Synthesis and optoelectrochemical properties of stilbenophanes having carbazole moieties

Article abstract of DOI:10.1055/s-0032-1317324

A series of stilbenophanes having N-arylated carbazole moieties possessing small and large cavities have been synthesized via McMurry coupling of the corresponding dialdehyde derived from N-arylation of carbazole with various dibromide followed by formylation. The electrochemical, photophysical, and complexation properties of all the stilbenophanes with electron-deficient guest molecules like TCNQ, TCNE, and PQT were also carried out at different concentrations.

Full text of DOI:10.1055/s-0032-1317324

2504▌
LETTER
lSetyternthesis and Optoelectrochemical Properties of Stilbenophanes Having
Carbazole Moieties
Synthesis of Stilbenophanes
Perumal Rajakumar,*a Karuppannan Sekar,b Nagarathinam Venkatesana
a
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
Fax +91(44)22352492; E-mail: perumalrajakumar@gmail.com
b
Department of Chemistry, Anna University Constituent College Dindigul, Dindigul 624 622, India
Received: 20.07.2012; Accepted after revision: 06.09.2012
a new type of conjugated shape-persistent stilbenophane
Abstract: A series of stilbenophanes having N-arylated carbazole
derivatives 1–5 (Figure 1) using various aromatic spacer
units through McMurry olefination reaction. The electro-
chemical and photophysical properties of the all the stil-
moieties possessing small and large cavities have been synthesized
via McMurry coupling of the corresponding dialdehyde derived
from N-arylation of carbazole with various dibromide followed by
formylation. The electrochemical, photophysical, and complexation benophanes were also carried out.
properties of all the stilbenophanes with electron-deficient guest
molecules like TCNQ, TCNE, and PQT were also carried out at dif-
ferent concentrations.
The synthetic pathway leading to stilbenophanes 1–5 hav-
ing N-arylated carbazole moieties is outlined in Scheme 1.
The McMurry reaction, in these cases, led to the reductive
coupling of two carbonyl groups to form intermolecular
dimerization products. The N-arylation of dibromides 6–
10 with 2.2 equivalents of carbazole in the presence of
CuI, 1,10-phenanthroline, and K2CO3 in p-xylene afford-
Key words: carbazole, stilbenophanes, fluorescence, redox poten-
tial
In cyclophanes,1 the π-electron-rich subsystems when
placed in the close proximity in parallel arrangement can
form intense intramolecular electronic interactions,2 both
through bonds as well as through space. Carbazole is a
well-known π-electron-rich chromophore which can act
as a good photoconducting material due to the strong elec-
tron-donating ability of the nitrogen atom. Carbazole-
based supramolecule systems are finding growing appli-
cations in the field of electronics and optoelectronics3,4 in-
cluding organic light-emitting diodes (OLED)5,6 and solar
cells.7 Though various carbazole-based oligomers and
polymers are reported in the literature, very few examples
are known of carbazole-based cyclophanes, including di-
ethynylcarbazole macrocycles with solar-cell properties,8
fluorescent nanofibril film,9 carbazole-linked fullerene
(C60),10 carbazolopyridinophane,11 macromolecules12–15
containing carbazole and its derivatives, have attracted
considerable interest on account of their unique electroop-
tical properties, which make such molecules potential
candidates for diverse applications in photoluminescence
and chemoluminescence. Recently, Chen et al.16 reported
stilbene-like carbazole dimer-based electroluminescent
materials for OLEDs. The McMurry reaction is an effec-
tive way to form a C=C bond under moderate conditions
and has been employed to form conjugated cyclophanes in
few cases.17,18 Though the intermolecular19 and
intramolecular20 McMurray coupling reaction in cyclo-
phane chemistry is well documented, to the best of our
knowledge, no carbazole-based conjugated stilbeno-
phanes with large cavities have been reported so far. We
report herein the design, synthesis, and characterization of
i
Ar
Ar
N
N
Br
Br
11–15
ii
Ar
iii
N
N
1–5
OHC
CHO
16–20
R1
S
Ar =
8
Et
Et
R2
10
6a R1 = Me, R2 = H
6b R1 = Me, R2 = OMe
Et
N
N
7
9
Scheme 1 Reagents and conditions: i) carbazole (2.2 equiv), CuI,
K2CO3, 1,10-phenanthroline, p-xylene, 180 °C, 48 h, 11a (82%), 11b
(73%), 12 (85%), 13 (60%), 14 (53%), 15 (72%); ii) POCl3, DMF,
DCE, reflux, 12 h, 16a (72%), 16b (67%), 17 (44%), 18 (48%), 19
(56%), 20 (51%); iii) TiCl4 (20 equiv), Zn (40 equiv), pyridine (2
drops), THF, reflux, 12 h, 1a (18%), 1b (15%), 2 (17%), 3 (15%), 4
(12%), 5 (15%).
SYNLETT 2012, 23, 2504–2510
Advanced online publication: 28.09.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1317324; Art ID: ST-2012-B0610-L
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Stilbenophanes
2505
R1
carbon at δ = 21.6 ppm, in addition to ten peaks in the ar-
omatic region. Further, the structure of the biscarbazole
compound 11a was confirmed by the appearance of the
molecular ion peak at m/z = 422 in the mass spectrum (EI)
and from elemental analysis. Similarly, the structure of
the biscarbazole compound 11b–15 was also confirmed
from spectroscopic and elemental analysis. Formylation
of biscarbazole 11–15 using POCl3–DMF in DCE under
refluxing conditions gave dialdehyde 16–20 in 72%, 67%,
44%, 48%, 56%, and 51% yields, respectively.
The 1H NMR spectrum of the dialdehyde 16a22 showed a
singlet at δ = 1.65 ppm for the methyl protons, and a one-
proton singlet at δ = 7.26 ppm for the inner proton of the
m-xylyl unit, a singlet at δ = 10.13 ppm for aldehyde pro-
tons in addition to the aromatic protons. In the 13C NMR
spectrum, dialdehyde 16a showed a methyl carbon at δ =
21.6 ppm, an aldehydic carbon at δ = 191.6 ppm in addi-
tion to 15 signals in the aromatic region. The mass spec-
trum (EI) of the dialdehyde 16a showed a peak at m/z =
478 corresponding to the molecular ion. Further, the struc-
tures of the dialdehydes 16b–20 were confirmed by spec-
troscopic and elemental analysis.
N
N
N
N
N
R2
R2
N
N
N
N
N
R1
2
1a R1 = Me, R2 = H
1b R1 = Me, R2 = OMe
Et
N
N
N
N
N
S
Addition of the dialdehyde 16–20 to a solution of 20
equivalents of TiCl4 and 40 equivalents of Zn in THF fol-
lowed by refluxing for 12 hours resulted in the formation
of aromatic stilbenophanes 1–5 in 18%, 15%, 17%, 15%,
S
1
N
N
N
12%, and 15% yields, respectively. The H NMR spec-
N
trum of the stilbenophane 1a23 (Figure 2) showed a six-
proton singlet at δ = 2.48 ppm for the methyl protons, a
four-proton singlet at δ = 6.83 ppm for olefinic protons,
and a two-proton singlet at δ = 7.57 ppm for the inner pro-
ton of the m-xylyl unit in addition to the other aromatic
protons. In the 13C NMR spectrum, stilbenophane 1a
showed a methyl carbon at δ = 21.5 ppm, in addition to 17
peaks in the aromatic region. Further, the structure of the
carbazolostilbenophane 1a was confirmed from the ap-
pearance of the molecular ion peak at m/z = 894 in the
FAB mass spectrum. Similarly, the structure of the stil-
benophane 1b–5 is also confirmed from spectral and ana-
lytical data.24–28 The 1H NMR spectrum of the
stilbenophanes 1–5 shows a single peak at δ = 6.81–6.87
ppm, which shows that all the stilbenophanes exist as the
cis-isomers in CDCl3 solution.
N
Et
4
3
N
N
Et
Et
Et
Et
N
N
The initial geometries of cis and trans isomers of 1a were
built using GaussView.29 These geometries (cis and trans)
were optimized using density functional theory30 (DFT)-
based Becke’s three-parameter hybrid exchange and Lee–
Yang–Parr correlation31,32 (B3LYP) functional employing
6-31G* basis set. The geometry optimizations were car-
ried out without any geometrical constrains. To ensure the
optimized geometries correspond to true minima in poten-
tial energy surface, vibrational frequencies were comput-
ed using DFT (B3LYP/6-31G*) level for both the
isomers. All these calculation were carried out using
Gaussian 09 package.33
5
Figure 1 Structures of the shape-persistent stilbenophanes 1–5
ed biscarbazole compounds 11–15 in 82%, 73%, 85%,
60%, 53%, and 72% yields, respectively.
The 1H NMR spectrum of the biscarbazole 11a21 showed
a three-proton singlet at δ = 1.63 ppm for the methyl pro-
tons, and two sets of three-proton triplet at δ = 7.30 ppm
(J = 7.5 Hz) and δ = 7.44 ppm (J = 7.8 Hz) for the protons
at 2-, 3- and 6-, 7-position of the carbazole unit, a singlet
at δ = 7.62 ppm for inner proton of the m-xylyl unit in ad-
dition to the other carbazole protons. In the 13C NMR
spectrum, biscarbazole compound 11a showed methyl
The optimized structures and their corresponding energy
values of cis and trans isomers of 1a are shown in Figure
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2504–2510

2506
P. Rajakumar et al.
LETTER
Figure 2 1H NMR spectrum (CDCl3, 300 MHz) of stilbenophanes 1a
3. The calculated minimized energy difference between fluorene. This is may be an effective π-conjugation in the
cis and trans isomer is 4.99 kcal/mol. Further the calculat- cyclophanes (Table 1). The broad absorption and emis-
ed HOMO–LUMO energy difference for the cis and trans sion spectra show no vibrational bands in the absorption
isomers are 4.00 and 3.71 eV, respectively. The results spectra of the cyclophanes and less shift value of nearly
obtained from the molecular orbital calculations further
reinforce that the cis isomer is more stable than the trans
isomer, which is in good agreement with the experimental
findings.
The photophysical properties of the stilbenophane deriva-
tives 1–5 were examined by UV-vis and fluorescence
spectroscopic techniques in CH2Cl2. The absorption and
emission spectra of the compounds in CH2Cl2 are shown
in Figure 4 and Figure 5. In general, absorption spectra of
all the stilbenophanes exhibited two absorption bands, a
strong absorption band ranged at λ = 294–348 nm being
assigned to the π–π* local electron transition of the carba-
zole and aromatic spacer unit and a less intense absorption
band at longer wavelength ranged at λ = 338–378 nm,
which was assigned to π–π* transition of the carbazole-di-
mer core of the stilbenophane.16 Stilbenophanes 1a, 1b, 2,
and 4 with spacer units such as benzene, anisole, pyridine,
and carbazole have no significant shift in the absorption
band. However, due to the presence of thiophene and
fluorene spacer units in stilbenophane 3 and 5 a red-shift
was observed along with their increasing intensity which
is due to high electron-donating ability and the extent of
π-conjugation length in the cyclophanes.34
Photoluminescence (PL) spectra of all the stilbenophanes
1–5 were recorded, and a strong absorption was observed
at λ = 294–348 nm with a broad band located in the region
at λ = 391–589 nm (blue to greenish region), and their
Figure 3 The optimized geometries and energy values of cis and trans
isomer (hydrogen atoms are omitted for clarity; gray color for carbon
and blue color for nitrogen). a) Relative energy (cis isomer) = 0.00
kcal/mol, HOMO–LUMO gap = 4.00 eV. b) Relative energy (trans
emission maxima were significantly red-shifted with al- isomer) = 4.99 kcal/mol, HOMO–LUMO gap = 3.71 eV
tering the spacer units such as carbazole, thiophene, and
Synlett 2012, 23, 2504–2510
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Stilbenophanes
2507
100 nm between the absorption and emission wavelength Half-wave redox potentials vs. Ag/AgCl of the stilbeno-
maxima, which shows that the stilbenophanes have high phanes 1–5 were obtained by cyclic voltammetry in
rigidity and planarity.35
CH2Cl2 at room temperature (scan rate: 100 mV/s, sup-
porting electrolyte: n-Bu4NPF6, Pt as a working and a
counter electrode). All the carbazolophanes exhibited one
set of redox waves corresponding to the carbazole moiety
attached to the aromatic spacer units (Figure 6). Usually
stilbene-like carbazole dimer exhibits16 two reversible
one-electron redox waves which show some electronic
communication between two carbazole moieties and
cause them to oxidize separately. However, stilbeno-
phanes 1–5 exhibit only one set of redox quasi-reversible
waves, which shows each carbazole unit is electronically
isolated from the other carbazole molecules.
Table 1 Optical Properties of Stilbenophanes 1–5
Stilbenophane
λmax (nm)a
Absorption (nm)
Emission (nm)
1a
1b
2
298, 340
299, 338
294, 338
328, 359
305, 342
348, 378
425b
427b
391b
526c
467d
589e
3
4
Compared with ferrocence (for which we found the differ-
ence between the anodic and cathodic peaks, ΔEp = 74 mv
vs. Ag/AgCl in CH2Cl2 at room temperature), all the redox
processes of the stilbenophanes 1–5 are quasi-reversible.
The redox potentials are found to be different ranging be-
tween 580–690 mV (Table 2) due to various spacer units
present in the molecules. In the presence of heterocyclic
spacer units like pyridine, carbazole, and thiophene the re-
dox potential decreases when compared to the benzene
spacer units. Such low redox-potential behavior may be
useful for electrochemical sensor studies of various elec-
tron-deficient guest molecules.
5
a All the spectra were recorded at 1×10–5 M in CH2Cl2.
b Excited at λ = 294 nm.
c Excited at λ = 330 nm.
d Excited at λ = 305 nm.
e Excited at λ = 348 nm.
Table 2 Electrochemical Parameters Obtained for the Cyclophanes
in CH2Cl2 at 25 °C
Carbazolophane
E11/2 (mV)a
ΔEp1 (mV)
1a
1b
2
640
630
580
600
590
690
240
210
200
160
190
200
3
4
Figure 4 UV-vis absorption of stilbenophanes 1–5 in CH2Cl2
(1×10–5 M solution)
5
a E11/2 is the average of the cathodic and anodic peak potential of the
redox process. ∆E1p is the difference between the cathodic and anodic
peak potential of the redox process.
Table 3 Complexation of TCNQ with Stilbenophanes 1–5
Carbazolophane
Ka (mol–1 dm3)
ε (M–1 cm–1)
1a
1b
2
2.00×104
3.37×104
5.00×104
4.00×104
5.00×103
4.00×103
2.50×105
3.33×105
2.00×105
2.50×105
2.00×106
2.50×106
3
4
Figure 5 Photoluminescence spectra of stilbenophanes 1–5 in
CH2Cl2 (1×10–5 M solution) excited in the range of λ = 294–348 nm
5
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2504–2510

2508
P. Rajakumar et al.
LETTER
denced by the absorption maxima at λ = 417, 426, 428,
and 431 nm, respectively. The stability constant for the
formation of the charge-transfer complex of 1–3 with
TCNE is 4.28×103, 2.60×104, 1.2×104, and 3.22×104 mol–1 dm3.
When such experiments were carried out with PQT,
charge-transfer complexation did not occur.
Table 4 Benesi–Hildebrand Treatment Data of the CT Complex
Formed between the Stilbenophane 2 and TCNQ (λmax = 412 nm)a,b
Concentration of the Absorbance
[D]/A0 M
1/[A] (M)
guest [A] (M)
[A0]
0.0000049
0.0000098
0.0000147
0.0000196
0.0000245
0.306
0.454
0.695
0.922
0.954
3.267×10–5
2.188×10–5
1.439×10–5
1.084×10–5
1.048×10–5
204081
102040
68027
51020
40816
a Concentration of cyclophane [D] 2 = 10–5
b Ka = 5.00×104 M–1, ε = 2.00×105 M–1cm–1, SD = 97.35%.
M
Figure 7 Plot between 1/[A] and [D]/[A0] for stilbenophane 2
Figure 6 Cyclic voltammograms of stilbenophanes 1a (a) and 3 (b) in
CH2Cl2 (1×10–5 M solution)
In conclusion, conjugated stilbenophanes 1–5 are readily
synthesized in a single step via tandem intermolecular
McMurry coupling reaction with alternating cavity size.
Preliminary electrochemical, photophysical, and com-
plexation studies shows this type of aromatic stilbeno-
phanes are useful candidates for further development of
organic light emitting diodes (OLED) and organic solar
cells (OSC). Further synthesis of similar stilbenophanes
and detailed investigations of the complexation behavior
with electron-deficient guest molecules are in progress.
The charge-transfer complexation behavior of the carba-
zolostilbenophanes 1–5 guest molecules like TCNQ,
TCNE, and PQT was then investigated.36 The stilbeno-
phanes having carbazole moiety showed UV-vis absorp-
tion maxima in the range of λ = 338–378 nm in MeCN–
CH2Cl2 medium, respectively. However, the acceptors
TCNQ, TCNE, and PQT showed absorption maxima at λ
= 286.8, 274.0, and 263.0 nm, respectively, in the same
solvent medium. Stilbenophanes 1a,b, 2–5 form charge-
transfer complexes with TCNQ as evidenced by the ap-
pearance of absorption maxima at λ = 410, 425, 412, 428,
434, and 512 nm, respectively. The equilibrium constant
for the charge-transfer complex was determined by the
Benesi–Hildebrand equation.37 From the stability con-
stant, it is clear that 2 and 3 complexes more strongly with
TCNQ than the stilbenophanes 1a, 1b, 4, and 5 (Table 3).
Acknowledgment
K.S. thanks CSIR-New Delhi for providing SRF. The authors thank
V. Rajapandian and Dr. V. Subramanian, Chemical Laboratory,
CSIR-CLRI, Adyar, Chennai-20 for molecular orbital calculations.
The authors thank CSIR-New Delhi, for financial assistance, DST-
FIST for providing NMR facility to the department and SAIF-CDRI
Lucknow for providing mass spectral data.
Among the stilbenophanes 1–5, small cavity cyclophanes
1–3 form charge-transfer complexes with TCNE as evi-
Synlett 2012, 23, 2504–2510
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Stilbenophanes
2509
J = 8.4 Hz), 7.27–7.43 (m, 16 H), 7.49 (d, 4 H, J = 8.1 Hz),
References and Notes
7.57 (s, 2 H), 8.01 (s, 4 H), 8.08 (d, 4 H, J = 7.5 Hz). 13
NMR (75 MHz, CDCl3): δ = 21.5, 109.4, 109.8, 120.2,
120.4, 121.4, 122.1, 123.4, 123.6, 126.0, 126.3, 126.7,
129.4, 130.0, 138.8, 139.5, 140.5, 141.6. MS–FAB:
C
(1) For an excellent recent monograph, see: Modern Cyclophane
Chemistry; Gleiter, R.; Hopf, H., Eds.; Wiley-VCH:
Weinheim, 2004.
(2) For a recent review, see: Tusji, T. In Modern Cyclophane
Chemistry; Gleiter, R.; Hopf, H., Eds.; Wiley-VCH:
Weinheim, 2004, 81–104.
(3) Morin, J.-F.; Leclere, M.; Adés, D.; Siove, A. Macromol.
Rapid Commun. 2005, 26, 761.
(4) Wong, K.-T.; Hung, T.-H.; Chao, T.-C.; Ho, T.-I.
Tetrahedron Lett. 2005, 46, 855.
(5) Adhikari, R. M.; Mondal, R.; Shah, B. K.; Neckers, D. C.
J. Org. Chem. 2007, 72, 4727.
(6) Promarak, V.; Ichikawa, M.; Meunmart, D.; Sudyoadsuk,
T.; Saengsuwana, S.; Keawin, T. Tetrahedron Lett. 2006,
47, 8949.
(7) Ning, Z.; Zhang, O.; Wu, W.; Pei, H.; Liu, B.; Tian, H.
J. Org. Chem. 2008, 73, 3791.
(8) Zhao, T.; Liu, Z.; Song, Y.; Xu, W.; Zhang, D.; Zhu, D.
J. Org. Chem. 2006, 71, 7422.
(9) Naddo, T.; Che, Y.; Zhang, W.; Balakrishnan, K.; Yang, X.;
Yen, M.; Zhao, J.; Moore, J. S.; Zang, L. J. Am. Chem. Soc.
2007, 129, 6978.
(10) Nakamura, Y.; Suzuki, M.; Imai, Y.; Nishimura, J. Org. Lett.
2004, 6, 2797.
(11) Brown, A. B.; Gibson, T. L.; Clayton Baum, J.; Ren, T.;
Smith, T. M. Sens. Actuators, B 2005, 110, 8.
(12) Sanda, F.; Nakai, T.; Kobayashi, N.; Masuda, K.
Macromolecules 2004, 37, 2703.
(13) Morin, J. F.; Leclerc, M.; Ades, D.; Siove, A. Macromol.
Rapid Commun. 2005, 26, 761.
(14) Brunner, K.; Dijken, A. V.; Börner, H.; Bastiaansen, J. J. A.
M.; Kiggen, N. M. M.; Langeveld, B. M. W. J. Am. Chem.
Soc. 2004, 126, 6035.
(15) Cabaj, J.; Idzik, K.; Soloducho, J.; Chyla, A. Tetrahedron
2006, 62, 758.
(16) Chen, C.-H.; Lin, J. T.; Yeh, M.-C. P. Tetrahedron 2006, 62,
8564.
(17) Chung, M.-K.; Qi, G.; Stryker, J. M. Org. Lett. 2006, 8,
1491.
m/z = 894 [M+]. Anal. Calcd (%) for C66H44N4: C, 88.76; H,
4.97; N, 6.27. Found: 88.92; H, 4.82; N, 6.42.
(24) Stilbenophane 1b
White solid; yield 15%; mp 164–166 °C. 1H NMR (300
MHz, CDCl3): δ = 2.43 (s, 6 H), 3.63 (s, 6 H), 6.84 (s, 4 H),
7.14 (d, 4 H, J = 8.3 Hz), 7.22–7.39 (m, 16 H), 7.47 (d, 4 H,
J = 8.1 Hz), 8.02 (s, 4 H), 8.06 (d, 4 H, J = 7.6 Hz). 13C NMR
(75 MHz, CDCl3): δ = 21.2, 52.8, 109.6, 109.9, 120.1, 120.6,
121.7, 122.4, 123.7, 123.9, 126.0, 126.4, 126.9, 129.7,
130.3, 138.7, 139.4, 140.5, 151.2. MS–FAB: m/z = 954
[M+]. Anal. Calcd (%) for C68H48N4O2: C, 85.69; H, 5.08; N,
5.88. Found: C, 85.82; H, 5.22; N, 5.98.
(25) Stilbenophane 2
White solid; yield 17%; mp 186–187 °C. 1H NMR (300
MHz, CDCl3): δ = 6.81 (s, 4 H), 7.18 (d, 4 H, J = 8.3 Hz),
7.24–7.40 (m, 12 H), 7.47 (d, 4 H, J = 8.1 Hz), 7.63 (d, 4 H,
J = 6.7 Hz), 7.87 (t, 2 H, J = 6.8 Hz), 8.04 (s, 4 H), 8.10 (d,
4 H, J = 7.6 Hz). 13C NMR (75 MHz, CDCl3): δ = 109.8,
110.4, 116.7, 120.2, 120.5, 121.6, 122.2, 123.6, 126.2,
126.6, 129.8, 130.4, 138.8, 139.6, 140.6, 151.6. MS–FAB:
m/z = 868 [M+]. Anal. Calcd (%) for C62H38N6: C, 85.89; H,
4.42; N, 9.69. Found: C, 85.72; H, 4.30; N, 9.60.
(26) Stilbenophane 3
White solid; yield 15%; mp 191–193 °C. 1H NMR (300
MHz, CDCl3): δ = 6.85 (s, 4 H), 7.23–7.47 (m, 20 H), 7.64
(d, 4 H, J = 6.9 Hz), 7.99 (s, 4 H), 8.08 (d, 4 H, J = 6.6 Hz).
13C NMR (75 MHz, CDCl3): δ = 109.8, 110.4, 120.3, 121.1,
121.4, 122.6, 123.8, 123.8, 126.4, 126.8, 129.5, 130.7,
136.0, 140.6, 141.7. MS–FAB: m/z = 878 [M+]. Anal. Calcd
(%) for C60H36N4S2: C, 82.16; H, 4.14; N, 6.39. Found: C,
82.27; H, 4.31; N, 6.52.
(27) Stilbenophane 4
White solid; yield 12%; mp 191–193 °C. 1H NMR (300
MHz, CDCl3): δ = 1.45 (t, 6 H, J = 7.1 Hz), 4.40 (q, 4 H,
J = 7.1 Hz), 6.87 (s, 4 H), 7.08 (s, 4 H), 7.12–7.27 (m, 8 H),
7.31–7.52 (m, 12 H), 7.61 (d, 4 H, J = 6.9 Hz), 7.72 (s, 4 H),
7.93 (d, 4 H, J = 8.1 Hz), 8.08 (d, 4 H, J = 6.6 Hz). 13C NMR
(75 MHz, CDCl3): δ = 13.7, 38.1, 109.1, 110.2, 111.2, 120.1,
121.2, 121.4, 122.3, 122.6, 123.4, 123.7, 126.4, 124.6,
126.7, 126.9, 129.4, 130.6, 136.2, 140.4, 141.8. MS–FAB:
m/z = 1100 [M+]. Anal. Calcd (%) for C80H54N6: C, 87.40; H,
4.95; N, 7.64. Found: C, 87.54; H, 4.82; N, 7.51.
(28) Stilbenophane 5
(18) Chen, H.-B.; Yin, J.; Wang, Y.; Pei, J. Org. Lett. 2008, 10,
3113.
(19) Hopf, H.; Mlynek, C. J. Org. Chem. 1990, 55, 1361.
(20) Heirtzler, F. R.; Hopf, H.; Jones, P. G.; Bubenitschek, P.
Tetrahedron Lett. 1995, 36, 1239.
(21) Compound 11a
White solid; yield 82%; mp 110–112 °C. 1H NMR (300
MHz, CDCl3): δ = 1.63 (s, 3 H), 7.30 (t, 4 H, J = 7.5 Hz),
7.44 (t, 4 H, J = 7.8 Hz), 7.51–7.56 (m, 6 H), 7.62 (s, 1 H),
8.15 (d, 4 H, J = 7.8 Hz). 13C NMR (75 MHz, CDCl3): δ =
21.6, 109.8, 120.2, 120.5, 122.5, 123.6, 126.1, 126.6, 139.2,
140.7, 141.7. MS (EI): m/z = 422 [M+]. Anal. Calcd (%) for
C31H22N2: C, 88.12; H, 5.25; N, 6.63. Found: C, 88.24; H,
5.34; N, 6.78.
White solid; yield 15%; mp 202–204 °C. 1H NMR (300
MHz, CDCl3): δ = 0.39 (t, 12 H, J = 7.2 Hz), 2.00 (q, 8 H,
J = 7.2 Hz), 6.84 (s, 4 H), 7.26–7.35 (m, 8 H), 7.46 (t, 4 H,
J = 6.9 Hz), 7.56 (s, 4 H), 7.60–7.68 (m, 12 H), 7.93 (d, 4 H,
J = 8.1 Hz), 8.11 (s, 4 H), 8.18 (d, 4 H, J = 7.8 Hz). 13C NMR
(75 MHz, CDCl3): δ = 8.6, 30.9, 56.5, 109.1, 110.2, 120.3,
121.8, 122.9, 125.2, 126.1, 129.8, 130.4, 133.8, 136.8,
138.2, 139.7, 140.8, 142.6, 146.5, 148.8, 151.7, 153.5. MS–
FAB: 1154 [M+]. Anal. Calcd (%) for C86H64N4: C, 89.55; H,
5.59; N, 4.86. Found: C, 89.72; H, 5.74; N, 4.96.
(29) Frisch, A.; Dennington, R. D. II.; Keith, T. A. GaussView
version 3.0; Gaussian Inc: Pittsburgh (PA, USA), 2003.
(30) Hehre, W. J.; Radom, L.; Schleyer, P. V. R.; Pople, J. A. Ab
Initio Molecular Orbital Theory; Wiley-Interscience: New
York, 1986.
(22) Dialdehyde 16a
White solid; yield 72%; mp 102–104 °C. 1H NMR (300
MHz, CDCl3): δ = 1.65 (s, 3 H), 7.26 (s, 1 H), 7.38–7.43 (m,
2 H), 7.52–7.59 (m, 8 H), 7.99 (dd, 2 H, J = 8.6, 1.2 Hz), 8.22
(d, 2 H, J = 7.5 Hz), 8.68 (s, 2 H), 10.13 (s, 2 H). 13C NMR
(75 MHz, CDCl3): δ = 21.6, 110.0, 110.3, 120.9, 121.6,
122.7, 123.4, 123.9, 127.3, 127.5, 127.7, 129.8, 138.4,
141.6, 142.6, 144.2, 191.6. MS (EI): m/z = 478 [M+]. Anal.
Calcd (%) for C33H22N2O2: C, 82.83; H, 4.63; N, 5.85.
Found: C, 82.96; H, 4.72; N, 5.94.
(31) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38,
3098.
(32) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens.
Matter 1988, 37, 785.
(23) Stilbenophane 1a
White solid; yield 18%; mp 172–173 °C. 1H NMR (300
MHz, CDCl3): δ = 2.48 (s, 6 H), 6.83 (s, 4 H), 7.18 (d, 4 H,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2504–2510

2510
P. Rajakumar et al.
LETTER
(33) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.;
Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.;
Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng,
G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda,
Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A. Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.;
(34) Promarak, V.; Ruchirawat, S. Tetrahedron 2007, 63, 1602.
(35) Lai, R. Y.; Kong, X.; Jenekhe, S. A.; Bard, A. J. J. Am.
Chem. Soc. 2003, 125, 12631.
(36) Determination of the Association Constant by UV-Vis
Spectroscopy (Benesi–Hildebrand Method)
In a typical experiment, 3 mL of a standard stock solution of
the cyclophane in MeCN–CH2Cl2 was placed in a quartz
cuvette. A known amount of the electron-deficient guest
molecule was added in incremental amounts and the changes
in absorbance of the CT bands were recorded. Table 4 shows
the charge-transfer complexation studies of stilbenophanes 2
with various concentrations of TCNQ. Plots of [concn of
cyclophane]/absorbance vs. 1/concentration of guest were
linear (Figure 7). From the slope and the intercept values Ka
(Ka = intercept × slope–1) and ε (ε = intercept–1) were
evaluated (Table 4). The plots were linear, suggesting that
the predominant species in solution was a 1:1 complex..
(37) Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71,
2703.
Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam,
J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski,
V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.;
Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09 Revision
A.02; Gaussian Inc: Wallingford (CT, USA), 2009.
Synlett 2012, 23, 2504–2510
© Georg Thieme Verlag Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not be copied or
emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.
However, users may print, download, or email articles for individual use.