Anion sensing by solution- and surface-assembled osmium(II) bipyridyl rotaxanes

Article abstract of DOI:10.1002/chem.201302886

We report the preparation of [2]rotaxanes containing an electrochemically and optically active osmium(II) bipyridyl macrocyclic component mechanically bonded with cationic pyridinium axles. Such interlocked host systems are demonstrated to recognise and sense anionic guest species as shown by ¹HNMR, luminescence and electrochemical studies. The rotaxanes can be surface assembled on to gold electrodes through anion templation under click copper(I)-catalysed Huisgen cycloaddition conditions to form rotaxane molecular films, which, after template removal, respond electrochemically and selectively to chloride. Copyright

Full text of DOI:10.1002/chem.201302886

DOI: 10.1002/chem.201302886
Anion Sensing by Solution- and Surface-Assembled Osmium(II) Bipyridyl
Rotaxanes
Joshua Lehr, Thomas Lang, Octavia A. Blackburn, Timothy A. Barendt,
Stephen Faulkner, Jason J. Davis,* and Paul D. Beer*[a]
Abstract: We report the preparation of
[2]rotaxanes containing an electro-
chemically and optically active os-
shown by 1H NMR, luminescence and
electrochemical studies. The rotaxanes
can be surface assembled on to gold
electrodes through anion templation
under click copper(I)-catalysed Huis-
gen cycloaddition conditions to form
rotaxane molecular films, which, after
template removal, respond electro-
chemically and selectively to chloride.
ACHTUNGTRENNUNGmium(II) bipyridyl macrocyclic compo-
nent mechanically bonded with cationic
pyridinium axles. Such interlocked host
systems are demonstrated to recognise
and sense anionic guest species as
Keywords: anion sensing · osmium ·
rotaxanes · self-assembly · surface
immobilization
Introduction
interlocked hosts with the capability of sensing anions by
electrochemical[5] or optical[3b,4,6] methods are rare.
Stimulated by the promise of mechanically interlocked mo-
lecular architectures with potential employment in future
nanotechnological applications such as in the development
of molecular machines and switches, the interest being
shown in their construction is ever increasing.[1] Rotaxane
and catenane species can also, however, be designed to func-
tion as selective host systems whereby the topologically
unique interlocked three-dimensional cavities are exploited
to selectively recognise specific guest species.[2] In previous
work, we have utilised anion templation to construct
a range of [2]rotaxanes and [2]catenanes, which, upon re-
moval of the template, bind anions strongly and selectively
in competitive solvent mixtures.[3] Furthermore, selective
anion binding can be exploited to bring about triggered
motion within the interlocked supramolecular architectures,
underlining the possible application of these systems in the
preparation of molecular switches.[4] To sense and monitor
anion binding (and/or binding-triggered motion), it is desira-
ble to integrate a redox- or photoactive reporter group in
proximity to the interlocked anion-binding site. Examples of
Herein, we report the preparation of the first anion-tem-
plated [2]rotaxane incorporating an optically- and electro-
active osmium(II) tris(bipyridine) reporter group. After re-
moval of the anion template, selective anion binding is in-
vestigated by monitoring the optical and electronic output
from the osmium(II) tris(bipyridine) reporter moiety. To de-
velop and fabricate a prototype molecular sensory system, it
is highly desirable to effectively immobilise the interlocked
host on a substrate. Surface association removes complica-
tions associated with Brownian motion, typically increases
conformational rigidity, and will underpin potential applica-
tions of such molecular architectures and, ultimately, device
integration.[1b] To date, only a limited number of surface-
bound interlocked structures have been reported.[5b,c,7]
Hence, we additionally report the anion-templated assembly
of these electrochemically active osmium(II) bipyridyl rotax-
ane structures on gold substrates and, after template remov-
al, the specific reporting of anion recruitment from solution
(Figure 1).
Results and Discussion
[a] Dr. J. Lehr, Dr. T. Lang, Dr. O. A. Blackburn, T. A. Barendt,
Prof. S. Faulkner, Dr. J. J. Davis, Prof. P. D. Beer
Department of Chemistry, University of Oxford
South Parks Road, Oxford, OX1 3QZ (UK)
E-mail: jason.davis@chem.ox.ac.uk
Design of the system: The target design for the mechanically
bonded host features the incorporation of the osmium(II)
tris(bipyridine) reporter group into the macrocyclic compo-
nent of a rotaxane molecular framework containing a conver-
gent hydrogen-bond-donor anion-binding interlocked cavity.
paul.beer@chem.ox.ac.uk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201302886.
The macrocycle contains the 4,4’-bisACTHNUTRGNEUNG(amide)-2,2’-bipyridyl
motif for coordination to the osmium(II) metal centre and
electron-rich hydroquinone units to facilitate supplementary
secondary aromatic donor–acceptor interactions with the
electron-deficient positively charged pyridinium axle.[3a] The
choice of the osmium(II) bipyridyl reporter group comes
ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited.
15898
ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2013, 19, 15898 – 15906

FULL PAPER
reaction between the acyl chloride derivative of 10 and
4’-(azidomethyl)biphenyl-4-yl-methanamine, followed by
methylation and anion exchange, produced axle precursor
14 (Scheme 2).
Rotaxanes 2 and 3 were obtained in 16 and 72% yield, re-
spectively, by “mono stoppering” reactions followed by
washing with NH4PF6/H2O to remove the chloride template
(see the Supporting Information, Scheme S1). Axle precur-
sors 13 and 14 were added to macrocycle 4 leading to chlo-
ride-anion-templated pseudo-rotaxane assembly. Subsequent
copper(I)-catalysed azide–alkyne cycloaddition (CuAAC)
reactions in dry dichloromethane using alkyne stopper 15,
copper(I) tetrakis(acetonitrile) hexafluorophosphate, tris(-
benzyltriazolylmethyl)amine (TBTA) and diisopropylethyla-
mine afforded the desired rotaxanes 2 and 3. Rotaxanes 1–3
were characterised by NMR spectroscopy (1H, 13C, 19F and
31P) and by mass spectrometry (MALDI-TOF). 1H NMR
spectra of rotaxanes 1–3 (Figure 2) reveal splitting and an
upfield shift of hydroquinone protons of the macrocycle
component, owing to aromatic donor–acceptor interactions
between the electron-rich hydroquinone groups and the
electron-deficient pyridinium moiety of the axle, characteris-
tic of an interlocked structure.
Figure 1. Schematic representation of the recognition and sensing of
anions for a surface-bound rotaxane. Axle in blue, macrocycle in green,
with anion binding functionalities shown in red.
from its established electro- and photochemical properties,
making the system an attractive probe to sense the anion-
binding event.
Synthesis of the [2]rotaxanes: Three distinct osmium(II) bi-
pyridyl (bipy) [2]rotaxanes, 1–3, were prepared by clipping
and stoppering anion-templated synthetic methodologies,
comprising the same macrocycle component and different
axle lengths (Scheme 1).
Rotaxane 1 was obtained in two steps by a chloride-
anion-templated “clipping” reaction between axle[3a] compo-
nents bisACHTUNGTRENNUNG(amine) 8 and 4,4’-bis(chlorocarbonyl)-2,2’-bipyri-
dine 9 in the presence of Et3N in dry dichloromethane
(Scheme 2 and Scheme S1 in the Supporting information).
The crude metal-free rotaxane intermediate was then treat-
ed with [OsACHTUNGTRENNUNG(bipy)2Cl2], 16, in an EtOH/H2O mixture at
reflux to give, after anion exchange using 0.1m aqueous
NH4PF6, rotaxane 1 in 6% overall yield. Macrocycle 19 was
synthesised in 37% yield by condensation of the bisACTHNUGTRNEUNG(amine)
8 with bis(acid chloride) 9 in the presence of Et3N and tem-
plate 17 in dry dichloromethane. Reaction of macrocycle 19
with 16 in an EtOH/H2O mixture at reflux afforded, after
anion exchange, macrocycle 4 in 74% yield. The reaction of
carboxy–terphenyl amide pyridine derivative 10[3f] with
oxalyl chloride produced the corresponding acid chloride,
which upon condensation with 3-bromopropylamine hydro-
bromide in the presence of Et3N in dry dichloromethane
Figure 2. 1H NMR spectra (500 MHz, [D6]acetone/D2O (7:3), 293 K) of
[2]rotaxanes 1 (a), 2 (c), 3 (e) and their chloride complexes 1Cl (b), 2Cl
(d), and 3Cl (f) after addition of one equivalent of chloride.
Anion-binding studies in solution: Anion binding was
probed by using NMR, luminescence and electrochemical
methods in assorted solvents as dictated by various factors.
These techniques all have dramatically different limits of de-
tection and different requirements from the system. In the
case of NMR titration, initial assessments in acetonitrile re-
vealed strong association with anions, compounded by the
low solubility of the generated complexes, a fact that neces-
gave bisACHTUNGTRENNUNG(amide) 11. This was converted to its azide deriva-
tive 12 by reaction with sodium azide in dimethylformamide.
Reaction of compound 12 with methyl iodide at reflux, fol-
lowed by anion exchange using 0.1m aqueous NH4PF6, gave
the desired axle precursor 13. An analogous condensation
Chem. Eur. J. 2013, 19, 15898 – 15906 ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemeurj.org
15899

J. J. Davis, P. D. Beer et al.
and the use of relatively con-
centrated electrolytes dictated
the use of acetonitrile as a sol-
vent system.
The results of these studies
are discussed in detail below.
1H NMR investigations: Pre-
liminary 1H NMR anion titra-
tion experiments between ro-
taxanes 1, 2 and 3 and various
anions
(ClÀ,
AcOÀ
and
À
H2PO4 ) were performed in
competitive [D6]acetone/D2O
(7:3) solvent mixtures. The ad-
dition of one equivalent of tet-
rabutylammonium (TBA) chlo-
ride resulted in
a downfield
shift of inner protons g (0.13,
0.05 and 0.29 ppm) and c (0.10,
0.05 and 0.34 ppm) for rotax-
anes 1, 2 and 3, respectively, in-
dicative of halide binding
within the rotaxaneꢁs inter-
locked
binding
cavity
(Figure 2).
In addition, modest upfield
perturbations of the macrocy-
clic hydroquinone protons of
the respective rotaxane were
observed, g (À0.02, À0.02 and
À0.06 ppm) and
h
(À0.03,
À0.02 and À0.03 ppm) for 1, 2
and 3, respectively. When ox-
oanions such as acetate or dihy-
drogen phosphate where added,
only a small perturbation was
observed for inner protons g. In
the case of rotaxane 3, the g
protons move upfield, an indi-
cation of the oxoanion binding
Scheme 1. The rotaxanes, macrocycle and axles studied.
on the periphery of the rotax-
ane.[9] WinEQNMR2 analysis[10]
sitated the use of a more competitive aqueous solvent mix-
ture, [D6]acetone/D2O (7:3).
Luminescence spectroscopy, offering much lower detec-
tion limits, presents a quantum yield weighted average; as
a consequence, the response of the observed luminescence
to anion concentrations varies between solvents. This is par-
of the binding isotherms with chloride and acetate anions,
obtained by monitoring the chemical-shift perturbation of
proton g of the axle component of the respective rotaxane
versus equivalent of anion (Figure 3), determined 1:1 stoi-
chiometric association constants (Table 1). It proved impos-
sible to obtain quantitative binding data from any of the di-
hydrogen phosphate titration experiments, indicative of
a complex equilibrium binding process (chemical shifts ob-
served were too small, association constants <100mÀ1, to be
sensibly fitted within error).
ticularly true in the case of osmium trisACTHNUTRGNEUNG(bipy) complexes, in
which solvation of the excited state plays an important role
in determining the form of the spectrum.[8] Small quantities
of water were added to the acetonitrile mixtures; it was
found that the addition of 3% water produced optimal and
reproducible changes to the osmium emission spectrum.
In the case of electrochemistry, the need for a large po-
tential window to resolve bipy-ligand-based voltammetry
The results indicate selectivity towards ClÀ, with only
À
weak and peripheral association with AcOÀ and H2PO4 .
The oxoanions are too large to penetrate the interlocked
binding domain, whereas chloride anions are of complemen-
15900
www.chemeurj.org ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2013, 19, 15898 – 15906

Anion Sensing by Osmium(II) Bipyridyl Rotaxanes
FULL PAPER
Scheme 2. Synthetic precursors 8–19.
Table 1. Association constants [mÀ1] of [2]rotaxanes 1, 2 and 3 in 7:3 ace-
tone/D2O and macrocycle 4 in 9:1 acetone/D2O with Cl and AcO (as
TBA salts) at 293 K.[a]
ClÀ
AcOÀ
1
2
750
250
50[a]
–
[d]
3
1400
–
4[b]
210[c]
–
[d]
[a] Obtained by monitoring proton g. Error <15% (for all values).
[b] Determined by monitoring proton c. Error <10%. [c] In 9:1 acetone/
D2O. [d] Chemical shift changes were too small to be reliably fitted.
This may reflect the optimal degree of preorganisation of
the interlocked binding domain of the respective rotaxane
as determined by the nature of the axle component. The rel-
atively more preorganised binding sites of rotaxanes 1 and
3, as compared with the flexible propyl-linked axle compo-
nent present in 2, potentially enhances chloride binding.
Steric congestion could be responsible for 1 being a relative-
ly inferior halide-complexing reagent in comparison with 3.
The binding of chloride anions by macrocycle 4 was also
investigated (Table 1 and Figure 3b). As expected, the bind-
ing is very weak in 7:3 acetone/water, as shown by the small
downfield shift of protons c, 0.03 ppm after addition of one
equivalent of chloride. The 1H NMR titration experiment
was repeated in 9:1 acetone/water, a less competitive solvent
mixture, which enabled a 1:1 stoichiometric association con-
stant of 210mÀ1 to be determined. Analogous titrations with
acetate anions revealed only small perturbations of the mac-
rocycle proton, indicative of weak binding. These observa-
tions serve to highlight the rotaxanesꢁ potency for chloride
anion recognition as a consequence of their three-dimen-
sional binding cavities being capable of encapsulation of this
guest.
Figure 3. a) Chemical-shift perturbation of proton g upon addition of ClÀ
À
(^), AcOÀ (&) and H2PO4 (~) (as the TBA salt) to a solution of [2]
rotaxane 1 (unfilled), 2 (half-filled) and 3 (filled) in 7:3 [D6]acetone/D2O
at 293 K. b) Chemical-shift perturbation of proton c upon addition of ClÀ
(as the TBA salt) to a solution of macrocycle 4 in 7:3 [D6]acetone/D2O
^
(
) and in 9:1 [D6]acetone/D2O (^) at 293 K. Symbols represent experi-
mental data; continuous lines represent calculated curves.
tary size and shape leading to strong binding even in this
competitive 30% aqueous solvent mixture.
Comparing the strength of chloride anion binding for the
three rotaxanes, the interlocked host 3, containing a rigid bi-
phenyl axle linkage, exhibits significantly stronger binding.
Luminescence studies: The binding of anions was further in-
vestigated by using luminescence spectroscopy. Macrocycle
4 and the rotaxanes (1–3) all display two emission bands in
the near-IR region centred at approximately 800 and
Chem. Eur. J. 2013, 19, 15898 – 15906 ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemeurj.org
15901

J. J. Davis, P. D. Beer et al.
presented in Table 2. The data indicate that the binding of
chloride anions with the rotaxanes is two orders of magni-
tude greater than that with the macrocycle. The chloride
anion association constants obtained from luminescence
measurements for the three rotaxanes confirm the observa-
tions from NMR spectroscopy of strong binding of chloride
ions by rotaxane 3. It should be noted that the change in sol-
vent system will also be reflected in differences in binding
owing to different solvation of the host. In this relatively un-
competitive solvent system, it is likely that many anions will
associate with the cationic receptors; indeed, studies on di-
hydrogen phosphate and acetate bear out this hypothesis. It
is important to point out that it is likely such optical titra-
tions are notably less reflective of binding selectivity in that
they report anion association, be it cavity confined or pe-
ripheral.
Electrochemical investigations: Electrochemical studies
were initially carried out on macrocycle 4. Cyclic voltam-
metric scans (Figure 5) of an acetonitrile solution containing
Figure 4. a) Titration of rotaxane 1 with TBACl in 97:3 acetonitrile/water,
showing emission spectra uncorrected for detector sensitivity; (›) in-
creasing chloride anion concentration. b) Binding isotherms and fits from
the same titration following the two emission bands.
925 nm (Figure 4) following excitation into metal-to-ligand
charge transfer (MLCT) absorption bands at 430 nm, with
the lifetimes of the two bands determined to be 44 and 35 ns
at 800 and 950 nm, respectively.
These observations are consistent with those of Nozaki
and co-workers,[8] who assigned the presence of two bands
in the emission spectra of osmium bipyridyl complexes to
subtle variations in the osmium environment arising from
solvation-induced polarisation of the triplet state. Upon ti-
tration with TBACl in 97:3 acetonitrile/water, an increase in
emission intensity was observed for all four species, with the
increases being more pronounced for the higher-energy
bands. Given the conclusions of Nozaki regarding solvent-
induced distortions to the triplet-state structure, it is plausi-
ble that anion binding will also influence local structure to
differing degrees. Representative spectra are shown in
Figure 4 along with the corresponding binding isotherms
and fits. Association constants were obtained with the Dyna-
fit software using a 1:1 binding
Figure 5. Cyclic voltammetric scans of 0.2 mm of macrocycle 4 in 0.15m
TBAPF6/CH3CN; scan rate=0.1 VsÀ1. Insert: Electrochemical titrations
of 4 with TBACl monitoring bipy couples x, y and z.
macrocycle 4 revealed an electrochemical redox system at
0.605 V vs. Ag/Ag+, assigned to the reversible Os
ACHTUNGTRENNUNG(+2/+3)
redox couple.[12] In addition, the three bipyridyl-ligand-cen-
tred redox systems were observed at À1.375, À1.715 and
À1.975 V vs. Ag/Ag+ (labelled x, y, z, respectively) consis-
tent with previous reports of
a trisACHTUNGTNRUEGN(bipy) ruthenium
model (Table 2).[11]
Table 2. Association constants [mÀ1] determined by luminescence titration of macrocycle 4 and rotaxanes 1, 2
Acetate
and
dihydrogen
and 3 in 97:3 acetonitrile/water, with chloride, dihydrogen phosphate and acetate anions, as TBA salts.[a]
phosphate (as their TBA salts)
were also titrated with rotaxane
1 and the macrocycle 4 for
comparison, although with the
latter, phosphate anion binding
could not be determined owing
À
ClÀ
H2PO4
AcOÀ
1
2
3
4
2.0ꢂ105 [1.5–2.4ꢂ105]
2.1ꢂ105 [1.5–2.8ꢂ105]
3.0ꢂ105 [2.3–3.8ꢂ105]
3.1ꢂ103 [2.8–3.4ꢂ103]
3.5ꢂ105 [2.8–4.7ꢂ105]
4.9ꢂ104 [3.5–7.3ꢂ104]
[b]
[b]
–
–
–
–
[b]
[b]
[c]
–
2.4ꢂ103 [2.2–2.6ꢂ103]
[a] 99% confidence intervals given in square brackets. A 1:1 binding model was used in all cases. [b] No data
to precipitation. The results are was obtained owing to insufficient material. [c] Could not be determined owing to precipitation.
15902
www.chemeurj.org ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2013, 19, 15898 – 15906

Anion Sensing by Osmium(II) Bipyridyl Rotaxanes
FULL PAPER
moiety.[13] These assignments were confirmed by equivalent
cavity. Dynafit modelling analysis of a simultaneous fit of
integration of the charges associated with the Os
G
both the metal-centred OsACTHNGUTERNNU(G +2/+3) couple and the least-
redox system and the bipyridyl-ligand-centred redox events,
as expected as all are one-electron redox systems on the
same species. In accordance with our previous report,[13] the
least-cathodic bipy redox couple (x, Figure 5) is assigned to
the amide-substituted bipyridyl, located next to the anion-
binding site (in light of the electron-withdrawing nature of
the carbonyl amide moieties).
Titrations of macrocycle 4 with TBACl or TBAOAc were
carried out to determine the ability of ligand- and metal-
centre-based redox potentials to report on anion association.
As shown in Figure 6a, cathodic perturbations of approxi-
cathodic ligand-centred (x) potential perturbations as a func-
tion of anion concentration gave 1:1 stoichiometric associa-
tion constants of 2.5ꢂ103 [2.2–2.7ꢂ103] and 1.5ꢂ104 [1.1–
2.1ꢂ104] mÀ1, for chloride and acetate anions, respectively.
The larger association constant (and potential shifts) ob-
served after addition of TBAOAc, compared with TBACl,
can be attributed to the stronger association of AcOÀ to the
amide-based binding site than ClÀ, owing to the relative ba-
sicities of the anions.[13]
We assign the higher luminescence and electrochemically
defined association constants, in comparison to those ob-
tained by NMR spectroscopy, to the more competitive aque-
ous solvent system used for the latter, but we acknowledge
also that optical and redox transitions may not be exactly
equivalent in their response to specific anion association.
Indeed, optical transition energies are likely to be sensitive
to broad electrostatic/dielectric change in the vicinity of rel-
evant chromophore orbitals; redox signatures are more spe-
cifically sensitive to electron density at the bipyridyl and
osmium centres and, hence, may be more reflective of spe-
cific anion association. Resolved fundamental electrochemi-
cal characteristics of the rotaxane hosts are similar to those
of the macrocycle and are reported in the Supporting Infor-
mation (page 4). Unfortunately, a combination of sluggish
diffusion and strong physical-adsorption-based electrode
fouling precluded the attainment of reliable electrochemical
anion-binding data with the rotaxanes.
Surface immobilisation of the rotaxane: The CuI-catalysed
Huisgen cycloaddition of axles 13 and 14 to prepared
alkyne-terminated molecular films on gold (see the Experi-
mental Section) in the presence of templating chloride
anions and a 5-fold excess of macrocycle 4, generates sur-
face-confined rotaxane assemblies (Scheme 3). Accompany-
ing ellipsometry-defined increases in film thickness ((1.3Æ
0.1) nm) are consistent with axle-to-surface orientations
being normal or close to normal. Control surface analyses,
in the absence of CuI catalyst, confirm this surface assembly
to be specifically click-chemistry driven. The associated tem-
plate locking of the osmium bipy macrocycle at the surface
by this process is confirmed by resolved osmium-based (+2/
+3) electrochemical signatures (Figure 7). An integration of
these signals resolves surface macrocycle concentrations of
1.05 and 2.5ꢂ10À11 molcmÀ2 for axles 13 and 14, respective-
ly, corresponding to 20 and 45% of a densely packed mono-
layer, based on a macrocycle footprint of 3.0 nm2. Control
experiments confirm that the macrocycle–surface association
is both stable to ultrasonic washing and only observed with
the chloride anion template specifically involved (important-
ly, no macrocycle-osmium-based (+2/+3) electrochemical
response is observed if the PF6 salts of 13 or 14 are used).
Figure 6. Redox transduction of cavity occupancy of compound 4. E1/2 of
a) OsACHTUNGTRENNUNG(+2/+3) and b) bipy couple versus equivalents of TBACl (*) and
TBAAcO (*) added.
mately 20 mV and 40 mV of the metal-centred osmium-
based (+2/+3) couple are observed upon the addition of
~5 molar equivalents of TBACl and TBAOAc, respective-
ly.[13] The bipy-ligand-centred responses scale in accordance
with their vicinity to the anion-association site, with x show-
ing the strongest perturbations and z the weakest, in the
presence of 5-fold excess of ClÀ and AcOÀ (see insert
Figure 5, Schemes S2 and S3 in the Supporting Information).
These observations are fully consistent with both anionic
The linear scaling of OsACTHNUTRGNEU(GN +2/+3) redox peak current with
voltage scan rate is further confirmatory of surface entrap-
ment. The surface-density differences between axle-only and
rotaxane films are, additionally, resolvable through both
species being bound in the vicinity of the bisACHTNUTRGNE(NUG amide) bipy
Chem. Eur. J. 2013, 19, 15898 – 15906 ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemeurj.org
15903

J. J. Davis, P. D. Beer et al.
systems but, to the best of our
knowledge, are also the first in-
corporating a redox-active os-
mium(II) bipy reporter motif.
We have also investigated the
possibility that surface-present-
ed vacant interlocked cavities
(generated by using axle 14)
can provide a means of selec-
tively recruiting and electro-
chemically sensing chloride
anions. The chloride anion tem-
plate was initially removed by
washing with copious amounts
of 0.1m NH4PF6/H2O. Pleasing-
ly, subsequent halide anion re-
cruitment is both detectable
and selective, exhibiting no
cathodic perturbation upon im-
mersion in a 50 mm solution of
Scheme 3. Rotaxane immobilisation onto alkyne-modified gold by copper(I)-catalysed Huisgen cycloaddition.
acetate anions (the observed 2 mV shift is less than the
3 mV error of the reference electrode), but a 14 mV catho-
dic shift upon immersion in a chloride-anion-containing so-
lution of the same concentration(with both solutions being
formed from the TBA salt in anhydrous CH3CN, Figure 7).
No potential shift was observed when the cavity was not de-
populated prior to immersion in the chloride solution, as ex-
pected for a cavity exhibiting 1:1 binding stoichiometry.
These results are consistent with those presented in
Table 1 and confirm the selectivity of the three-dimensional
cavity towards chloride anion binding. Furthermore, the
smaller potential shift observed here upon binding of chlo-
ride anions, in comparison with that observed of the macro-
cycle, is attributed to the electron-withdrawing nature of the
positively charged pyridinium motif of the axle component,
mitigating donation of electron density to the osmium
centre, and is indicative of the interlocked surface-bound
structure.
Figure 7. Cyclic voltammogram (background subtracted) signatures of ro-
taxane films based on 14. Stable over repeated cycling (>10 cycles). Esti-
mated surface concentration as 50% of theoretical maximum (calculated
from a molecular footprint of the macrocycle, 3.0 nm2). Distance of fara-
daic exchange estimated at approximately 2 nm based on localisation of
the macrocycle at the pyridinium station and a perpendicular orientation
of the axle to the underlying gold surface. Insert: Potential shifts of sur-
face-bound OsACHTUNGTRENNUNG(+2/+3) couple, after immersion of rotaxane interface in
Conclusion
TBAAcO/CH3CN and TBACl/CH3CN solutions following washing with
NH4PF6/H2O to remove ClÀ template. Plotted data is the mean of several
measurements.
Interlocked structures can be engineered to bind specific
guests within the topologically constrained three-dimension-
al cavities created during their template-driven syntheses.
This binding ability, when coupled to the signal-transduction
capabilities associated with appended reporter groups, make
catenanes and rotaxanes highly promising candidates for the
development of molecular sensors.
electrode access of a solution-phase faradaic redox probe
and surface-capacitance analysis; an axle-only film being sig-
nificantly more densely packed (10 mFcmÀ2) than a rotaxane
film with
a “mushroom-shaped” component (25 and
15 mFcmÀ2 for surfaces prepared with 13 and 14, respective-
ly; Scheme S4 in the Supporting Information).
We have reported herein the solution and surface synthe-
sis of a number of anion-templated rotaxanes incorporating
It is notable that axle 14 generates a significantly higher
(>200%) macrocycle capture on the surface than that ob-
served with axle 13, consistent with both increased axle ri-
gidity and a higher associated chloride anion template asso-
ciation constant (Table 1). These films constitute not only an
addition to the few surface-confined tethered interlocked
the photo- and electroactive trisACTHNGUTERNNU(G bipy) osmium moiety.
1
Upon removal of the chloride anion template, H NMR ti-
tration of the solution rotaxanes with a number of anions
(chosen on the basis of their contrasting size, shape and ba-
sicity) showed selectivity for chloride anions over acetate
anions and dihydrogen phosphate oxoanions, observations
15904
www.chemeurj.org ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2013, 19, 15898 – 15906

Anion Sensing by Osmium(II) Bipyridyl Rotaxanes
FULL PAPER
slowly stirred for 1 h in 25 mL of dry dichloromethane. After removal of
the solvent, the residue was dissolved in 25 mL of dry and degassed di-
chloromethane. Stopper 15 (19 mg, 35 mmol, 1 equiv), CuACTHNUTRGNE(UNG CH3CN)4PF6
broadly supported by associated perturbations in osmium lu-
minescence or redox character. Rotaxane immobilisation
onto an alkyne-modified gold electrode substrate by cop-
per(I)-catalysed Huisgen cycloaddition produced molecular
films capable of responding electrochemically and selective-
ly to chloride anions. Notably, perturbation is only observed
on prior cavity depopulation. This work clearly demon-
strates the successful application of self-assembled monolay-
ers to the electrochemical sensing of halide ions.
(2.6 mg, 7 mmol, 0.2 equiv), TBTA (3.7 mg, 7 mmol, 0.2 equiv) and diiso-
propylethylamine (DIPEA) (12 mL, 70 mmol, 2 equiv) were successively
added and the reaction mixture stirred at room temperature (21Æ38C)
for 3 d. Then, 10 mL of KNO3(sat.aq.) was added, vigorously stirred for
30 min and the organic layer was extracted. After removal of the solvent,
the crude product was purified by preparative TLC (SiO2, CH3CN/H2O/
KNO3(sat.aq.) 14:2:1). Rotaxane 2 (16 mg, 16%) was obtained as a brown
solid after anion exchange to the hexafluorophosphate salt by washing
a chloroform solution of the rotaxane with 0.1m NH4PF6(aq.) (8ꢂ15 mL)
1
and H2O (2ꢂ15 mL). H NMR (500 MHz, [D6]acetone): d=10.06 (1H, s;
NHd), 9.42 (1H, s; Pyg), 9.36 (3H, m; Pyb/b’, ArHc and ArHc’), 9.20 (1H,
s; Pyb/b’), 8.82 (2H, d, 3J=7.5 Hz; bipy), 8.77 (2H, d, 3J=8.2 Hz; bipy),
8.74 (2H, d, 3J=8.2 Hz; bipy), 8.36 (1H, s; NHd’), 8.20 (2H, m; ArHa),
8.04 (1H, s; Hc), 7.96–8.03 (8H, m; bipy), 7.78, (2H, d, 3J=6.1 Hz;
ArHbJ), 7.74 (2H, d, 3J=5.8 Hz; ArHe), 7.51 (4H, m; bipy), 7.14–7.39
Experimental Section
General procedure: Commercially available solvents and chemicals were
used without further purification unless otherwise stated. Where dry sol-
vents were used, they were degassed with nitrogen, dried by passing
through an MBraun MPSP-800 column and then used immediately. Trie-
thylamine was distilled from and stored over potassium hydroxide. Water
was deionised and microfiltered by using a Milli-Q Millipore machine.
1H, 13C, 19F and 31P NMR spectra were recorded on a Varian Mercury-VX
300, and a Bruker AVII500 spectrometer. Mass spectrometry was carried
out on a Bruker micrOTOF spectrometer.
3
(29H, m; ArHstopper), 6.90 (2H, d, J=8.8 Hz; ArHe’), 6.63 (4H, s; ArHg),
6.47 (4H, s; ArHh), 5.03 (2H, s; Hl), 4.65 (3H, s; Ha), 4.44 (2H, t, 3J=
6.8 Hz; HnJ), 4.04 (4H, m; OCH2), 3.99 (4H, m; OCH2), 3.91 (8H, s;
NCH2 and OCH2), 3.63 (4H, m; OCH2), 3.48 (2H, m; Hr), 2.19 (2H, m;
Hk), 1.29 (18H, s; tBuH), 1.27 ppm (27H, s; tBuH); 13C NMR (125 MHz,
[D6]acetone): d=164.4, 160.8, 159.8, 159.7, 159.6, 157.4, 153.3, 152.5,
152.4, 152.0, 151.7, 149.6, 149.3, 148.0, 145.3, 144.8, 144.2, 142.3, 140.8,
138.9, 132.9, 132.4, 131.8, 131.5, 131.4, 129.6, 129.4, 128.5, 127.2, 126.9,
125.7, 125.4, 125.2, 125.2 sic, 125.1, 123.4, 121.0, 120.9, 116.6, 115.5, 115.5
sic, 114.3, 71.5, 70.9, 68.5, 67.5, 67.4, 64.8, 64.0, 62.2, 55.0, 50.2, 48.5, 40.3,
36.2, 34.9, 31.7 ppm; 19F NMR (282.5 MHz, [D6]acetone): d=À72.5 ppm
(d, 1J=708 Hz; PF6); 31P NMR (121.6 MHz, [D6]acetone): d=
À144.3 ppm (sept, 1J=709 Hz; PF6); MS (MALDI-TOF): m/z calcd for
ACTHNUTRGNEUNG
Synthesis: Macrocycle 19,[6b] axle 5,[3a] bis(amine) 8,[9] thread 17,[3a] and
axle 14[14] have been synthesized according to reported procedures. The
syntheses of 11, 12 and 13 along with electrochemical, surface analysis
and luminescence anion titration details are given in the Supporting In-
formation.
Rotaxane 1: In a 50 mL round-bottom flask, 2,2’-bipyridine-4,4’-dicarbox-
ylic acid (60 mg, 245 mmol, 1.2 equiv) was suspended in 10 mL of thionyl
chloride, a drop of DMF was added and the solution was heated at reflux
under N2 for 16 h. After removal of the solvent, the residue was dissolved
in 10 mL of dry dichloromethane and added dropwise to a 50 mL dry di-
[C138H147F18N14O11OsP3] [MÀ
(PF6)]+: 2658.03; found: 2658.26.
ACHTUNGTRENNUNG
Rotaxane 3: In a 50 mL round-bottom flask, osmium macrocycle 4
(100 mg, 70 mmol, 2 equiv) and thread 14 (31 mg, 35 mmol, 1 equiv) were
slowly stirred for 1 h in 25 mL of dry dichloromethane. After removal of
the solvent, the residue was dissolved in 25 mL of dry and degassed di-
chloromethane solution containing bisCAHTUNGTRNE(NUG amine) 8 (86 mg, 204 mmol,
chloromethane. Stopper 15 (19 mg, 35 mmol, 1 equiv), CuACTHNUTRGNE(UNG CH3CN)4PF6
1 equiv), axle 5 (220 mg, 204 mmol, 1 equiv) and triethylamine (71 mL,
510 mmol, 2.5 equiv). The reaction mixture was stirred at room tempera-
ture (21Æ38C) for 2 h, washed with 10% HCl(aq.) (2ꢂ50 mL) and water
(2ꢂ50 mL) and dried over MgSO4. After removal of the solvent, the resi-
due was dissolved in 10 mL of acetonitrile, filtered and solvent removed
in vacuo to give 121 mg of a crude mixture containing rotaxane and mac-
rocycle 19. This crude material (121 mg, 71 mmol, 1 equiv) was suspended
(2.6 mg, 7 mmol, 0.2 equiv), TBTA (3.7 mg, 7 mmol, 0.2 equiv) and
DIPEA (12 mL, 70 mmol, 2 equiv) were successively added and the reac-
tion mixture was stirred at room temperature (21Æ38C) for 3 d. Then,
10 mL of KNO3(sat.aq.) was added, vigorously stirred for 30 min and the or-
ganic layer was extracted. After removal of the solvent, the crude prod-
uct was purified by preparative TLC (SiO2, CH3CN/H2O/KNO3(sat.aq.)
14:2:1). Rotaxane 3 (74 mg, 72%) was obtained as a brown solid after
anion exchange to the hexafluorophosphate salt by washing a chloroform
solution of the rotaxane with 0.1m NH4PF6(aq.) (8ꢂ15 mL) and H2O (2ꢂ
15 mL). 1H NMR (500 MHz, [D6]acetone): d=9.92 (1H, s; NHd), 9.44
(1H, s; Pyg), 9.34 (1H, s; Pyb/b’), 9.27 (1H, s; ArHc/c’), 9.23 (1H, s; Pyb/b’),
9.12 (1H, s; ArHc/c’), 8.78 (4H, d, 3J=8.5 Hz; bipy), 8.36 (1H, s; NHd’),
in 20 mL of a 4:1 EtOH/H2O mixture and [OsACHTNUGTRNEUNG(bipy)2Cl2] 16 (82 mg,
142 mmol 2 equiv) was added. The solution was heated at reflux for 16 h
under N2. After removal of the solvent, the crude product was purified
by preparative TLC (SiO2, CH3CN/H2O/KNO3(sat.aq.) 14:2:1). Rotaxane
1 (30 mg, 6%) was obtained as a brown solid after anion exchange to the
hexafluorophosphate salt by washing a dichloromethane solution of the
rotaxane with 0.1m NH4PF6(aq.) (8ꢂ15 mL) and H2O (2ꢂ15 mL).
1H NMR (500 MHz, [D6]acetone/D2O (7:3)): d=9.40 (2H, s; Pyb), 9.33
3
8.18 (2H, d, J=6.1 Hz; ArHa), 8.17 (1H, s; Hc), 8.03 (4H, m; bipy), 7.87
(4H, m; bipy), 7.80 (2H, m; ArHb), 7.70 (2H, s; ArHe), 7.48 (4H, m;
bipy), 7.09–7.42 (37H, m; ArHstopper and ArHbiphenyl), 6.92 (2H, d, 3J=
9.0 Hz; ArHe’), 6.61 (4H, m; ArHg), 6.41 (4H, m; ArHh), 5.67 (2H, s;
Hn), 5.16 (2H, s; Hl), 4.67 (3H, s; Ha), 4.08 (4H, m; OCH2), 4.04 (4H,
m; OCH2), 3.94 (4H, m; OCH2), 3.87 (8H, m; NCH2 and OCH2), 3.71
(2H, s; H1), 1.30 (18H, s; tBuH), 1.28 ppm (27H, s; tBuH); 13C NMR
(125 MHz, [D6]acetone): d=163.8, 162.4, 160.3, 159.4, 159.1, 157.1, 152.8,
152.2, 151.9, 151.4, 151.3, 151.2, 149.1, 148.8, 147.6, 146.4, 144.9, 144.3,
141.8, 140.3, 138.5, 137.6, 135.8, 132.4, 132.0, 131.3, 131.1, 131.0, 129.2,
129.1, 129.0, 128.7, 128.1, 127.6, 127.5, 127.0, 126.5, 125.3, 125.0, 124.7,
123.2, 122.7, 120.5, 116.3, 116.2, 115.0, 113.9, 71.0, 70.4, 68.0, 67.2, 67.0,
64.4, 63.4, 61.9, 54.6, 53.6, 49.7, 39.8, 35.8, 34.6, 34.5, 31.3 ppm;19F NMR
(282.5 MHz, [D6]acetone): d=À72.5 ppm (d, 1J=708 Hz; PF6); 31P NMR
(121.6 MHz, [D6]acetone): d=À144.3 ppm (sept, 1J=709 Hz; PF6); MS
3
(1H, s; Pyg), 9.29 (2H, s; ArHc), 8.75 (2H, d, J=8.4 Hz; bipy), 8.71 (2H,
d, 3J=8.4 Hz; bipy), 8.05 (2H, d, 3J=6.2 Hz; ArHa), 8.02 (2H, t, 3J=
8.1 Hz; bipy), 7.90 (2H, t, 3J=8.1 Hz; bipy), 7.78 (2H, d, 3J=5.6 Hz;
bipy), 7.71 (2H, d, 3J=5.6 Hz; bipy), 7.66 (2H, dd, 3J=6.1.4 Hz, 4J=
1.7 Hz; ArHb), 7.59 (4H, s, 3J=8.9 Hz; ArHe), 7.46 (2H, t, 3J=6.7 Hz;
bipy), 7.06–7.27 (28H, m; ArHstopper and bipy), 6.50 (4H, m, 3J=8.9 Hz;
ArHg), 6.39 (4H, m, 3J=9.1 Hz; ArHh), 4.61 (3H, s; Ha), 3.92 (4H, m;
CH2), 3.86 (4H, m; CH2), 3.79 (4H, m; CH2), 3.77 (4H, s; CH2), 3.54
(4H, m; CH2), 1.18 ppm (36H, s; tBuH); 13C NMR (125 MHz,
[D6]acetone): d=164.0, 160.7, 159.7, 159.5, 152.4, 151.7, 149.5, 147.9,
144.7, 138.9, 138.8, 132.3, 131.7, 131.4, 129.4, 129.3, 128.4, 127.4, 126.9,
125.7, 125.7, 125.3, 123.2, 121.1, 116.5, 115.4, 71.4, 70.9, 67.5, 64.7, 40.4,
34.9, 31.7 ppm; 19F NMR (282.5 MHz, [D6]acetone): d=À72.4 ppm (d,
1J=707 Hz; PF6); 31P NMR (121.6 MHz, [D6]acetone): d=À144.3 ppm
(sept, 1J=707 Hz; PF6); MS (MALDI-TOF): m/z calcd for
(MALDI-TOF): m/z calcd for [C149H153F18N14O11OsP3] [MÀ
2796.07; found: 2796.10.
ACHTUNGTRENNUNG
(PF6)]+:
[C128H130F18N11O10OsP3] [MÀHÀ3
(PF6)]2+: 1085.98; found: 1085.98.
ACHTUNGTRENNUNG
Macrocycle 4: In a 250 mL round-bottom flask, macrocycle 19 (168 mg,
270 mmol, 1 equiv) was suspended in 100 mL of a 4:1 EtOH/H2O mixture
and [OsACHTNURGTNE(NUG bipy)2Cl2] 16 (153 mg, 142 mg, 2 equiv) was added. The solution
Rotaxane 2: In a 50 mL round-bottom flask, osmium macrocycle 4
(100 mg, 70 mmol, 2 equiv) and thread 13 (26 mg, 35 mmol, 1 equiv) were
Chem. Eur. J. 2013, 19, 15898 – 15906 ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.chemeurj.org
15905

J. J. Davis, P. D. Beer et al.
was heated at reflux for 36 h under N2. The brown solution was left to
cool to room temperature (21Æ38C) and then filtered through a Celite
bed before the solvent was removed in vacuo. The brown residue was
then redissolved in 20 mL of H2O and NH4PF6(s) was added to the solu-
tion until precipitation ceased. The precipitate was collected by vacuum
filtration and dried under vacuum to give macrocycle 4 as a black solid
(282 mg, 198 mmol, 74%). 1H NMR (300 MHz, [D6]acetone): d=9.14
(2H, s; ArHc), 8.82 (4H, m; bipy), 8.51 (2H, t, 3J=5.3 Hz; NHd), 8.19
(2H, d, 3J=5.6 Hz; ArHa), 8.05 (4H, t, 3J=7.9 Hz; bipy), 7.97 (4H, t,
[5] a) N. H. Evans, P. D. Beer, Org. Biomol. Chem. 2011, 9, 92–100;
b) N. H. Evans, H. Rahman, A. V. Leontiev, N. D. Greenham, G. A.
Orlowski, Q. Zeng, R. M. J. Jacobs, C. J. Serpell, N. L. Kilah, J. J.
Davis, P. D. Beer, Chem. Sci. 2012, 3, 1080–1089; c) S. R. Bayly,
T. M. Gray, M. J. Chmielewski, J. J. Davis, P. D. Beer, Chem.
Commun. 2007, 2234–2236; d) N. H. Evans, C. J. Serpell, P. D. Beer,
Chem. Commun. 2011, 47, 8775–8777; e) N. H. Evans, C. J. Serpell,
N. G. White, P. D. Beer, Chem. Eur. J. 2011, 17, 12347–12354.
[6] a) M. J. Langton, P. D. Beer, Chem. Eur. J. 2012, 18, 14406–14412;
b) L. M. Hancock, E. Marchi, P. Ceroni, P. D. Beer, Chem. Eur. J.
2012, 18, 11277–11283; c) C. G. Collins, E. M. Peck, P. J. Kramer,
B. D. Smith, Chem. Sci. 2013, 4, 2557–2563.
[7] a) N. Weber, C. Hamann, J. M. Kern, J. P. Sauvage, Inorg. Chem.
2003, 42, 6780–6792; b) E. Katz, O. Lioubashevsky, I. Willner, J.
Am. Chem. Soc. 2004, 126, 15520–15532; c) L. Raehm, C. Hamann,
J. M. Kern, J. P. Sauvage, Org. Lett. 2000, 2, 1991–1994; d) T. B. Lu,
L. Zhang, G. W. Gokel, A. E. Kaifer, J. Am. Chem. Soc. 1993, 115,
2542–2543; e) E. Coronado, P. Gavina, S. Tatay, Chem. Soc. Rev.
2009, 38, 1674–1689; f) I. Willner, V. Pardo-Yissar, E. Katz, K. T.
Ranjit, J. Electroanal. Chem. 2001, 497, 172–177; g) C. P. Collier,
J. O. Jeppesen, Y. Luo, J. Perkins, E. W. Wong, J. R. Heath, J. F.
Stoddart, J. Am. Chem. Soc. 2001, 123, 12632–12641; h) H. R.
Tseng, D. M. Wu, N. X. L. Fang, X. Zhang, J. F. Stoddart, Chem-
PhysChem 2004, 5, 111–116; i) J. Bernꢃ, D. A. Leigh, M. Lubomska,
S. M. Mendoza, E. M. Perez, P. Rudolf, G. Teobaldi, F. Zerbetto,
Nat. Mater. 2005, 4, 704–710; j) S. Richter, J. Poppenberg, C. H. H.
Traulsen, E. Darlatt, A. Sokolowski, D. Sattler, W. E. S. Unger,
C. A. Schalley, J. Am. Chem. Soc. 2012, 134, 16289–16297; k) R.
Klajn, L. Fang, A. Coskun, M. A. Olson, P. J. Wesson, J. F. Stoddart,
B. A. Grzybowski, J. Am. Chem. Soc. 2009, 131, 4233–4235; l) L.
Zhao, J. J. Davis, K. M. Mullen, M. J. Chmielewski, R. M. J. Jacobs,
A. Brown, P. D. Beer, Langmuir 2009, 25, 2935–2940; m) L. Zhao,
K. M. Mullen, M. J. Chmielewski, A. Brown, N. Bampos, P. D. Beer,
J. J. Davis, New J. Chem. 2009, 33, 760–768; n) J. J. Davis, G. A. Or-
lowski, H. Rahman, P. D. Beer, Chem. Commun. 2010, 46, 54–63.
[8] K. Nozaki, K. Takamori, Y. Nakatsugawa, T. Ohno, Inorg. Chem.
2006, 45, 6161–6178.
4
3J=6.0 Hz; bipy), 7.80 (2H, dd, 3J=6.1 Hz, J=1.7 Hz; ArHb), 7.53 (2H,
t, 3J=6.8 Hz; bipy), 7.47 (2H, t, 3J=6.8 Hz; bipy), 6.88 (8H, m; ArHg,h),
4.14 (4H, t, 3J=5.3 Hz; CH2), 4.06 (4H, t, 3J=4.5 Hz; CH2), 3.73–3.85
(8H, m; CH2), 3.67 ppm (4H, s; CH2); 13C NMR (75.5 MHz,
[D6]acetone): d=163.6, 160.8, 159.7, 153.9, 152.4, 152.2, 151.7, 142.4,
138.8, 129.4, 127.5, 125.6, 122.7, 116.5, 116.3, 71.4, 70.4, 68.9, 67.4,
40.5 ppm; 19F NMR (282.5 MHz, [D6]acetone): d=À72.5 ppm (d, 1J=
708 Hz; PF6); 31P NMR (121.6 MHz, [D6]acetone): d=À144.3 (sept, 1J=
709 Hz; PF6); MS (MALDI): m/z calcd for [C54H52F12N8O8OsP2] [MÀ-
ACHTUNGTRENNUNG
(PF6)2]2+: 1132.35; found: 1132.38.
Acknowledgements
The research leading to these results has received funding from the Euro-
pean Research Council under the European Unionꢁs seventh Framework
Programme (FP7/2007_2013)/ERC-Advanced Grant Agreement Number
267426.
[1] a) W. Yang, Y. Li, H. Liu, L. Chi, Y. Li, Small 2012, 8, 504–516;
b) A. C. Fahrenbach, S. C. Warren, J. T. Incorvati, A.-J. Avestro, J. C.
Barnes, J. F. Stoddart, B. A. Grzybowski, Adv. Mater. 2013, 25, 331–
348; c) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew.
Chem. 2000, 112, 3484–3530; Angew. Chem. Int. Ed. 2000, 39, 3348–
3391.
[2] M. J. Chmielewski, J. J. Davis, P. D. Beer, Org. Biomol. Chem. 2009,
7, 415–424.
[9] L. M. Hancock, L. C. Gilday, S. Carvalho, P. J. Costa, V. Felix, C. J.
Serpell, N. L. Kilah, P. D. Beer, Chem. Eur. J. 2010, 16, 13082–
13094.
[3] a) J. A. Wisner, P. D. Beer, M. G. B. Drew, M. R. Sambrook, J. Am.
Chem. Soc. 2002, 124, 12469–12476; b) D. Curiel, P. D. Beer, Chem.
Commun. 2005, 1909–1911; c) M. R. Sambrook, P. D. Beer, M. D.
Lankshear, R. F. Ludlow, J. A. Wisner, Org. Biomol. Chem. 2006, 4,
1529–1538; d) L. M. Hancock, P. D. Beer, Chem. Eur. J. 2009, 15,
42–44; e) A. Brown, K. M. Mullen, J. Ryu, M. J. Chmielewski, S. M.
Santos, V. Felix, A. L. Thompson, J. E. Warren, S. I. Pascu, P. D.
Beer, J. Am. Chem. Soc. 2009, 131, 4937–4952; f) A. J. McConnell,
C. J. Serpell, A. L. Thompson, D. R. Allan, P. D. Beer, Chem. Eur. J.
2010, 16, 1256–1264; g) G. T. Spence, P. D. Beer, Acc. Chem. Res.
2013, 46, 571–586.
[10] M. J. Hynes, J. Chem. Soc. Dalton Trans. 1993, 311–312.
ˇ
[11] P. Kuzmic, Anal. Biochem. 1996, 237, 260–273.
[12] M. Rodriguez, A. J. Bard, Anal. Chem. 1990, 62, 2658–2662.
[13] F. Szemes, D. Hesek, Z. Chen, S. W. Dent, M. G. B. Drew, A. J.
Goulden, A. R. Graydon, A. Grieve, R. J. Mortimer, T. Wear, J. S.
Weightman, P. D. Beer, Inorg. Chem. 1996, 35, 5868–5879.
[14] L. M. Hancock, P. D. Beer, Chem. Commun. 2011, 47, 6012–6014.
[4] a) G. T. Spence, M. B. Pitak, P. D. Beer, Chem. Eur. J. 2012, 18,
7100–7108; b) J. J. Gassensmith, S. Matthys, J.-J. Lee, A. Wojcik,
P. V. Kamat, B. D. Smith, Chem. Eur. J. 2010, 16, 2916–2921.
Received: July 23, 2013
Published online: October 14, 2013
15906
www.chemeurj.org ꢀ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2013, 19, 15898 – 15906