand 5a has much larger rim edges and cavity height. This macrocyclic host adopts a linear
head-to-tail “hand-shake” self-inclusion arrangement in the crystalline state. The fluorescence of 5a
was considerably quenched upon the addition of C60, with a binding constant of 78 700 2300 dm3
mol-1 and a 1 : 1 stoichiometry according to the Job’s plot. The interaction of C60 with 5a in the excited
state is stronger than that with CTV, which could be attributed to more binding sites in the extended
arms of 5a. Moreover, optically active C3-symmetric cavitands (+)- and (-)-6 were easily obtained with
high efficiency through chemical resolution.
version through the twist-saddle conformations, giving rise to
Introduction
racemisation in solution.4 Because of the convergent binding
Cyclotriveratrylene (CTV, 1, Scheme 1) is a versatile macrocyclic
modes of CTV-type ligands, they are capable of constructing
organic5 or metallo-supramolecular6 assemblies. CTV analogues
can also be easily functionalized to form various host molecules,
such as extended-CTVs, speleands and cryptophanes, as well as
hemicryptophanes.1,7 These CTV-based artificial receptors could
be utilized to bind neutral molecules, cations, or anions in solution
as well as in the solid state.8–14 Recent progress in the study of CTV-
hosts includes C60/C70 binding and separations,8 ion sensing,9–11
chiral inclusion,12 and cryptophane-type hyperpolarized 129Xe
biosensing.13
molecule formed by the condensation of veratrole and formalde-
hyde, and the crown conformation gives it a bowl-shaped and
electron-rich cavity.1 The saddle conformation of CTV is very
rare, and can only be isolated from quenching the melt2 or be
observed in the “imploded” cryptophane.3 If the substituents
of the upper rim are different, such CTV analogues are chiral.
On the other hand, the enantiomers undergo slow intercon-
The bowl-shaped cavity of CTV is quite shallow. So in most
cases, guest molecules cannot be included in its cavity but can
only occupy the channels of the lattice in the crystalline state.14
Extended-CTVs can be obtained by appending side-arms to the
upper rims of hexameric CTC (2) or C3-symmetric CTG (3)
by etherification/esterification. Amino derived CTV analogues
have also been developed in recent years.15 Compared with the
nonchiral C3v-symmetric CTV (1) and CTC (2), inherently chiral
macrocycles (CTG analogues) are more attractive. Their recogni-
tion and assembly properties could be applied in supramolecular
asymmetric catalysis or utilized as chiral materials. To achieve
these goals, we firstly need to enlarge the cavity of CTV. However,
because of the free rotation of the “extended arms” around oxygen
atoms, the substituents can bend outward or downward of the
bowl, which is unfavourable for further recognition and assembly,
according to the preorganization principles. Thus, we would like
to attach rigid substituents (e.g. aryls) to the phenyl motifs of
the CTV-core directly. CTV analogues with rigid arms do have
unique advantages in the construction of functional materials.
Scheme 1 Chemical structures of CTV analogues.
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory
of Molecular Recognition and Function, Institute of Chemistry, Chinese
Academy of Sciences, Beijing, 100190, China. E-mail: zhengqy@iccas.ac.cn;
Fax: (+86) 10 6255 4449
† Electronic supplementary information (ESI) available: Characterization
of all new compounds. Copies of 1H and 13C NMR spectra. UV-
vis spectra, HPLC data. CCDC reference numbers 841556. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1ob06465g
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Table 1 Palladium-catalyzed Suzuki–Miyaura coupling of 4 and aryl
Results and discussion
boronic acidsa,b
Synthesis
Entry
Ar
Pd-cat, ligand, base
( )-5
Yield [%]c
The classic conditions for Suzuki–Miyaura coupling were initially
examined: in the presence of Pd(PPh3)4 and anhydrous K2CO3, the
reactions of phenyl, 4-tolyl or 4-(ethoxycarbonyl)-phenyl boronic
acid with 4 did give rise to the desired products. However, the yields
were far from satisfactory (Table 1, entries 1, 3 and 12). According
to Miyaura and Suzuki’s point of view, in this coupling reaction,
the oxidative addition is often the rate determining step, and
aryl halides with electron-donating groups are less reactive to the
oxidative addition than those with electron-withdrawing groups.18
Thus the low efficiency could be attributed to the strong electron-
donation from the o-methoxy as well as the steric hindrance in
the upper rim of the CTV.19 In addition, the introduction of three
aryl groups into one substrate molecule at the same time gives a
lower overall yield.20 Hence, we need to find a catalytic system with
much higher activity. The indolyl phosphane ligand L (Scheme 2)
has been determined to be very efficient in the catalytic Suzuki–
Miyaura coupling reaction.21 By using this Pd(OAc)2/L catalytic
system, we have succeeded in the construction of C(sp2)-C(sp2)
linkage between CTV with phenyl and aryl/heteroaryl groups.
After careful optimization of the reaction conditions, we finally
chose anhydrous K3PO4 as a base, and the reaction was conducted
1
2
3
4
5
6
7
8
Ph
Ph
Pd(PPh3)4, K2CO3
Pd(OAc)2, L, K3PO4
Pd(PPh3)4, K2CO3
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
Pd(PPh3)4, K2CO3
Pd(OAc)2, L, K3PO4
Pd(OAc)2, L, K3PO4
5a
5a
5b
5b
5c
5d
5e
5f
5g
5h
5i
5j
5j
5k
58
76
35
67
46
45
67
65
73
5
68
28
42
23
4-MeC6H4
4-MeC6H4
4-ButC6H4
4-PhC6H4
3-MeOC6H4
4-MeOC6H4
4-FC6H4
4-ClC6H4
4-MeCOC6H4
4-EtOCOC6H4
4-EtOCOC6H4
9
10
11
12
13
14
15
Pd(OAc)2, L, K3PO4
5l
21
a Reaction conditions for entry 1, 3, 12: 4 (0.16 mmol), boronic acid (4.5 eq,
0.72 mmol), anhydrous K2CO3 (6 eq, 0.96 mmol), Pd(PPh3)4 (10 mol%),
DMF (6 mL), H2O (0.5 mL), 95 ◦C, 48 h. b Reaction conditions for other
entries: 4 (0.16 mmol), boronic acid (6 eq, 0.96 mmol), anhydrous K3PO4
(9 eq, 1.44 mmol), Pd(OAc)2/L (10 mol%), ButOH (15 mL), 130 ◦C, 44 h.
c Yields of isolated products.
◦
at 130 C in dry t-BuOH for about 44 h, and the corresponding
products were obtained in good to moderate yields (Table 1, entries
2, 4–11, 13–15).
In general, using this Pd(OAc)2/L catalytic system, we could
get better yields than under classic conditions. Aryl boronic acids
with electron-donating and electron-withdrawing substituents
both worked well. For each CTV-Br3 molecule, three aromatic
substituents were introduced by coupling reaction at the same
time. Therefore, in most cases, the transformation of each bromide
group was very efficient, although the overall yield was moderate.
However, the yield of 5h that was obtained by coupling between
p-chlorophenyl boronic acid and 4 was only 5% (Table 1, entry 10),
which could be due to the high reactivity of the catalyst system:
aryl chloride was activated, thus the homo-coupling product
(biphenyl) was predominant for this boronic acid substrate. As
we all know, the reactivity of aryl bromide is much higher than
aryl chloride in coupling reactions,18 thus such a low yield of
5h further confirmed the difficulty of coupling on the upper rim
of CTV-Br3. For the two heteroaryl boronic acids, the yields of
For example, aryl decorated CTV-type ligands can coordinate with
metal ions or metal clusters to form chiral cryptophanes or robust
metal–organic nanotubes by self-assembly.16 While the study of
the preparation of CTV analogues with “flexible” arms has been
fruitful, when it comes to synthetic methods for rigid substituents,
only very few examples are reported, but without experimental
details included.16 Here, for the first time, we systematically inves-
tigate a facile way to deepen the CTV’s cavity with rigid aryl arms
using palladium-catalyzed Suzuki–Miyaura coupling (Scheme 2).
A variety of easily obtained aryl/heteroaryl boronic acids were
chosen for coupling with CTV-Br3 (4)17 (Table 1). Moreover, we
also measured the recognition property between compound 5a
and fullerene molecules, which gave stronger interactions in the
excited state than that of CTV (1). The resolution of enantiomer
(+)- and (-)-6 is also investigated preliminarily.
Scheme 2 Palladium-catalyzed Suzuki-Miyaura coupling of CTV-Br3 with aryl/heteroaryl boronic acids.
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coupling were also unsatisfactory (Table 1, entries 14 and 15).
The pyridin-4-ylboronic acid is naturally inert in Suzuki–Miyaura
coupling.22 The yield of this reaction could not be improved much
even under optimized conditions and with much longer time. The
nature of thiophen-2-ylboronic acid is that it is of lower stability
and it is easily decomposed at higher temperatures. In addition,
the product of 5l was not very stable in air, which could change its
colour from colourless to grey–green within 24 h in the solution
of dichloromethane.
Cph–H ◊ ◊ ◊ p interaction) between the phenyl and the cavity became
the main driving force for the self-inclusion. The shortest distance
˚
of Cph–H ◊ ◊ ◊ p was 2.744 A. Each two adjacent molecules in this
1D polymeric self-inclusion chain were a pair of enantiomers.
Therefore, the whole crystal of 5a is racemic.
Fullerene binding studies of 5a
Because of the concave skeleton structure and the electron-
rich nature of CTV, it can complementally bind molecules with
convex electron-poor surfaces such as fullerene C60, to form “ball
and socket” structures.23a Since C60 is much bigger than CTV,
great efforts have been made to design CTV-type receptors to
increase the binding affinity for fullerenes. Among them, CTV-
based tweezer hosts,8b,8d hydrogen bonding-driven dimers8e and
three-dimensional capsular receptors8h are found to be effective
hosts for fullerene binding and separation. They tend to enclose
fullerene molecules tightly in their relatively closed cavities. We
speculate that these extended rigid hosts that we have obtained
may be another choice for binding normal fullerene guests. Here
we made a preliminary study of 5a for its binding property with
fullerenes. By UV-vis spectra titration, neither very obvious shifts
nor isosbestic points were observed in the absorption curves of
C60, upon addition of compound 5a in toluene solution. (see ESI†,
Fig. S1) It indicates that there is no strong interaction between 5a
and C60 in the ground state. To further study the recognition of
C60 by 5a, a fluorescence titration was conducted (Fig. 2). The
fluorescence intensity of 5a at about lem = 346 nm decreased
constantly with increasing concentration of C60. To eliminate
the competitive adsorption of C60 at excitation and emission
wavelengths, the fluorescence intensity Fexp of 5a was calibrated
to Fcal according to a literature method.28 The quenching was
found to follow the Stern–Volmer equation, and the dependence
of the calibrated F0/Fcal on the concentration of C60 is illustrated
Crystal structure of 5a
CTV can form solid-state inclusion compounds with many
small potential guest molecules such as benzene, toluene, water,
acetone, etc.14 CTV alone does not usually form intra-cavity
host–guest complexes, except for spherical guests such as C60
and carborane.8,23 However, the host cavity is easily occupied by
another CTV molecule, as for a- and b-phase CTV,14,24 where CTV
molecules stack into misaligned columns and guest molecules
are packed in the crystal channels. For CTV derivatives with
stretched functional arms on the upper rims, they tend to form
self-inclusion associations: the arm of one host is included in
the hydrophobic cavity of itself or an adjacent host molecule.25
A single crystal of 5a was obtained by slow evaporation in the
solution of acetone and methanol. The X-ray structure analysis
shows that it has a rigid and deeper cavity26 (Fig. 1a). The edge
of the upper triangle rim and height of the cavity in the original
˚
CTV (1) was 6.7 and 2.2 A on average, which increased to 12.8
˚
and 4.6 A in 5a, respectively. Similar to other reported crystal
structures of the C3-symmetric CTG-derived macrocycles, we also
found self-inclusion phenomenon in the crystal structure of 5a
(Fig. 1b, 1c). A linear chain of 5a is formed through host–guest
inclusion: one extended phenyl group was oriented into the bowl
cavity of the adjacent cavitand, whose one extended phenyl arm
was oriented into the cavity of the third cavitand, and so on.
Note that, only one of the three phenyl arms is involved in this
interaction, which is similar to linear head-to-tail associations of
functionalised calixarenes.27 Here, T-shaped p–p interaction (or
Fig. 2 Emission spectra (lex = 305 nm, lem = 346 nm.) of 5a (3.2 ¥ 10-6
mol dm-3) in the presence of C60 in toluene at 25 ◦C. The concentrations
of C60 for curves a–n (from top to bottom) were 0, 0.096, 0.192, 0.288,
0.384, 0.480, 0.576, 0.672, 0.768, 0.864, 0.960, 1.152, 1.248, 1.44 (¥ 10-5
mol dm-3). Insets: The top inset is the variation of fluorescence intensity
F0/Fcal of 5a with increasing C60 concentration. The bottom inset is the
Job’s plot for the 5a–C60 complex in toluene solution ([5a] + [C60] = 6.4 ¥
10-6 mol dm-3).
Fig. 1 (a) Ball-and-stick view of molecular structure of 5a. (b) Asymmet-
ric unit cell of 5a. (c) The 1D chain of racemic 5a connected by Cph–H ◊ ◊ ◊ p
interactions. Two adjacent cavitands are shown as light blue and light
brown, respectively.
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in the top inset to Fig. 2. The stability constant Ks calculated
from the plot of F0/Fcal versus C60 concentration is 78 700 2300
dm3 mol-1.29 There is a shift from 344.8 nm to 354.2 nm in the
emission maximum of the quenching curves upon increasing the
C60 concentration, which indicates the formation of the charge–
transfer complex. The excited state of 5a is more stabilized by
C60 molecules than the ground state, and this kind of interaction
leads to the red-shift of the emission spectra.30 The Job’s plot
indicates 1 : 1 complexation between 5a and C60 in toluene (Fig. 2,
bottom inset). This kind of binding could be due to photo induced
charge transfer interactions between the electron-rich cavitand 5a
and the relatively electron-poor fullerene at the excited state. This
value is a little bigger than the binding constant between 1 and C60
(51 900 1100 dm3 mol-1) measured under the same conditions
in our laboratory, which indicates that the rigid extended CTV is
a better C60 host. The fluorescence quenching phenomenon also
occurred between 5a and gradual addition of C70, with a binding
constant of 69 200 1800 dm3 mol-1, (see ESI†) a little smaller
than that of C60, and with less red shifts. Which means that, due
to the relatively small cavity of 5a and the oval shape of C70, the
charge transfer complex is not so stable. Another driving force for
fullerene recognition between fullerenes and 5a may be the van der
Walls force between sterically fitted concave and convex p faces,
which has been confirmed by the crystalline structure of the CTV-
C60 complexes.23a Although we can’t obtain the same evidence for
the 5a–C60 complex, the primary theoretical calculations indicate
that there are weak interactions between the extended arms and
C60. (see ESI, Fig. S4†)
Scheme 3 The chemical resolution of 6.
Chemical resolution of 6
C3-symmetric molecules have been widely applied in the area of
asymmetric catalysis, molecular recognition and chiral nanoma-
terials in recent years.31 The conformational inversion of the 9-
membered ring of CTV is quite slow at room temperature,4b so the
C3-symmetric CTV analogues can be resolved to obtain optical
active isomers. Traditional method involve the introduction of
appropriate chiral auxiliary groups to form diastereoisomers,
which were then separated by chromatographic separation or
recrystallization, followed by cleavage of the chiral groups.32
Warmuth developed a new method of asymmetric synthesis
through dynamic thermodynamic resolution.5a Here, in order to
prepare the optically active CTVs, the chemical resolution method
has been investigated. Firstly, 5a was demethylated with BBr3 in
anhydrous dichloromethane to prepare ( )-6, which then reacted
with (-)-w-camphanic acid chloride to give a diastereoisomer
mixture. By column chromatography, this diastereoisomer mixture
could be separated easily. After reductive cleavage, (+)- and (-)-
6 were obtained with 93 and 96% ee. The [a]2D0 (CHCl3, c =
0.12) values were +500.8◦ and -498.3◦, respectively. (Scheme 3,
see ESI for HPLC details†) The CD spectra of (+)- and (-)-
6 were measured and they were mirror images of each other,
indicating their enantiomeric nature and the successfulness of the
separation process (Fig. 3). Actually, optically pure (+)- and (-)-3
has been obtained by this method before in our laboratory, but
it required the preparative TLC technique with more than one
operation according to our experimental experiences. But with
the introduction of rigidly linked phenyl groups, we could prepare
Fig. 3 CD spectra of (-)-6 and (+)-6 (1.0 ¥ 10-4 M) in MeOH at 25 ◦C.
the optically pure C3-symmetrical cavitands more conveniently,
which is important for optical resolution on a larger scale.
Conclusions
In summary, in the presence of an active indolyl phosphane ligand,
efficient palladium-catalyzed Suzuki–Miyaura coupling of CTV-
Br3 with a variety of aryl boronic acids has been developed.
A series of novel C3-symmetric cavitands with rigid and deep
cavities have been prepared, and enriched the family of CTV-
type hosts. X-ray crystal structure analysis showed that the phenyl
substituted cavitand 5a adopted a linear head-to-tail self-inclusion
arrangement in the crystalline state. Its deeper cavity is a better
C60 host than simple CTV (1), and can form a photoinduced
charge transfer complex at the excited states. Optically active C3-
symmetric cavitands (+)- and (-)-6 have been obtained through
chemical resolution. Further investigation of chiral recognition
and assembly of these new macrocycles is ongoing.
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allowed to warm to room temperature and stirred under argon
for 5 h, poured into 10 g of ice, stirred, the precipitate was
filtrated, dried under vacuum and an off-white powder of ( )-6
was obtained, 255 mg, 91% yield.
Experimental section
General
Melting points were taken on an electrothermal melting point
apparatus and without correction. IR spectra were recorded on
a FT-IR-480 spectrometer using KBr discs. The UV-vis and fluo-
rescence titration experiments were performed on Shimadzu UV-
1601PC and Hitachi F-4500 FL spectrophotometers, respectively.
CD spectra were conducted on JASCO J-810 spectropolarimeter.
HPLC chromatography was conducted on a VARIAN Prostar
335 spectrometer. Elemental analyses were performed by a Flash
EA 1112 elemental analyzer. Mass spectra were recorded on a
Thermal Finnigan Surveyor MSQ Plus Mass Detector. 1H NMR
and 13C NMR spectra were recorded at ambient temperature on a
Bruker (400 MHz) NMR spectrometer. X-ray diffraction data
on single crystals were collected on a Rigaku RAXISRAPID
Optical Resolution. To a solution of (( )-6 (200 mg, 0.44
mmol) in 10 mL anhydrous pyridine was added 380 mg of (-)-
w-camphanic acid chloride (1.74 mmol), and the reaction mixture
was stirred under room temperature for 12 h, then 20 mL of cold
water was added, a precipitation of the solid diastereomers were
collected by suction filtration, washed with water, and dried. This
crude 1 : l mixture was separated by chromatography.
Cleavage of the diastereomers. To a solution of 150 mg of
one pure diastereomer (0.14 mmol) in 5 mL of freshly distilled
◦
THF was added 25 mg of LiAlH4, and it was stirred at 0 C for
2 h. The reaction was quenched by dropwise addition of ethyl
acetate, and 10% aqueous H2SO4 (ice bath), extracted with ethyl
acetate followed by evaporation of the solvent under vacuum
without heating. The desired triphenol was isolated by column
chromatography, and about 70 mg (98% yield) of (-)-6 was
obtained, ([a]2D0 -498.3 (CHCl3, c = 0.12) 96.3 ee% (HPLC)) (or
(+)-6 ([a]2D0 = +500.8 (CHCl3, c = 0.12) 99.3% ee (HPLC))).
diffractometer with graphite monochromated Mo-Ka radiation
(lMo-Ka = 0.71073 A) at 173 K. CTV (1) and CTV-Br3 (4)17 were
33
˚
synthesized according to the literature method. Unless otherwise
noted, all reagents were purchased from commercial suppliers and
used without purification.
General procedures for Pd(PPh3)4 catalyzed Suzuki–Miyaura
couplings
Acknowledgements
A two-neck round-bottom flask was charged with 4 (100 mg, 0.16
mmol), boronic acid (4.5 eq, 0.72 mmol), anhydrous K2CO3 (6
eq, 0.96 mmol) and Pd(PPh3)4 (18 mg, 10 mol%), evacuated and
flashed with argon for three times. Then, degassed DMF (6 mL),
H2O (0.5 mL) was added. The mixture was allowed to heat at 95 ◦C
for 48 h, and then cooled to room temperature, extracted with
CH2Cl2 (3 ¥ 15 ml). The organic layer was washed with brine, dried
over anhydrous Na2SO4 and concentrated under reduced pressure.
The desired product was then isolated by chromatography on silica
gel (200–300 mesh).
This work was supported by the National Natural Science
Foundation of China (20932004), the Major State Basic Research
Development Program of China (2011CB932501), and the Chi-
nese Academy of Sciences.
Notes and references
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2 H. Zimmermann, P. Tolstoy, H.-H. Limbach, R. Poupko and Z. Luz,
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3 S. T. Mough, J. C. Goeltz and K. T. Holman, Angew. Chem., Int. Ed.,
2004, 43, 5631.
General procedures for Pd(OAc)2/L catalyzed Suzuki–Miyaura
couplings
4 (a) A. Collet, J. Gabard, J. Jacques, M. Cesario, G. Guilhem and C.
Pascard, J. Chem. Soc., Perkin Trans. 1, 1981, 1630; (b) A. Collet and
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Nicoud and N. Armaroli, Tetrahedron Lett., 1999, 40, 5681; (b) H.
Matsubara, T. Shimura, A. Hasegawa, M. Semba, K. Asano and K.
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K. Shiwaku, K. Asano, M. Uno, S. Takahashi and K. Yamamoto,
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Pd(OAc)2 (3.8 mg, 0.016 mmol, 10 mol%) and L (26 mg, Pd: L = 1:
4) were loaded into a Schlenk tube equipped with a Teflon-coated
magnetic stirring bar. Precomplexation was applied by adding
freshly distilled dichloromethane (0.5 mL) and Et3N (50mL) into
the tube. The solution was stirred and quickly heated until the
solvent started boiling and then evaporated under high vacuum. 4
(100 mg, 0.16 mmol), arylboronic acid (6 eq, 9.6 mmol) and K3PO4
(9 eq, 1.44 mmol) were loaded into the tube under argon, degassed
tert-butanol (15 mL) was then added. The tube was stirred at room
temperature for 5 min and then placed into an oil bath and allowed
◦
to reach 130 C rapidly. After about 44 h, the reaction tube was
cooled to room temperature and quenched with water, extracted
with CH2Cl2 (3 ¥ 15 ml). The desired product was then isolated by
chromatography on silica gel (200–300 mesh).
Chiral separation of compound ( )-6
Synthesis of racemic ( )-6. 0.3 mL (2.1 mmol) of BBr3 was
added dropwise to a solution of ( )-5a (300 mg, 0.51 mmol) in
10 mL of freshly distilled CH2Cl2 in ice bath. The mixture was
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˚
26 Crystal data for 5a: C42H36O3, M = 588.71, triclinic, a = 13.215(3) A, b◦=
◦
◦
˚
˚
14.889(3) A, c = 17.810(4) A, a = 89.02(3) , b = 85.32(3) , g = 65.87(3) ,
3
¯
˚
V = 3187.0(11) A , T = 173(2)K, space group P1, Z = 4, 11187 reflections
measured, 11187 independent reflections (Rint = 0.0000). The final R1
values were 0.1220 (I > 2s(I)). The final wR(F2) values were 0.3169 (I
> 2s(I)). The final R1 values were 0.1407 (all data). The final wR(F2)
values were 0.3300 (all data). The goodness of fit on F2 was 1.125†.
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1−exp(−e1c1l)
e1c1l
e3c3l
1−exp(e3c3l)
(e1c1l +e2c2l)
1−exp(−e1c1l −e2c2l)
F
= F
•
•
cal
exp
Where e1c1l is the absorption of 5a at the excitation wavelength, e2c2l is
the absorption of the guest at the excitation wavelength, and e3c3l is the
absorption of the guest at the emission wavelength.
29 J. Wang, D. Wang, E. K. Miller, D. Moses, G. C. Bazan and A. J.
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where F0 is the fluorescence intensity of the host in the absence of the
guest, Fcal is the calculated fluorescence intensity from the experimental
data in the presence of the guest according to the equation in ref. 28.
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1364 | Org. Biomol. Chem., 2012, 10, 1359–1364
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The Royal Society of Chemistry 2012
©