Linear and Radial Conjugation in Extended π-Electron Systems

Article abstract of DOI:10.1021/jacs.9b10785

We describe the synthesis and electronic properties of new π-conjugated small molecules and polymers that combine the linear intramolecular conjugation pathways commonly associated with organic electronic materials with the emerging properties of radial c

Full text of DOI:10.1021/jacs.9b10785

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Article
Linear and radial conjugation in extended pi-electron systems
Garvin M Peters, Girishma Grover, Ruth L. Maust, Curtis E. Colwell, Haley Bates,
William Alexander Edgell, Ramesh Jasti, Miklos Kertesz, and John D. Tovar
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 14 Jan 2020
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Linear and radial conjugation in extended pi-electron systems
[1]
[3]
[4]
[4]
[1]
Garvin M. Peters, Girishma Grover, Ruth L. Maust, Curtis E. Colwell, Haley Bates,
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William A. Edgell, Ramesh Jasti, * Miklos Kertesz, * and John D. Tovar[1,2]*
[4]
[4]
[3]
[1] Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore,
Maryland 21218, United States
[2] Department of Materials Science and Engineering, Johns Hopkins University, 3400 North
Charles Street, Baltimore, Maryland 21218, United States.
[3] Chemistry Department and Institute of Soft Matter, Georgetown University, 37th and O Streets,
NW, Washington, DC, 20057, United States.
[4] Department of Chemistry and Biochemistry, Materials Science Institute, and Knight Campus
for Accelerating Scientific Impact, University of Oregon, Eugene, OR 97403 (USA)
*Corresponding author emails: rjasti@uoregon.edu, kertesz@georgetown.edu, tovar@jhu.edu
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Abstract
We describe the synthesis and electronic properties of new pi-conjugated small molecules and
polymers that combine the linear intramolecular conjugation pathways commonly associated with
organic electronic materials with the emerging properties of radial conjugation found in
cyclo(para-phenylene)s (CPPs) and other curved pi-surfaces. Using arylene ethynylenes as
prototypical linear segments and [6]/[8]CPP as the radial segments, we demonstrate the formation
of new electronic states that are not simply additive responses from the individual components.
Quantum chemical calculations of model oligomeric structures reveal these electronic processes
to arise from the hybrid nature of wavefunction delocalization over the linear and radial
contributors in the photophysically relevant electronic states.
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Introduction
Molecules with radial pi-conjugation as opposed to the more standard manifestations of
linear pi-conjugation have fascinated chemists for decades.1-3 Several isolated examples appeared
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during this time, including phenylene ethynylene macrocycles and picotubes, but the associated
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synthetic approaches entailed low-yielding multistep routes. In 2008, Jasti and Bertozzi
demonstrated an efficient chemical synthesis of one class of radially-conjugated macrocycles, the
cycloparaphenylenes (CPPs), an achievement that catalyzed renewed interest in the area of radial
pi-conjugation. Alternative synthetic methods were developed (such as those pioneered by Itami7
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9-12
and Yamago ), and new arylene units were incorporated into the belt-like structures.
The study
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of more general principles about strain-assisted reactivity, and supramolecular interactions was
enabled by the size-selective availability of CPPs ranging from 5 to 18 arylene units. CPPs and
related curved aromatic molecules can be thought of as diametral segments of (n,n) armchair
carbon nanotubes. Indeed, these structures serve as attractive precursors to extended carbon
nanotube segments: latently reactive pi-conjugated functionality can be incorporated on the CPP
“
edges” for potential chemistry to zip up a torsionally dynamic precursor into a rigid nanotube
segment.15,16 These and many other studies demonstrate that atomic control over [n]CPP structure
allows for new architectures and reactivities beyond models for graphene-like derivatives.
Despite all of these advances, the use of CPP radial conjugation has not been utilized in
the design of pi-conjugated polymeric materials, where the nature of the pi-electron circuits play
a critical role in defining the resulting electronic properties. Given that radical ions created within
CPPs are known to delocalize partially or entirely around the cyclic frameworks depending on the
molecular size,17-20 we felt this would be an attractive motif to extend delocalization in conjugated
polymer systems whereby excitons or charge carriers would freely migrate along the linear pi-
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conjugated backbone as well as radially through the CPP structure. This combination of radial
and linear conjugation could open up new possibilities for inter-polymer energy migration or even
supramolecular sensing schemes that blend the molecular selectivity expected for CPPs with the
sensitivity enhancements known for pi-conjugated electronic polymers. In this report, we describe
the synthesis of polymerizable CPP monomers and their subsequent polymerization into
conjugated polymers. We present computational studies to better understand the observed
electronic processes and to provide insight for future designs. The electronic properties of these
materials reveal unusual modes of delocalization not afforded by either the curved or linear pi-
conjugation pathways in isolation and offers a new vista for conjugated polymer electronics.
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Results and Discussion
Design
To extend linear pi-extension onto the CPP cores, [6]- and [8]CPP macrocycles were
synthesized with alkynes positioned para to each other on one phenylene unit thus establishing
nascent linear conjugation pathways. These pi-extending units were necessarily ortho-substituted
to the macrocycle ring connections, and this tetra-substituted phenylene unit effectively acts as a
central hub for both cyclic/radial conjugation around the curved macrocycle, and linear
conjugation through the conjugated alkyne substitutions (Figure 1, right). One would expect
electronic delocalization to be distributed over both the linear π system of the conjugated backbone
and that of the orthogonal curved CPP unit. Thus, intermolecular interactions could be facilitated
not only by the planar, rod like π surfaces of the main chain, but also by the convex and concave
surfaces of the off-chain CPPs. We initially targeted a series of conjugated materials that showed
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intimate mixing of CPP and linear polymer electronic states. To help understand these properties,
we also prepared a series of well-defined polymer and small molecule model systems for
spectroscopic
and
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comparisons.
Figure 1. Linear and curved delocalization pathways (left) can be conceptually merged into new
pi-electron materials (right).
Linear pi-extension of the CPP cores was first realized in the simplest cases through
diarylation, where either phenylene or thiophene rings were incorporated to produce small
molecules [n]-Ph and [n]-Th (Chart 1a). Model systems T-Ph and T-Th are based on terphenyl,
in which the central benzene is analogous to the tetrasubstituted ring featured in these CPPs, was
also synthesized to allow for comparisons between curved orthogonal pi-systems and those that
are linear. This also bears other consequences: while the phenylene units within the macrocycle
have a small amount of conformational freedom, they are relatively rigid in comparison to the
phenylenes present in terphenyl. These small model systems were then extrapolated to the
analogous polymer systems (P[n]-Ph and P[n]-Th, Chart 1b), which features a further-extended
linear conjugated backbone but also introduces isomeric variance. For example, one would expect
that for the polycondensations reported herein, the pendant macrocycles along the conjugated
backbone can orient themselves parallel to each other, zig-zagged, or a combination of the two.
These hybrid polymers are compared to model terphenyl polymers (PT-Ph and PT-Th) where the
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off-chain phenylene units are also free to rotate to avoid steric congestion unlike the constrained
CPP phenylene units.
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Chart 1. Structures of small molecule and polymeric CPP systems with linear pi-extension along
with model terphenyl variants (R = 2-ethylhexyl, R’ = octyl, Ph = phenyl, Th = thiophen-2-yl)
Synthesis
In order to incorporate polymerizable functionality into CPP monomers, we adapted our
well-established modular building block approach using cyclohexadiene moieties as masked
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benzene rings (Scheme 1). The key tetrasubstituted benzene ring linchpin 1 was prepared on
multigram scale from dibromo diiodo benzene via successive Sonogashira couplings (to install
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TMS acetylene) and Suzuki-Miyaura borylation (to install pinacolborane). Advanced CPP
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intermediates 2 and 3 were prepared using known synthetic methods developed previously by
Jasti and coworkers involving lithiation-addition steps with high control of diastereoselectivity,
followed by protection of the resultant alcohols as methyl or triethylsilyl ethers. In this manner,
curved intermediates with varying numbers of phenyl rings or cyclohexadienes as masked
phenylenes could be assembled rapidly, allowing formation of macrocycles in the next step.
Macrocyclizations of either 2 or 3 with bisboronate 1 were then carried out under dilute Suzuki
cross-coupling conditions to yield 4 and 5 in 22% and 29% yield, respectively. Finally, global
deprotection of the silyl groups and reductive aromatization using mild tin chloride conditions25
yielded the final dialkyne CPP monomers m[6] and m[8] in modest yields (Scheme 1). A
dialkynylated terphenyl model system mT (2’,5’-diethynyl-p-terphenyl) was also prepared with
relative ease in a route mirroring that of 1. 1,4-dibromo-2,5-diiodobenzene was subjected to double
Suzuki cross coupling to chemoselectively assemble the terphenyl core while Sonogashira
coupling of TMS acetylene and subsequent silyl deprotection afforded mT.
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Scheme 1. Synthesis of dialkynes m[6] and m[8] for linear pi-extension via Sonogashira
couplings. Reaction conditions: (a) 1, SPhos Pd Gen II, K PO (aq.), dioxane, 80° C; (b) (n-
3
4
Bu) NF, THF, r.t.; (c) H SnCl , THF, r.t.
4
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4
With the three monomers m[6], m[8] and mT in hand, further linear backbone π-extension
was accomplished through Sonogashira cross coupling reactions leading to well-defined small
molecule model systems (Chart 1, top) as well as polymers (Chart 1, bottom). The small molecules
([6]-Ph, [6]-Th, [8]-Ph and [8]-Th) consisted of [6]- and [8]CPP with central phenylacetylene and
thienylacetylene attachments. The polymers (P[6]-Ph, P[6]-Th, P[8]-Ph and P[8]-Th) were
prepared by copolymerization with the respective dialkyne monomers m[6] and m[8] with the
corresponding alkylated arylene dihalides. Terphenyl molecular (T-Ph and T-Th) and polymer
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(
PT-Ph and PT-Th) models were derived from similar couplings with mT. While these molecular
reactions went smoothly, there was a fair amount of insoluble compound obtained from the
polymerization reactions. Soxhlet extractions with methanol and acetone were used to remove
lower molecular weight impurities and the chloroform extracts were used for photophysical
analyses presented here. The GPC molecular weight data for all polymers are presented in Table
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1
. Although the GPC data for many of the CPP-containing polymers reflect small oligomers, we
noted substantial insolubilities in the concentrated THF solutions needed to introduce the polymers
into the mobile phase, so the data of Table 1 only reflect the smaller THF soluble oligomers. This
insoluble material was similar in appearance to the soluble polymers reported here, and potentially
represents higher molecular weight material that either was simply insoluble or may have been
supramolecularly crosslinked during polymerization by way of rotaxanation.
Table 1. Distribution of weight average (M ) and number average (M ) molecular weight and
dispersity (D) for the polymer systems as determined by Gel Permeation Chromatography in THF
along with the approximate numbers of repeat units.
w
n
PT-Ph
PT-Th
P[6]-Ph
P[6]-Th
P[8]-Ph
P[8]-Th
6877
Mw (~12
repeats)
771
175548
14765
21599
6333
9061
(~292 repeats)
50419
~8 repeats)(~84 repeats)
(~18 repeats) (~27 repeats)
(~7 repeats)(~9 repeats)
4482 6668
(~5 repeats)(~7 repeats)
1.41 1.36
4
(
6053
6535
Mn
(~8 repeats)
(~8 repeats)
D
1.44 3.48
2.44
3.36
Photophysical Properties
Extension of conjugation in m[6] and m[8] along the alkyne-containing pathway proved
to be more than a mere amalgamation of the two orthogonal π-systems (Figure 2 and Figure S21)
in line with our design expectation. In general, [n]CPPs have a characteristic peak absorption at
roughly the same energy (λ ≈340 nm) regardless of size. This corresponds to HOMO -1 and
abs
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HOMO-2 to LUMO, or HOMO to LUMO+1 or LUMO+2 transitions, as the HOMO-LUMO
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transition is for the most part forbidden. Smaller CPPs, such as [6]CPP, also feature a very broad
low energy absorption spanning ca. 400-525 nm (Figure 2 top, inset), which is proposed to be a
minor contribution from the forbidden HOMO-LUMO transition.27 Both [6]-Ph and [6]-Th also
have this feature (Figure 2 top inset and Figures S16, S17), though it is bathochromically shifted
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and with increased molar absorptivity. The low-energy shoulder seen in [8]CPP (ca. 405 nm) is
likely buried in the broad low-energy tails of [8]-Ph and [8]-Th. Diarylated monomers [6]-Ph and
[6]-Th possessed broadened absorptions that encompass the main CPP absorption, though [6]-Ph
has a more pronounced blue-shift of the major transition (λmax at 322 nm vs the λmax of 338 nm for
[6]-Th). [8]-Ph and [8]-Th similarly demonstrated pronounced blue-shifts and broadened spectral
footprints compared to parent [8]CPP (λmax= 321 nm and λmax= 329 nm vs λmax= 338, respectively,
Figure 2 bottom). The broadness of these absorptions can be attributed to the superimposition of
the alkyne-containing linear system with that of the curved CPP macrocycle. The diphenylated
CPPs [6]-Ph and [8]-Ph appears to have stronger contributions from the linear segment compared
to thienylated species [6]-Th and [8]-Th, where CPP is clearly the major contributor.
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Figure 2. UV-Vis spectra for oligomeric [6]-Ph (top) and [8]-Th (bottom) in comparison with the
respective CPP and terphenyl model compounds. Top: [6]-Ph (red dotted), T-Ph (gray solid),
[6]CPP (blue dashed). The low energy spectral region is magnified in the inset. Bottom: [8]-Th
(red dotted), T-Th (gray solid), [8]CPP (blue dashed).
To further understand the extent of linear and cyclic conjugation in these well-defined
arylene ethynylene/CPP hybrids, their spectral properties were compared to a truncated model
whereby the arylene ethynylene is attached to the central ring of a linear p-terphenyl chromophore
yielding T-Ph and T-Th (Chart 1). These models both have a high-energy signature associated
with the p-terphenyl core along with structured low-energy absorptions arising from the arylene
ethynylene segment (Figure S20) at ca. 330 nm and 350 nm (for T-Ph) or at ca. 360 nm and 375
nm (for T-Th). These structured low-energy features coincide with those from the CPP itself as
well as from the respective [6]-Ph/Th and [8]-Ph/Th small molecule systems but the lack of fine
structure coupled with the spectral broadening in the latter molecules clearly show that the
electronic properties of CPP and the orthogonal arylene ethynylenes are not simply additive but
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rather that new electronic states are emerging even at this small molecule level. The decreased
torsional freedom of the phenylenes when constrained within the CPP core vs the linear terphenyl
unit is recognized.
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Short π-extensions through addition of benzene or thiophene on the dialkynylated core had
subtle but important impacts on the resulting photophysics, and these effects were strongly
magnified in the corresponding conjugated polymers. m[6], m[8] and the linear terphenyl model
mT were polymerized with either a dialkylated phenyl or thienyl co-monomer. As a benchmark,
the terphenyl-based polymer with the phenylene-ethynylene backbone PT-Ph presented a low
energy absorption at 389 nm (with a pronounced shoulder at ca. 415 nm) associated with the
linearly conjugated backbone, along with higher-energy absorption around 285 nm associated with
the terphenyl moiety. P[6]-Ph possessed one major absorption at 348 nm which correlates with
the pendant CPP macrocycle along the polymer backbone (Figure 3), along with a lower energy
broad feature at 438 nm that we assign to the conjugated polymer backbone and the shallow
absorption out to 550 nm also found for the parent [6]CPP and [6]-Ph (Figure 2a inset). Because
the shoulder is further red-shifted and broader compared to that of the model polymer’s sharp onset
of absorption, this is not simply an artifact of any inherent molecular weight differences but
suggests new electronic states that are not additive from the [6]CPP and the associated phenylene
ethynylene backbone. The analogous thienylene ethynylene P[6]-Th demonstrated similar
photophysical responses, showing a broad low energy ethynylene-based band at 450 nm along
with a higher-energy CPP-based band at 350 nm. Here, the low-energy band corresponding to the
alkyne-containing conjugated pathway is more coincident with that of the model species PT-Th
(abs at 440 and 465 nm albeit lacking the vibronic structure) and of the shallow tail of the CPP
core extending to 550 nm.
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Figure 3. Absorption spectra of [6]CPP polymers with phenylene ethynylene (P[6]-Ph, top) and
thienylene ethynylene (P[6]-Th, bottom) linear conjugation linkages, illustrating the impact of
gradually extending the orthogonal conjugated system relative to the small molecule models and
the polymerized terphenyl analogues. Top: P[6]-Ph (black solid), [6]-Ph (red dotted), PT-Ph
(gray solid), [6]CPP (blue dashed). Bottom: P[6]-Th (black solid), [6]-Th (red dotted), PT-Th
(gray solid), [6]CPP (blue dashed).
As with [6]CPP containing polymers P[6]-Ph and P[6]-Th, there is little change in the
energy of the major [8]CPP-based transition at 335-340 nm upon polymerization of m[8] (Figure
). Both P[8]-Ph and P[8]-Th contain this characteristic signature along with the absorption
4
arising from the conjugated polymer backbone, with variances due to the extent of polymerization.
Since the low energy shoulder (ca. 400-450 nm) associated with [8]CPP molecules extends to a
lesser degree into the visible region than [6]CPP, it is more effectively masked by the polymer
absorption. However, the much stronger intensities for the low energy absorptions of the P[8]-Ph
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and -Th polymers suggests these are not arising solely from CPP-based transitions but rather
reflect the dual nature of the cyclic and linear conjugation. This is most pronounced in P[8]-Th
where the broad shoulder extending from ca. 400-500 nm is quite distinct from the vibronic
features present in the PT-Th model polymer at 440 nm and 465 nm (Figure 4).
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Figure 4. Absorption spectra of [8]CPP polymers with phenylene ethynylene (P[8]-Ph, top) and
thienylene ethynylene (P[8]-Th, bottom) linear conjugation linkages, illustrating the impact of
gradually extending the orthogonal conjugated system relative to the small molecule models and
the polymerized terphenyl analogues. Top: P[8]-Ph (black solid), [8]-Ph (red dotted), PT-Ph (gray
solid), [8]CPP (blue dashed). Bottom: P[8]-Th (black solid), [8]-Th (red dotted), PT-Th (gray
solid), [8]CPP (blue dashed).
To further probe the electronic processes operative within the hybrid radial-linear pi-
electron materials, photoluminescence spectra were recorded (Figure 5). [6]CPP by itself is
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negligibly photoluminescent, and this carried over into [6]-Ph/Th and the corresponding polymers
P[6]-Ph/Th. [8]CPP in contrast shows a peak luminescence at 535 nm, and the hybrid materials
also show different extents of photoluminescence. The emission profile for the oligomeric and
polymeric phenylated [8]CPPs are very similar to this parent CPP emission although slightly
redshifted (ca 10-25 nm: Figure 5, top). Notably, the luminescence from the phenylene ethynylene
backbone of PT-Ph falls at a much higher energy (430 nm peak emission with a 460 nm vibronic
shoulder), which suggest that the CPP moiety is dominating the excited state processes for these
structures albeit with some energetic influence from the attached linearly conjugated chains. In
the phenylated CPP cases, the substantial Stokes’ shifts indicate pronounced excited state
planarization/reorganization. In contrast, the emission profile for the thienylated [8]CPP
analogues demonstrate much more pronounced differences (Figure 5, bottom). [8]-Th
fluorescence almost mirrors that of [8]-Ph falling at 560 nm, again redshifted by 25 nm from the
[8]-CPP core. The corresponding CPP-based thienylene ethynylene polymer P[8]-Th is more
drastically blue-shifted and vibronically structured (peaks at 515 nm and 560 nm) than is [8]-Th
but is more red shifted than is the corresponding terphenyl model PT-Th (with peaks at 485 nm
and 520 nm). Clearly the excited state electronic structure of P[8]-Th is much more than an
additive response from the thienylene ethynylene linear backbone and the CPP radial pendant
components.
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Figure 5. Photoluminescence spectra for [8]CPP-based pi-extended small molecules and polymers
compared to those of the linear analogues. Top: P[8]-Ph (black solid), [8]-Ph (red dotted), PT-
Ph (gray dotted). Bottom: P[8]-Th (black solid), [8]-Th (red dotted), PT-Th (gray dotted).
Computational Studies
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All calculations were performed using Gaussian 16. All optimizations on small molecules
and oligomers were performed using ground state DFT calculations with PBE1PBE/6-31G(d). 8,9
Excited state calculations were performed using TD-DFT. All the UV-Vis absorption spectra were
-1
obtained with broadening of Half Width at Half Height of 0.2 eV or 1613 cm .
We present here our results on oligomeric repeat units of the corresponding polymers.
These are named here as nT-Th/Ph and n[6/8]-Th/Ph where n refers to the length of the
oligomeric repeat unit. For simplifying the calculations all alkyl groups of the n[6/8]-Th/Ph
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oligomers were replaced by methyl groups (See details in SI and Figure S1). For example, the
trimeric structure of P[6]-Ph with the alkyl groups replaced by methyl groups is named 3[6]-Ph.
Before modeling the UV-vis spectra associated with these defined oligomers, we validated our
computational approach by using the well-defined molecular structures listed in Chart 1a.
Accordingly, the average predicted UV-vis peak positions are 8 nm shifted to the longer
wavelengths compared to the respective experiments. The range of this prediction error is between
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-29 and 24 nm, the maximum error is 8 %. The high reliability of the computations is essential in
evaluating the polymer predictions. Furthermore, we assessed the effect of
conformational/torsional degrees of freedom along the linear backbones on the UV-vis spectra, an
essential element in the discussion of polyaromatic conjugated polymers. As shown in the SI
section, variations of the main peak at 450 nm can be as large as 100 nm due to the conformational
flexibility around the linear C alkyne group. Thus, it is possible that in solution various
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conformers coexist such that in some molecules the extended conjugation is disrupted limiting the
effective conjugation length along the main chain as known in other conjugated polymers as well.28
The polymer UV-vis spectra for all six polymer systems in Table 1 were modeled by a
succession of different size oligomers with n=2, 3, and in some cases 4, with details provided in
the SI. The extrapolation to polymers of infinite length was based on a linear regression between
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/λ of the lowest energy transition as a function of 1/n.29 Accordingly, the predicted long
wavelength polymer peak is very substantially red shifted, as shown in Table S2. For example, for
PT-Th, the predicted maximum is at 605 nm, while the experimental low energy peak value is
around 440-500 nm. This difference is much larger than expected based on the validation described
above. We can see that the corresponding predicted wavelengths for other polymers are still
significantly larger (red shifted) as well compared to the experiment. Using the 1/λ vs. 1/n linear
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fit, and substituting the experimental peak value for the polymer we obtained approximate
conjugation lengths that are shown in Table S2. The observed peak wavelength of 440-500 nm of
PT-Th corresponds to a chain length of only 1.7 – 2.7 units, an effective conjugation length
corresponding to a dimer or trimer. The fact that the polymer absorption bands are broader than
the bands of the monomers then can be attributed to a distribution of different chain lengths and
different conformational defects limiting the range of delocalization to about two to three units on
average. The corresponding conjugation lengths ranges are shown in Table S2.
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The experimental molecular weight data indicate diverse ranges of average chain lengths
for different polymers ranging from approx. 5 to 292 units (Table 1, which is likely an
underestimate based on solubility in the GPC analyte solution and the restricted hydrodynamic
radii of the CPP units on the polymer backbones). On the other hand, the computed UV-vis spectra
data indicate that the effective conjugation length is typically limited to about 1 to 3 units for these
polymers, except for P[6]-Th which is in the 1-10 unit range (Table S2). For this reason, we argue
that conformational defects must be present that reduce the effective conjugation length and limit
it to only a few repeat units. With this interpretation, we should not be surprised that the
experimentally observed peaks are close to the predicted peaks for the systems such as 2T-Th, 2T-
Ph, 2[8]-Th, and 3[6]-Th and not the predicted extrapolated polymer values (Table S2).
The low energy shoulder observed for the P[n]-Th and -Ph polymers in the UV-Vis
experiment, especially for P[8]-Th, are indicative of a broad distribution of conjugation lengths.
However, the UV-vis spectra alone cannot provide detailed information on such a distribution. It
is interesting that the respective UV-Vis experimentally observed bands for the model systems
without CPP units, PT-Th and PT-Ph are also very broad but appear at a larger relative intensity
compared to the higher energy peaks. The HOMO-LUMO transitions in [n]CPPs are forbidden in
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26,30,31
the ideal D symmetry or nearly forbidden in the real systems that have a lower symmetry.
nh
The respective lowest energy peaks show up as weak absorption peaks that are increasing in
relative intensity as the CPPs are substituted by linearly conjugated side groups. This effect is a
proof of the linear-radial conjugation that was postulated at the onset of this study. This linear-
radial conjugation effect is completely absent in the terphenyl derivatives, where this long
wavelength tail is missing in the absorption spectrum.
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It is important to recognize that the enhanced low energy shoulder seen in the experimental
spectra for the polymers, especially most clearly for P[8]-Th, is not simply an enhanced HOMO-
LUMO transition of the [8]CPP part of the polymer. This is most clearly seen in the computed
spectrum of 2[8]-Th and 3[8]-Th (Figures S8c, S8f) where the lowest energy transition (HOMO
to LUMO) with oscillator strength of 1.4 and 2.4, respectively, is localized on the linear conjugated
components, unlike the monomer 1[8]-Th (Figures S8a, S8b) where the major contribution from
the radial conjugated component makes the HOMO to LUMO transition with oscillator strength
of 0.09 only slightly allowed. These strongly allowed transitions overwhelm the weakly allowed
HOMOLUMO transitions of the CPP moieties. The polymers containing [6]CPP are different:
here the CPP and the linear conjugated parts display significant mixing in the HOMO, while the
LUMO is localized mostly on the linear part (Figure 6).
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Figure 6. The conjugation in an optimized geometry of 3[6]-Th in HOMO (bottom) and LUMO
(top) orbitals showing the hybrid contributions from both the linear and radial components.
On the other hand, the next two to three higher energy transitions for all four CPP polymers
display various signs of unique behavior not seen in isolated CPPs or in linear conjugated
polymers. While each individual case is different, the following types of such new transitions are
seen in the oligomer computations: transitions involving orbitals localized mostly on the CPP part
to orbitals localized mostly on the linear part or vice versa. Then some transitions are comprised
of orbitals containing genuine mixing between the linear and radial conjugated components for
either one or both orbitals involved in the transition. For example, a strong radial to linear
conjugated transition for 3[6]-Ph at 460 nm has a dominant contribution from HOMO-1 to
LUMO+1 as illustrated in Figure 7.
Figure 7. The mixing of linear vs. radial conjugation in the computed absorption spectrum of 3[6]-
Ph at 460 nm is evident in the HOMO-1 (top) and LUMO+1 (bottom) surfaces.
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The situation for the model systems with terphenyl in place of the CPP components is
somewhat different. For both 3T-Th and 3T-Ph, the lowest energy transition is mostly HOMO
LUMO, and includes primarily the main chain. However, this transition does not overlap with the
low energy transition of the terphenyl component, since that is not forbidden as opposed to the
CPP case. The higher energy transitions involve orbitals for 3T-Ph that are mostly confined to the
main chain. However, in the case of 3T-Th, the higher energy transitions are similar to those of
the CPP based polymers. The thiophene is linked to the linear chain at the 2,5 positions in 3T-Th
resulting in a slight bending of the backbone contributing to the disruption of the extended
conjugation and thus delocalization on terphenyl. On the other hand, in the case of the phenyl
substituted polymer, the linkage at 2,5 positions makes the backbone more linear and thus, the
delocalization within the backbone is retained in a larger degree as illustrated in Figure S22. In
case of 3T-Ph, we observed similar behavior as in the CPPs except the oscillator strength is
comparatively smaller.
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Conclusions
Novel CPP syntheses and functionalizations have provided access to a wide range of
curved pi-conjugated systems possessing intriguing electronic properties. We report late stage
modifications of a proven synthetic path towards CPPs to realize dialkyne-functionalized CPP
monomers containing 6- and 8 phenylene units. Both short and long pi-extensions of the radial
CPP core were prepared and compared to linear terphenyl model systems to investigate the impact
of having a hybrid linear-radial conjugated system. Differences in the absorption and
photoluminescence profiles of extended small molecules and polymers attest to the non-additive
combinations of linear and radial pi-conjugation, indicting the crafting of new electronic processes
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in these hybrid materials. Computational modeling suggests that, while the effective conjugation
lengths of these systems may be limited, there are many accessible electronic states that are well
beyond simple combinations of the separate linear and radially-oriented conjugation pathways.
Our future work will examine new ways to encourage intramolecular and intermolecular electronic
delocalization that may take advantage of this merger of linear and radial conjugation.
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Supporting Information. Synthetic and computational procedures, comparisons of
calculated and experimental UV-vis absorption energies, computed UV-vis spectra, torsional angle
variation studies, orbitals for important energy levels, additional UV-vis experimental spectra,
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GPC chromatographs, and H and C NMR spectra.
Acknowledgements. We thank the Department of Energy Office of Basic Energy Science
for support of this research (DE-SC0019017). R. M. was supported by the NSF Graduate Research
Fellowship (1309047). We thank Mr. Eric Peterson (JHU) for assistance with spectral
measurements.
References
(
1)
Indian Chemical Society 1934, 11, 95-100.
2) Friederich, R.; Nieger, M.; Vögtle, F. Auf dem Weg zu makrocyclischen para-
Phenylenen. Chemische Berichte 1993, 126, 1723-1732.
3) Scott, L. T. Conjugated Belts and Nanorings with Radially Oriented p Orbitals.
Angewandte Chemie International Edition 2003, 42, 4133-4135.
4) Kawase, T.; Darabi, H. R.; Oda, M. Cyclic [6]- and [8]Paraphenylacetylenes.
Angewandte Chemie International Edition in English 1996, 35, 2664-2666.
(5) Kammermeier, S.; Jones, P. G.; Herges, R. Ring-Expanding Metathesis of
Parekh, V. C.; Guha, P. C.: Synthesis of p,p-diphenylene disulfide Journal of the
(
(
(
Tetradehydro-anthracene—Synthesis and Structure of a Tubelike, Fully Conjugated
Hydrocarbon. Angewandte Chemie International Edition in English 1996, 35, 2669-2671.
22
ACS Paragon Plus Environment

Page 23 of 25
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
(
6)
Jasti, R.; Bhattacharjee, J.; Neaton, J. B.; Bertozzi, C. R. Synthesis,
Characterization, and Theory of [9]-, [12]-, and [18]Cycloparaphenylene: Carbon Nanohoop
Structures. Journal of the American Chemical Society 2008, 130, 17646-17647.
(7)
of [12]Cycloparaphenylene. Angewandte Chemie International Edition 2009, 48, 6112-6116.
8) Yamago, S.; Watanabe, Y.; Iwamoto, T. Synthesis of [8]Cycloparaphenylene from
Takaba, H.; Omachi, H.; Yamamoto, Y.; Bouffard, J.; Itami, K. Selective Synthesis
(
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
a Square-Shaped Tetranuclear Platinum Complex. Angewandte Chemie International Edition
2010, 49, 757-759.
(
9)
models of helical (n,m)-single-wall carbon nanotubes. Nature Communications 2011, 2, 492.
10) Iwamoto, T.; Kayahara, E.; Yasuda, N.; Suzuki, T.; Yamago, S. Synthesis,
Hitosugi, S.; Nakanishi, W.; Yamasaki, T.; Isobe, H. Bottom-up synthesis of finite
(
Characterization, and Properties of [4]Cyclo-2,7-pyrenylene: Effects of Cyclic Structure on the
Electronic Properties of Pyrene Oligomers. Angewandte Chemie International Edition 2014, 53,
6
2
430-6434.
(11) Matsui, K.; Segawa, Y.; Itami, K. Synthesis and Properties of Cycloparaphenylene-
,5-pyridylidene: A Nitrogen-Containing Carbon Nanoring. Org Lett 2012, 14, 1888-1891.
(12) Tran-Van, A.-F.; Huxol, E.; Basler, J. M.; Neuburger, M.; Adjizian, J.-J.; Ewels, C. P.;
Wegner, H. A. Synthesis of Substituted [8]Cycloparaphenylenes by [2 + 2 + 2] Cycloaddition. Org
Lett 2014, 16, 1594-1597.
(13) Schaub, T. A.; Margraf, J. T.; Zakharov, L.; Reuter, K.; Jasti, R. Strain-Promoted
Reactivity of Alkyne-Containing Cycloparaphenylenes. Angewandte Chemie International
Edition 2018, 57, 16348-16353.
(14) Xu, Y.; Wang, B.; Kaur, R.; Minameyer, M. B.; Bothe, M.; Drewello, T.; Guldi, D.
M.; vonꢀDelius, M. A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in
Modular Porphyrin–[10]CPP⊃Fullerene Complexes. Angewandte Chemie International Edition
2018, 57, 11549-11553.
(
15) Golling, F. E.; Quernheim, M.; Wagner, M.; Nishiuchi, T.; Müllen, K. Concise
Synthesis of 3D π-Extended Polyphenylene Cylinders. Angewandte Chemie International Edition
014, 53, 1525-1528.
16) Golder, M. R.; Colwell, C. E.; Wong, B. M.; Zakharov, L. N.; Zhen, J.; Jasti, R.
2
(
Iterative Reductive Aromatization/Ring-Closing Metathesis Strategy toward the Synthesis of
Strained Aromatic Belts. Journal of the American Chemical Society 2016, 138, 6577-6582.
(17) Fujitsuka, M.; Tojo, S.; Iwamoto, T.; Kayahara, E.; Yamago, S.; Majima, T. Radical
Ions of Cycloparaphenylenes: Size Dependence Contrary to the Neutral Molecules. The Journal
of Physical Chemistry Letters 2014, 5, 2302-2305.
(18) Kayahara, E.; Kouyama, T.; Kato, T.; Yamago, S. Synthesis and Characterization of
[
n]CPP (n = 5, 6, 8, 10, and 12) Radical Cation and Dications: Size-Dependent Absorption, Spin,
and Charge Delocalization. Journal of the American Chemical Society 2016, 138, 338-344.
19) Toriumi, N.; Muranaka, A.; Kayahara, E.; Yamago, S.; Uchiyama, M. In-Plane
(
Aromaticity in Cycloparaphenylene Dications: A Magnetic Circular Dichroism and Theoretical
Study. Journal of the American Chemical Society 2015, 137, 82-85.
(20) Talipov, M. R.; Jasti, R.; Rathore, R. A Circle Has No End: Role of Cyclic Topology
and Accompanying Structural Reorganization on the Hole Distribution in Cyclic and Linear Poly-
23
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Page 24 of 25
1
2
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7
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1
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1
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4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
p-phenylene Molecular Wires. Journal of the American Chemical Society 2015, 137, 14999-
1
5006.
(21) Darzi, E. R.; Sisto, T. J.; Jasti, R. Selective Syntheses of [7]–
[12]Cycloparaphenylenes Using Orthogonal Suzuki–Miyaura Cross-Coupling Reactions. The
Journal of Organic Chemistry 2012, 77, 6624-6628.
(22) Duhović, S.; Dincă, M. Synthesis and Electrical Properties of Covalent Organic
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
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0
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2
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4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Frameworks with Heavy Chalcogens. Chem Mater 2015, 27, 5487-5490.
(23) Darzi, E. R.; White, B. M.; Loventhal, L. K.; Zakharov, L. N.; Jasti, R. An
Operationally Simple and Mild Oxidative Homocoupling of Aryl Boronic Esters To Access
Conformationally Constrained Macrocycles. Journal of the American Chemical Society 2017,
1
39, 3106-3114.
24) Lovell, T. C.; Colwell, C. E.; Zakharov, Lev N.; Jasti, R. Symmetry breaking and the
turn-on fluorescence of small, highly strained carbon nanohoops. Chemical Science 2019, 10,
786-3790.
25) Patel, V. K.; Kayahara, E.; Yamago, S. Practical Synthesis of
n]Cycloparaphenylenes (n=5, 7–12) by H2SnCl4-Mediated Aromatization of 1,4-
Dihydroxycyclo-2,5-diene Precursors. Chemistry – A European Journal 2015, 21, 5742-5749.
26) Iwamoto, T.; Watanabe, Y.; Sakamoto, Y.; Suzuki, T.; Yamago, S. Selective and
(
3
(
[
(
Random Syntheses of [n]Cycloparaphenylenes (n = 8–13) and Size Dependence of Their
Electronic Properties. Journal of the American Chemical Society 2011, 133, 8354-8361.
(
27) Xia, J.; Jasti, R. Synthesis, Characterization, and Crystal Structure of
[6]Cycloparaphenylene. Angewandte Chemie International Edition 2012, 51, 2474-2476.
28) Patel, G. N.; Chance, R. R.; Witt, J. D. A planar–nonplanar conformational
transition in conjugated polymer solutions. The Journal of Chemical Physics 1979, 70, 4387-
392.
(
4
(29) Cui, C. X.; Kertesz, M.; Jiang, Y. Extraction of polymer properties from oligomer
calculations. The Journal of Physical Chemistry 1990, 94, 5172-5179.
30) Nishihara, T.; Segawa, Y.; Itami, K.; Kanemitsu, Y. Excited States in
(
Cycloparaphenylenes: Dependence of Optical Properties on Ring Length. The Journal of Physical
Chemistry Letters 2012, 3, 3125-3128.
(31) Adamska, L.; Nayyar, I.; Chen, H.; Swan, A. K.; Oldani, N.; Fernandez-Alberti, S.;
Golder, M. R.; Jasti, R.; Doorn, S. K.; Tretiak, S. Self-Trapping of Excitons, Violation of Condon
Approximation, and Efficient Fluorescence in Conjugated Cycloparaphenylenes. Nano Letters
2
014, 14, 6539-6546.
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