Doublet Chirality Transfer and Reversible Helical Transition in Poly(3,5-disubstituted phenylacetylene)s with Pyrene as a Probe Unit?

Article abstract of DOI:10.1002/cjoc.202000020

A novel doublet chirality transfer (DCT) model was demonstrated in cis poly(3,5-disubstituted phenylacetylene)s, i.e., S-I, R-I, and S-I-NMe. The chiral message from the stereocenter of alkylamide substituent at 3-position induced the polyene backbone to take cis-transoid helical conformation with a predominant screw sense. And in turn the helical backbone acted as a scaffold to orient the pyrene probes, which was linked to phenyl rings through 5-position, to array in an asymmetric manner. A combinatory analyses of ¹H NMR, Raman, FTIR, UV-vis absorption, CD, and computer simulation suggested that the main-chain stereostructure, solvent nature, and intramolecular hydrogen bonds played important and complex roles on DCT. High cis-structure content and intramolecular hydrogen bonds were beneficial for the realization of DCT. Reversible helix-helix transition was observed in S-I by changing the nature of solvents. In DMF, S-I adopted a relatively contracted helix, where the main chain exhibited strong optical activity, but that of pyrene was weak. In contrast, a relatively stretched helix formed in CHCl₃, in which the optical activity of pyrene was much larger, whereas that of the polyene backbone was the weakest. This helix-helix transition was attributed to the intramolecular hydrogen bonds, which was confirmed by solution-state FTIR spectra and computer calculations.

Full text of DOI:10.1002/cjoc.202000020

Chinese Journal
of Chemistry
CJC
中 国 化 学 - An International Journal
Accepted Article
Title: Doublet Chirality Transfer and Reversible Helical Transition in Poly(3,5-
disubstituted phenylacetylene)s with Pyrene as a Probe Unit
Authors: Sheng Wang, Xuanyu Feng, Jie Zhang, and Xinhua Wan*
This manuscript has been accepted and appears as an Accepted Article online.
This work may now be cited as: Chin. J. Chem. 2020, 38, 10.1002/cjoc.202000020.
The final Version of Record (VoR) of it with formal page numbers will soon be
published online in Early View: http://dx.doi.org/10.1002/cjoc.202000020.
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Doublet Chirality Transfer and Reversible Helical Transition in
Poly(3,5-disubstituted phenylacetylene)s with Pyrene as a Probe Unit
Sheng Wang,a Xuanyu Feng,a Jie Zhang,a and Xinhua Wan*,a
aBeijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
Summary of main observation and conclusion A novel doublet chirality transfer (DCT) model was demonstrated in cis poly(3,5-disubstituted
phenylacetylene)s, i.e., S-I, R-I, and S-I-NMe. The chiral message from the stereocenter of alkylamide substituent at 3-position induced the polyene
backbone to take cis-transoid helical conformation with a predominant screw sense. And in turn the helical backbone acted as a scaffold to orient the
pyrene probes, that was linked to phenyl rings through 5-position, to array in an asymmetric manner. A combinatory analyses of 1H NMR, Raman, FTIR,
UV-vis absorption, CD, and computer simulation suggested that the main-chain stereostructure, solvent nature, and intramolecular hydrogen bonds
played important and complex roles on DCT. High cis-structure content and intramolecular hydrogen bonds were beneficial for the realization of DCT.
Reversible helix-helix transition was observed in S-I by changing the nature of solvents. In DMF, S-I adopted a relatively contracted helix, where the main
chain exhibited strong optical activity, but that of pyrene was weak. In contrast, a relatively stretched helix formed in CHCl3, in which the optical activity of
pyrene was much larger, whereas that of the polyene backbone was the weakest. This helix-helix transition was attributed to the intramolecular hydrogen
bonds, which was confirmed by solution-state FTIR spectra and computer calculations.
MB bridged by Azo-POM. Yashima and co-workers dexterously
Background and Originality Content
used the induced helical PPAs as a novel template for the
Since the discovery of helical conformations in biopolymers,[1]
formation of supramolecular helical aggregates of achiral
porphyrin[12] and cyanine[13] dyes in water, also embodying the
synthetic scientists have developed various artificial helical
polymers and supramolecules,[2] some of which have been utilized
in chiral separation,[3] asymmetric synthesis,[4] and so on.[5] When
functionalized units are introduced, they are usually linked
directly with or close to the chiral centers for the better chiral
transition.[6] Such a strategy not only makes molecular design less
flexible, but could bring about some undesired effects. As an
example, optical active helical poly(phenylacetylene)s (PPAs)
containing cinchona alkaloid pendants were found to promote
asymmetric synthesis.[4a,7] However, the enantioselectivities of
some polymers were lower than the corresponding monomers
due to the antagonism effect exerted by the configuration chirality
of stereo centers and the conformation chirality of polymer
idea of DCT. Recently, Lee[14] and Maeda[15] actualized DCT in
poly(phenylacetylene)-g-poly(isocyanate) by means of domino
effect and a preferred-hand helicity was unerringly imparted to
the PPA backbone. However, the examples on DCT were very
limited and astaticism in supramolecular system hampered the
development of DCT. Universal DCT system is to be empoldered to
realize the functionalization of helical polymers.
PPAs are a classical type of dynamic helical polymers. They
have attracted wide attentions for their robust tunable
conformations and multiple functions.[2a,16] Most PPAs reported in
literature
are
derived
from
para-substituted
phenylacetylenes.[2a,16a] Introducing two or more substituents on
the phenyl ring of PPA could supply more structural variety and
function capacity for material design, but is seldom approached.[17]
backbone. In
a contrast, Feringa, Roelfes, and co-workers
successfully built an interesting chiral catalyst system by linking
achiral catalytic sites to DNA double helices and achieved
excellent enantioselectivities (up to 99 ee%).[8] Similarly,
Recently, we have designed and synthesized
a series of
poly(3,5-disubstituted phenylacetylene)s, and carefully studied
their helical structures and chirality amplification.[18] Herein, we
give a new model of DCT based on 3,5-disubstituted PPAs
(Scheme 1), in which functional and chiral inducing substituents
are separated. At first, chirality is transferred to PPA backbone
Suginome
et
al.
prepared
a
series
of
poly(quinoxaline-2,3-diyl)-based chiral catalysts through the
copolymerization of chiral quinoxaline-2,3-diyl monomers without
metal-binding
sites
and
achiral
monomers
bearing
diarylphosphino pendant as the metal-binding sites.[9] The 3D
asymmetric environment provided by the single-handed helical
structure of poly(quinoxaline-2,3-diyl) endowed the polymeric
metal complex with an excellent enantioselectivity in a number of
organic reactions. These results suggest a route to construct novel
chiral materials avoiding antagonism by separating functional sites
and chiral inducing groups.
from the chiral amide pendant and induces
a preferred
one-handed helical conformation of polyene main chain. Then the
achiral functional group is further dictated to arrange in helical
form for the transition of chirality from the main-chain helical
conformation. This separation of functional group and chiral
inducing group not only enhances flexibility of molecular design,
but also provides a novel type of chiral transfer, which may be
able to attenuate the antagonism.
Doublet chirality transfer (DCT), first mentioned by Gawrooski
et al. and applied to determine the absolute configuration of
chiral amines,[10] is seldom employed in the helical polymer
system. Wu et al. built a three component system consisting of
azobenzene-modified Anderson-type polyoxometalate (POM),
α-CD, and methylene blue dye (MB) via multi-supramolecular
interactions.[11] Chirality was efficiently transferred from α-CD to
Scheme 1 Synthesis of R-I, S-I, and S-I-NMe
*E-mail: xhwan@pku.edu.cn
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
10.1002/cjoc.202000020
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Wang et al.
Report
thermal resistance and possessed the temperatures of 5% weight
loss (Tds) under inert atmosphere above 310 oC.
Results and Discussion
Three novel PPAs, i.e., R-I, S-I, and S-I-NMe, were designed
and synthesized in the present work. Disubstitution at
meta-positions could endow the polymer with great
macromolecular design freedom and robust functional capacity.
The amide hydrogen of S-I was substituted by methyl group as in
S-I-NMe to understand how the intramolecular hydrogen bonds
influence DCT.
Synthesis. As outlined in Scheme S1, the monomer
preparation
(R)/(S)-3-methoxycarbonyl-5-[(1-phenylethyl)carbamoyl]phenylac
etylene (R-III/S-III) and
began
with
(S)-3-methoxycarbonyl-5-[N-methyl-(1-phenylethyl)carbamoyl]ph
enylacetylene (S-III-NMe), the synthesis of which was reported
previously.[18b] The ester bonds in R-III, S-III and S-III-NMe were
cleaved in a strong basic medium. The followed acidification gave
the corresponding acid. The resultant acids underwent
esterification with 1-pyrenemethanol, in the presence of
1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride
(EDC) and 4-(dimethylamino)pyridine (DMAP) to yield the target
monomers, R-II, S-II, and S-II-NMe. R-II and S-II precipitated from
CH2Cl2, the reaction solvent, for their poor solubility, and were
obtained with enough purity just by filtration and washing with
CH2Cl2 for three times to remove the residual impurities. The
crude product of S-II-NMe was purified by column
chromatography. All of the new compounds were identified by 1H
NMR and 13C NMR spectroscopy as well as high-resolution mass
spectrometry (Figures S1-S9).
Figure 1 1H NMR spectra (400 MHz) of S-II and S-I-HE in d6-DMSO.
1
Figure 1a depicts the H NMR spectrum of monomer S-II in
DMSO-d6. The resonance absorption at δ = 4.41 ppm was
assigned to ethynylic proton. The protons of phenyl ring bearing
acetylene triple bond and those of pyrene group resonated from
8.57 to 8.03 ppm. The signal of amide proton was observed at δ =
9.10 ppm. Although well-resolved proton NMR spectrum was
recorded for S-II, S-I was unable to be characterized clearly in
either CDCl3 or DMF-d7 (Figure S10) for its large and crowded
side-groups, which restricted proton mobility and shielded
backbone signal. To characterize the stereostructure of S-I, this
polymer was transformed to S-I-HE through hydrolysis by TFA and
subsequent esterification with trimethylsilyldiazomethane
(Scheme 2). As shown in Figure 1b, the resonances of protons of
the ester (CO2CH3), chiral carbon atom (HC), and amide (HNCO)
groups were observed at 3.55, 5.04, and 8.82 ppm, respectively.
Moreover, the resonance absorption of ethynylic proton at 4.41
ppm disappeared after polymerization, and a new olefinic proton
peak at δ = 5.67 ppm appeared from the conjugated main chain.
The cis-structure content of S-I was estimated as 97%, according
to the calculation method developed by Percec and co-workers.[19]
The stereostructure of R-I was characterized with a similar
method. The detailed results are summarized in Table 1.
Table 1 Polymerization results and properties of polymersa
Monomer Solventb Conv. (%)c Mn/104e
PDIe
1.71
1.85
2.12
Cis (%)f Td (oC)h
93
22.9
20.8
7.4
S-II
R-II
DMF
DMF
THF
97
95
315
316
315
90
87d
g
S-II-NMe
-
aCarried out at room temperature under nitrogen for 12 h; [M] = 0.06 M,
[cat.]
=
1.5 mM. bPolymerization solvent. cAcetone-insoluble part.
dAcetone/CH3OH (v/v, 1/1)-insoluble part. eEstimated by GPC in THF on
the basis of a polystyrene calibration. fDetermined by 1H NMR analysis.
gUnable to be accurately determined by 1H NMR analysis. h5% weight loss
temperature under nitrogen atmosphere at a heating rate of 20 oC/min.
Polymerization. The monomers were polymerized in solution
at 25 oC by using [Rh(nbd)Cl]2 as the catalyst with a constant
monomer/catalyst molar ratio of 40/1 (Scheme 1). DMF was
chosen as the polymerization solvent of S-II and R-II while THF
was chosen as the solvent for S-II-NMe, depending on their
solution power toward both monomers and polymers. The
reaction mixtures became very viscous within 30 min in all cases.
After 12 h, the obtained polymers R-I/S-I and S-I-NMe were
collected by precipitation in acetone and the mixture of acetone
and methanol (v/v, 1/1), respectively. All the monomers were
converted to the corresponding polymers with high yields and
molar masses (Table 1). The resultant polymers displayed good
Scheme 2 Hydrolysis and esterification reaction
2
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However, their polymers S-I/R-I not only showed the similar
characteristic absorptions of pyrene units at 315 nm, 329 nm, and
346 nm, but also a broad absorption from 380 nm to 520 nm,
which was assigned to the conjugated polyene backbone. As
shown in CD spectra, S-II and R-II were optical inactive and no
obvious Cotton effects were observed in the range 280~600 nm,
while S-I and R-I presented strong CD signal at around 450 nm
associated with the absorption of its conjugated main chain,
proving that the polyene backbone adopted
a stretched
cis-transoid helix with an excess one-handedness. Moreover, the
characteristic Cotton effects of pyrene units appeared in the range
300–350 nm, which strongly evinced that chirality was
successfully transferred from the chiral amide to PPA backbone
then to the achiral pyrene. Namely, doublet chirality transfer (DCT)
was realized in S-I/R-I and the achiral pyrene moieties took a
preferred one-handed helical arrangement around the main
chain.[22] R-I presented a mirror CD image to that of S-I, illustrating
the enantiomeric conformations with opposite helicities adopted
by them.
As for S-I-NMe, the signal of methine proton overlapped with
that of polyene backbone (Figure S12).[18b] As a result, its
cis-structure content was unable to be calculated accurately by
NMR method and Raman spectroscopy was employed instead.[20]
As shown in Figure 2, S-I exhibited intense peaks at 1590, 1236,
and 1000 cm-1, which could be ascribed to the C=C, C−C, and C−H
vibrations of cis PPAs, respectively.[20] S-I-NMe showed the Raman
spectra similar to S-I, evincing its cis-transoid main-chain
structure.
Figure 3 UV-vis absorption and CD spectra of R-II, S-II, R-I, S-I, and
trans-S-I in DMF. The spectra were measured in a 10 mm quartz cell at
a concentration of 5.0×10-5 mol/L (monomer unit).
Figure 2 Raman spectra of S-I, S-I-NMe, and trans-S-I obtained via
grinding.
One prerequisite for a poly(phenylacetylene) molecule to take
a predominant helical conformation is the high cis-structure
content. And helical polyene backbone serves as a scaffold to
induce chiral array of pyrene groups. In this context, the
stereoregularity of polymer backbone should exert remarkable
effect on DCT. To make this point clear, a trans-enriched polymer,
i.e. trans-S-I, was obtained from S-I through grinding.[23] As
depicted in Figure 3, trans-S-I exhibited much broader and
obviously red-shifted absorption of polyene backbone than S-I,
suggesting a cis-to-trans isomerization. Such a stereostructure
change increased the stereoirregularity and conjugation length of
polymer backbone. Whereas, the spectrum in pyrene absorption
region showed no discernible variation, implying inert chemical
structure of S-I toward grinding. The lack of Cotton effects in
polyene backbone absorption region of trans-S-I suggested the
vanishment of helical structure, while the reduced Cotton effects
belong to pyrene moiety corroborated the significant role of
main-chain secondary structure on DCT.
Table 2 Specific optical rotations in different solvents
*α+20D (o)a
*α+20D (o)b
THF
Sample
Sample
DMF
+32
-36
THF
CHCl3
+26
DMF
+378
-409
×
CHCl3
+106
-149
S-II
R-II
+9
S-I
R-I
+303
-12
-20
-381
S-II-NMe -64
-68
-86 S-I-NMe
+486
+610
ac = 0.2 g/dL. bc = 0.02 g/dL. ×: insoluble.
The optical rotations of polymers and monomers measured in
CHCl3, THF, and DMF, respectively, were summarized in Table 2.
The monomers displayed specific optical rotations (*α+20D) ranging
from -86o to +32o. Their corresponding polymers presented rather
larger optical rotations, implying the formation of chiral secondary
structures. Moreover, the sign and magnitude of optical rotations
depended on the solvent nature and polymer structure. In DMF,
S-I and R-I also exhibited very large optical rotations. However,
their optical rotations in CHCl3 were apparently poorer than those
in THF and DMF, indicating an interesting solvent effects, which
would be discussed later.
Figure 3 depicts the UV-vis absorption and CD spectra of R-II,
S-II, and their polymers in DMF at a concentration of 5.0×10-5
mol/L.[21] S-II/R-II exhibited strong absorptions at 312 nm, 327 nm,
and 343 nm, which were attributed to pyrene units. No obvious
absorption above 380 nm was observed in the absorption spectra.
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Wang et al.
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units probably existed in CHCl3. In DMF, the main chain of S-I
absorbed strongly at 440 nm, which shifted to longer wavelengths,
444 nm and 450 nm, respectively, when the solvent was changed
to THF and CHCl3. It implied that the polyene backbone took a
more extended planar conformation in CHCl3 with a longer
conjugated length. Moreover, the optical activity of S-I also
presented strong solvent dependence. The pyrene units exhibited
the strongest CD intensity in CHCl3, whereas the CD intensity of
polyene backbone was the weakest which probably stemmed
from the formation of intramolecular hydrogen bonding.
Furthermore, reversible helix-helix transition in S-I can be
achieved by altering the ratios of DMF and CHCl3. As shown in
Figure 5, with the addition of DMF in CHCl3 solution, the CD
intensity of polyene backbone gradually increased and that of
pyrene decreased slowly. Meanwhile, in UV-vis absorption spectra,
the absorption of main chain shifted to the shorter wavelength
and the absorption intensity of pyrene gradually increased. With
the content of CHCl3 increasing in DMF solution, opposite
phenomenon occurred in CD and UV-vis spectra, indicating a good
reversibility of conformation modulation.
To further investigate the effect of hydrogen bonds on DCT,
the hydrogen atoms of amide groups in S-I were substituted by
methyl pendants. As shown in Figure 6, the absorption intensities
of pyrene in S-I-NMe were apparently stronger than those in S-I,
and nearly equal to the intensities of pyrene of the monomer
S-II-NMe (Figure S14), implied the lack of π-π interactions
between pyrene pendants. Although the main-chain CD intensity
of S-I-NMe in CHCl3 was obviously stronger than that of S-I due to
the increased steric hindrance, the CD signal of pyrene was much
weaker demonstrating the important role of hydrogen bonds in
DCT. The helical arrangement of pyrene units was destroyed for
the existence of methyl groups in amide groups and the lack of
intramolecular hydrogen bonds. The strong Cotton effect of
polyene backbone in S-I-NMe further authenticated that the
decrease of the main-chain CD signal of S-I in CHCl3 originated
from the strong intramolecular hydrogen bonding. Without
hydrogen bond interaction, the CD spectra of S-I-NMe in CHCl3
didn’t change with the addition of DMF (Figure S15).
Figure 4 CD (a) and UV-vis absorption (b) spectra of R-I and S-I in
THF, DMF, and CHCl3. The spectra were measured at a concentration of
5.0×10-5 mol/L (monomer unit).
R-I and S-I showed good solubility in THF, DMF, and CHCl3.
Their CD and UV-vis spectra in these three solvents are displayed
in Figure 4. The absorption wavelengths of pyrene in different
solvents showed no obvious shifts. The absorption intensities of
pyrene in DMF were the strongest, but those in CHCl3 were the
weakest, suggested that strong π-π interactions between pyrene
Figure 5 CD (a) and UV-vis absorption (b) spectra of DMF solution of S-I added different CHCl3 fractions; CD (c) and UV-vis absorption (d)
spectra of CHCl3 solution of S-I added different DMF fractions.
4
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Running title
Chin. J. Chem.
bonds between amide groups in the CHCl3 solution of S-I, which
led to the above spectral differences of main chain and pyrene
unit.
Table 3 Solution-state IR absorption data.a
Sample
S-II
Amide I [cm-1]
Amide II [cm-1]
NH Stretching [cm-1]
3438
1510
1666
(-28)
(+3)
1539
S-I
1638
1624
1627
(+29)
3271
(-167)
S-II-NMe
S-I-NMe
a
Measured in CHCl3, c = 5-10 mg/mL. The wavenumber difference
between the monomer and the corresponding polymer is given in
parentheses.
To further characterize the helical conformations of the
resultant polymers, computer calculations were carried out. The
most energetically favored helical conformations of S-I were
simulated using the S-II 50mer as the model compound. Set the
initial dihedral angle (θ) of C−C=C−C as 0o and rotate the dihedral
angle (φ) 5o around C−C bond in the C=C−C=C moiety of the main
chain. Figure 7 displays the optimized contracted and stretched
helices, which are in accordance with the spectral results in DMF
and CHCl3, respectively. The detailed helical parameters are listed
in Table 4. As shown in Figure 7, they both presented a 2/1 helix in
either solvents. In DMF, the helical structure was relatively more
contracted than that in CHCl3. The overlapped extent of adjacent
pyrene pendants in n th and (n+2) th monomer units was lower
with a longer parallel distance, resulting in the weaker π-π
interactions (Figure 7c,d). However, in CHCl3, the adjacent pyrene
pendants exhibited the larger overlapping with a shorter distance
(Figure 7g,h). Therefore, the pyrene pendants are prone to
interact with each other strongly, giving rise to the stronger
Cotton effects and lower absorption intensities in CHCl3.
Figure 6 UV-vis absorption and CD spectra of S-I and S-I-NMe in
CHCl3. The spectra were measured at a concentration of 5.0×10-5 mol/L
(monomer unit).
Then the solution-state IR spectra of S-II, S-II-NMe, and their
corresponding polymers in CHCl3 at c = 5-10 mg/mL were
performed to check the presence of hydrogen bonds. The
solution-state IR spectra are shown in Figure S18, and the
eventual results are listed in Table 3. The amide I absorption (C=O
stretching) peak of S-II was observed at about 1638 cm-1, whereas
that of corresponding polymer appeared at 28 cm-1 lower position.
The amide II (N−H bending) peak of S-II was observed at 1510
cm-1, while that of its polymer appeared at 29 cm-1 higher position.
Furthermore, the N−H stretching peak of S-I was observed at 3272
cm-1, 167 cm-1 lower than that of its monomer, which further
verified the formation of strong intramolecular hydrogen bonding
in S-I.[18a,24] Different from S-I, the solution-state IR spectrum of
S-I-NMe was nearly the same with its monomer. These results
clearly convinced the existence of strong intramolecular hydrogen
Figure 7 Possible 3D helical models of S-I in DMF (a-d) and CHCl3 (e-h). (c), (d), (g), and (h) are the partial amplifications. The blue dot lines in (e)
are the possible intramolecular hydrogen bonds.
Chin. J. Chem. 2019, 37, XXX－XXX
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5

Wang et al.
Report
one direction. Nevertheless, the main chain of S-I in CHCl3 was a
relatively stretched helix with many helical reversals, and achiral
pyrene units arranged in a better helical form for the formation of
intramolecular hydrogen bonds supported by solution-state IR
spectra. This work provided a new promising model for designing
functionalized PPA materials. Taking advantage of doublet
chirality transfer, the novel asymmetric catalyst and
stimulus-responsive chiral electroptical materials based on
poly(3,5-disubstituted phenylacetylene) could be anticipated. The
related work is under way.
Table 4 Dihedral angles and length of N−H∙∙∙O in S-Ia
θ0 = 0o, φ0 = -155o
θ0 = 0o, φ0 = -170o
Bond
number
φ
θ
N−H∙∙∙O
φ
θ
N−H∙∙∙O
1.96
1.72
1.74
1.86
1.79
1.75
1.82
1.81
1.73
1.79
1.95
1.93
1.74
1.92
1.86
1.82
6.21
4.06
4.46
4.99
4.48
4.55
4.41
3.47
3.96
5.04
3.49
3.11
2.22
2.74
3.74
3.51
3.88
1
2
-166.23
-169.64
-172.46
-164.83
-165.11
-168.60
-160.17
-152.30
-153.18
-172.05
-159.04
-153.21
-152.92
-159.23
-168.60
-162.50
-169.67
-162.30
-167.80
-172.42
-165.17
-155.81
-159.57
-173.53
-175.36
-175.93
-172.98
-166.63
-173.32
-174.86
-168.07
-168.90
-5.80
-8.59
1.69
6.08
-6.64
-0.54
-9.83
6.71
1.95
-4.46
7.71
-0.66
5.36
-4.07
11.50
0.08
4.90
6.20
3
15.22
-0.17
6.77
4
5
Supporting Information
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
6
7.35
7
-11.28
2.98
8
9
Acknowledgement
The financial support of the National Natural Science
Foundation of China (Nos. 51833001, 21674002) is greatly
appreciated.
10.15
-4.82
12.04
7.34
10
11
12
13
14
15
av.
Energy
References
7.07
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4.78
1484 kJ/(unit mol)
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As shown in Table 4, in contracted helix, the average values of
dihedral angle θ and φ were 4.78o and -162.50o, respectively.
Along the main chain, most φ values were positive, suggesting the
polyene backbone mainly twisted in one-handed direction. So less
defects would exist leading to the stronger CD signal of main chain
in DMF. Moreover, the average length of N−H∙∙∙O was 3.88 Å,
which was too large to form intramolecular hydrogen bonds. In
stretched helix, the average values of dihedral angle θ and φ were
0.08o and -168.90o, respectively. The numbers of positive and
negative φ values were almost the same, suggesting that many
helical reversals probably existed along the main chain. On the
other hand, the average length of N−H∙∙∙O was 1.82 Å, which was
beneficial to form strong intramolecular hydrogen bonding. For
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in stretched helix, the pyrene pendants still could keep in a good
helical arrangement.
Conclusions
Three novel poly(3,5-disubstituted phenylacetylene)s with
pyrene pendant were designed and synthesized. Based on this
disubstitution structure, a new model of doublet chirality transfer
was put forward. Achiral pyrenes were chosen as probe unit,
which were induced to helically arrange around the polyene
backbone through DCT, demonstrated by CD spectra and
computer calculations. The main-chain stereostructure and
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roles in realizing DCT. To achieve a good DCT, high cis structure of
main chain, and strong intramolecular hydrogen bonds were
indispensible. Reversible helix-helix transition was achieved in S-I
by altering the nature of solvents. According to CD, UV-vis spectra,
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a relatively contracted helix which twisted along a predominant
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Chin. J. Chem.
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(The following will be filled in by the editorial staff)
Manuscript received: XXXX, 2019
Manuscript revised: XXXX, 2019
Manuscript accepted: XXXX, 2019
Accepted manuscript online: XXXX, 2019
Version of record online: XXXX, 2019
[21] The molar concentration is based on monomer unit. It is calculated
by the equation c = m/(M•V), in which m, M, and V represent the
weight of sample, molar weight of repeated monomer unit, and the
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Chin. J. Chem. 2019, 37, XXX－XXX

Running title
Chin. J. Chem.
Entry for the Table of Contents
Page No.
Doublet Chirality Transfer and Reversible
Helical Transition in Poly(3,5-disubstituted
phenylacetylene)s with Pyrene as a Probe Unit
A new model of doublet chirality transfer (DCT) was put forward based on the disubstitution
structure of poly(3,5-disubstituted phenylacetylene)s. High cis structure content and
intramolecular hydrogen bonds were beneficial for the realization of DCT. And reversible
helix-helix transition was observed by altering the nature of solvents
Sheng Wang, Xuanyu Feng, Jie Zhang, Xinhua
Wan*
Chin. J. Chem. 2019, 37, XXX－XXX
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9