Sequence-defined oligo(: Ortho -arylene) foldamers derived from the benzannulation of ortho (arylene ethynylene)s

Article abstract of DOI:10.1039/c6sc02520j

A Cu-catalyzed benzannulation reaction transforms ortho(arylene ethynylene) oligomers into ortho-arylenes. This approach circumvents iterative Suzuki cross-coupling reactions previously used to assemble hindered ortho-arylene backbones. These derivatives form helical folded structures in the solid-state and in solution, as demonstrated by X-ray crystallography and solution-state NMR analysis. DFT calculations of misfolded conformations are correlated with variable-temperature ¹H and EXSY NMR to reveal that folding is cooperative and more favorable in halide-substituted naphthalenes. Helical ortho-arylene foldamers with specific aromatic sequences organize functional π-electron systems into arrangements ideal for ambipolar charge transport and show preliminary promise for the surface-mediated synthesis of structurally defined graphene nanoribbons.

Full text of DOI:10.1039/c6sc02520j

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EDGE ARTICLE
Sequence-Defined Oligo(ortho-Arylene) Foldamers Derived From the
Benzannulation of ortho(Arylene ethynylene)s
Received 00th January 20xx,
Accepted 00th January 20xx
Dan Lehnherr,a Chen Chen,b Zahra Pedramrazi,b Catherine R. DeBlase,a Joaquin M. Alzola,a
Ivan Kerezstes,c Emil B. Lobkovsky,d Michael F. Crommie,b,* and William R. Dichtela,e,
*
DOI: 10.1039/x0xx00000x
A Cu-catalyzed benzannulation reaction transforms ortho(arylene ethynylene) oligomers into ortho-arylenes. This
approach circumvents iterative Suzuki cross-coupling reactions previously used to assemble hindered ortho-arylene
backbones. These derivatives form helical folded structures in the solid-state and in solution, as demonstrated by X-ray
crystallography and solution-state NMR analysis. DFT calculations of misfolded conformations are correlated with variable-
temperature 1H and EXSY NMR to reveal that folding is cooperative and more favorable in halide-substituted
naphthalenes. Helical ortho-arylene foldamers with specific aromatic sequences organize functional π-electron systems
into arrangements ideal for ambipolar charge transport and show preliminary promise for the surface-mediated synthesis
of structurally defined graphene nanoribbons.
www.rsc.org/
polymerization of aryne intermediates.8 These pioneering
studies revealed that o-phenylenes adopt specific folded
structures, which might organize functional aromatic systems
Introduction
Oligomers and polymers based on linking arenes are
ubiquitous in materials chemistry, with applications that
include photovoltaics, field effect transistors, light emitting
diodes, sensing, dielectrics, dyes, and coatings.1 Many of these
applications achieve optimal performance by controlling the
relative distance and orientation between key aromatic
if more powerful synthetic protocols are developed.
systems. From
a
structural standpoint, oligo- and
polyphenylenes are among the most simple motifs, and high
molecular weight poly(p-phenylene)s and poly(m-phenylene)s
have been studied extensively.2 p-Phenylenes have served as
precursors to graphene nanoribbons, while m-phenylenes
provide improved solubility3 and have found use in display
technologies, including electrophosphorescent devices and
liquid crystal displays.4
Oligo and poly(o-arylene)s are much less explored because
they are more difficult to access (Scheme 1). Hartley5 prepared
oligo(o-phenylene)s using iterative Suzuki cross-couplings,
while Aida6 oxidized Lipshutz cuprates to prepare longer
oligomeric mixtures (Scheme 1). Ito and Nozaki synthesized
poly(o-arylene)s via formal aryne polymerizations,7 and most
recently Mikami and Uchiyama developed a copper-mediated
Scheme 1 Synthetic approaches to o-arylenes.
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Scheme 2 Synthesis of sequence-defined o-arylene oligomers from o-arylethynylenes via a cycloaddition strategy.
Cycloaddition reactions that convert oligo(o-phenyl preference for folding, often >95%, whereas o-phenylene
ethynylene)s to oligo(o-arylene)s offer means to oligomers range from 49–96% folded, with electron
a
simultaneously avoid challenging cross-coupling reactions and withdrawing substituents needed to achieve higher values.
provide access to novel oligo-arene sequences. We recently These o-arylenes are also precursors to graphene-like
expanded the scope of the Asao and Yamamoto9 nanostructures, which we demonstrate through surface
benzannulation, which transforms alkynes into 2,3- mediated synthesis.
disubstituted naphthalenes, to provide heavily substituted
naphthalenes as single regioisomers.10,11 The reaction tolerates
Results and Discussion
Synthesis
congested aromatic structures and is applicable to both small
molecules12 and polymers.13 Here we apply this transformation
to o-(arylene ethynylene)s and related structures containing
Various hydrocarbon and halogenated benzaldehyde reagents
strategically placed diynes. The resulting o-arylene structures
convert o-(arylene ethynylene)s to o-arylenes with different
adopt helical conformations in solution and the solid state,
sequences and halogenation patterns. Oligo(o-arylene)s of
such that the specific pattern of alkynes and diynes in the
varying length and an alternating phenylene/ethynylene
starting material is translated into predictive arrangement of
repeating pattern [(ab)n] were reacted with three different
stacked aryl groups in the product. The naphthalene groups
benzaldehydes, to access hydrocarbon, fluorine-, or chlorine-
incorporated into these structures provide
a stronger
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substituted structures. Despite observing complete conversion calculating their relative energies and the energy barrier for
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DOI: 10.1039/C6SC02520J
of the starting material in all cases, isolated yields decrease for the conformational interconversion between the two lowest
precursors bearing more alkyne functions, which we attribute energy structures. 1D and 2D NMR experiments provided
to their lower stability under the acidic reaction conditions. In experimental validation of the solution-state structure and the
these cases, the degradation products are easily removed folding dynamics (see Supporting Information for details).
during chromatography. In the future, alternative
Many of the o-arylenes illustrated in Scheme 1 were
benzannulation conditions14 with reduced acid concentrations characterized using single-crystal X-ray diffraction. These
might provide improved yields. Sequence-defined o-arylene structures reveal their ability to fold in a “closed” helical
oligomers are available from o-phenylene ethynylene conformation, enabling analysis of dihedral angles and
,
precursors containing mono- and diyne groups. For example, distances between aromatic systems (Fig. 1 and Table S3).16 17
complex sequences such as “(abb)2a” and “(ab)2(ba)2” (Scheme The dihedral angles (φi, see Fig. 2) associated with the biaryl
2) are achieved via cycloadditions starting from either diyne- linkages that define the conformation of H-Ar-2, H-Ar-3 and H-
based precursor 5, or mixed systems containing both mono- Ar-4 consistently fall between –42° and –64° (or +42° and +64°
and diynes, such as precursor 6.
for its enantiomer; these interconvert rapidly in solution at
room temperature). The intramolecular π-stacking between
the ith and (i + 3)th arene is evident in the crystal structures,
Structural Characterization
One of the defining characteristics of foldamers is that they with non-covalent C••C distances ranging from 3.1–3.5 Å. The
have more than one conformation accessible, which includes a solution-state structures of each foldamer were determined
folded state and one or more unfolded, or partially unfolded, using 2D NMR techniques (COSY, NOSEY, ROSEY, HSQC, and
state.15 We used density functional theory (DFT) to investigate
the conformational behaviour of our foldamers, including
Fig. 1 X-ray crystallographic structures of foldamers (left to right): H-Ar-2, H-Ar-3, H-Ar-4 and F-Ar-6. (Top) Line representation with selected carbon-carbon distances, (middle) top
view and (bottom) side view with each repeat unit colored differently.
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Fig. 2 (Top left) Definition of dihedral angles φi and associated conformer letter code for o-arylenes using H-Ar-3 as an example. (Bottom left) Partial 1H NMR spectra
(800 MHz, CDCl3, 0 °C) of X-Ar-3 illustrate the hydrogen signal used for determining the ratio and kinetics for the equilibrium and exchange between conformer AAAA
and AAAB. (Right) DFT structures of various conformations of H-Ar-3 calculated using M06-2X/6-31G.
HMBC) and support a folded structure analogous to that dihedral angles of aryl-aryl linkages (see Fig. 2 for the
1
observed in the solid-state. The H NMR spectra of the X-Ar-3 definition of φi). Within the context of foldamers X-Ar-[n], the
foldamers (X = H, F, Cl) reveal one major set of signals in CDCl3, relaxed potential energy surface analysis associated with C–C
corresponding to the folded structure. An additional set of bond rotation of between the outermost naphthalene and its
signals in the 1H NMR spectra are observed, which correspond neighbouring phenylene ring provides two local minima,
to a minor, partially unfolded conformer (vide infra). The ratio defined as A and B, corresponding to dihedral angles of ca.
between the folded and partially unfolded conformers is –50° and +135° (or +50° and –135° for its enantiomer),
influenced by halogen substituents introduced during the respectively (see Supporting Information for details). The
benzannulation reaction. The minor conformation is most series of all the aryl-aryl linkages of the foldamer defines the
prominent in the spectra of hydrocarbon H-Ar-3, and conformation, which we classify with a letter (A or B) and the
decreases as X changes from H to Cl to F in the X-Ar-3 series series of these letters are arranged in order to provide an n-
(Fig. 2). DOSY NMR was inconsistent with these signals letter code for an oligomer of (n–3)-arenes using the following
corresponding to different aggregation states, as the self- definition for φ2 to φn–1
. Following Hartley’s naming
diffusion coefficients measured for both species were nearly convention,19 dihedral angle φi is classified as: A if (0° < φi <
identical. Furthermore, EXSY cross peaks between these two –90°), B (90° < φi < 180°), or C if (–90° ≤ φi < –180°); the
sets of signals establishes the ability for these species to opposite signs correspond to the analogous enantiomeric
interconvert in solution (see SI for details).
conformation. The “C” state emerges due to intramolecular
DFT calculations performed using the M06-2X functional18 edge-to-face π-stacking interactions between the ith and (i +
and the 6-31G basis set provide additional insight into the 4)th arene, although these are often significantly less stable
conformational structure of the oligo(o-arylene)s. This conformers than those that do not contain such C states.20 For
functional was chosen because it accurately describes non- example, the folded X-ray crystallographic geometries of
covalent interactions, including aromatic stacking interactions. trimeric and tetrameric foldamers H-Ar-3 and H-Ar-4 shown in
The conformation of the o-arylene foldamer is defined by the Fig. 1 correspond to conformer AAAA and AAAAA, respectively.
Table 1 Comparison of the folded population between various structurally related o-arylene foldamers.
Percentage of Population in the Folded Conformation An–3
in CDCl3 Solutions at 0 °C
Number of Arenes in
the Oligomer (n) &
Compound Number
7 (X-Ar-3)
Compound Class
o-Phenylene-alt-o-Naphthalene
o-Phenylene
X = H
86%
91%
X = Cl
88%
96%
–
–
ND
ND
X = F
94%
97%
–
9 (X-Ar-4)
6 (oP6(H))
49% (–5 °C)[19]
>96% (–5 °C)[19]
ND
6 (oP6(CN)
–
o-Phenylene-mix-o-Naphthalene
7 (F-Ar-5)
9 (F-Ar-6)
99%
≥99%
ND
a ND = not determined.
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The most stable conformations of the X-Ar-3 o-arylenes (X properties (vide infra). Additionally, the consVisietwenArttilcyle Ohnilginhe
= H, F, or Cl, Supporting Information, Table S5) have folded population of the folded conformerDOrI:e1g0a.1r0d3l9e/sCs6SCo0f25t2h0eJ
forms AAAA, which are significantly more stable than the substituents or sequence in these o-arylenes illustrates the
unfolded forms BBBB for all substitution patterns. benefit of incorporating naphthalenes into foldamers (Table 1).
Conformation BBBB is 16.1 (X = H), 17.2 (X = F), and 17.6 Additional details regarding thermodynamic and kinetic
kcal/mol (X = Cl) higher in energy relative to the corresponding parameters (rate & activation barriers) associated with the
AAAA conformer (Fig. 2). Solution-state NMR analysis supports folding/unfolding equilibrium for these o-arylenes, including
AAAA being the most stable conformation, which is also the van ’t Hoff and Eyring analyses is provided in the Supporting
conformation observed by X-ray crystallography. Defect states Information.
are least energetically costly at the ends of the foldamer
instead of the middle, as conformation AAAB is more stable
Optical & Electrochemical Properties
than AABA. The AAAB structures are 4.9 (X = H), 5.3 (X = F), The foldamers show UV-vis absorption and emission
and 5.4 kcal/mol (X = Cl) higher in energy than AAAA, characteristics that are sensitive to the presence of
compared to 19.2 (X = H), 19.8 (X = F), and 19.8 kcal/mol (X = naphthalene-naphthalene intramolecular π-stacking (Fig. 3).
Cl) for AABA relative to AAAA.
Longer oligomers of the X-Ar-1 to X-Ar-4 series show increased
The energy differences between AAAB and AAAA are larger molar absorptivity associated with their larger number of
for the halogenated foldamers (+5.3 and +5.4 kcal/mol for X = chromophores but no major shift of λmax to lower energy
F and Cl, respectively, relative to their AAAA conformation) associated with coplanar conjugated systems. Instead a slight
compared to the hydrocarbon foldamer (+4.9 kcal/mol). This blue-shift in λmax and a narrowing of the absorption band is
stabilization suggests that halogenation of the foldamer will observed. The photoemission spectra of F-Ar-4 to F-Ar-6
lead to a higher population of AAAA-folded molecules, indeed reflect differences in the helical structures. F-Ar-4 contains
this is observed in solution. NMR spectroscopy of X-Ar-3 in only phenylene-naphthalene through-space interactions and
CDCl3 indicates that AAAB is the structure of the minor exhibits the most blue-shifted photoemission (λmax,em = 370
conformer observed in Fig. 2. The population of folded state nm).21 Both F-Ar-5 and F-Ar-6 have two naphthalene-
AAAA increases from 86% to 88% to 94% as X changes from H naphthalene interactions, which leads to 12 and 10 nm
to Cl to F, respectively, for CDCl3 solutions at 0 °C (Table 1). The emission red shifts, respectively, relative to F-Ar-4. It is unclear
population of the folded conformer increases as a function of whether the small differences in λmax,abs and λmax,em between F-
oligomer length, specifically, the folded population for X-Ar-4 Ar-5 and F-Ar-6 originate from differences in their arylene
are 91% for X = H, 96% for X = Cl, and 97% for X = F). The sequences or subtle differences of their through-space
modified sequence of arenes in foldamers F-Ar-5 and F-Ar-6 interactions.
leads to naphthalene–naphthalene π-stacking, in contrast to
Cyclic voltammetry (CV) experiments (CH3CN, 0.1M
phenylene–naphthalene π-stacking present in X-Ar-3 and X-Ar- Bu4NClO4 supporting electrolyte) reveal progressively more
4. Increased stabilization of the folded state derives from the facile oxidation with increased oligomer length (Fig. 4).
larger cofacial π-stacking surface area provided by the Namely, the onset of oxidation (vs. Ag/AgClO4) decreases
naphthalene–naphthalene interactions in F-Ar-5 and F-Ar-6, monotonically from 1.184 V (H-Ar-1) to 1.090 V (H-Ar-2), 1.006
resulting in nearly quantitative folding (99% and ≥99% folded, V (H-Ar-3) and finally 0.979 V (H-Ar-4), indicative of a lowering
,
respectively) as determined by 1H NMR spectroscopy. DFT of the HOMO energy for longer oligomers.22 23 This trend is
calculations correctly predict increased folding population for likely to arise from intramolecular through-space interactions
F-Ar-6 compared to F-Ar-5, with both superior to F-Ar-4 (see SI that stabilize the electrochemically generated radical cation. It
for details). These observations highlight one of the benefits of is also possible that oxidation occurs from an unfolded
sequence-defined oligomers, as a simple change in sequence conformation that is a more planar, delocalized structure, but
can influence folding behaviour and optical/electronic we judge this possibility less likely given the high energetic
Fig. 3 UV-vis absorption and emission spectra (λexc = 260 nm) of oligomeric series in CH2Cl2: (left) H-Ar-1 to H-Ar-4, (right) F-Ar-4 to F-Ar-6.
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Fig. 4 Cyclic voltammetry of foldamers H-Ar-1 to H-Ar-4 in CH3CN containing 0.1
M TBAP measured at 50 mV•s–1.
Scheme 3 o-Arylenes as precursors to nanographenes H-8 and F-8 with control of
width and length dimensions in addition to potential control of edge-
functionalization. Dimensions shown are estimated for H-8 based on DFT
calculations and measurements between the furthest hydrogen atoms.
penalty for this process in the neutral form. The oxidation
process is chemically irreversible as shown from the mismatch
in current density between the anodic and cathodic peak for aromatic hydrocarbon H-8 via a surface-mediated process.
the oxidation wave in the CV. Electrochemical oxidation might Evaporation of H-Ar-3 in ultra high vacuum enabled its
induce full or partial oxidative cyclodehydrogenation to form deposition onto Au(111). The STM image in Fig. 5a illustrates a
larger aromatic structures (vide infra). This possibility led us to surface coverage of 0.8 monolayers of H-Ar-3 on Au(111)
explore the conversion of foldamer structures into defined obtained after deposition of the H-Ar-3 molecules. The
larger aromatics (e.g. nanographenes).
molecules are seen to form ordered crystalline domains
approaching ca. 20 nm (a diagonal grain boundary separating
two such domains is visible in Fig. 5a). At lower surface
On-Surface Nanographene Synthesis
The ability to access o-arylenes and introduce functionality, coverage, H-Ar-3 selectively attaches to step edges of Au(111)
such as halides, on the arenes in the final step opens up new (Fig. 5b). A close up of several molecules (Fig. 5c) clearly shows
opportunities. For example, polymeric derivatives of these the non-planarity of H-Ar-3, which exhibits an apparent height
foldamers might serve as precursors to graphene nanoribbons, of 3–5 Å depending on molecular conformation.
in which this bottom-up approach enables the control of
Upon annealing the H-Ar-3/Au(111) to 286 °C, a change in
width, length, and edge structure (e.g., hydrogen vs halogen the shape of the molecules is observed consistent with
,
edge termination).24 25 The oxidative cyclodehydrogenation of conversion to H-8.26 Fig. 5d shows the dominant product
X-Ar-[n] could enable exquisite control in forming armchair (60%): a planar, trapezoidal molecule with measured height of
graphene nanoribbons of 8 carbons in width and varying 1.9 ± 0.1 Å. The dimensions of this structure (1.9 ± 0.2 nm x
length up to 20 carbons with the potential for one edge of the 1.3 ± 0.2 nm) are consistent with DFT predicted dimensions of
ribbon being halogenated while the opposing edge is hydrogen H-8 (Fig. 5e). It should be noted that an intermediate annealing
terminated (Scheme 3). As a proof of principle, herein we temperature of 250°C is enough to convert some molecules
report the conversion of foldamer H-Ar-3 to polycyclic
(~10%) to the desired H-8 product, but with the remaining
sample still consisting of non-planar molecules.
Fig. 5 STM images of H-Ar-3 and H-8 molecules on Au(111). (a) 0.8 monolayer coverage of H-Ar-3 as deposited shows well-ordered crystalline domains. (b) Lower
surface coverage of H-Ar-3 as deposited shows molecular adhesion to step edges of Au(111) crystal. (c) Close-up of several molecules of H-Ar-3 before annealing
reveals non-planarity. (d) Individual nanographene H-8 obtained after annealing to 286 °C. (e) DFT optimized structure of H-8 overlaid on top of STM image of H-8
shown in Fig. 5d. Scanning parameters: (a) sample bias: 1.0 V, tunnelling current: 10 pA; (b) 1.0 V, 2 pA; (c) 1.0 V, 2 pA; and (d) 0.1 V, 200 pA. All images were obtained
at T = 7 K.
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N. Mártin, L. Sánchez, M. Á. Herranz,DBO.I:I1l0le.1s0c3a9s/Ca6nSdC0D25.2M0J.
Guldi, Acc. Chem. Res., 2007, 40, 1015–1024. (g) M. T. Dang,
L. Hirsch, G. Wantz and J. D. Wuest, Chem. Rev., 2013, 113,
3734–3765. (h) A. C. Arias, J. D. MacKenzie, I. McCulloch, J.
Rivnay and A. Salleo, Chem. Rev., 2010, 110, 3–24. (i) A. W.
Hains, Z. Liang, M. A. Woodhouse and B. A. Gregg, Chem.
Rev., 2010, 110, 6689–6735. (j) J. Mei, Y. Diao, A. L. Appleton,
L. Fang and Z. Bao, J. Am. Chem. Soc., 2013, 135, 6724–6746.
2. B. A. G. Hammer and K. Müllen, Chem. Rev., 2016, 116,
2103–2140.
Conclusions
We have developed a direct synthetic approach to oligomeric
o-arylenes based on a cycloaddition strategy using acetylenic
motifs to control arylene sequence. Characterization of these
oligomers reveals they are able to fold into helical structures
due to intramolecular non-covalent interactions, which are
influenced by sequences of naphthalene and phenylene units
as well as by halogen substituents. The folded structures are
observed in the solid state by X-ray crystallography and in the
solution state by NMR spectroscopy. DFT calculations shed
light into the various conformations available, their relative
energies and selected energy barriers for their
interconversion. The sequence of the o-arylenes influences
both folding properties and optical properties. These
foldamers hold potential for sensing guests capable of
disrupting intramolecular π-stacking or intercalating between
arenes. Extending these methods to longer oligomers or
polymers will provide structurally defined graphene
nanoribbons with unsymmetrical edge functionalization (i.e., H
vs F edge termination). These studies highlight the utility of
this cycloaddition approach for the realization of functional
carbon nanostructures via a bottom up approach.
3
V. Percec, S. Okita and R. Weiss, Macromolecules, 1992, 25,
1816–1823.
(a) J. Liu, C. Gong, Z. Yu and Q. Pei, Q. J. Mater. Chem., 2011,
21, 9772–9777. (b) K. Suda and K. Akagi, Macromolecules,
2011, 44, 9473–9488.
4
5
(a) J. He, J. J. L. Crase, S. H. Wadumethrige, K. Thakur, L. Dai,
S. Zou, and R. Rathore and C. S. Hartley, J. Am. Chem. Soc.,
2010, 132, 13848–13857. (b) C. S. Hartley and J. He. J. Org.
Chem., 2010, 75, 8627–8636. (c) S. M. Mathew and C. S.
Hartley, Marcomolecules, 2011, 44, 8425–8432. (d) S. M.
Mathew, J. T. Engle, C. J. Ziegler and C. S. Hartley, J. Am.
Chem. Soc., 2013, 135, 6714–6722. (e) S. M. Mathew, L. A.
Crandall, C. J. Ziegler and C. S. Hartley, J. Am. Chem. Soc.,
2014, 136, 16666–16675. (f) C. S. Hartley, Acc. Chem. Res.,
2016, 49, 646–654. (g) For related oligo(o-naphthalene)s,
see; T. Motomura, H. Nakamura, M. Suginome, M.
Murakami, Y. Ito. Bull. Chem. Soc. Jpn., 2005, 78, 142–146.
E. Ohta, H. Sato, S. Ando, A. Kosaka, T. Fukushima, D.
Hashizume, M. Yamasaki, K. Hasegawa, A. Muraoka, H.
Ushiyama, K. Yamashita and T. Aida, Nat. Chem., 2011, 3,
68–73.
6
Acknowledgements
7
8
9
S. Ito, K. Takahashi and K. Nozaki, J. Am. Chem. Soc., 2014,
136, 7547–7550.
Y. Mizukoshi, K. Mikami and M. Uchiyama, J. Am. Chem. Soc.,
2015, 137, 74–77.
N. Asao, T. Nogami, S. Lee and Y. Yamamoto, J. Am. Chem.
Soc., 2003, 125, 10921–10925.
This research was supported by the Army Research Office
Multidisciplinary University Research Initiative (MURI) program
under grant no. W911NF-15-1-0447 (molecular synthesis and
STM imaging), a Beckman Young Investigator Award (to
W.R.D.), the NSF (CHE-1124754, structural characterization),
and by the US Department of Energy, Office of Basic Energy
Sciences Nanomachine Program under contract no. DE-AC02-
05CH11231 (molecular deposition). C.R.D was supported by an
NSF GRFP (DGE-1144153). This work made use of the Cornell
Center for Materials Research Shared Facilities which are
supported through the NSF MRSEC program (DMR-1120296),
an NMR spectrometer at Cornell supported by the NSF-MRI
program (CHE-1531632), and an 800 MHz NMR instrument at
the State University of New York College of Environmental
Science and Forestry in Syracuse facilities purchased using NIH
grant no. 1S10OD012254-01A1. We thank David Kiemle for his
assistance in acquiring the 800 MHz NMR data and Samantha
N. MacMillan (X-ray Laboratory, Cornell) for additional X-
crystallography presented in the SI.
10 D. Lehnherr, J. M. Alzola, E. B. Lobkovsky and W. R. Dichtel,
Chem Eur. J., 2015, 21, 18122–18127.
11 H. Arslan, K. L. Walker and W. R. Dichtel, Org. Lett., 2014, 16,
5926–5929.
12 S. Hein, H. Arslan, I. Keresztes and W. R. Dichtel, Org. Lett.,
2014, 16, 4416–4419.
13 H. Arslan, J. D. Saathoff, D. N. Bunck, P. Clancy, and W. R.
Dichtel, Angew. Chem. Int. Ed., 2012, 51, 12051–12054.
14 X.-L. Fang, R.-Y. Tang, X.-G. Zhang, P. Zong, C.-L. Deng and J.-
H. Li, J. Organomet. Chem. 2011, 696, 352–356.
15 (a) J. C. Nelson, J. G. Saven, J. S. Moore and P. G. Wolynes,
Science, 1997, 277, 1793–1796. (b) D.-W. Zhang, X. Zhao and
J.-L. Hou, Chem. Rev., 2012, 112, 5271–5316.
16 It should be noted that both o-phenylenes and o-(phenylene
ethynylene)s can adopt helical conformation, see reference 2
and 17, respectively.
17 (a) R. H. Grubbs and D. Kratz, Chem. Ber., 1993, 126, 149–
157. (b) T. V. Jones, R. A. Blatchly and G. N. Tew, Org. Lett.,
2003, 5, 3297–3299. (c) J. Jiang, M. M. Slutsky, T. V. Jones
and G. N. Tew, New J. Chem., 2010, 34, 307–312. (d) T. V.
Jones, M. M. Slutsky and G. N. Tew, New. J. Chem., 2008, 32,
676- 679.
Notes and references
18 Y. Zhao, Y and D. G. Truhlar, Theor. Chem. Acc., 2008, 120,
215–241.
1
(a) T. M. Figueira-Duarte and K. Müllen, Chem. Rev., 2011,
111, 7260–7314. (b) A. W. Hains, Z. Liang, M. A. Woodhouse
and B. A. Gregg, Chem. Rev., 2010, 110, 6689–6735. (c) B.
Lucas, T. Trigaud and C. Videlot-Ackermann, Polym. Int.,
2012, 61, 374–389. (d) P. M. Beaujuge and J. M. J. Fréchet, J.
Am. Chem. Soc., 2011, 133, 20009–20029. (e) Y.-J. Cheng, S.-
H. Yang and C.-S. Hsu, Chem. Rev., 2009, 109, 5868–5923. (f)
19 S. M. Mathew, J. T. Engle, C. J. Ziegler and C. S. Hartley, J.
Am. Chem. Soc., 2011, 135, 6714–6722.
20. The A and B states in oligo(o-arylene)s, such as oligo(o-
phenylene)s, is well documented, whereas the
C state
described herein is unprecedented and it is unclear whether it
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DOI: 10.1039/C6SC02520J
is unique to our system or if it is also attainable with oligo(o-
phenylene)s.
21 The photoemission spectra of o-phenylenes is known to
exhibit a blue shift with increasing oligomer length, similar to
that observed with [X]-Ar-1 to [X]-Ar-4, a phenomenon
associated with folding, see: (a) reference 5c, (b) P. Guiglion,
M. A. Zwijnenburg, Phys. Chem. Phys. 2015, 17, 17854–
17863.
22 A similar observation is made in the series comparing F-Ar-
[n] (with n = 1–4). The onset of oxidation is generally less
electropositive for longer oligomers, namely, 1.320 V (F-Ar-
1), 1.279 V (F-Ar-2), 1.265 V (F-Ar-3), 1.180 V (F-Ar-4) vs
Ag/AgClO4 measured in MeCN containing Bu4NClO4.
23 The sequence of the arenes within the o-arylene can also
affect the onset of oxidation, specifically, 1.180 V (F-Ar-4),
1.172 V (F-Ar-6), 1.212 V (F-Ar-5) vs Ag/AgClO4 measured in
MeCN containing Bu4NClO4.
24 (a) Y.-W. Son, M. L. Cohen and S. G. Louie, Phys. Rev. Lett.
2006, 97, 216803. (b) S. Dutta and S. K. Pati, J. Mater. Chem.
2010, 20, 8207–8223.
25 (a) J. Cai, P. Ruffieux, R. Jaafar, M. Bieri, T. Braun, S.
Blankenburg, M. Muoth, A. P. Seitsonen, M. Saleh, X. Feng, K.
Müllen, K. and R. Fasel, Nature 2010, 466, 470–473. (b) L.
Lafferentz, V. Eberhardt, C. Dri, C. Africh, G. Comelli, F. Esch,
S. Hecht and L. Grill, Nature Chem. 2012, 4, 215–220. (c) Y.-C.
Chen, T. Cao, C. Chen, Z. Pedramrazi, D. Haberer, D. G. de
Oteyza, F. R. Fischer, S. G. Louie and M. F. Crommie, Nature
Nanotech. 2015, 10, 156–160.
26 Other metallic surfaces such as Cu(111) were explored but
Au(111) provide the best results.
8 | Chem. Sci.
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