Design, modeling and synthesis of molecular tweezers with self-assembly properties

Article abstract of DOI:10.1016/j.molstruc.2011.01.032

Development of molecular tweezers depends on the design and synthesis of reliable spacers. Two new classes of spacers based on functionalized dibenzo[a,j]xanthene are described. Molecular tweezers 4, 5 and 6 with adjustable cavity are designed and synthesized. Single crystal X-ray diffraction shows self-assembly and recognition of 4 in the solid state; with the π-stacking, CH/O and CH/π interactions being the driving forces. The intermolecular interactions in 5 and 6 are so strong that do not allow dissolution of 5 and 6 in any known solvent.

Full text of DOI:10.1016/j.molstruc.2011.01.032

Journal of Molecular Structure 990 (2011) 140–151
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Design, modeling and synthesis of molecular tweezers
with self-assembly properties
⇑
Mohsen Ghodratbeigi, Parviz Rashidi-Ranjbar , Alireza Abbasi
School of Chemistry, University of Tehran, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2010
Received in revised form 19 January 2011
Accepted 19 January 2011
Available online 24 January 2011
Development of molecular tweezers depends on the design and synthesis of reliable spacers. Two new
classes of spacers based on functionalized dibenzo[a,j]xanthene are described. Molecular tweezers 4, 5
and 6 with adjustable cavity are designed and synthesized. Single crystal X-ray diffraction shows self-
assembly and recognition of 4 in the solid state; with the p-stacking, CH/O and CH/p interactions being
the driving forces. The intermolecular interactions in 5 and 6 are so strong that do not allow dissolution of
5 and 6 in any known solvent.
Keywords:
Ó 2011 Elsevier B.V. All rights reserved.
Dibenzo[a,j]xanthene
p-stacking
Weak interactions
Molecular tweezers
Self-assembly
Molecular recognition
1. Introduction
unsubstituted 4H-pyran is planar, but substitution of 4H-pyran at
C-4 position with bulky substituents drives the molecule towards
Synthetic molecular receptors have been designed and synthe-
sized for studying the molecular recognition processes and the
weak intermolecular forces operative in drug-receptor binding.
Molecular tweezers are a class of synthetic receptors with open cav-
ities which are capable of binding guest molecules using non-cova-
lent interactions [1]. Most studies of molecular tweezers are
focused on tweezers having rigid spacer and usually two aromatic
pincers [2]. It has been shown that neutral aromatic substrates bind
flattened boat form with pseudo axial orientation of substituent
[7]. It has been shown that ring inversion in some substituted
4H-pyrans do not take place even at high temperature [8]. These
conformational behaviors are completely imitated by 14H-2,12-
dihydroxydibenzo[a,j]xanthene
1
and 14-(4-methylphenyl)
14H-2,12-dihydroxydibenzo[a,j]xanthene 2. Furthermore, the bay
region tolyl of 2 at C14 has proper conformation [9] for construction
of self-assembled structure. The hydroxyl groups at C2 and C12
positions in 1 and 2 are very suitable for building up pincers due
to appropriate distance from each other (Figs. 1 and 2).
Geometry optimization of 1 by AM1 shows two conformations,
planar and flattened boat, with planar form being more stable than
the flattened boat by 5.3 kJ/mol, while DFT calculations by B3LYP
method using 6-31GÃÃ basis set indicates the planar form as the
only minimum energy conformation of 1 (Fig. 1). Geometry optimi-
zation of 2 by AM1 and DFT/B3LYP/6-31GÃÃ methods show the flat-
tened boat as the only minimum energy form. The tolyl moiety in 2
could be oriented in two directions, eclipsed and gauche, defined
by the dihedral angle of H14AC14AC15AC16 (Fig. 2). The AM1 calcu-
lations shows that eclipsed form is 13.5 kJ/mol more stable than
the gauche one while DFT calculations shows that eclipsed form
is the only minimum energy conformation (Fig. 2).
to the cavity of tweezer pincers by
p–p and CH/p interactions
[1f,1g]. In molecular tweezers, the spacer should maintain the pin-
cers in parallel alignment at effective distance normally about 7 Å
[1g–3]. The requirement of keeping parallel pincers at a suitable
distance from each other is limiting so there are not many known
structural motifs to be used as spacer. Functionalized dib-
enzox[a,j]xanthene with proper structural units are good candi-
dates for constructing reliable rigid spacers to be used for
building up the molecular tweezers; dibenzo[a,j]xanthene has
shown therapeutic, biological and anti-inflammatory activities as
well [4–6].
2. Results and discussion
The spacers 1 and 2 were synthesized according to the Scheme
1. In contrast to the 14aryl-14H-dibenzo[a,j]xanthenes which are
synthesized in high yields [10], synthesis of 1 and 2 suffers some
drawbacks [11]. The yield of products could be increased by start-
ing from the adduct 3 (Scheme 1). The molecular tweezers 4 and 5
In xanthenes and dibenzo[a,j]xanthenes, 4H-pyran moiety
determines the conformation of whole molecule. Conformation of
⇑
Corresponding author.
E-mail address: ranjbar@khayam.ut.ac.ir (P. Rashidi-Ranjbar).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.01.032

M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
141
syn-a, syn-a should be the most populated form in the gas phase
(Table 2); in the solid state syn-a, syn-a form is the only observed
one.
If syn-a and syn-g conformations of benzyl 2-naphthyl ether
moiety are considered for conformational analysis of 4, six possible
combinations of syn-a and syn-g conformations (without counting
enantiomers) are possible for the two benzyl 2-naphthyl ether
moiety in 4, i.e. syn-a, syn-a; syn-a, syn-g-up; syn-a, syn-g-down;
OH
OH
HO
OH
R
AcOH
HCl
2
+
RCHO
Fig. 1. The B3LYP/6-31GÃÃ optimized structure of spacer 1. r = 0.823 nm, the
distance of oxygen atoms of hydroxyl groups.
OHHO
3
Ar
Ar
CH2
O
were synthesized by reacting 2 with benzyl and 1-(chloromethyl)
naphthalene; 6 was synthesized by reacting 2 with 1-(2-bromoeth-
oxy) naphthalene (Scheme 1).
CH2
O
-H2O
OH
OH
For conformational analysis of 4, 5 and 6; conformations of sub-
structures were considered. The conformation of ACH2R group
attached to 2-hydroxy naphthalene moiety in 4, 5 and 6 could be
derived from the 2-methoxy naphthalene. It has been shown that
2-methoxy naphthalene adopts syn (s-cis, U = 0°) and anti (s-trans,
U = 180°) forms [12] with a population ratio 19:1 between syn and
anti rotameric isomers at 305 K [13].
R
R
Ary-CH2-Cl
DMF, K2CO3
O
4, 5
O
1, 2
R=H, Tolyl
R =Tolyl and Ar = Benzyl , Naphthyl
Conformational analysis of syn and anti forms of benzyl 2-naph-
thyl ether moiety in 4 were performed by AM1 and energy minima
thus obtained were re-optimized by B3LYP/6-3GÃÃ calculations.
Two conformations were found for syn and anti forms, i.e. syn-a;
syn-g and anti-a; anti-g (Fig. 3, Table 1). It should be mentioned
that in syn-g and anti-g forms, the dihedral angle of
Br
O
O
O
O
CH3
O
Csp2ACsp2AOACsp3 is close to zero as found in aryl methyl ethers
[14]. It has been shown in a recent study that the conformational
preference of benzyl methyl ether is type and basis set dependent
[15], however this was not taken into consideration for the confor-
mational analysis of benzyl 2-naphthyl ether moiety in 4.
K2CO3
DMF
2
+
2
In 4, considering syn-a and anti-a conformations of benzyl 2-
naphthyl ether moiety, the two O-benzyl arms could be oriented
in three distinct directions; syn-a, syn-a; anti-a, anti-a and syn-a,
anti-a (or anti-a, syn-a) (Fig. 4). The AM1 calculations shows that
O
6
Scheme 1. The paths for synthesis of spacers 1 and 2 and molecular tweezers 4–6.
Fig. 2. The B3LYP/6-31GÃÃ optimized structure of spacer 2 (left, side view; right, top view). r = 0.819 nm, the distance of oxygen atoms of hydroxyl groups.

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M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
Fig. 3. The structure of benzyl 2-naphthyl ether conformations, optimized by the B3LYP/6-31GÃÃ method.
Table 1
non bonded interactions in the complex formation between
bis(phenanthryl) derivatives of all-trans-fused perhydronaphta-
cene moiety and 1-cyano-3,5-dinitrobenzen [16]. Also the driving
force for the host–guest interactions of buckycatcher and C60 is re-
Calculated relative energies of benzyl 2-naphthyl ether by the B3LYP/6-31GÃÃ method.
Conformer
syn-a
0.0
syn-g
0.27
anti-a
1.41
anti-g
1.39
Energy difference (kcal molÀ1
)
ported to be ‘‘pure’’ concave–convex
the interaction of tolyl ring with neighboring benzylic pincers,
CH/O and CH/ interactions are found in the crystal structure of 4
p–p interactions [17]. Besides
p–p
p
syn-g-up, syn-g-up; syn-g-up, syn-g-down; syn-g-down, syn-g-
down (Fig. 5, Table 3). The syn-g form of benzyl 2-naphthyl ether
moiety in 4 does not reside a planar form as found in aryl methyl
as well. Two types of CH/O interactions are observed in the crystal
structure of 4. The first one is between H (3, 11) of one molecule of
4 and O (2, 12) of the neighbor molecule (Fig. 7) in the b direction
of the unit cell, with the CAO distance of 0.369 nm and CHAO an-
gle of 135.5°. The CAO distance in these kinds of weak interactions
have been reported to vary between 0.3 and 0.4 nm and CHAO an-
gle between 120° and 180° [18]. The second CH/O interaction is be-
tween O (2, 12) of one molecule of 4 and the meta hydrogen of
benzylic arm ring in the c direction of the unit cell; the distance
of CAO and angel of CHAO are 0.38 nm and 147.3° respectively
(Fig. 8).
ethers, but
sp2ACsp2AOACsp3 is about 55°.
Single crystal X-ray diffraction shows self-assembly and recog-
a gauche form where the dihedral angle of
C
nition of 4 molecules in the solid state. The experimental details
about the crystal structure determination are presented in Table
4. In the solid state, the tolyl ring is located between the two pin-
cers of the neighbor molecule by driving force of
p–p interaction
(Fig. 6); interactions have been shown to be the only operative
p–p

M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
143
Fig. 4. The AM1 optimized structures of syn-a, syn-a; syn-a, anti-a and anti-a, anti-a conformations of 4 (top view). r is centroid to centroid distance of pincers and are 0.815,
0.860 and 0.950 nm respectively.
Table 2
The second CH/
found between the ortho hydrogen of benzylic arms and the
p
interaction in the c direction of the unit cell is
sys-
Relative energies for the combination of syn-a and anti-a forms of 4 calculated by the
AM1 method.
p
tem of naphthylic ring of 4 (Fig. 10). The centroid-to-centroid dis-
tance of two interacting aromatic rings is 0.45 nm, giving the CH
hydrogen-to-centroid distance of 0.28 nm and centroid-H-centroid
angle of 124.3°. These values are in good agreement with those
found experimentally and theoretically in other systems [20].
The alignments of molecules in self-assembled structure of 4 in
the solid state are opposite, presumably for the better inter-align-
Conformer
Energy difference
(kcal molÀ1
)
syn-a, syn-a
syn-a, anti-a
anti-a, anti-a
0.0
0.9
1.9
ment of molecules to make strong CH/O and CH/p interactions
(Fig. 11).
There are two types of CH/p interactions in the crystal structure
For conformational analysis of 5, the reported structure of 1-
methyl naphthalene [21] and syn conformation of 2-methoxy
naphthalene were considered. Two conformations for 1-naphthale-
nyl 2-naphthalene ether moiety (Fig. 12) with 1.02 kcal/mol energy
difference were found, i.e. syn-a and syn-g (Table 5); syn-a was the
global minimum energy. Conformational analysis of tweezers 5
was performed by considering syn-a conformation of 1-naphthale-
nyl 2-naphthalene ether moiety. Three orientations of the two 1-
naphthalenyl pincers are possible: syn-a-up, syn-a-up; syn-a-up,
of 4. In the first CH/p interaction in the b direction of the unit cell,
one of the hydrogen of naphthyl ring is oriented toward the center
of aromatic ring of benzylic pincer (Fig. 9), with centroid-to-cen-
troid distance of 0.48 nm, CH hydrogen-to-centroid distance of
0.28 nm and centroid-H-centroid angle of 135.8°. In proteins, there
is a preference for the edge to face type of interaction between the
phenyl rings with a predominance of structures with distance be-
tween the phenyl rings centroids of 0.45–0.7 nm and H to centroid
distance of 0.25–0.35 nm [19].

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M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
Fig. 5. The AM1 optimized structure of 4 based on syn conformation of benzyl 2-naphthyl ether moiety.
syn-a down; syn-a-down, syn-a-down (Fig. 13). Energy minimiza-
tion of the starting conformations by AM1 shows that syn-a-down,
syn-a-down is the global minimum energy (Table 6). Starting
structure with syn-a-up conformation of 1-naphthenyl pincer
ended with a gauche conformation of this moiety (Fig. 13).
The self organization and inter molecular interactions in 5 are
so strong that attempts to dissolve it in any known solvent to make
crystals were failed. It is expected that by using 3,5-di-tert-buthyl
benzaldehyde a soluble substituted tweezer 5 will be formed [22]
to allow for host–guest interaction studies.

M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
145
Table 3
Relative energies for the six possible syn forms of 4, calculated by the AM1 method.
Table 4
The crystallographic data for 4.
Conformer
Energy difference (kcal molÀ1
)
Formula
C42H32O3
syn-a, syn-a
syn-a, syn-g-up
syn-a, syn-g-down
syn-g-up, syn-g-up
syn-g-up, syn-g-down
syn-g-down, syn-g-down
0.0
2.6
3.3
5.0
3.0
4.7
M (g molÀ1
Crystal system
Space group
a (Å)
b (Å)
c (Å)
)
584.68
monoclinic
P 21/m
6.7147(13)
24.857(5)
9.6912(19)
90
a
(°)
b (°)
106.44(3)
90
1551.4(5)
2
c
(°)
V (Å3)
Z
Conformational analysis of 6 was based on three distinct moie-
ties, i.e. 2-methoxy naphthalene, gauche conformation of 1,2-
dimethoxy ethane [23] and 1-methoxy naphthalene [24]. Only
syn-a conformation of the aryl alkyl etheric bond was considered
for conformational analysis. Three energy minima were found,
i.e. syn-a-g+up, syn-a-gÀ- up; syn-a-g+up, syn-a-g+down and syn-
a-gÀ-down, syn-a-g+down, the second one was the global mini-
mum energy (Fig. 14, Table 7). The first and third conformations
could act as a tweezer, there have been reports on the tweeze func-
tion of some hosts when they bind guests [25]. The self organiza-
tion and inter molecular interactions in 6 are so strong that
attempts to dissolve it in any known solvent to make crystals were
failed, using a suitable aldehyde like 3,5-di-tert-buthyl benzalde-
hyde is predicted to make a soluble 6 derivative [22] for further
studies.
T (K)
295
2
l
(VoÀK
a
) (mmÀ1
)
0.077
1.252
6830
3061 (Rint = 0.0421)
1856
Dcalcd (g cmÀ3
)
Measured reflections
Unique reflections
Observed reflections
R1, wR2 [I > 2
(all data)
r
(I)]
0.0529, 0.1175
0.1009, 0.1338
2.1. Conclusion and outlook
Synthesis of dibenzo[a,j]xanthene with functional groups at
appropriate positions, introduces a new class of rigid spacers
Fig. 6. Parallel displaced p–p stacking in 4 (up, side view; down, front view). Hydrogen atoms have been omitted for clarity.

146
M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
Fig. 7. The CH/O interaction in 4, in the b direction of the unit cell. Distance of CAO and angle of CAHAO are 0.369 nm and 135.5° respectively.
Fig. 8. The CH/O interaction in 4, in the c direction of the unit cell. Distance of CAO and angle of CAHAO are 0.382 nm and 147.3° respectively.
Fig. 9. The CH/p interactions in 4, in the b direction of the unit cell.
which have interesting properties for constructing molecular
tweezers with self-assembly and adjustable cavity properties.
These molecular tweezers have also suitable structural motif to
develop other types of molecular receptors.
2.2. Computational
The initial structures were constructed by Chem3D (Ultra 6,
ChemOffice 2004, Cambridge Soft Corporation). Initial geometry

M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
147
Conformations of benzyl (or naphthalenyl) 2-naphthyl ether were
constructed by replacing methyl protons of 2-methoxy naphtha-
lene by phenyl (or naphthyl) group. The optimized structure of
two benzyl (or naphthalenyl) 2-naphtyl ether moiety were put to-
gether by constructing a pyran ring to construct the initial struc-
ture of 4 or 5. For 6, the optimized structure of syn form of 2-
methoxy naphthalene, gauche conformation of 1, 2-dimethoxy
ethane and 1-methoxy naphthalene were put together and initial
structure of 6 was constructed as explained for 4. Mercury 2.3
[29] was used for presentation of structures.
2.3. Experimental
All the materials were received from Merck and used without
further purification. 1H NMR and 13C NMR spectra were recorded
on a Bruker Avance 500 MHz spectrometer.
The X-ray crystallography data collection was made on small
crystal enclosed in thin-walled glass capillary at room temperature
by means of a STOE imaging-plate diffractometer. The structure
was solved by direct methods using SHELXS97 and refined using
full-matrix least-squares method on F2, SHELXL97 [30]. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
for aromatic, methylene and methyl groups were positioned geo-
metrically and constrained to ride on their parent atoms, with Ui-
so(H) = 1.5 times Ueq(carrier C) for methyl group and 1.2 for
methylene and aromatic-H groups. While the H atoms for CH were
located from electron density map and refined with Uiso(H) = 1.2
Ueq(C).
Fig. 10. The CH/p interactions in 4, in the c direction of the unit cell.
2.3.1. 1-((2,7-Dihydroxynaphthalen-8-yl)methyl)naphthalene-2,7-
diol 3
optimizations were carried out by the molecular mechanics meth-
od using MM force fields implemented in ChemOffice 2004. The
resulting geometries were optimized further by semi-empirical
AM1 [26] calculations implemented in MOPAC 6.0 program [27].
The AM1 optimized geometries were re-optimized by DFT method
at the B3LYP/6-31GÃÃ level of theory using Gaussian 98 suits of pro-
grams [28]. The syn and anti conformations of 2-methoxy naphtha-
lene were constructed by Chem3D and optimized as explained.
In a 50 ml round bottom flask was dissolved 2,7-naphthalenedi-
ol (1 g, 6.25 mmol) in ethanol 96% (5 ml) and stirred at 45 °C.
Hydrochloric acid 5% (30 ml) and formaldehyde 37% (0.3 g) were
added to the mixture. After several minutes a white precipitate
was formed. The precipitate was washed with water and dried un-
der vacuum. Yield was 90%. Mp 190–191 °C, 1H NMR 500 MHz
(DMSO) d 4.48 (s, 2H) 6.74 (d, 2H, J = 7.5 Hz), 7.00 (d, 2H,
Fig. 11. The self-assembled structure of 4 in the crystalline phase.

148
M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
Fig. 12. The B3LYP/6-31GÃÃ optimized structure of syn 1-naphthalenyl 2-naphthalene ether conformations.
Table 5
2.3.5. General method for the synthesis of molecular tweezers 4–6
Spacer 2 (1 mmol), potassium carbonate (2.5 mmol) and benzyl
chloride, 1-(chloro methyl) naphthalene or 1-(2-bromoethoxy)
naphthalene(excess) were dissolved in DMF and the mixturepurged
by argon and stirred at 50–60 °C for 24 h. The reaction mixture
poured in water and the organic layer was separated from the pre-
cipitate by separatory funnel. The precipitate was filtered and
washed with water and hexane: ethyl acetate (60:40) several times.
Calculated relative energies of 1-naphthalenyl 2-naphthalene ether by the B3LYP/6-
31GÃÃ method.
Conformer
syn-a
0.0
syn-g
1.02
Energy difference (kcal molÀ1
)
J = 8.5 Hz), 7.39 (s, 2H), 7.43 (d, 2H, J = 8.5 Hz), 7.47(d, 2H,
J = 8.5 Hz), 9.17(s, 2H), 9.70 (s, 2H). 13C NMR, 125 MHz (DMSO) d
20.40, 118.06, 119.37, 122.06, 123.7, 125.40, 127.42, 128.01,
128.40, 133.7, 151.7.
2.3.6. Molecular tweezer 4
This compound was obtained as a pale solid (yield ꢀ 90%) Mp
240–242 °C. 1H NMR 500 MHz (CDCl3) d 2.2 (s, 3H), 5.26 (d, 2H,
J = 11.7 Hz), 5.35 (d, 2H, J = 11.7 Hz), 6.04 (s, 1H), 6.9 (d, 2H,
J = 7.90 Hz), 7.18 (d, d, 2H, J = 8.21 Hz, J = 2.25 Hz), 7.28 (d, 2H,
J = 8.02 Hz), 7.36 (d, 2H, J = 8.80 Hz), 7.43 (t, 2H, J = 7.32 Hz),
7.51(t, 2H, J = 7.51 Hz), 7.61(d, 4H, J = 7.40 Hz), 7.68 (s, 2H), 7.73
(d, 2H, J = 8.84 Hz), 7.76(d, 2H, J = 8.85 Hz); 13C NMR, 125 MHz
(CDCl3) d 21.6, 37.4, 68.30, 104.7, 115.08, 116.23, 116.35, 125.9,
127.7, 127.9, 128.5, 128.6, 128.9, 130.2, 131.5, 131.7, 132.20,
135.15, 137.0, 142.12, 148.3, 157.22, 166.9.
2.3.2. General method for the synthesis of spacers 1 and 2
2,7-Naphthalenediol (2.5 mmol) was dissolved in acetic acid
and heated to 50–60 °C. Concentrated hydrochloric acid
(0.15 mmol) and aldehyde (1 mmol) were added slowly and stirred
for 24 h at this temperature. The reaction mixture was cooled and
poured in cold water to precipitate the crude product. The product
was separated by preparative TLC with hexane: ethyl acetate
(80:20) as eluent.
2.3.7. Molecular tweezer 5
2.3.3. 14H-2,12-dihdroxydibenzo[a,j]xanthene 1
This compound was obtained as a pale solid (yield ꢀ 90%). Mp
248–250 °C, 1H NMR 500 MHz (DMSO) d 1.99(s, 3H), 5.71 (d, 2H,
J = 12.3 Hz), 5.94 (d, 2H, J = 12.3 Hz), 6.50 (s, 1H), 6.61 (d, 2H,
J = 7.60 Hz), 7.21 (d, 2H, J = 8.37 Hz), 7.27 (d, 2H, J = 7.43 Hz),
7.37(t, 4H, J = 9.05 Hz), 7.45 (t, 2H, J = 7.75 Hz), 7.52 (t, 2H,
J = 7.41 Hz), 7.70(d, 2H, J = 6.82 Hz), 7.85(t, 4H, J = 10.0 Hz),
7.95(t, 4H, J = 10.0 Hz), 8.07(s, 2H), 8.16(d, 2H, J = 8.31 Hz) 13C NMR
125 MHz (DMSO) d 20.2, 36.5, 67.87, 104.77, 115.0, 116.26, 116.37,
123.6, 125.3, 125.8, 125.9, 126.2, 126.3, 127.9, 128.4, 128.54,
128.57, 130.19, 131.0, 132.2, 132.3, 133.3, 135.0, 142.1, 148.2,
157.1.
This compound was obtained as a violet powder (yield, 40%).
Mp 253–254 °C, 1H NMR 500 MHz (DMSO) d 4.36 (s, 2H), 7.09 (d,
d, 2H, J = 10.7 Hz, J = 2.07 Hz), 7.12 (d, 2H, J = 8.80 Hz), 7.33 (d,
2H, J = 1.97 Hz), 7.76 (d, 2H, J = 8.82 Hz), 7.83 (d, 2H, J = 8.05 Hz),
9.91(s, 2H); 13C NMR, 125 MHz (DMSO) d 21.26, 105.05, 109.5,
114.35, 118, 124.14, 129.51, 132.26, 133.37, 149.1, 156.5.
2.3.4. 14-(4-Methylphenyl)14H-2,12-dihydroxydibenzo[a,j]xanthene 2
This compound was obtained as a gray powder (yield, 50%).
Mp > 280 °C (dec), 1H NMR 500 MHz (DMSO) d 2.10(s, 3H), 6.07(s,
1H), 6.98–7.01(m, 4H), 7.26 (d, 2H, J = 8.81 Hz), 7.38 (d, 2H,
J = 8.12 Hz), 7.67 (d, 2H, J = 2.0 Hz), 7.75 (d, 4H, J = 8.78 Hz), 9.88
2.3.8. Molecular tweezer 6
(s, 2H); 13C NMR, 125 MHz (DMSO)
d
21.26, 37.73, 106.04,
This compound was obtained as a pale solid (yield ꢀ90%). Mp
266–267 °C, 1H NMR 500 MHz (DMSO) d 2.00(s, 3H), 4.55 (broad,
4H), 4.61(d, 2H, J = 11.7 Hz), 4.87(d, 2H, J = 11.7 Hz), 6.54 (s. 1H),
114.98, 116.48, 117.29, 125.85, 128.8, 129.5, 129.71, 131.1, 133.5,
136.23, 142.96, 149.17, 157.2.

M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
149
Fig. 13. The AM1 optimized structure of 5 conformations. Only syn conformation of 1-naphthalenyl 2-naphthalene ether moiety is considered.
Table 6
Relative energies for the conformers of 5 calculated by the AM1 method.
Table 7
Relative energies for the conformers of 6 calculated by the AM1 method.
Conformer
Energy difference (kcal molÀ1
)
Conformer
Energy difference (kcal molÀ1
)
syn-a-down, syn-a-down
syn-a-down, syn-a-up
syn-a-up, syn-a-up
0.0
1.5
4.9
syn-a-g+-up, syn-a-g+-down
syn-a-g+-up, syn-a-gÀ-up
0.0
1.3
2.5
syn-a-gÀ-down, syn-a-g+-down
6.85 (d, 2H, J = 8.50 Hz), 7.02 (d, 2H, J = 8.55 Hz), 7.17 (d, d, 2H,
J = 10.5 Hz, J = 2.45 Hz), 7.35 (d, 2H, J = 9.05 Hz), 7.38–7.49 (m,
11H), 7.81–7.85 (m. 6H), 8.00 (d. 2H, J = 2.45 Hz), 8.13 (d, 2H,
66.67, 104.97, 10,552, 115.1, 116.07, 116.24, 120.23, 121.46,
124.90, 125.23, 125.91, 126.11, 126.42, 127.42, 128.14, 128.66,
128.72, 130.25, 132.35, 134.02, 135.19, 142.54, 148.19, 153.80,
157.06.
J = 9.60 Hz); 13C NMR 125 MHz (DMSO)
d 20.33, 36.5, 66.61,

150
M. Ghodratbeigi et al. / Journal of Molecular Structure 990 (2011) 140–151
Fig. 14. The AM1 optimized structure of 6 conformations. Only syn conformation of 2-naphthalene alkyl ether moiety is considered. The g + and g- is viewed from the
xanthene side.
[5] R.W. Lambert, J.A. Martin, J.H. Merrett, K.E.B. Parkes, G.J. Thomas, PCT Int.
Acknowledgment
Appl.(1997) WO 9706178.
[6] J.P. Poupelin, G. Saint-Rut, O. Fussard-Blanpin, G. Narcisse, G. Uchida-Ernouf, R.
Author thanks the research council of University of Tehran for
financial support.
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