Tweezers-like aromatic molecules and their luminescent properties depending on the structures

Article abstract of DOI:10.1016/j.tetlet.2011.05.080

Di(hydroxyphenyl)pyrimidine with two anthryl substituents 1a was synthesized and characterized by X-ray crystallography and NMR spectroscopy. The molecule prefers 'U'-shaped conformation supported by intramolecular O-H?N hydrogen bonds in the solid state

Full text of DOI:10.1016/j.tetlet.2011.05.080

Tetrahedron Letters 52 (2011) 3883–3885
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Tweezers-like aromatic molecules and their luminescent properties depending
on the structures
⇑
Yuji Suzaki, Yoshitaka Tsuchido, Kohtaro Osakada
Chemical Resources Laboratory (Mail Box R1-3), Tokyo Institute of Technology, 4259 Nagatduta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Di(hydroxyphenyl)pyrimidine with two anthryl substituents 1a was synthesized and characterized by
X-ray crystallography and NMR spectroscopy. The molecule prefers ‘U’-shaped conformation supported
by intramolecular O–HꢀꢀꢀN hydrogen bonds in the solid state and in solution. The CHCl3-solvated com-
pound binds two CHCl3 molecules between the two parallel anthryl planes. Hexylation of the OH groups
of 1a produces 1c whose diarylpyrimidine core contains these aromatic planes with OꢀꢀꢀH–C interaction
Received 21 April 2011
Revised 13 May 2011
Accepted 16 May 2011
Available online 24 May 2011
and helical alignment. Compound 1c shows strong emission from the anthryl groups (410 nm,
u = 0.39),
Keywords:
Anthracene
Hydrogen bonds
Luminescent properties
while luminescence is not observed for 1a partly due to quenching via PET (photo-induced electron trans-
fer) process.
Ó 2011 Elsevier Ltd. All rights reserved.
Compounds having polyaromatic partial structure, such as an-
thryl and pyrenyl groups in their molecules have potentially pho-
toluminescent properties, but they sometimes show no emission
due to quenching via energy transfer or electron transfer.1–3 Con-
formation of the molecules influences the quenching process and
their photoluminescent efficiency. The aromatic molecules with
flexible skeleton are used as the molecular tweezers which are
capable of binding the guest molecules, such as TCNQ (tetracyano-
quinodimethane), TCNE (tetracyanoethylene) and trinitrofluore-
none, by their two arms.4,5 Functionalization of silica surface by
the compounds and selective separation of aromatic hydrocarbon
molecules were also reported.6 Luminescent properties of the
tweezers-like molecules are often used as probes for change in
the intermolecular interactions between the arms of molecular
tweezers and the guest molecules.7,8 In this study, we synthesized
the new aromatic compounds having two anthryl groups which
change relative positions of the two aromatic arms like a pair of
tweezers depending on the substituents. Luminescence properties
depending on the molecular structures are also mentioned.
2-methylpyrimidine and 5-bromo-2-methoxyphenyl boronic acid
in dioxane/water yields 4,6-di(bromoaryl)-2-methylpyrimidine in
44% yield. Subsequent Suzuki–Miyaura coupling reaction of the
product with 9-anthrylboronic acid forms 1b in 71% yield. Demeth-
ylation of 1b by BBr3 in CH2Cl2 yields 1a (68%). Hexylation of 1a,
giving 1c, was achieved by using 1-iodohexane and K2CO3 (65%
yield).
Figure 2 shows structures of 1a(CHCl3)2 and 1c determined by
X-ray crystallography. The molecule 1a adopted ‘U’-shape confor-
mation having two parallel anthracene units.9 Position of the OH
hydrogen atom, H1, of 1a was determined from Fourier synthesis.
Short contact between H1 and N1 keeps planarity of the rings A
and B. Two anthryl planes are situated at parallel positions with
distance of 8.0 Å. Two CHCl3 molecules exist between them and
keep the conformation by C–Hꢀꢀꢀ
p interaction with the anthryl
groups. Close contact of the CHCl3 hydrogen, H18, and the centroid
of the C ring of 1a and almost liner C25–H18ꢀꢀꢀcentroid of C angle
are consistent with the C–Hꢀꢀꢀ
p
attractive interaction.10 These
CHCl3 molecules in the crystals of 1a were confirmed by elemental
Our design of the molecules is shown in Figure 1. Di(hydroxy-
phenyl)pyrimidine units of compound 1a should form a
p-conju-
gated plane owing to the O–HꢀꢀꢀN hydrogen bonds. Rotation of
C–C bonds between the pyrimidine and aryl groups would change
the conformation of the molecule and spacial relation between the
two anthryl groups. Scheme 1 summarizes synthesis of 1a, 1b and
1c. Their model compounds 9-(4-hydroxyphenyl)anthracene (2a)
and 9-(4-methoxyphenyl)anthracene (2b) (Fig. 1) were also pre-
pared. The Pd-complex-catalyzed coupling reaction of 4,6-diiodo-
R1O
N
OR2
N
R1O
R
1 = H (1a), Me (1b), n-hex(1c) R2 = H (2a), Me (2b)
Figure 1. Structure of 1a–1c and 2a–2b.
⇑
Corresponding author.
E-mail address: kosakada@res.titech.ac.jp (K. Osakada).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.05.080

3884
Y. Suzaki et al. / Tetrahedron Letters 52 (2011) 3883–3885
I
I
O1
H1
N1
(A)
N
N
MeO
Br
B
+
(HO)2B
C
A
MeO
N
Br
H18
Pd(PPh3)4
K2CO3
C25
N
Dioxane/Water
80 oC, 18 h
MeO
Br
44%
B(OH)2
(B)
MeO
PdCl2(PhCN)2
P(t-Bu)3, K3PO4
N
N
N1
N2
O1
DMF
H4
MeO
90 oC, 24 h
O2
1b, 71 %
g
f
j
i
h
e
k
d
HO
c
BBr3
N
N
a
b
CH2Cl2
Reflux, 3 h
HO
Figure 2. Molecular structure of (A) 1a (CHCl3)2 and (B) 1c. ORTEP drawings are
shown in 50% probability. A part of hydrogen atoms were omitted for simplicity.
1a, 68 %
e'
f'
d'
g'
(A)
d
e
h
g
j
c
f
h'
b
i
i'
j'
c'
k
I
O
K2CO3
N
N
a'
b'
(B)
Ethylmethylketone
80 oC, 24 h
O
d’
b’
h’
g’
j’
i’ f’
e’ c’
1c, 65 %
Scheme 1. Synthesis of 1a–1c.
14 8.5
8.0
7.5
analyses as well as the thermogravimetric analysis (TGA) showing
weight loss in two stages at 140 °C (11%) and at 180 °C (12%). Fur-
ther significant weight loss was not observed below 400 °C, which
suggests thermal stability of 1a.
Figure 3. 1H NMR spectra of (A) 1a and (B) 1c in CDCl3 (400 MHz, rt).
molecular absorption coefficient
e of 1a and 1c (24500 and
IR spectrum of 1a in KBr disk shows a broad
m
(OH) peak at
25700 Mꢁ1 cmꢁ1) are larger than the double of those of 2a and
2710 cmꢁ1 shifted by the O–HꢀꢀꢀN hydrogen bond. 1H NMR signals
of 1a and 1c in Figure 3 were assigned by the 1H-1H and 13C-1H
COSY spectra. 1H NMR signal at dY 14.0 (Hk) is assigned to that hav-
ing O–HꢀꢀꢀN hydrogen bond in the di(hydroxyaryl)triazine group.
The position is at lower magnetic field position than that reported
for 2,4-di(20-hydroxyaryl)-1,3,5-triazine by Kramer and co-work-
ers (dY 13.2).11 The pyrimidine hydrogen and a C6H3 hydrogen,
Hb and Hc of 1a (dY 7.85, 7.73), were observed at higher magnetic
field positions than Hb and Hc of 1c (dY 7.49, 8.04), which are as-
cribed to the shielding effect on Hb by the C6H3 rings and the
hydrogen bond between Hc and N atom in 1c, respectively. These
results suggest that 1a and 1c adopt the conformation shown in
Scheme 1 not only in the solid state but also in the CDCl3 solution.
Figure 4 shows the absorption and emission spectra of 1a and
1c as well as their model compounds, 2a and 2b (Figure 1), whose
data were summarized in Table 1. Compounds 1a, 1c, 2a, and 2b,
show typical absorption band of the anthryl group at similar
positions (kmax = 368 nm) in CHCl3. The absorption band of 1a is
trailed up to ca. 440 nm, and the compound shows yellow color
in its CHCl3 solution, while CHCl3 solution of 1c is colorless. The
2b (9700 and 9100 Mꢁ1 cmꢁ1).
Excitation of a CHCl3 solution of 1c at 368 nm, corresponding to
p
(
–
p⁄ transition of the anthryl group, causes emission at 410 nm
u = 0.39). Photoluminescence of 1a under same conditions is al-
most negligible (
u <0.01). In order to obtain further insights on dif-
ferent optical properties of 1a and 1c, luminescent properties of 2a
and 2b were investigated. Compound 2a with OH groups in the
phenyl group bonded to anthryl group shows luminescence
(
u = 0.31) similar to 2b with OMe group (u = 0.33), although emis-
sion from 1a having pyrimidine core is quenched efficiently. Addi-
tion of excess pyridine to the solution ([2a] = 1.0 ꢂ 10ꢁ3 mM,
[pyridine] = 1.0 ꢂ 102 mM) causes decrease of the intensity to
u
= 0.05.
Efficient quenching of luminescence of 2a in the presence of
pyridine is ascribed to intramolecular photo-induced electron
transfer (PET) between the excited state of anthryl group and elec-
tron rich phenoxy group formed by partial deprotonation with pyr-
idine.12,13 Much weaker emission intensity of 1a than that of 1c can
be also explained by significant quenching of the luminescence of
1a. The stable canonical form 1a0 has the phenoxy groups formed

Y. Suzaki et al. / Tetrahedron Letters 52 (2011) 3883–3885
3885
3.0
Acknowledgments
(A)
(B)
We thank our colleagues in the Center for Advanced Materials
Analysis, Technical Department, Tokyo Institute of Technology for
FABMS measurement. This work was supported by a Grant-in-
Aid for Scientific Research for Young Scientists from the Ministry
of Education, Culture, Sports, Science and Technology, Japan
(19750044), and by the Global COE program ‘Education and Re-
search Center for Emergence of New Molecular Chemistry’.
(b)
(a)
(c)
(d)
ε
0
300
350
400
450
Supplementary data
λ /nm
600
Supplementary data (experimental procedures and spectral
data for new compounds associated with this article can be found,
in the online version. CCDC nos. 822408 and 822409 contain the
supplementary crystallographic data for 1a(CHCl3)2 and 1c,
respectively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif) associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2011.05.080.
(b)
I
(d)
(c)
(e)
(a)
450
λ /nm
0
350
550
References and notes
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Angew. Chem., Int. Ed. 2005, 44, 5592; (d) De Schryver, F. C.; Vosch, T.; Cotlet,
M.; Van der Auweraer, M.; Müllen, K.; Hofkens, J. Acc. Chem. Res. 2005, 38, 514;
(e) Yamamoto, T. Macromol. Rapid Commun. 2002, 23, 583.
Figure 4. (A) Absorption (1.0 ꢂ 10ꢁ2 mM) and (B) emission (1.0 ꢂ 10ꢁ3 mM)
spectra of (a) 1a, (b) 1c, (c) 2a, (d) 2b, and (e) 2a (1.0 ꢂ 10ꢁ3 mM) + pyridine
(1.0 ꢂ 102 mM) (CHCl3, 20 °C).
2. (a) Brédas, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J. Am. Chem. Soc. 1983,
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Table 1
Absorption and emission data of 1a, 1c, 2a, 2b, and anthracene
Absorptiona
kmax/nm
Emissionb
kmax/nm
Compound
e
/Mꢁ1 cmꢁ1
uc
1a
1c
2a
2a + py
2b
368
368
368
368
368
359
24500
25700
9700
14600
9100
—
<0.01
0.39
0.31 (0.35
0.05
0.33 (0.36
410, 428
412, 429
412. 428
414, 428
405
d
d
)
5. (a) Klärner, F.-G.; Kahlert, B. Acc. Chem. Res. 2003, 36, 919; (b) Harmata, M. Acc.
Chem. Res. 2004, 37, 862.
e
)
6. (a) Zimmerman, S. C.; Saionz, K. W.; Zeng, Z. Proc. Natl. Acad. Sci. U.S.A. 1993, 90,
1190; (b) Zimmerman, S. C.; Saionz, K. W. J. Am. Chem. Soc. 1995, 117, 1175.
7. Recent examples of molecular tweezers (a) Chen, G.; Bouzan, S.; Zhao, Y.
Tetrahedron Lett. 2010, 51, 6552; (b) Legouin, B.; Gayral, M.; Uriac, P.; Cupif, J.-
F.; Levoin, N.; Toupet, L.; van de Weghe, P. Eur. J. Org. Chem. 2010, 5503; (c)
Legouin, B.; Gayral, M.; Uriac, P.; Tomasi, S.; van de Weghe, P. Tetrahedron:
Asymmetry 2010, 21, 1307; (d) Hisamatsu, Y.; Aihara, H. Chem. Commun. 2010,
46, 4902; (e) Leblond, J.; Gao, H.; Petitjean, A.; Leroux, J.-C. J. Am. Chem. Soc.
2010, 132, 8544; (f) Ulrich, S.; Petitjean, A.; Lehn, J.-M. Eur. J. Inorg. Chem. 2010,
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C.-J.; Wixe, T.; Wendt, O. F.; Bergquist, K.-E.; Wärnmark, K. Chem. Eur. J. 2010,
d
Anthracene
7200
(0.09
)
a
b
c
[Compound] = 1.0 ꢂ 10ꢁ2 mM, CHCl3, 20 °C.
[Compound] = 1.0 ꢂ 10ꢁ3 mM, CHCl3, 20 °C, kex = kmax(absorption).
Quantum yield. Standard sample: quinine (1.0 ꢂ 10ꢁ3 mM) in H2SO4(aq),
u
std = 0.546.
d
[Compound] = 2.0 ꢂ 10ꢁ3 mM.
e
[pyridine]/[2a] = 1.0 ꢂ 105.
ˇ
´
16, 3994; (i) Tatar, A.; Cejka, J.; Král, V.; Dolensky, B. Org. Lett. 2010, 12, 1872; (j)
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Nishinaga, T.; Iyoda, M. Chem. Eur. J. 2009, 15, 6838.
O
H
O
N
N
O
H
H
N
N
H
O
8. Hunter, C. A.; Lawson, K. R.; Perkins, J.; Urch, C. J. J. Chem. Soc., Perkin Trans. 2
2001, 651.
9. A molecule of 1a in the single crystal, obtained from a CHCl3 solution, has
crystallographic C2. The crystallographically independent unit observed by X-
ray crystallography is composed of half of 1a and one molecule of CHCl3.
10. Suezawa, H.; Yoshida, T.; Umezawa, Y.; Tsuboyama, S.; Nishio, M. Eur. J. Inorg.
Chem. 2002, 3148.
11. Stueber, G. J.; Kieninger, M.; Schettler, H.; Busch, W.; Goeller, B.; Franke, J.;
Kramer, H. E. A.; Hoier, H.; Henkel, S.; Fischer, P.; Port, H.; Hirsch, T.; Rytz, G.;
Birbaum, J.-L. J. Phys. Chem. 1995, 99, 10097.
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5746.
1a
1a'
Scheme 2. Canonical forms of 1a.
by strong O–HꢀꢀꢀN hydrogen bonds with the neighboring pyrimi-
dine group (Scheme 2).
In summary, we obtained new aromatic compounds 1a and 1c.
The intramolecular hydrogen bonds of di(hydroxyphenyl)pyrimi-
dine group in 1a maintain the ‘U’-shape conformation in the solid
as well as in the solution, while 1c adopts quite different confor-
mation due to C–HꢀꢀꢀO interaction. These molecules with similar
chemical structures but different conformation and optical proper-
ties can be employed as the fundamental motif of the compounds
which show switching behavior. Further studies on the compounds
and the derivation are now in progress.14
14. Preliminary studies were conducted on the host–guest complexation of 1a
with the guest molecules. The 1H NMR measurement of a mixture of 1a and
p-
acceptors, such as TCNQ, TCNE and PFB (pentafluorobenzene), in CDCl3, DMSO-
d6 and benzene-d6 ([1a] = [Guest molecule] = 1.0 mM, rt and 50 °C, 24 h),
however, did not show shift of the signals caused by the complexation. We are
exploring the conditions suited for the formation of the host–guest complexes.