Thiophene donor - Acceptor [2]rotaxanes

Article abstract of DOI:10.1021/ol800624c

(Chemical Equation Presented) A series of the thiophene donor-acceptor [2]rotaxanes have been synthesized based on the inclusion complexes of cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) with thiophene, bithiophene, and terthiophene. The maximum wavelength of the charge-transfer band strongly depends on the number of thiophene units, while the association constant does not. These donor-acceptor pairs will be fascinating constituents for optoelectronic and electromechanical materials.

Full text of DOI:10.1021/ol800624c

ORGANIC
LETTERS
2
008
Vol. 10, No. 11
215-2218
Thiophene Donor-Acceptor
2]Rotaxanes
2
[
,
†
†
Taichi Ikeda,* Masayoshi Higuchi, Akira Sato, and Dirk G. Kurth
†
†,‡
Functional Modules Group, Organic Nanomaterials Center, National Institute for
Materials Science, 1-1 Namiki, Tsukuba 305-0044 Japan, and Max Plank Institute of
Colloids and Interfaces, Research Campus Golm, D-14424, Potsdam, Germany
ikeda.taichi@nims.go.jp
Received March 18, 2008
ABSTRACT
A series of the thiophene donor-acceptor [2]rotaxanes have been synthesized based on the inclusion complexes of cyclobis(paraquat-p-
4+
phenylene) (CBPQT ) with thiophene, bithiophene, and terthiophene. The maximum wavelength of the charge-transfer band strongly depends
on the number of thiophene units, while the association constant does not. These donor-acceptor pairs will be fascinating constituents for
optoelectronic and electromechanical materials.
Inclusion complexation between electron-deficient (acceptor)
pair results in the formation of the charge-transfer (CT)
complexes with fascinating electrochemical and optical
7
8
cyclophanes, i.e., cyclobis(paraquat-p-phenylene) (CB-
4
+
1
PQT ), and electron-rich (donor) aromatic compounds,
2
3
4
e.g., 1,4-hydroxybenzene, 1,5-dioxynaphthalene, biphenol,
(6) (a) Philp, D.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.; Williams,
4,5
6
benzidine, and tetrathiafulvalene derivatives, has attracted
D. J. J. Chem. Soc., Chem. Commun. 1991, 1548. (b) Anelli, P.-L.; Asakawa,
M.; Ashton, P. R.; Bissell, R. A.; Clavier, G.; G o´ rski, R.; Kaifer, A. E.;
Langford, S. J.; Mattersteig, G.; Menzer, S.; Philip, D.; Slawin, A. M. Z.;
Spencer, N.; Stoddart, J. F.; Tolly, M. S.; Williams, D. J. Chem. Eur. J.
muchattention.Thecombinationofdonor-acceptorhost-guest
1
997, 3, 1113. (c) Jeppesen, J. O.; Becker, J. Eur. J. Org. Chem. 2003,
3245.
(7) (a) Bissell, R. A.; C o´ rdova, E.; Kaifer, A. E.; Stoddart, J. F. Nature
†
National Institute for Materials Science.
Max Plank Institute of Colloids and Interfaces.
‡
(
1) Odell, B.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.;
Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. 1988, 27, 1547.
2) Ashton, P. R.; Odell, B.; Reddington, M. V.; Slawin, A. M. Z.;
Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. 1988, 27, 1550.
3) Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.;
Vicent, C.; Williams, D. J. J. Chem. Soc., Chem. Commun. 1991, 630.
4) C o´ rdva, E.; Bissel, R. A.; Spencer, N.; Ashton, P. R.; Stoddart, J. F.;
Kaifer, A. E. J. Org. Chem. 1993, 58, 6440.
5) Ikeda, T.; Aprahamian, I.; Stoddart, J. F. Org. Lett. 2007, 9, 1481
1994, 369, 133. (b) Asakawa, M.; Ashton, P. R.; Balzani, V.; Credi, A.;
Hamrs, C.; Mattersteig, G.; Montalti, M.; Shipway, A. N.; Spencer, N.;
Stoddart, J. F.; Tolley, M. S.; Venturi, M.; White, A. J. P.; Williams, D. J.
Angew. Chem., Int. Ed. 1998, 37, 333.
(
(
(8) (a) Steuerman, D. W.; Tseng, H.-R.; Peters, A. J.; Flood, A. H.;
Jeppesen, J. O.; Nielsen, K. A.; Stoddart, J. F.; Heath, J. R. Angew. Chem.,
Int. Ed. 2004, 43, 6486. (b) Ikeda, T.; Saha, S.; Aprahamian, I.; Leung,
K. C.-F.; Williams, A.; Deng, W.-Q.; Flood, A. H.; Goddard, W. A., III;
Stoddart, J. F. Chem. Asian J. 2007, 2, 76.
(
(
.
10.1021/ol800624c CCC: $40.75
Published on Web 05/03/2008
 2008 American Chemical Society

properties. Therefore, the interlocked donor-acceptor com-
pounds have been used to fabricate molecular electronic
9
10
Scheme 1. Synthesis of Diethyleneglycol-Substituted Thiophene
devices and nanoelectromechanical systems. Despite
extensive studies over two decades, inclusion complexation
Derivatives and Labeling Scheme for 2T-DEG
4
+
of CBPQT with thiophene derivatives has not been
reported so far. The oligo- and polythiophene derivatives
have been widely applicable to optoelectronic devices and
1
1
sensors because of their well-established chemical modi-
1
2
fication protocols. Although some groups have reported
13
thiophene [n]rotaxanes, the formation of CT complexes as
4
+
in the host-guest pair CBPQT -thiophene has not been
explored. We expect the donor-acceptor interlocked com-
4
+
pounds, consisting of CBPQT and thiophene, to be
attractive candidates for optoelectronic and electromechanical
materials.
Here, we describe the synthesis of a series of new guest
compounds, diethyleneglycol-substituted thiophenes (nT-
4
+
DEG, n ) 1s3), for the host CBPQT , as well as a series
of thiophene donor-acceptor [2]rotaxanes (nT-Rx, n ) 1s3)
using nT-DEG as precursors for the dumbbells.
First, we synthesized the diethyleneglycol-substituted
thiophene derivatives (nT-DEG). The routes employed in
the synthesis of nT-DEG (n ) 1s3) are summarized in
Scheme 1. 2,5-Dihydroxymethylthiophene (2) was synthe-
sized by the reduction of 2,5-thiophenedicarboxaldehyde (1)
a
BNGDP: bis(neopentylglycolato)diboron.
DEG, a small amount of 2T-DEG was also obtained as a
side product. Thus, we purified the product using preparative
HPLC.
When CBPQT·4PF sa white powderswas added to a
6
solution of nT-DEG in MeCN, the color of the solution
4
with NaBH . THP-protected diethyleneglycol-substituted
thiophene (4) was prepared by alkylation of two hydroxyl
groups in 2 with 2-(2-(2-chloroethoxy)ethoxy)tetrahydro-2H-
8
b
pyran 3.
1T-DEG was obtained by deprotection of the
terminal THP groups with pyridinium p-toluenesulfonic acid
14
changed immediately, indicating the formation of the pseu-
(
PPTS). Mono(diethyleneglycol)-substituted thiophene bro-
2–6
dorotaxane. This new absorption band arises from the CT
band between the electron-rich thiophene unit and the
electron-deficient bipyridinium units (Table 1). We confirmed
mide 7 was prepared through alkylation of 5-bromo-2-
1
5
hydroxymethylthiophene (5) with 3, followed by the
deprotection of 6. 2T-DEG was synthesized via a one-pot
tandem Miyaura boronic ester formation and Suzuki cou-
1
6
pling with the base (K
bis(neopentylglycolato)diboron]. 3T-DEG was synthesized
using the palladium-catalyzed Stille coupling with 2,5-
2 3
CO ) and the boron reagent
[
Table 1. Maximum Absorption Wavelength (λmax) in UV-vis
Spectra for π-π* and CT Bands and Association Constants (K )
a
1
7
stannylated thiophene (8) and 7. In the synthesis of 3T-
λmax, nm
π-π* band
λmax, nm
CT band
a
b
Ka M-1
guest
(
9) (a) Collier, C. P.; Mattersteig, G.; Wong, E. W.; Luo, Y.; Beverly,
K.; Sampaio, J.; Raymo, F. M.; Stoddart, J. F.; Heath, J. R. Science 2000,
89, 1172. (b) Green, J. E.; Choi, J. W.; Boukai, A.; Bunimovich, Y.;
c
1
T-DEG
230
302
352
∼400
1900
2800
2200
2
2T-DEG
T-DEG
467
507
J-Halperin, E.; Delonno, E.; Luo, Y.; Sheriff, B. A.; Xu, K.; Shin, Y. S.;
3
Tseng, H. R.; Stoddart, J. F.; Heath, J. R. Nature 2007, 445, 414.
a
b
π-π* transition band of the thiophene derivatives. Charge-transfer
band of the complex. CT band overlaps the absorption peak of CBPQT
(
10) (a) Huang, T. J.; Brough, B.; Ho, C.-M.; Liu, Y.; Flood, A. H.;
c
4+
.
Bonvallet, P. A.; Tseng, H.-R.; Stoddart, J. F.; Baller, M.; Magonov, S.
Appl. Phys. Lett. 2004, 85, 5391. (b) Saha, S.; Leung, L. C.-F.; Nguyen,
T. D.; Stoddart, J. F.; Zink, J. I. AdV. Funct. Mater. 2007, 17, 685.
(
11) (a) Fichou, D. J. Mater. Chem. 2000, 10, 571. (b) Murphy, A. R.;
Freshet, M. J. Chem. ReV. 2007, 107, 1066. (c) McQuade, D. T.; Pullen,
that the maximum wavelengths of the CT bands correlate
well with those of the nT-DEG π-π* bands (Table 1). From
the Job plot using UV-vis absorption measurements, the
stoichiometry of inclusion complex was confirmed to be 1:1
in all cases (Figure 1a).
A series of the [2]rotaxanes nT-Rx·4PF were prepared
6
through the capping reaction of the terminal hydroxyl groups
of the [2]pseudorotaxanes with TIPS triflate in MeCN laced
with 2,6-lutidine (Scheme 2). 1T-, 2T-, and 3T-Rx·4PF
A. E.; Swager, T. M. Chem. ReV. 2000, 100, 2537.
(
(
12) McCullough, R. D. AdV. Mater. 1998, 10, 93.
1
8a
13) (a) V o¨ gtle, F.; J a¨ ger, R.; H a¨ ndel, M.; Ottens-Hildebrandt, W.;
Schmidt, W. Synthesis 1996, 353. (b) Sakamoto, K.; Takashima, Y.;
Yamaguchi, H.; Harada, A. J. Org. Chem. 2007, 72, 459.
(
14) Miyashita, M.; Yoshikoshi, A.; Grieco, P. A. J. Org. Chem. 1977,
4
2, 3772.
(
15) Hagen, S. E.; Domagala, J.; Gajda, C.; Lovdahl, M.; Tait, B. D.;
Wise, E.; Holler, T.; Hupe, D.; Nouhan, C.; Urumov, A.; Zeikus, G.; Zeikus,
E.; Lunney, E. A.; Pavlovsky, A.; Gracheck, S. J.; Saunders, J.; Roest, S. V.;
Brodfuehrer, J. J. Med. Chem. 2001, 44, 2319.
19
6
(
(
16) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
17) Wei, Y.; Yang, Y.; Yeh, J.-M. Chem. Mater. 1996, 8, 2659.
were obtainable as yellow, red, purple solids, respectively.
2216
Org. Lett., Vol. 10, No. 11, 2008

Figure 1
CBPQT·4PF
titration (2T-DEG vs CBPQT·4PF
of CBPQT·4PF : 2.1 mM). The curve fit is depicted as dot line
) 2800).
. (a) Job plot for inclusion complexation of 2T-DEG and
1
6
(MeCN, rt). (b) Chemical shift change in H NMR
, MeCN, 288 K, concentration
6
6
(K
a
1H NMR spectra of (a) 1:1 mixture of 2T-DEG capped
, (b) 1:1 mixture of 2T-DEG
. CD CN, 300 MHz,
The absorption maximum of the CT band of each [2]rotaxane
nT-Rx is identical to the observed value of the corresponding
Figure 2
with TIPS groups and CBPQT·4PF
and CBPQT·4PF , (c) [2]rotaxane 2T-Rx·4PF
88 K, X: solvent peaks.
.
6
6
6
3
[
2]pseudorotaxane (Table 1).
2
Scheme 2
.
Synthesis of the Thiophene [2]Rotaxanes
Table 1 summarizes the association constants obtained
1
from H NMR titration. Stoddart et al. pointed out that the
electrostatic interaction and the hydrogen bond between the
ether oxygen atoms and the cationic bipyridinium unit play
1
9
important roles in stabilizing the complex. In addition,
2
0
Kaifer reported a drastic change in the K
to the extension of the aromatic repeating units. For example,
the K values of the diethyleneglycol-substituted 1,4-dihy-
a
values in response
a
1
9
4
-1
droxybenzene and 4,4′-biphenol are 2200 and 140 M ,
respectively. In the cases of nT-DEG (n ) 1-3), we detected
a
no dramatic change in the K values. Although the longer
thiophene moiety pushes its arms away from the cavity, the
diethyleneglycol can wrap around and interact with the
positive bipyridinium unit even in the case of 3T-DEG.
Interestingly, the observed K
800) is much smaller than that reported for the diethyl-
eneglycol-substituted tetrathiafulvalene derivatives (TTF-
a
value for 2T-DEG (K
a
)
1
Figure 2 shows the H NMR spectra of (a) 1:1 mixture of
2
the dumbbell (2T-DEG capped with the TIPS groups) and
CBPQT·4PF , (b) 1:1 mixture of the thread (2T-DEG) and
6
CBPQT·4PF , and (c) the thiophene [2]rotaxane 2T-Rx·4PF .
In the first case (Figure 2a), the bulky end groups of the
dumbbell hinder inclusion complexation. We confirmed that
the chemical shifts of the peaks in Figure 2a are identical to
those obtained from the dumbbell and the macrocycle
independently. Figure 2b shows single broad peak for each
proton on the thread, especially proton b, suggesting that
the complexed and uncomplexed species are in fast exchange
6
21
DEG, K ) 380000). Before the experiment, we expected
a
6
that these two aromatic units (2T and TTF) should arrange
their ethyleneglycol chains in a similar manner around the
bipyridinium units and would have comparable binding
affinities because of their similar molecular shapes. The most
important factor in differentiating the binding affinities is
considered to be the bond order of the inter-ring bond. In
the case of TTF-DEG, the inter-ring double bond inhibits
the free rotation of the binding unit. On the other hand, the
free rotation between two thiophene rings should be sup-
pressed after inclusion complexation. This entropically
1
on the H NMR time scale. Since the chemical shift change
of the p-phenylene protons depends on the molar ratio of
the thread and the macrocycle, we could calculate the
a
association constant (K ) of the inclusion complex (Figure
a
unfavorable process is attributable to the smaller K value
for 2T-DEG in comparison with TTF-DEG. The weaker
electron-donating property of 2T compared to TTF may also
contribute to reducing the binding affinity. It is interesting
1
8b
1
b).
(
18) (a) Schneider, H.-J.; Yatsimirsky, A. Principles and Methods in
Supramolecular Chemistry; John Wiley & Sons: Chichester, West Sussex,
000; p 148. (b) Reference 18a, p 142.
19) Anelli, P. L.; Ashton, P. R.; Ballardini, R.; Balzani, V.; Delgado,
M.; Gandolfi, M. T.; Goodnow, T. T.; Kaifer, A. E.; Philp, D.; Pietraszk-
iewicz, M.; Prodi, L.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.;
Stoddart, J. F.; Vicent, C.; Williams, D. J. J. Am. Chem. Soc. 1992, 144,
2
(20) Castro, R.; Nixon, K. R.; Evanseck, J. D.; Kaifer, A. E. J. Org.
Chem. 1996, 61, 7298.
(
(21) Choi, J. W.; Flood, A. H.; Steuerman, D. W.; Nygaard, S.;
Braunschweig, A. B; Moonen, N. N. P.; Laursen, B. W.; Luo, Y.; DeIonno,
E.; Peters, A. J.; Jeppesen, J. O.; Xu, K.; Stoddart, J. F.; Heath, J. R Chem.
Eur. J. 2006, 12, 261.
9
3.
Org. Lett., Vol. 10, No. 11, 2008
2217

that such a small structural difference between 2T and TTF
aromatic rings gives rise to such a large difference in K
between two pyridine ring mean planes: 15°), the π-system
in the bithiophene unit is completely planarized (dihedral
angle between two thiophene ring mean planes: 0°). The tilt
angle of the central C-C vector between two thiophene rings
a
.
1
In the H NMR spectrum of the [2]rotaxane 2T-Rx·4PF
Figure 2c), we confirmed the sharp resonances of the
thiophene protons. Compared to the free dumbbell (Figure
6
(
+
+
relative to the bipyridinium N -N vector is 71°. This value
2
2
a), the signals for the thiophene protons in the [2]rotaxane
T-Rx·4PF are shifted to higher field. In particular, a
is close to the tilt angle observed in the X-ray structure of
7
b
6
the TTF-included [2]catenane (74°). The dihedral angles
of the mean planes of the p-phenylene and the bipyridinium
units with respect to the mean plane of the thiophene units
are 3° and 85°, respectively. These results are in good
agreement with the molecular orientation deduced from the
dramatic upfield shift was observed for the protons b (6.99
f 4.32 ppm). This upfield shift is attributed to the shielding
effect on the guest protons situated within the CBPQT
cavity. Of the protons associated with the CBPQT ring,
the chemical shifts for the R and CH protons are almost
4
+
2–7
4+
1
2
H NMR result. The complex is stabilized by the [C-H ···
identical (cf. parts a and c of Figure 2), while the ꢀ and
p-phenylene protons are shifted to higher and lower fields,
respectively. These observations strongly suggest that the
plane of the thiophene rings is parallel to the bipyridinium
units and perpendicular to the p-phenylene aromatic rings
O] hydrogen bonds between the ether oxygen and R-bipy-
ridinium hydrogen (Figure 3a) as well as π-π stacking
interactions (Figure 3b). However, no T-type CH-π interac-
4
+
tion, which has been usually observed for the CBPQT
2
,3,19
inclusion complex,
is detectable between the thiophene
4
+
present in the CBPQT . The [2]rotaxanes 1T-Rx·4PF
T-Rx·4PF show similar results.
An X-ray analysis revealed the interlocked structure of
the [2]rotaxane 2T-Rx·4PF (Figure 3). The bithiophene unit,
6
and
hydrogen atom and the p-phenylene aromatic ring ([H ··· π]
2
3
3
6
distance: 4.21 Å).
2
2
In conclusion, we have synthesized a series of new guest
4+
6
compounds containing the thiophene units for the CBPQT
host (nT-DEG, n ) 1-3). We confirmed inclusion com-
4
+
plexation between nT-DEG and CBPQT . Furthermore,
we have obtained a series of the thiophene donor-acceptor
[2]rotaxanes. The maximum wavelength of the CT band
strongly depends on the number of thiophene unit, while the
association constant does not. Increasing the number of
thiophene units (n > 3) will further induce red shift of the
CT band. In addition, extended thiophene moiety will afford
a long, rigid, and multidentate binding site. The thiophene
[2]rotaxanes reported herein have demonstrated that the
thiophene derivatives will be fascinating constituents of
functional interlocked molecules. The synthesis of the oligo-
thiophene rotaxanes (nT-Rx, n > 3) and the characterization
of electromechanical properties are now in progress.
Figure 3
thiophene [2]rotaxane 2T-Rx·4PF
hydrogen atoms not participating in the hydrogen bonds are omitted
for clarity. (a) hydrogen bond (C···O), (H···O) distances and C-H···
O angle: 3.18, 2.27 Å and 165°. (b) π-π stacking distance: 3.43 Å.
.
X-ray crystallographic structure of the donor-acceptor
. The counterions and the
6
Acknowledgment. The authors thank Dr. Tadateru Nish-
ikawa (Bruker BioSpin K.K.) for the 2D NMR measurement.
This work was financially supported by the Iketani Science
and Technology Foundation.
in which the sulfur atoms possess an anti orientation, is
inserted centrosymmetrically through the center of the
tetracationic cyclophane. While the bipyridinium units are
distorted from the normal planar geometries (dihedral angle
Supporting Information Available: Experimental pro-
1
cedures, full spectroscopic data for all new compounds, H
NMR titration results, and X-ray crystallographic data (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(
22) The single crystals of the [2]rotaxane 2T-Rx·4PF6 were grown by
vapor diffusion of i-Pr2O into a MeCN solution of 2T-Rx·4PF6. Crystal
data for [2T-Rx·4PF6·6MeCN]: C72H98N4O6S2Si2·4PF6·6MeCN, M )
2
)
062.07, triclinic, a ) 11.323(4) Å, b ) 11.942(4) Å, c ) 20.512(7) Å, R
OL800624C
3
91.128(5)°, ꢀ ) 101.002(5)°, γ ) 114.600(5)°, V ) 2460.2(15) Å , space
-3 -1
j
group P1, Z ) 1, rcalcd ) 1.392 g cm , µ(Mo KR) ) 2.43 cm , F(000)
826.0, T ) 120 K, red plate crystal, 0.60 × 0.30 × 0.10 mm, R1 )
.0650, wR2(F2) ) 0.1648, goodness of fit ) 1.045.
)
0
(23) The distance between the proton b of the thiophene unit and the
centroid of the p-phenylene unit.
2218
Org. Lett., Vol. 10, No. 11, 2008