Conducting polymetallorotaxanes: Metal ion mediated enhancements in conductivity and charge localization

Article abstract of DOI:10.1021/ja972794w

In this paper we describe polymers of two metallorotaxane systems, Rot(1,M) and Rot(2,M) (M = Zn²⁺ or Cu¹⁺), which are formed by complexing a macrocyclic phenanthroline, a 5,5'-bis([2,2'-bithiophen]-5-yl)-2,2'- bipyridine (ligand 1) or 5,5'-bis(3,4:3',4'-bis(ethylenedioxy)[2,2'- bithiophen]-5-yl)-2,2'-bipyridine (ligand 2), and Zn²⁺ or Cu¹⁺ ions. The corresponding polymetallorotaxanes, PolyRot(1,M) and PolyRot(2,M), are produced by oxidative polymerization of Rot(1,M) and Rot(2,M). The investigations of the electrochemical, conducting, and optical properties of the metallorotaxanes and polymetallorotaxanes as well as related nonrotaxane polymers Poly(1) and Poly(2) are reported. The combined electrochemical and conductivity studies of PolyRot(1,M) and PolyRot(2,M) indicated that the polymetallorotaxane's redox and conducting properties were dramatically affected by the Lewis acidic and redox properties of the coordinated metal ions. The Lewis acidity produces charge localization and a redox conduction process in both polymetallorotaxane systems. The matching of the polymer and Cu(1+/2+) couple redox potentials in PolyRot(2,Cu) resulted in a Cu(1+/2+) contribution to conductivity. The metal-free PolyRot(1) and PolyRot(2) were produced by extracting the metal ions, and these polymers reversibly bound Zn²⁺ or Cu²⁺ ions in solution. The Cu²⁺ dopes the films of PolyRot(2) and Poly(2), which have lower oxidation potential than those of PolyRot(1), to produce 10⁶-10⁷-fold conductivity increases. In the case of PolyRot(1) and Poly(1), the rotaxane structure was demonstrated to be key for reversible complexation of metal ions.

Full text of DOI:10.1021/ja972794w

12568
J. Am. Chem. Soc. 1997, 119, 12568-12577
Conducting Polymetallorotaxanes: Metal Ion Mediated
Enhancements in Conductivity and Charge Localization
S. Sherry Zhu†,‡ and Timothy M. Swager*,†
Contribution from the Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, and Department of Chemistry, UniVersity of PennsylVania,
Philadelphia, PennsylVania 19104
X
ReceiVed August 11, 1997
2
+
Abstract: In this paper we describe polymers of two metallorotaxane systems, Rot(1,M) and Rot(2,M) (M ) Zn
1+
or Cu ), which are formed by complexing a macrocyclic phenanthroline, a 5,5′-bis([2,2′-bithiophen]-5-yl)-2,2′-
2
+
bipyridine (ligand 1) or 5,5′-bis(3,4:3′,4′-bis(ethylenedioxy)[2,2′-bithiophen]-5-yl)-2,2′-bipyridine (ligand 2), and Zn
or Cu1 ions. The corresponding polymetallorotaxanes, PolyRot(1,M) and PolyRot(2,M), are produced by oxidative
polymerization of Rot(1,M) and Rot(2,M). The investigations of the electrochemical, conducting, and optical properties
of the metallorotaxanes and polymetallorotaxanes as well as related nonrotaxane polymers Poly(1) and Poly(2) are
reported. The combined electrochemical and conductivity studies of PolyRot(1,M) and PolyRot(2,M) indicated that
the polymetallorotaxane’s redox and conducting properties were dramatically affected by the Lewis acidic and redox
properties of the coordinated metal ions. The Lewis acidity produces charge localization and a redox conduction
+
1
+/2+
process in both polymetallorotaxane systems. The matching of the polymer and Cu
couple redox potentials in
contribution to conductivity. The metal-free PolyRot(1) and PolyRot(2) were
produced by extracting the metal ions, and these polymers reversibly bound Zn or Cu ions in solution. The
Cu dopes the films of PolyRot(2) and Poly(2), which have lower oxidation potential than those of PolyRot(1), to
PolyRot(2,Cu) resulted in a Cu1
+/2+
2
+
2+
2+
6
7
produce 10 -10 -fold conductivity increases. In the case of PolyRot(1) and Poly(1), the rotaxane structure was
demonstrated to be key for reversible complexation of metal ions.
the polymers.9
-15
Critical to their utility is the design of
Introduction
structures that enhance the electron transfer rate between metal
centers relative to nonconjugated polymeric or molecular
assemblies. The principles controlling electron transfer rates
are largely unexplored, and there have been few studies that
probe the ability of a conjugated polymer to mediate redox
conductivity. Previous studies have investigated conducting
Conjugated polymer-based sensory schemes developed in our
laboratory have made use of extended electronic communication
between receptor sites to produce amplified responses for the
1
-4
detection of organic molecules and alkaline metal cations.
As part of our continued interest in the high sensitivity of a
conjugated polymer’s conductivity and/or fluorescence to analyte
14,15
12
polymers containing Ru(bpy)nL3-n,
ferrocene, and transi-
5
,6
binding, we are endeavoring to create highly conducting
metallopolymers. Transition metals offer unique and desirable
characteristics for the creation of sensory materials that are
sensitive to anions as well as small molecules (CO, O2, NO,
etc.).7 In spite of this and other potential applications, few
1
6
tion metal ions. In general, the results suggest that the redox
conductivity is enhanced by a conjugated polymer. Systematic
studies to optimize redox conductivity have only begun to
1
5
appear.
,8
The creation of optimal conducting systems that actively
utilize a transition metal’s redox properties will most likely
require extensive mixing of the metal-centered electronic states
with those of the organic polymer. In our investigations we
have targeted systems with well-defined structures that are
capable of complexing both redox-active and redox-inactive
metal ions. By making systematic comparisons between these
materials, the relative contribution of the organic polymer and
the metal-centered redox processes to the conductivity can be
determined. To accomplish this, we have found the phenan-
throline macrocycle developed by Sauvage and co-workers to
studies have been directed at the development of transition
metal/conducting polymer hybrid systems.9
-17
Additionally, in
only a few of these cases was the metal directly interacting with
†
Massachusetts Institute of Technology.
University of Pennsylvania.
Abstract published in AdVance ACS Abstracts, December 1, 1997.
‡
X
(
(
1) Marsella, M. J.; Swager, T. M. J. Am. Chem. Soc. 1993, 115, 12214.
2) Marsella, M. J.; Carroll, P. J.; Swager, T. M. J. Am. Chem. Soc.
1
994, 116, 9347.
3) Marsella, M. J.; Newland, R. J.; Carroll, P. J.; Swager, T. M. J. Am.
Chem. Soc. 1995, 117, 9842.
4) Marsella, M. J.; Carroll, P. J.; Swager, T. M. J. Am. Chem. Soc.
995, 117, 9832.
(
(
1
18
be particularly useful for the formation of metallorotaxanes.
(
(
(
5) Zhou, Q.; Swager, T. M. J. Am. Chem. Soc. 1995, 117, 7017.
6) Zhou, Q.; Swager, T. M. J. Am. Chem. Soc. 1995, 117, 12593.
7) (a) Tovrog, B. S.; Drago, R. S. J. Am. Chem. Soc. 1974, 96, 6765.
(13) (a) Reddinger, J. L.; Reynolds, J. R. Macromolecules 1997, 30, 673.
(b) Reddinger, J. L.; Reynolds, J. R. Synth. Met. 1997, 84, 225.
(14) (a) Peng, Z.; Yu, L. J. Am. Chem. Soc. 1996, 118, 3777. (b)
Yamamoto, T.; Maruyama, T.; Zhou, Z.; Ito, T.; Fukuda, T.; Yoneda, Y.;
Begum, F.; Ikeda, T.; Sasaki, S.; Takezoe, H.; Fukuda, A.; Kubota, K. J.
Am. Chem. Soc. 1994, 116, 4832.
(
9
b) Hoffman, B. M.; Szymanski, T.; Basolo, F. J. Am. Chem. Soc. 1975,
7, 637.
8) (a) Cini, R.; Orioli, P. L. J. Chem. Soc., Chem. Commun. 1981, 196.
b) Zanello, P.; Cini, R.; Cinquantini, A.; Orioli, P. L. J. Chem. Soc., Dalton
Trans. 1983, 2159.
9) Zhu, S. S.; Carroll, P. J.; Swager, T. M. J. Am. Chem. Soc. 1997,
18, 8713.
(
(
(15) Pickup, P. G.; Cameron, C. G. Chem. Commun. 1997, 303.
(16) (a) Bidan, G.; Divisia-Blohorn, B.; Lapkowski, M.; Kern, J. M.;
Sauvage, J. P. J. Am. Chem. Soc. 1992, 114, 5986. (b) Bidan, G.; Divisia-
Blohorn, B.; Billon, M.; Kern, J. M.; Sauvage, J. P. J. Electroanal. Chem.
1993, 360, 189. (C) Kern, J. M.; Sauvage, J. P.; Bidan, G.; Billon, M.;
Divisia-Blohorn, B. AdV. Mater. 1996, 8, 580.
(
1
(
(
(
10) Zhu, S. S.; Swager, T. M. AdV. Mater. 1996, 8, 497.
11) Wolf, M. O.; Wrighton, M. S. Chem. Mater. 1994, 6, 1526.
12) Zotti, G.; Zecchin, S.; Schiavon, G.; Berlin, A.; Pagani, G.; Canavesi,
A. Chem. Mater. 1995, 7, 2309.
(17) Deronzier, A.; Moutet, J. C. Acc. Chem. Res. 1989, 22, 249.
S0002-7863(97)02794-7 CCC: $14.00 © 1997 American Chemical Society

Conducting Polymetallorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12569
Scheme 1
9
In a previous communication, we described two conducting
mediated conductivity whereas PolyRot(1,Cu) displayed no
detectable conductivity which could be ascribed to the copper
ions.
polymetallorotaxanes, PolyRot(1,Zn) and PolyRot(1,Cu), which
are formed from anodic polymerization of preassembled met-
allorotaxanes, Rot(1,Zn) and Rot(1,Cu). Once synthesized, the
macrocycles are trapped on the polymer, presumably by physical
or chemical cross-links, as they are retained after removal of
the metal ion templates. This assembly of receptors allows for
the investigation of polymers in complexed as well as metal-
free states, and enables the determination of the contribution
of metal ions to the electronic properties of the polymers. We
found that both PolyRot(1,Cu) and PolyRot(1,Zn) displayed
similar conducting properties which are attributed to the organic
portion. Nevertheless, in the case of PolyRot(1,Cu), both metal-
and polymer-based faradaic processes were observed. We
further demonstrated that the structures may be reversibly
converted between the metal-free PolyRot(1) and the PolyRot-
(
1,Zn) forms in CH3CN solution.9
Reasoning that matching the polymer and copper-centered
redox potentials would enhance the communication between
these two elements, we have developed additional polymetal-
lorotaxanes, PolyRot(2,Cu) and PolyRot(2,Zn), with 3,4-(eth-
ylenedioxy)thiophene (EDOT) groups in place of thiophenes
in the polymer backbone. The EDOT substitution makes the
polymer much more electron-rich. Herein we report detailed
synthetic, electrochemical, and optical studies of the polymet-
allorotaxanes, PolyRot(1,Cu), PolyRot(1,Zn), PolyRot(2,Cu),
and PolyRot(2,Zn), and the corresponding metal-free polyro-
Results and Discussion
a. Syntheses and Characterization of Metallorotaxane
Monomers. The bithienyl-substituted bipyridine 1 functions
as a polymerizable monomer, a chelating component, and a
threading element. We have previously demonstrated the utility
of 1 in the formation of a conducting polymer, Poly(1), and
related conducting polymer transition metal hybrid materials.
In our first attempt to produce a more electron-rich threading
component, we synthesized 5,5′-bis(3,4-(ethylenedioxy)thien-
2
+
taxanes, PolyRot(1) and PolyRot(2). We found that Zn
complexation induces charge localization and produces polymers
with redox conductivity. The incorporation of EDOT units in
1+/2+
PolyRot(2)-derived materials results in a matching of the Cu
redox couple with the potential at which the polymers are
10
6
7
oxidized. This enables a 10 -10 increase in conductivity by
the complexation of Cu2 ions. An additional outcome of this
+
1
+/2+
redox matching is that PolyRot(2,Cu) shows large Cu
-
2
-yl)-2,2′-bipyridine (3) by a Stille coupling of 5,5′-dibromo-
1
9
(
18) (a) Dietrich-Buchecker, C.; Sauvage, J. P. Tetrahedron 1990, 46,
2,2′-bipyridine with 2-(tributylstannyl)-3,4-(ethylenedioxy)-
thiophene (Scheme 1). Although compound 3 can be oxidatively
5
03. (b) Sauvage, J. P. Acc. Chem. Res. 1990, 23, 321. (c) Armaroli, N.;
Balzani, V.; Barigelletti, F.; Cola, L. D.; Flamigni, L.; Sauvage, J. P.;
Hemmert, C. J. Am. Chem. Soc. 1994. 116, 5211.
(19) Whittle, C. P. J. Heterocycl. Chem. 1977, 14, 191.

12570 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Zhu and Swager
Scheme 2
polymerized, we were unsuccessful at producing polymeric films
from rotaxane complexes, Rot(3,Zn). We had experienced
similar difficulties in other systems, which were eliminated by
extending the thiophene segment.10 Therefore, we synthesized
an extended 3,4:3′,4′-bis(ethylenedioxy)[2,2′-bithiophen]-5-yl
sensitive yellow-brown solid which rapidly decomposes on silica
gel. Recrystallization from CH2Cl2/hexanes afforded pure
compound 2 which was characterized by NMR and MS. Dilute
CH2Cl2 solutions of 2 are bright yellow and display green
emission.
(BEDOT) substituted threading component, 2 (Scheme 1).
We have previously described the syntheses and characteriza-
tion of metallorotaxanes, Rot(1,Zn) and Rot(1,Cu) (Scheme 2).9
A crystal structure determination of Rot(1,Zn) confirmed the
formation of the metallorotaxane. UV-vis (Figure 1) and NMR
are also diagnostic and indicate that Rot(1,Zn) and Rot(1,Cu)
are fully associated in solution. Concurrent with the assembly
of metallorotaxanes, the optical transitions of the threading
component, 1 and 2, display a pronounced red shift. Similar
effects have been observed with protonation of other conducting
polymers which have electron-poor pyridine groups alternating
2
0b
with more electron-rich moieties.
The red shift suggests
charge transfer character in the electronic transitions since
protonation or metal coordination stabilizes negative charge
transferred to the bipyridine residues in the excited state.20 Also
consistent with this description, the rotaxanes formed with more
We initially attempted to synthesize compound 2 by a Stille
2
+
Lewis acidic Zn display larger red shifts than those formed
coupling between 5,5′-dibromo-2,2′-bipyridine and 2-(tributyl-
stannyl)-3,4:3,′4′-bis(ethylenedioxy)-5,5′-bithiophene. The highly
electron-rich character of 3,4:3′,4′-bis(ethylenedioxy)-2,2′-
bithiophene (BEDOT) apparently precludes an efficient prepara-
tion of 2-(tributylstannyl)-3,4:3′,4′-bis(ethylenedioxy)-5,5′-
bithiophene by standard lithiation methods (Scheme 1). Thus,
an alternative procedure was developed by brominating 3 with
NBS. Stille coupling of 2-(tributylstannyl)-3,4-(ethylenedioxy)-
thiophene with 5,5′-bis(5-bromo-3,4-(ethylenedioxy)thien-2-yl)-
1
+
with Cu (Figure 1). We also observed larger shifts in the
rotaxanes assembled with 2 than those with 1. Accordingly,
the respective λmax centered on the 1 and 2 moieties are red
2
+
shifted by 60 and 80 nm in the Zn rotaxanes and by 23 and
1
+
13
3
3 nm in the Cu rotaxanes. 1H and C NMR indicate
complete formation of the rotaxanes in solution and the phenyl
protons meta and ortho to the phenanthroline display respective
(
20) (a) Fu, D.; Xu, B.; Swager, T. M. Tetrahedron 1997, 53 (45), 15487.
b) Zhou, Z.; Maruyama, T.; Kanbara, T.; Ikeda, T.; Ichimura, K.;
Yamamoto, T.; Kubota, K. J. Chem. Soc., Chem. Commun. 1991, 1210.
2
5
,2′-bipyridine produced compound 2 in moderate yield (30-
5%, depending on the scale). Compound 2 is an air- and light-
(

Conducting Polymetallorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12571
+
i.e., [A] ) [A ]. Thus, if a redox polymer’s cyclic voltammo-
gram exhibits multiple redox peaks, so too will the conductivity
2
3
profile.
The electrochemical and conducting properties of Poly(1)
10
have been reported. Poly(1) displays two unresolved oxidation
peaks and resembles the behavior typical of polythiophene
derivatives. Due to the electron-deficient character of its
bipyridine moiety, Poly(1) is easier to reduce than poly-
thiophene, and conductivity measurements indicate that Poly-
(
1) displays a stable conducting current in both p- and n-doping
1
0
states. As shown in Scheme 3, the corresponding metalloro-
taxane monomers, Rot(1,Zn) and Rot(1,Cu), are oxidatively
polymerized to generate polymetallorotaxanes, PolyRot(1,Zn)
9
and PolyRot(1,Cu).
As expected, the oxidation potential required to polymerize
2
(polymerized by cycling the working electrode between -0.22
and +0.95 V) is lower than that required to polymerize 1
cycling between -0.2 and +1.2 V). The resulting films of
(
Poly(2) are dark purple in their reduced form. Electrochemical
and conductivity measurements on films of Poly(2) using
interdigitated microelectrodes show several interesting properties
(Figure 2a). The cyclic voltammogram of Poly(2) displays two
oxidation waves (Table 1 and Figure 2a) with almost equal peak
currents. A linear relationship between the peak currents and
scan rate confirms that the electroactive species are surface
confined. The conductivity profile shows the first maximum
to be at the same potential as the first oxidation wave. After
passing through the first wave, a slight drop in the conductivity
Figure 1. Top: UV-vis absorption of the phenanthroline macrocycle
(dashed line, a), monomer 1 (solid line, b), Rot(1,Cu) (dotted line, c),
and Rot(1,Zn) (dotted-dashed line, d) in CH
absorption of monomer 2 (solid line, e), Rot(2,Cu) (dotted-dashed line,
f), and Rot(2,Zn) (dashed line, g) in CH Cl
2 2
Cl . Bottom: UV-vis
2
2
.
upfield shifts from 7.16 and 8.40 ppm (CDCl3) to 6.63 and 7.68
ppm (acetone-d6) upon formation of Rot(1,Cu) and to 6.31 and
1+
7.47 ppm on the formation of Rot(2,Cu). Numerous other Cu
complexation-induced shifts are observed in the other proton
2+
signals, and similar shifts are observed in the Zn complexes.
b. Electrochemical Studies. All of the polymers investi-
gated were synthesized by anodic electrochemical deposition.
By this method, polymers can be deposited on microelectrode
arrays for in situ cyclic voltammetry and relative conductivity
measurements. Likewise deposition on an indium-tin-oxide
is observed before reaching a second maximum (σ ) 3.5 ×
-2
1
0
S/cm) at the half-wave potential of the second oxidation
wave. In other words, the conductivity of Poly(2) results from
two discrete redox waves which produce two windows of peak
conductivity. This correspondence between redox processes and
the conductivity suggests that Poly(2) behaves as a charge-
localized redox conductor.
(
ITO) sheet enables UV-vis spectroelectrochemical measure-
21
ments. Using techniques described elsewhere, the conductivity
is determined as a function of the applied electrochemical
potential on the same functionalized electrodes that are used
for cyclic voltammetry analysis. All electrochemical polym-
erization measurements were performed in 0.1 M (n-Bu)4NPF6/
CH2Cl2 electrolyte solution in an air-free drybox under low-
intensity lighting. A Ag wire was used as the quasi-reference
Considering that the electrochemical polymerization process
produces protons, we suspected that the as-synthesized film of
Poly(2) may be protonated. Indeed, rinsing films of Poly(2)
with base (ethylenediamine) immediately transformed the films
to a red color and also produced a broader and less defined
cyclic voltammogram. As shown in Figure 2b, the cyclic
voltammogram still displays the two oxidation waves and two
conductivity maxima after ethylenediamine treatment. However,
deprotonation results in a negative shift of the oxidation
potentials (Table 1), indicating that the neutralized polymer is
easier to oxidize. Base treatment also changes the shape of the
conductivity profile, and we observed a decrease in the first
conductivity wave and a slight conductivity increase com-
mensurate with the second oxidation wave.
0
electrode, and ferrocene (E ′ ) 0.40 V) was used as a reference
potential.
Typical thiophene-based conducting polymers exhibit cyclic
voltammograms which are composed of broad unresolved waves
indicating a high degree of delocalization.2 Additionally, the
conductivity profiles of thiophene-based conductors generally
display a single window of conductivity for a given type of
doping.21 In polymers displaying redox-based conductivity,
electrons hop between localized redox centers. For systems
having equivalent structures and oxidation potentials, the rate
of self-exchange (SE) electron transfer (ET) processes conforms
2
9
As we have reported previously, PolyRot(1,Zn) displays a
cyclic votammogram with two partially resolved one-electron
waves. Additionally, the conductivity exhibits the characteristics
of a localized redox system with conductivity peaks (σmax )
+
to the simple equation RSE ) kET[A][A ], indicating a propor-
-
4
3
.7 × 10 S/cm) corresponding directly with the half-wave
tional relationship to the product of the concentrations of the
potentials. PolyRot(1,Cu) displays two less resolved waves
similar to those of PolyRot(1,Zn) and an additional Cu
at a less positive potential. The Cu
+
reduced (A) and oxidized (A ) species. This dictates that for
1+/2+
wave
+
a fixed amount of redox-active species ([A] + [A ] ) constant)
1
+/2+
wave displays a large
the self-exchange rate between the oxidized and reduced states,
and hence conductivity, will reach a maximum when the
concentrations of the oxidized and reduced species are equal,
hysteresis (∆Ep ) Epc - Epa ) 118 mV at 50 mV/s), and due
to this kinetic sluggishness, no measurable redox conductivity
1
+/2+
was associated with the Cu
wave.
(21) (a) Kittlesen, G. P.; White, H. S.; Wrighton, M. S. J. Am. Chem.
The polymetallorotaxanes formed with 2 display interesting
electrochemical behaviors which are dramatically influenced by
metal ion complexation. Electrolyte solutions of either Rot-
Soc. 1984, 106, 7389. (b) Ofer, D.; Crooks, R. M.; Wrighton, M. S. J. Am.
Chem. Soc.. 1990, 112, 7869. (c) Paul, E. W.; Ricco, A. J.; Wrighton, M.
S. J. Phys. Chem. 1985, 89, 1441. (d) Thackeray, J. W.; White, H. S.;
Wrighton, M. S. J. Phys. Chem. 1985, 89, 5133.
(
22) Handbook of Conducting Polymers; Skotheim, T. J., Ed.; Dekker:
(23) ElectroactiVe Polymer Electrochemistry; Lyons, M. E. G., Ed.;
Plenum Press: New York, 1994; see also references therein.
New York, 1986.

12572 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Zhu and Swager
Scheme 3
0
Table 1. Apparent Formal Reduction Potential E ′ (V vs Ag
a
Wire) of the Two Redox Processes of Each Polymer
E0′ (V) (metal-free
polyrotaxanes)
E0′ (V) (polymers)
Poly(1)
Poly(2)
PolyRot(1,Zn) 0.96
PolyRot(1,Cu) 0.98
PolyRot(2,Zn) 0.41
PolyRot(2,Cu) 0.49
1.12
0.43 (0.34)
1.29
0.79 (0.74)
1.24
1.26
0.74
b
b
0.96-1.24c
0.98-1.26c
0.36
0.41
0.64
0.71
c
0.79
a
E ′ ) (Epa + Epc)/2. b Values in parentheses are for the material
0
c
after treatment with ethylenediamine. After base treatment, the two
polymer-based redox peaks lose their definition and give a broad redox
wave over the indicated potential region.
Figure 3. Column A: cyclic voltammograms (top) and conductivity
profile (bottom) of PolyRot(2,Zn) on interdigitated electrodes. Column
B: cyclic voltammograms (top) and conductivity profile (bottom) of
PolyRot(2,Cu) on interdigitated electrodes. Cyclic voltammograms of
PolyRot(1,Cu) at 25 and 50 mV/s scan rates are shown as an inset in
(B, top) for comparison.
feature of the cyclic voltammogram is the well-resolved
localized nature of the redox waves. Both PolyRot(2,Zn) and
PolyRot(2,Cu) display behavior typical of reversible surface-
confined localized redox sites with small ∆Ep and a linear
relationship between the scan rate and peak currents. PolyRot-
(2,Zn) displays two polymer-based redox peaks with equal peak
currents (Figure 3a). The relative conductivity (current) of
PolyRot(2,Zn) correlates with this electroactivity and reaches
a local maximum at the half-wave potential of the first oxidation
peak. The conductivity then drops nearly to a baseline level
before rising to its highest level (σ ) 6.8 × 10 S/cm) at a
potential which is coincident with the second redox wave. From
these cyclic voltammogram and conductivity investigations we
conclude that PolyRot(2,Zn) behaves as a redox conductor with
rapid electron transfer between localized redox states in the
polymer backbone. The localized redox conductor character-
Figure 2. Columns A and B show the cyclic voltammograms (top)
and relative conductivity profiles (bottom) of Poly(2) on interdigitated
electrodes. (a) Poly(2) film as synthesized. (b) Poly(2) after treatment
with base (ethylenediamine).
-
4
(2,Zn) (0.77 mM) or Rot(2,Cu) (0.46 mM) were electrochemi-
cally polymerized by cycling between -0.4 and +1.15 V to
generate green-blue films. As shown in Figure 3, a striking

Conducting Polymetallorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12573
istics are more pronounced in PolyRot(2,Zn) than in Poly(2),
which indicates that the complexation of Zn2 ions results in
enhanced charge localization in the polymer backbone. We also
note that PolyRot(2,Zn)’s behavior is consistent with the
behavior of Poly(2) which displays more localized behavior in
its protonated form.
+
PolyRot(2,Cu) displays two oxidation waves in its cyclic
votammogram (Figure 3). A comparison with the electrochemi-
cal behavior of PolyRot(1,Cu), shown as an inset in Figure 3,
top, illustrates how the electron-rich character of the Poly(2)
backbone produces a negative shift of the two polymer-centered
1
+/2+
oxidation peaks to a region which overlaps with the Cu
wave. This results in a 0.49 V wave that is approximately twice
as large as the wave at higher potential. Close inspection
indicates that the former contains two unresolved waves. The
conductivity profile of PolyRot(2,Cu) shown in Figure 3 is also
indicative of redox behavior. However, this behavior is different
from that of PolyRot(2,Zn) in that the first conducting peak (σ
Figure 4. UV-vis absorption of Poly(2) on ITO glass as a function
of the applied electrochemical potential.
(2) is also achieved by holding the potential of the dark purple
-
3
films at -0.36 V for 20 min, indicating that reducting potentials
can also affect deprotonation. Presumably, in this case the
supporting electrode surface or other generated species remove
the protons. Due to an erosion of the electrochemical behavior
of Poly(2) on ITO after ethylenediamine treatment, we have
used this reductive method to deprotonate the polymer. The
neutral form of Poly(2) displays an interband transition at 540
nm, which is to the red of both polythiophene and poly(EDOT).
This bathochromic shift is due to the alternating donor-acceptor
structure ((EDOT)4 ) donor, bipyridine ) acceptor) of Poly-
)
1.3 × 10 S/cm) for PolyRot(2,Cu) is now considerably
larger than the second peak. This last feature is significant since
our investigations of PolyRot(1,Zn), PolyRot(1,Cu), PolyRot-
(2,Zn), Poly(1), and Poly(2) consistently show a smaller relative
conductivity associated with the wave at lower potential and
maximum at higher potential. The Cu1
+/2+
waves in both
PolyRot(1,Cu) and PolyRot(2,Cu) also provide an internal
Coulometric reference, which indicates that the threading
polymers (i.e., Poly(1) and Poly(2)) of the polyrotaxanes exhibit
two sequential one-electron oxidation processes for each repeat-
ing unit.
(2) which creates a lower energy charge transfer absorption.
With initial oxidation, a single lower energy absorption appears
at 670 nm. This new band grows at the expense of the 540 nm
peak, and at an applied potential of 0.64 V (a state between the
first and the second oxidation waves), the interband absorption
is absent and the dominant feature is a broad absorption at 706
nm. Increasing the applied oxidation potential to 0.84 V, which
corresponds to the center of the second oxidation wave and the
point of the highest conductivity, gives a spectrum with the 706
nm absorption displaying the same intensity and a new
absorption tail from approximately 880 into the near-IR. At a
potential of 1.24 V, where the conductivity is low, a feature is
observed that resembles a typical free carrier tail extending into
the near-IR. This result is in stark contrast to those of
polythiophene derivatives and other conducting polymers which
display this spectroscopic feature in their highly conducting
states. Thus, it is surprising that the free-carrier tail is largest
in the low conductivity state. On the return (reductive) scan
from +1.24 to -0.36 V, the absorption shows some hysteresis
c. Optical Studies. Given the interesting redox and conduc-
tion behaviors of these materials, we have performed in situ
UV-vis spectroscopy as a function of applied electrochemical
potential. Spectroelectrochemical measurements were carried
out in a home-built sealed cell using indium-tin-oxide (ITO)
as a working electrode. The UV-vis absorption spectra were
measured at electrochemical potentials chosen to interrogate the
nature of the polymer. To confirm that the polymer had come
to an equilibrium at each potential, we performed measurements
in both the oxidative cycle and the subsequent reductive cycle.
The spectra at each potential were nearly the same for both
cycles, confirming that the films were in equilibrium with the
electrodes.
It has been reported by others that polythiophene and poly-
(
EDOT) show strong interband absorptions with λmax at 480
24
and 511 nm, respectively. Upon doping, the intensity of this
interband transition was found to decrease, and two new
absorption peaks appear at lower energies.24 With increasing
doping levels, the interband absorption peaks disappear and the
two low-energy absorption peaks gain intensity and eventually
merge. In the heavily doped state, the spectra show increasing
intensity at long wavelengths that extend into the near-IR. This
latter feature is generally considered to be characteristic of free
carriers in the metallic state and is referred to as a free carrier
(Figure 4). This effect appears to be the result of a small amount
of protonation of Poly(2) with oxidation, which results from a
reversal of the initial reductive treatment. The spectrum of
neutral Poly(2) is again recovered after reducing Poly(2) at
-
0.36 V for 20 min.
The interaction of the Poly(2) backbone with Zn2 and Cu1+
+
in the polymetallorotaxane systems produces effects similar to
those reported for the monomers in Figure 1. In their undoped
form, PolyRot(2,Zn) and PolyRot(2,Cu) display absorption
maxima at 630 and 618 nm, respectively (Figure 5), which are
considerably red shifted from the 540 nm maximum of Poly-
2
4
tail.
The UV-vis spectra of Poly(2) are very different from those
of simple polythiophene derivatives. As shown in Figure 4,
the as-synthesized dark purple films of Poly(2) exhibit a broad
absorption with two unresolved intensity maxima at 540 and
(
2). The bipyridine moiety is a stronger acceptor when
6
80 nm. After treatment with base (ethylenediamine), the film
2
+
1+
complexed with Zn ions as compared to Cu ions, and
consistently the PolyRot(2,Zn) shows a larger red shift. The
UV-vis spectral changes observed as a function of applied
electrochemical potential for PolyRot(2,Cu) and PolyRot(2,Zn)
are similar. As shown in Figure 5, these materials differ from
Poly(2) in that the peaks which correspond to the initial
absorption maxima remain throughout the entire cycle. Similar
appears red and displays a well-defined absorption peak centered
at 540 nm. This optical change further confirms our earlier
assertion that the Poly(2) is protonated during oxidative po-
lymerization. A similar change in the UV-vis spectra of Poly-
(
24) (a) Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. ReV. 1988, 88, 183.
(
b) Chen X.; Ingan a¨ s, O. J. Phys. Chem. 1996, 100, 15202.

12574 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Zhu and Swager
Figure 6. Top: cyclic voltammograms of PolyRot(1,Zn) (solid line);
after treatment with base to form polyRot(1) (dotted-dashed line), and
then immersed in Zn(ClO
PolyRot(1) after treatment with a CuBF
4
)
2
/CH
3
CN (dotted line). Bottom: metal-free
(CH CN) /CH CN solution.
4
3
4
3
produces a similar red shift in the UV-vis absorption. The
cyclic voltammogram of PolyRot(1) after treatment with Cu2
only exhibits a very small peak at 0.49 V corresponding to the
+
1
+
2+
1+
Cu /Cu redox couple. The Cu -treated PolyRot(1), how-
ever, produces a relatively large redox wave at 0.49 V associated
with an electrochemically irreversible peak (Figure 6). It is
Figure 5. UV-vis absorption as a function of applied electrochemical
potentials. Top: PolyRot(2,Zn). Bottom: PolyRot(2,Cu). Note the
nearly identical spectra obtained in both oxidation and reduction cycles.
1+
apparent that PolyRot(1) has a higher affinity for Cu with
respect to Cu , which is to be expected for the polyrotaxane
structure with preassembled tetrahedral binding sites. Dipping
the macrocycle-free Poly(1) in Cu solutions broadens the
absorption spectrum, but no visible Cu
2
+
to Poly(2), at intermediate and high oxidation levels a new peak
appears at lower energy and a feature resembling a free carrier
tail absorption dominates the spectra at the highest oxidation
potentials. Also consistent with the behavior of Poly(2), both
PolyRot(2,Cu) and PolyRot(2,Zn) are in their lower conducting
states when the new absorption tails which extended into the
near-IR are at their highest intensity.
2+
1+/2+
wave appears in
1+
the cyclic voltammogram. The interaction of Poly(1) with Cu
1+/2+
solutions produces neither an absorption change nor a Cu
redox wave in the cyclic voltammogram. Thus, the rotaxane
structure is key to metal binding, and Poly(1) shows no evidence
2+
9
of Zn binding under the same conditions.
d. Reversible Complexation of Metal Ions. Polyrotaxanes
with preorganized binding sites are potential sensory materials
for transition metal ions. Critical to the sensory properties of
conducting polyrotaxanes is the reversibility of metal ion
In the case of the PolyRot(2) system, the contribution of the
copper ion to the conductivity of PolyRot(2,Cu) makes this a
particularly interesting system to study the reversible binding
of Cu and Cu . Our investigations of Cu and Cu
complexation by PolyRot(2) have focused on electrochemical
and conductivity studies.
1+
2+
1+
2+
2+
binding. We have demonstrated the reversible binding of Zn
9
to metal-free PolyRot(1) through optical absorption changes.
Noting that the UV-vis spectrum only reflects the changes in
local electronic structure,25 we have further investigated the
effects of interaction between polyrotaxane and the metal ions
on the conductivity, which is a collective property. As shown
in Figure 6, the cyclic voltammogram of PolyRot(1,Zn) films
displays two well-defined oxidation waves. Upon extraction
of the Zn2 with base (ethylenediamine) treatment, the two
oxidation waves lose definition and form a broad oxidation
wave. Meanwhile, the UV-vis spectrum displays a blue shift
of the interband absorption, indicating generation of metal-free
PolyRot(1). Immersion of PolyRot(1) in a saturated MeCN of
Metal-free PolyRot(2) is produced by ethylenediamine extrac-
tion of the metal ion from PolyRot(2,Cu) or PolyRot(2,Zn). The
green-blue films of PolyRot(2,Cu) and PolyRot(2,Zn) turn red
after ethylenediamine treatment, and electrochemistry displays
features similar to those of Poly(2) (Figures 7a and 8a),
suggesting the formation of metal-free PolyRot(2). The relative
conductivity of PolyRot(2) is higher than those of PolyRot(2,-
Zn) and PolyRot(2,Cu), indicating that the increased flexibility
in the metal-free structure allows for greater interchain interac-
tions. UV-vis spectroscopy of PolyRot(2) shows absorptions
from the macrocycle phenanthroline between 250 and 400 nm
after removal of the metal ions, thereby confirming that the
rotaxane structures persist. The green-blue color is restored after
dipping the metal-free PolyRot(2) into a saturated Cu(BF4)2/
CH3CN solution. As shown in Figures 7b and 8b, cyclic
voltammograms of the reconstituted PolyRot(2,Cu) are the same
as those for PolyRot(2,Cu) obtained from the polymerization
of Rot(2,Cu). Also apparent from Figures 7 and 8 is the fact
that the same material is formed regardless of which polyro-
taxane is the starting material, PolyRot(2,Zn) or PolyRot(2,-
Cu). The conductivity profiles shown in Figure 7 indicate some
+
2+
Zn solution again produces PolyRot(1,Zn) with two unre-
solved oxidation waves and a red shift of the polymer-based
UV-vis absorption (Figure 6). The partial recovery of the
oxidation peaks suggests that the PolyRot(1) is only partially
complexed with Zn2 ions. The weak binding effect probably
results from the flexibility of the macrocycles to rotate or slide
along the threading polymers after removal of the metal ions.
+
Immersion of PolyRot(1) into saturated Cu1 or Cu solutions
+
2+
(25) Thienpont, H.; Rikken, G. L. J. A.; Meijer, E. W.; Tenhoeve, W.;
Wynberg, H. Phys. ReV. Lett. 1990, 65, 2141.

Conducting Polymetallorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12575
Figure 7. Column A: cyclic voltammogram (top) and relative
conductivity profile (bottom) of PolyRot(2) formed by treatment of
PolyRot(2,Zn) with ethylenediamine. Column B: cyclic voltammo-
grams (top) and relative conductivity profiles (bottom) of PolyRot(2)
after dipping in Cu(BF ) /CH CN solution to generate PolyRot(2,Cu):
4 2 3
the first scan (solid line); the third scan (dotted-dashed line).
Figure 9. Cyclic voltammogram (top) and relative conductivity profile
(
bottom) of Poly(2) on an interdigitated microelectrode after treatment
2
+
with base (ethylenediamine) and followed by complexation with Cu
ions on interdigitated microelectrodes.
films of Poly(2) turned blue after dipping into Cu2 solution.
Although the cyclic voltammogram and conductivity profiles
are similar to those of PolyRot(2,Cu) (Figure 9), close inspection
reveals that the second oxidation wave is 120 mV more positive
+
2+
than that of PolyRot(2,Cu). Treating Poly(2) with Zn ions
2
+
revealed that neutral Poly(2) also binds Zn to produce a
positive shift of the cyclic voltammograms to the potentials near
which the protonated Poly(2) was oxidized. These results imply
that 2 is a stronger chelating ligand than 1. However, the
2
+
difference between the electrochemistry of Cu -treated Poly-
2) and PolyRot(2,Cu) indicates that the binding mode is
(
different in Poly(2,Cu). Considering that nitrogen, sulfur, and
oxygen are all good donors, a variety of binding modes can
2+
exist. One possibility is interchain coordination of Cu ;
however, it will be difficult to elucidate the binding modes.
Figure 8. Column A: cyclic voltammogram (top) and relative
conductivity profile (bottom) of PolyRot(2,Cu) after treatment with
ethylenediamine to form PolyRot(2). Column B: cyclic voltammogram
As mentioned in the Introduction, the close match of the
1+/2+
oxidation potentials of the Cu
couple and Poly(2) or
PolyRot(2) enables the polyrotaxanes to be oxidatively doped
(top) and relative conductivity profile (bottom) of PolyRot(2) after
2+
with Cu binding. Since complexation and oxidation of the
dipping in Cu(BF /CH CN solution to generate PolyRot(2,Cu).
4
)
2
3
2
+
polyrotaxanes by Cu will transform the insulated polyrotax-
anes to conducting polymetallorotaxanes, the polymer’s resis-
tance should dramatically change. To detect these changes in
resistance, we used an electrometer to measure the resistance
of the undoped PolyRot(2,Zn) deposited on the interdigitated
electrodes. We also measured the resistance changes after
structural evolution since the conductivity of the third scan is
larger than that of the first scan. However, cyclic voltammetry
displays identical behavior over several cycles. This last point
speaks to the high sensitivity of conductivity to minor differ-
ences in a material. Both the electronic and structural properties
2
+
2+
of PolyRot(2) contribute to its strong affinity for Cu ions.
removal of Zn ions to form PolyRot(2) and in doped PolyRot-
2+
2+
Recall that PolyRot(1) does not display a high affinity for Cu .
The electron-rich and bulky EDOT moiety enhances the
chelating ability of PolyRot(2) by increasing the basicity of the
bipyridine and by biasing the macrocycle to prefer bipyridyl
sites along the threading polymer. Thus, the EDOT-based
polyrotaxane likely maintains rigid preorganized coordination
sites and displays a qualitatively higher binding constant than
PolyRot(1). We also investigated the interaction of PolyRot-
(2,Cu) formed by treatment with Cu ions. The polymer films
were taken out of the electrolyte solutions and dried under
vacuum for 10 min before resistance measurements were
performed.
1
2
The blank interdigitated microelectrodes exhibited 1 × 10
Ω resistance, and when the electrodes were coated with undoped
9
PolyRot(2,Zn) films, the resistance dropped to 7.0 × 10 Ω.
2
+
Removal of the Zn ions to give PolyRot(2) increased the
2
+
10
(
2) in a saturated Zn /MeCN solution. As expected, treating
resistance slightly to 4.0 × 10 Ω. More significantly,
2+
4
the PolyRot(2) with Zn ions shifts the cyclic voltammogram
such that it coincides with that of as-synthesized PolyRot(2,-
Zn), which indicates the reconstruction of PolyRot(2,Zn). This
however, the resistance dropped dramatically to 3.2 × 10 Ω
2
+
after treating PolyRot(2) with Cu solution. Cyclic voltam-
metry and conductivity measurements confirm the formation
2+
2+
result is consistent with PolyRot(1), which reversibly binds Zn
of PolyRot(2,Cu). Thus, Cu complexation to PolyRot(2)
6
ions in MeCN solution.
produces a >10 -fold increase in conductivity. This result
For comparison, we conducted the same Cu2 and Zn2+
treatment with neutral Poly(2), which has no macrocyclic
component. In contrast to what we observed for Poly(1), the
+
suggests that the PolyRot(2) backbone is oxidized by Cu ions
2+
to generate PolyRot(2,Cu) with charge carriers in the polymer
backbone. In a control experiment, we have shown PolyRot-

12576 J. Am. Chem. Soc., Vol. 119, No. 51, 1997
Zhu and Swager
(
2) shows less than a 10-fold change in resistance after treatment
the CH
2
Cl
2
electrolyte solution, the potentials of all cyclic voltammo-
1+
2+
grams obtained were checked for accuracy by adding ferrocene as the
reference compound in the same electrolyte medium used for the
electrochemical studies. The electrochemical potentials were corrected
with Cu or Zn ions. In a similar resistance experiment,
PolyRot(1), which has higher oxidation potential than PolyRot-
2
(2), only produces a 10 -fold resistance decrease when interact-
0
such that the E ′ of ferrocene is 0.40 V in 0.1 M (n-Bu)
4
NPF
6
/CH
2
Cl
2
2
+
ing with Cu .
vs Ag wire. The saturated Zn2 ion solution was made from Zn(ClO
+
4
)
2
Similar resistance measurements were carried out on mac-
rocycle-free Poly(2) and Poly(1). The same electrode coated
with a protonated film of Poly(2) displayed a resistance of 2.3
2+
dissolving in MeCN solvent, the saturated Cu solution was made
1+
from Cu(BF
ion solution is made from Cu(CH
-(Tributylstannyl)-2,2-bithiophene. A 1.0 g (6 mmol) sample of
)
4 2
dissolving in MeCN solvent, and the saturated Cu
3
CN) BF and MeCN.
4
4
6
×
10 Ω. Removal of the protons increased the resistance to
5
1
0
2+
2
.6 × 10 Ω. Treatment with Cu results in a resistance as
2,2′-bithiophene in 30 mL of THF was treated dropwise with 3.54 mL
(6 mmol) of 1.70 M n-butyllithium and stirred for 0.5 h at -78 °C
under N atmosphere. A 1.96 mL portion of tributylstannyl chloride
2
(7.2 mmol) was then added to the solution. After the solution was
stirred at room temperature for 6 h, the solvent was evaporated and
the residue was dissolved in 20 mL of hexane and filtered. The filtrate
was evaporated to produce 3.4 g of crude 5-(tributylstannyl)-2,2′-
3
7
small as 1.0 × 10 Ω (a drop of >10 ), which again suggests
that Cu2 is not only functioning as a Lewis acid but also doping
+
2
Poly(2). However, Poly(1) only generates a 10 -fold decrease
in resistance when interacting with Cu2+ ions. This further
2
+
demonstrates that the doping of the polymer by Cu is the
major contribution to the conductivity increase in Poly(2).
1
bithiophene as a light yellow liquid for the next reaction. H NMR
(
250 MHz, CDCl
3
): δ (ppm) 7.27 (d, 1H), 7.15 (2d, 2H), 7.03 (d,
Conclusions
1
9
1
H), 6.98 (t, 1H), 1.54 (m, 6H), 1.31 (m, 6H), 1.10 (t, 6H), 0.89 (m,
13
H). C NMR (125 MHz, CDCl ): δ (ppm) 136.28, 127.98, 127.94,
3
We have described the syntheses, UV-vis spectroscopy,
25.19, 124.56, 124.17, 123.97, 123.66, 29.10, 27.50, 13.91, 11.11.
electrochemistry, and conducting properties of conducting
+
polymetallorotaxanes containing Zn2 and Cu and their
+
1+
MS (FAB): (M ) found 456, calcd for C20
H
32
S
2
Sn 455.28.
5
,5′-Bis([2,2′-bithiophen]-5-yl)-2,2′-bipyridine (1). A 0.3 g (1.1
corresponding metal-free polyrotaxanes. In all the polymetal-
lorotaxanes, we observe two discrete redox processes which are
mmol) sample of 5-(tributylstannyl)-2,2′-bithiophene, 0.1 g (0.3 mmol)
of 5,5′-dibromo-2,2′-bipyridine, and 0.014 g (5%) of trans-dichlorobis-
(
DMF and heated at 80-90 °C overnight under argon. After removal
of the DMF under vacuum, the resulting solid was chromatographed
(silica gel, CH Cl ) to give a yellow compound in 60% yield. For
associated with two conductivity maxima. For PolyRot(1,Cu),
triphenylphosphine)palladium (II) catalyst were mixed in 40 mL of
the Cu1
+/2+
redox couple produces no measurable conductivity.
1
+/2+
However, in the redox matched PolyRot(2,Cu), the Cu
redox couple gives greatly enhanced conductivity. The Cu
2
+
2
2
1
treatment of metal-free PolyRot(2) readily regenerates PolyRot-
large-scale reactions, recrystallization is suggested. H NMR (250
MHz, CDCl ): δ (ppm) 8.92 (d, 2H), 8.42 (d, 2H), 7.98 (dd, 2H), 7.35
d, 2H), 7.19 (m, 4H), 7.04 (t, 4H). The extremely poor solubility of
2,Cu), which also exhibits a Cu1
+/2+
-mediated conductivity
(
3
(
enhancement.
13
this compound prevented characterization by C NMR. MS (FAB):
The spectroelectrochemistry displays trends which are dif-
ferent from those of typical conducting polymers. An important
deviation from other systems is that the polymers investigated
show a low conductivity in their highest oxidation level but at
the same time display absorption features which resemble free-
carrier states.
By measuring the resistance changes of the metal-free
PolyRot(2) and Poly(2) before and after Cu treatment, we
demonstrated that Cu binds and dopes these polymers to
produce a 10 - to 10 -fold increase in the polymer’s conductiv-
ity. The observation of such large metal-mediated conductivity
enhancements suggests a new approach to sensory schemes for
the detection of a variety of transition metal ions.
+
(M ) found 485.0268, calcd 485.0274. Anal. Calcd for C26
H N S
16 2 4
:
C, 64.46; H, 3.33; N, 5.79. Found: C, 63.88; H, 3.43; N 5.49. Mp
under argon): 259 °C, (dec).
-(Tributylstannyl)-3,4-(ethylenedioxy)thiophene. A 2.0 g (14
(
2
mmol) sample of 3,4-(ethylenedioxy)thiophene in 150 mL of dry THF
was treated dropwise with 10 mL (16.2 mmol) of 1.6 M n-butyllithium
at -78 °C under argon. After the solution was stirred for 0.5 h and
warmed to -40 °C, 5.95 g (18.8 mmol) of tributylstannyl chloride was
added to the solution, and the new solution was warmed to room
temperature. The solvent was removed by rotary evaporation after the
solution was stirred for 8 h. The residue was dissolved in hexanes
and filtered. The filtrate was dried in vacuum to afford 6.0 g of
2+
2+
6
7
2
-(tributylstannyl)-3,4-(ethylenedioxy)thiophene as a yellow liquid. The
compound was used for the next reaction as obtained, with no further
purifications. 1H NMR (250 MHz, CDCl
) δ (ppm) 6.56 (s, 1H); 4.16
3
Experimental Section
(s, 4H); 1.61-1.49 (m, 6H); 1.39-1.22 (m, 6H); 1.09 (t, 9H); 0.90 (q,
13
6
1
4
H). C NMR (125 MHz, CDCl
3
): δ (ppm) 147.88, 142.65, 109.08,
General Procedures. Air- and moisture-sensitive reactions were
carried out in oven-dried glassware using standard Schlenk techniques
under an inert atmosphere of dry argon. Dry DMF was used from
+
05.99, 64.86, 64.80, 29.08, 27.40, 13.79, 10.71. MS: (M + H) found
31, calcd for C18
32 2
H O SSn 430.11
Aldrich Kilo-lab metal cylinders or sure-seal bottles. Anhydrous CH
2
-
5,5′-Bis(3,4-(ethylenedioxy)thien-2-yl)-2,2′-bipyridine (3). A 0.1
Cl and CH CN used for electrochemistry studies were obtained from
2
3
g (0.16 mmol) sample of 5,5′-dibromo-2,2′-bipyridine, 0.4 g (0.5 mmol)
of 2-(tributylstannyl)-3,4-(ethylenedioxy)thiophene, and 0.022 g (5%)
of trans-dichlorobis(triphenylphosphine)palladium(II) catalyst were
mixed in 50 mL of dry DMF and heated to 110°C for 6 h under argon.
After removal of the DMF under vacuum, the residue was purified by
Aldrich as sure-seal bottles. 3,4-(Ethylenedioxy)thiophene (EDOT) was
obtained from Bayer, and other reagents were used as received from
Aldrich unless otherwise noted. NMR spectra were recorded with a
1
1
13
Bruker AC-250 ( H) or Varian 500 MHz ( H and C) spectrometer.
UV-vis absorption spectroscopy was performed on a Hewlett-Packard
column chromatography (2% MeOH/CH
yellow solid. Yield: 95%. 1H NMR (250 MHz, DMSO-d
8.96 (s, 2H); 8.39 (d, 2H, J ) 10 Hz); 8.14 (d, 2H, J ) 7.5 Hz); 6.79
2
Cl
2
) to generate 0.14 g of a
8
453 diode array spectrophotometer. Resistances of dried films were
6
): δ (ppm)
measured on an interdigitated electrode using a Keithley Instruments
solid state electrometer, model 610CR. Electrochemical measurements
were performed in an air-free drybox under reduced lab lighting using
a computer-controlled Autolab Model PGSTAT 20 potentiostat from
Eco Chemie. All electrochemical measurements shown were performed
on interdigitated array microelectrodes purchased from AAI-ABTECH
and having an interelectrode spacing of 5 µm. The electrolyte solutions
used for all electrochemistry and conductivity measurements were 0.1
13
6
(s, 2H); 4.39 (s, 4H), 4.29 (s, 4H). C NMR (125 MHz, DMSO-d ):
δ (ppm) 162.26, 155.35, 152.10, 149.79, 143.0, 142.86, 138.93, 130.12,
109.72, 74.82, 73.94. MP (under argon): 228-229 °C. MS (FAB):
+
(M + H) found 437.063, calcd for C22
16 2 4 2
H N O S 436.055.
5,5′-Bis(5-bromo-3,4-(ethylenedioxy)thien-2-yl)-2,2′-bipyridine. A
70 mg (0.16 mmol) sample of 5,5′-bis(3,4-(ethylenedioxy)thienyl)-2,2′-
bipyridine was suspended in 10 mL of DMF and stirred for 10 min
under reduced-lighting conditions. To the solution was added 57 mg
(0.32 mmol) of NBS. Stirring overnight at room temperature resulted
in the precipitation of a yellow solid from the solution, which was
M (n-Bu)
4 6 2 2
NPF in CH Cl , and all electrochemical potentials are
reported relative to an isolated silver wire quasi-reference electrode.
Because of the instability of the Ag wire quasi-reference electrode in

Conducting Polymetallorotaxanes
J. Am. Chem. Soc., Vol. 119, No. 51, 1997 12577
collected by filtering and washing with a small amount of acetone.
(500 MHz, acetone-d
6
): δ (ppm) 9.25 (d, 2H), 8.63 (s, 2H); 8.55 (m,
Drying the yellow solid under vacuum provided 70 mg of 5,5′-bis(5-
8H); 7.67 (d, 2H); 6.78 (s, 2H); 6.61 (d, 4H); 4.35 (m, 8H); 3.85 (m,
20H). C (125 MHz, acetone-d ): δ (ppm) 161.61, 160.65, 146.89,
6
146.88, 145.58, 143.72, 143.00, 142.65, 138.16, 133.57, 132.59, 130.56,
129.50, 128.10, 126.38, 123.64, 116.20, 111.81, 103.02, 71.69, 71.52,
70.04, 69.23, 66.24, 65.35, 62.99. Mp (under argon): 175 °C dec.
1
13
bromo-3,4-(ethylenedioxy)thienyl)-2,2′-bipyridine. Yield: 74%.
NMR (250 MHz, DMSO-d
H
6
): δ (ppm) 8.92 (s, 2H); 8.39 (d, 2H, J )
1
0 Hz); 8.13 (d, 2H, J ) 7.5 Hz); 4.41 (m, 8H). The poor solubility
13
of this compound precluded obtaining a C NMR on this compound.
+
MS (FAB): (M ) found 595, calcd for C34
H
24
N
2
O
8
S
4
594.29. Mp
4 2
Rot(2,Zn)(ClO ) . To a 50 mL air-free Schlenk flask containing
(
under argon): 260 °C dec.
,5′-Bis(3,4:3′,4′-bis(ethylenedioxy)[2,2′-bithiophen]-5-yl)-2,2′-bi-
pyridine (2). A 35 mg (0.06 mmol) sample of 5,5′-bis(5-bromo-3,4-
ethylenedioxy)thienyl)-2,2′-bipyridine, 100 mg (0.24 mmol) of 2-(tri-
2
0 mg (0.027 mmol) of 2 and 15.8 mg (0.027 mmol) of the macrocycle
5
16
phenanthroline was added 25 mL of dry deoxygenated CH
orange-yellow solution was stirred for 10 min under argon, and then
0.4 mg (0.027 mmol) of Zn(ClO in 2 mL of deoxygenated CH CN
2 2
Cl . The
(
1
4
)
2
3
butylstannyl)-3,4-(ethylenedioxy)thiophene, and 7 mg (10%) of tetra-
kis(triphenylphosphine)palladium(0) were refluxed in 30 mL of dry
DMF for 6 h under argon. The solvent was removed under vacuum.
The resulting red solid was dissolved in CH
Cl and filtered under argon.
2 2
The filtrate’s volume was reduced to approximately 5 mL, and the
brown-yellow product precipitated upon the addition of hexanes to the
solution was added. The solution turned red immediately, and after
the mixture was stirred at room temperature for 10 h, the solvent was
removed under vacuum. The crude product was dissolved in 5 mL of
acetone under argon and filtered. The red product was precipitated
from the filtrate with addition of ether and cooling to 0 °C under argon.
A red solid was collected and dried to produce 20 mg of Rot(2,Zn).
2
CH Cl
2
solution. The compound was collected and dried to afford 23
1
This compound was stored in a refrigerator under argon. H NMR
mg of 5,5′-bis(3,4:3′,3′-(ethylenedioxy)[2,2′-bithiophen]-5-yl)-2,2′-bi-
6
(500 MHz, acetone-d ): δ (ppm) 9.26 (d, 2H, J ) 8.5 Hz); 8.63 (s,
1
pyridine (2) as a brown-yellow solid. Yield: 54%. H NMR (250
2
6
H); 8.52 (m, 8H); 7.68 (d, 4H J ) 8.5 Hz); 6.64 (d, 4H, J ) 8.5 Hz);
MHz, DMSO-d
6
): δ (ppm) 8.98 (s, 2H); 8.39 (d, 2H); 8.13 (d, 2H);
13
.58 (s, 2H); 4.44-4.30 (m, 16H); 3.96-3.74 (b, 20H). C (125 Mhz,
): δ (ppm) 164.02, 161.68, 156.53, 146.73, 145.00, 142.97,
42.57, 141.50, 141.00, 138.38, 137.29, 132.60, 130.60, 128.13, 126.44,
6
.66 (s, 2H); 4.45-4.27 (b, 16H). The poor solubility of this compound
acetone-d
6
13
+
prevented characterization by C NMR. MS (FAB): (M + H ) found
17.0494, calcd for C34 716.0417. Mp (under argon): >260
C.
Rot(1,Zn)(ClO
the macrocyclic phenanthroline and 0.042 g of 1 was added to 0.033
g of Zn(ClO ‚xH O in 3 mL of CH CN, and the mixture was stirred
1
1
7
7
°
24 2 8 4
H N O S
23.40, 116.68, 116.24, 116.22, 111.00, 109.78, 102.79, 100.609, 71.57,
1.55, 70.02, 70.00, 69.20, 66.39, 66.37, 66.25, 65.54. Mp (under
4 2 2 2
) . A 25 mL CH Cl solution containing 0.05 g of
argon): 175 °C dec.
1
6
Rot(2,Cu)(BF ). To make Rot(2,Cu), we used a method similar to
4
4
)
2
2
3
that reported for Rot(2,Zn). The compound is brick red in color and
was stored in a refrigerator under argon. 1H NMR (300 MHz, acetone-
for 2 h at room temperature. After filtering, the solvent was removed,
and the residue was dissolved in 20 mL of acetone and filtered. Diethyl
d ): δ (ppm) 9.25 (d, 2H, J ) 9 Hz); 8.67 (s, 2H); 8.51(m, 8H), 7.69
6
ether was added to the red-orange filtrate to precipitate a red-orange
(
(
d, 4H, J ) 9 Hz), 6.65 (d, 4H, J ) 8.1 Hz); 6.58 (s, 2H); 4.30-4.26
m, 16H), 3.73 (m, 20H). Mp (under argon): 170 °C dec. The poor
1
solid at 0 °C. Yield: 71%. H NMR (500 MHz, acetone-d
6
): δ (ppm)
9
.23 (d, 2H, J ) 8.5 Hz); 8.70 (s, 4H); 8.61 (s, 2H); 8.53 (s, 2H); 8.49
1
3
solubility of this compound prevented characterization by C NMR.
(
2
4
d, 2H, J ) 8.5 Hz); 7.685 (d, 4H, J ) 2 Hz); 7.66 (m, 2H); 7.55 (dd,
H, J ) 4.5 Hz, J ) 1); 7.40 (d, 4H, J ) 4 Hz); 7.15 (m, 2H); 6.63 (d,
H, J ) 8.5 Hz); 3.94 (t, 4H, J ) 4.5 Hz); 3.88 (m, 8H); 3.79 (t, 4H,
3
,4-(Ethylenedioxy)-2,2′-bithiophene. A 2.0 g (14 mmol) sample
of EDOT and 1.63 g (28 mmol) of TMEDA were dissolved in 50 mL
1
3
of dry THF, and the solution was cooled to -10 °C under argon. A
J ) 4 Hz); 3.75 (t, 4H, J ) 4 Hz). C NMR (125 MHz, CDCl
3
): δ
8
.8 mL portion of 1.6 M n-BuLi was slowly added to the solution.
(ppm) 160.05, 159.0, 145.5, 145.0, 141.8, 141.25, 141.24, 140.0, 137.5,
After being stirred for 30 min, this reaction mixture was transferred to
0 mL of refluxing THF containing 4.97 g (14 mmol) of Fe(acac)
under argon. The THF was removed after refluxing for 6 h. The
resulting red solid was dissolved in CHCl , and quickly passed through
a short bed of silica gel using CHCl as eluent. The filtrate was dried
1
1
36.47, 135.5, 132.01, 129.34, 128.66, 128.11, 127.02, 125.79, 125.58,
24.92, 124.79, 122.57, 115.04, 115.0, 70.87, 70.71, 70.5, 69.34, 68.41.
5
3
Anal. Calcd for C60
Found: C, 54.43; H, 4.17; N, 3.49. Mp (under argon): >260 °C.
Rot(1,Cu)(BF ). This compound was synthesized by the same
method as Rot(1,Zn)(ClO
NMR (250 MHz, acetone-d
50 4 2 4
H N O14Cl S Zn: C, 54.87; H, 3.84; N, 4.27.
3
3
4
1
and washed with ether. The resulted yellow solid was filtered and dried
4
)
2
in 70% yield as a green-black solid.
): δ (ppm) 9.37 (d, 2H); 8.89-8.78 (m,
0H); 8.11 (d, 4H); 8.00 (d, 2H); 7.93 (d, 2H); 7.79 (d, 4H); 7.57 (t,
H
1
under vacuum to afford 0.99 g of product. Yield: 99%. H NMR
6
(
250 MHz, CD
2
Cl
2
): δ (ppm) 6.25 (s, 2H), 4.31 (m, 8H); 4.21 (m,
1
2
13
1
3
8H). C (125 MHz, acetone-d ): δ (ppm) 141.23, 137.03, 109.90,
H), 6.83 (d, 4H); 4.27 (m, 20H). C NMR (125 MHz, acetone-d
6
):
6
9
7.53, 64.99, 64.59. GC/MS: found 282, calcd for C12
H O S
10 4 2
282.00.
δ (ppm): 160.64, 158.83, 150.44, 145.89, 144.83, 143.18, 138.63,
1
1
7
37.36, 134.56, 132.32, 130.45, 129.28, 127.95, 127.39, 126.68, 126.06,
25.58, 125.56, 123.70, 117.0, 116.90, 114.79, 114.77, 71.75, 71.63,
1.55, 70.28, 69.12. Anal. Calcd for C60H N O S BF Cu: C, 59.99;
50 4 6 4 4
Acknowledgment. Funding from the Office of Naval
Research is greatly appreciated. S.S.Z. is grateful for a Dis-
sertation Fellowship from the School of Arts and Sciences,
University of Pennsylvania.
H, 4.20; N, 4.67. Found: 59.92; H, 4.41; N, 4.14. Mp (under argon):
1
63 °C dec.
Rot(3,Zn)(ClO
4
)
2
. This compound was synthesized by the same
in 60% yield as a yellow solid. 1H NMR
method as Rot(1,Zn)(ClO
4
)
2
JA972794W