Topochemical polymerization of unsymmetrical aryldiacetylene supramolecules with nitrophenyl substituents utilizing C-H...π interactions

Article abstract of DOI:10.1039/c5ob00435g

Diacetylenes are versatile building blocks, in which many functional groups can be incorporated for the construction of new materials with desirable properties. In this study, 6-(p or m-nitrophenyl)-3,5-hexadiyne-1-ol (4a or 4b) containing nitrophenyl groups (host) and 2-hydroxyethyl groups (guest) in different diacetylene terminals were designed to establish an ordered supramolecular assembly that is complied with the strict requirements for the topochemical polymerization of diacetylenes. Crystal film and bulk crystals of compound 4b were obtained successfully by cast film and re-precipitation methods. Both of these could photopolymerize to the corresponding regular poly(diacetylene) polymer, as evidenced by UV-vis, IR, FL and Raman spectroscopy. The electrochemical properties and behaviors of 4a and 4b were also investigated, and the results show that the differences between the para and meta positions of the mono-phenylacetylene substituents probably result from the topochemical polymerization. Thus, m-nitrophenylbutadiyne derivatives with sizeable C-H...π interactions seemed to be effective for the formation of a polymerizable packing, which is appropriate for topochemical polymerization.

Full text of DOI:10.1039/c5ob00435g

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Page 1 of 11
Organic & Biomolecular Chemistry
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DOI: 10.1039/C5OB00435G
Topochemical Polymerization of Unsymmetrical Aryldiacetylenes
Supramolecule with Nitrophenyl Substituents Utilizing C–H…π
Interactions
Shichao Wang1, Yong Li1, Hui Liu1, 2, Jinpeng Li1, Tiesheng Li1 *, Yangjie Wu1, Shuji Okada3, and
Hachiro Nakanishi4
1College of Chemistry and Molecular Engineering, The Key Lab of Advanced Information
Materials of Zhengzhou, Zhengzhou University, Kexuedadao100, Zhengzhou 450052, P.R. China
2Department of Chemistry, Zhengzhou Normal University, Zhengzhou 450003, P.R. China
3Graduate School of Science and Engineering, Yamagata University 4-3-16 Jonan, Yonezawa
992-8510, Japan
4Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1
Katahira, Sendai 980-8577, Japan
Abstract
Diacetylenes are versatile building block in which many functional groups can be incorporated for
the construction of new materials with desired properties. In this paper, 6-(p or m-nitrophenyl)-3,
5-heaxdiyne-1-ol (4a, 4b) containing the nitrophenyl group (host) and 2-hydroxyethyl group
(guest) in different terminals of diacetylenes were designed to establish an ordered supramolecular
assembly that is commensurate with the strict requirement for topochemical polymerization of
diacetylenes. Crystal film and bulk crystal of compound 4b were obtained successfully by cast
film and re-precipitation method. They both could photopolymerize to the corresponding regular
poly(diacetylene) polymer, as evidenced by UV-vis, IR, FL spectra and Raman spectroscopy.
Electrochemical properties and behaviors of 4a and 4b were also investigated, and it shows that
the differences between para and meta position of mono-phenylacetylene substituent probably
results from the topochemical polymerization. Thus, m-nitrophenylbutadiyne derivatives with
sizeable C–H…π interactions seemed to be effective to form a polymerizable packing which is
appropriate for the topochemical polymerization.
Keywords: diacetylene; self-assembly; supramolecule; topochemical polymerization
Introduction
Polydiacetylenes (PDAs) are unique conjugated
polymers with a highly crystalline feature obtained by
the solid-state topochemical polymerization of 1,
3-butadiynes[1] or diacetylene[2]. The moieties linking
with diacetylene (DA) are versatile building block for
the construction of molecular complexes, polymer
composites and supramolecular structure[3,4], which is
linear, rigid and conjugated to make it ideal for the
placement of metal centers at precise distances from
each other[5]. Similarly, diacetylenes have been used
to connect various organic functionalities, including
the linking of aromatic rings to extended conjugated
structure or other structures[6,7]
in which these
conjugated structures have attracted much attention
for applications[8-11]
The resulting polymers are
,
.
highly conjugated, deeply colored and display
important optical and non-linear optical properties and
have potential applications as optical limiters and
waveguides, and sensitivity to environmental changes
that make them ideal candidates for the synthesis of
chemical or biological sensors[12,13]. In addition to
serving as a static scaffold, DAs could be useful for

Organic & Biomolecular Chemistry
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engineering larger structures, such as oxidation
resistance, temperature, mechanical properties and
polymerization[22]
.
Through these approaches
DOI: 10.1039/C5OB00435G
mentioned above, the DAs might have a structure
which matches the requirement for regular
polymerization, but all of these operations are
complexes. The traditional way is the directly design
surface
hardening
of
polymers
upon
incorporation[14,15]
.
of the monomer structure through amide groups[23]
fluorine containing phenyl
groups[24]
,
,
perfluorophenyl-phenyl groups[25] and so on.
Especially, C–H…π and π…π interactions as a wide
array of supramolecular phenomena in biology and
chemistry can also be used for the structure design. In
addition to this, aryl-substituted PDAs have been of
considerable interest[26, 27], because they offer a way to
extend the conjugation of the polymer onto the side
chains and, consequently, enhancing the photoelectric
properties of such architectures. In this connection,
several monophenylbutadiyne derivatives with
simpler structures were investigated[28]. However, no
topochemical polymerization was confirmed.
Scheme 1 The topochemical polymerization of DA. The values
for 1, 4 addition polymerization are d ≈ 4.9 Å; φ ≈ 45˚; a ≈ 3.5 Å
Despite these excellent properties, the design of
DAs remains a challenge. In principle, this reaction is
usually a photochemical process, though it also occurs
thermally[16]
.
With
only
minimal
packing
rearrangements, DA monomers can be polymerized in
the topochemical manner which the single crystals of
the monomer can be transformed into polymer single
crystals. The molecular alignment to satisfy
topochemical polymerization is at least threefold
(Scheme 1): first, the identity period d of the
monomer is about 4.9 Å. Second, the distance a is at
approximately 3.5 Å, which represents the van der
Waals contact between adjacent molecules. Third, the
This solution is simple to implement, but it is
hardly predictable. First, various intramolecular forces
must be considered. Second, the difficulties in
topochemical polymerization of aryldiacetylenes are
attributed to the rigidity of aromatic pedant groups
because of movement of the rigid ring which may just
be too disruptive for the crystal lattice to remain intact
which was proved by both Lando’s and Nakanishi’s
inclination angle
φ between the DA axe and
translational vector is close to 45°. The difficulty is
that the vast majority of DA monomers do not
crystallize in accordance with these structural
parameters and undergo random 1,2- or
1,4-polymerization, which resulted in unknown
disordered polymer material. Empirically, the
appearance of an intense blue color that corresponds
to a maximum absorption wavelength of 640nm
generally mean that the packing parameters of the
monomer crystal meet geometrical criteria as shown
results[29]
.
Lauher proposed that perhaps an
unsymmetrical aryldiacetylene could provide an
alternate route to the preparation of PDA single
crystals[30]. The remaining required design element is
an appropriate set of matched substituents that will
assure a strong intermolecular interaction between
adjacent molecules. In order to establish a crystalline
lattice commensurate with the repeat distance of the
desired polymer, our effort is made to develop rational
and simple design for the preparation of DAs, in
which mono-aryl containing electro-withdrawing
group (host) and 2-hydroxyethyl group (guest) in
different terminals of DAs, with which these
molecules are expected to be gotten in predictable
structures based upon self-assembly via hydrogen
in scheme 1[17]
.
Interestingly, responding to
environmental stimulations,
(blue-to-red) of PDAs occurs.
a
phase transition
If a given DA does not crystallize properly, we
can adopt other ways to change the crystal structure,
such
copolymer[21]
as
Langmuir-Blodgett
and
technology[18-20]
pressure-catalyzed
,
bonds[31] and aromatic ring stacking[25]
.

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Organic & Biomolecular Chemistry
In
m-nitrophenyl)-3,5-heaxdiyne-1-ol(4a,4b) compounds
were synthesized and characterized with 1H NMR, 13
this
paper,
designed
6-(p
or
reaction was found to be complete after 8h. ThVeiew Article Online
DOI: 10.1039/C5OB00435G
solution were abstracted with dichloromethane
followed by wishing with NH4Cl and water, The
compound was passed through a silica gel column
using petroleum ester/ethyl acetate (2:1) as eluent and
4a and 4b were obtained.
C
NMR, IR, and GC/MS spectra. Solid-state
polymerization properties of compound 4a and 4b
were also systematic investigated by deep UV
irradiation and annealing. Cast film and
re-precipitation method were applied to align crystal
structure appropriately for the topochemical
polymerization. Crystal film and bulk crystal of
compound 4b were obtained successfully and
photopolymerized to the corresponding regular PDA
polymer, as evidenced by UV-vis, IR, FL spectra and
Raman spectroscopy, as well as single-crystal
structure analysis. Obviously, once our strategy is
proved to be successful in preparing aryl-substituted
PDAs, nitrophenylbutadiyne derivatives seem to be
effective to form a polymerizable packing which is
appropriate for a topochemical polymerization and
other more complex nitrophenyl-substituted PDAs
will be tested.
4a: Yellowish solid, yield: 65%, Mp: 120-122°C ,
IR (KBr pellet, cm-1): 3262, 3103, 2929, 2236, 1922,
1592, 1515, 1343, 1048, 852; 1H NMR (400MHz,
CDCl3):
δ 8.17-8.19 (d, J=8.8Hz, 2H, -C6H4),
7.59-7.62 (d, J=8.8Hz, 2H, -C6H4), 3.81-3.84(t,
J=6.4Hz, 2H, -CH2-OH), 2.66-2.69(t, J=6.0Hz, 2H,
≡C-CH2-), 1.872(s, 1H, -OH); 13C NMR(100 MHz,
CDCl3): δ 147, 133, 128, 123, 84, 79, 73, 66, 60, 24;
MS: 214 [M-1]+
4b: Yellowish solid, yield:63%, Mp: 70-72°C , IR
(KBr pellet, cm-1): 2958, 2925, 2855, 2236, 1733,
1635, 1531, 1458, 1351, 1261, 1089, 1042, 863, 801,
735; 1H NMR (400MHz, CDCl3): δ 8.30-8.31(t, J=
2.0Hz, 1H, -C6H4), 8.17-8.20(m, 1H, -C6H4),
7.74-7.77(m, 1H, -C6H4), 7.48-7.52(t, J=8.0Hz, 1H,
-C6H4), 3.81-3.84(t, J=6.4Hz, 2H, -CH2-OH),
2.65-2.68(t, J=6.0Hz, 2H, ≡C-CH2), 1.861(s, 1H,
-OH); 13C NMR(100 MHz, CDCl3): δ 148, 138, 129,
127, 124, 82, 72, 66, 60, 23; MS: 214[M-1]+
Preparation of cast film and crystal prepared by
re-precipitation
Experimental
Synthesis of diacetylene derivatives 4a and 4b
Cast film and crystal prepared were depicted in
Scheme 3.
Scheme 2 Synthetic procedure of 4a and 4b.
6-(p or m-nitrophenyl)-3, 5-heaxdiyne-1-ol (4a,
4b) were synthesized according to the route as shown
in Scheme 2. Preparation of 2, 3 has been reported
previously[32]. 4a and 4b that were not reported before
were obtained by the asymmetric coupling reaction of
3 with 3-butyn-1-ol, using Cu(OAc)2 as a catalyst.
In a 50 mL three-neck round-bottom flask fitted
with O2 inlet and outlet, 0.147g of 3-nitrophenyl
acetylene (1mmol) in 20mL of dichloromethane was
added. Piperidine (0.3mL, 3mmol) were added,
followed by 0.018g Cu(OAc)2 (0.1mmol) to it under
ice. The reaction solution was stirred throughout at
room temperature and was monitored by TLC. The
Scheme 3 Schematic route for preparation of 4a or 4b cast film
(up) and crystals via re-precipitation (low).
4a or 4b monomer was added to a flask
containing chloroform. The solution was stirred for 20
min and then the resulting solution was filtered
through a 0.2μm Teflon filter and was casted onto
quartz slides. Cast films were dried for 16 h in a
vacuum at room temperature.

Organic & Biomolecular Chemistry
Page 4 of 11
10 mg/mL 4a or 4b acetone solution (1 mL) was
injected into vigorously stirred super pure water (3mL)
at ambient temperature to give crystal dispersion. The
dispersion solution was put in static for some time.
Only 4b crystals were collected with size ranging
from 1cm to well over 3cm and width from 100 to
became red during UV irradiation at 365nm as showVniew Article Online
DOI: 10.1039/C5OB00435G
in Figure 1c, 1d.
200μm[33]
.
Results and discussion
In the synthesis process of compound 4b, an
unexpected purple solid insoluble in common
laboratory solvents appeared in 4b solution after
chromatographic purification. However, monomer 4a
and 4b were obtained as yellow solid after vacuum
and turned to a large number of deep yellow soluble
oligomers (poly-4a, poly-4b) upon UV irradiation.
Polymer molecular weight was obtained by gel
permeation chromatography analysis (Table S1). A
large polymerization degree about 70 was found in
poly-4b, which meant polymer materials with
disordered extended π-conjugation system were
obtained. Similarly, the high concentration liquid film
without vacuum process was attempted to undergo
UV irradiation, a yellow liquid oligomers appeared.
However, their structures are not regular PDAs, as
evidenced by the absence of new UV-vis absorption in
visible region (Figure S1, S2).
Fig. 1 Optical micrograph of 4b cast film (a, b) and 4b crystal
prepared by re-precipitation (c, d) before and after deep UV
irradiation at 250nm or 365nm UV light for 15min.
It is important that how about the yield of
polymer obtained by re-precipitation method.
Therefore, UV irradiation of the crystals 4b led to the
conversion into a red insoluble material. However,
UV light could not penetrate through the crystals due
to polymers produced on their surfaces. The pure
polymer 4b was obtained as fiber like about 12.2%
yield after Soxhlet extraction of residual monomer
with dichloromethane (DCM) after deep UV
irradiation for 1.5h. The optical micrograph and
scanning electron microscope (SEM) image of
polymer were shown in Figure 2.
Therefore, cast film and re-precipitation method
were applied to align crystal structure appropriately
for the topochemical polymerization. Crystal film and
bulk crystal of compound 4b were obtained
successfully and polymerized to the corresponding
regular PDA polymer. Color changes of 4b cast film
and crystals prepared by re-precipitation were
presented in Figure 1. In the case of 4b cast film, it is
well-known that the molecular packing in thin films
can significantly differ from the bulk crystal
structures[34]. It is worth mentioning that the casting
solution must be freshly prepared, and the vacuum
process was necessary for the formation of crystal
film.
Fig. 2 Optical micrograph (transmission (left) and reflection
(right)) of polymer after Soxhlet extraction. The inset shows
SEM image.
Crystal Structure of 4b
Several attempts were made to obtain 4a single
crystals, but these efforts were unsuccessful.
Eventually, an X-ray diffraction analysis (XRD) of 4a
solid was undertaken. A detailed description was
provided in the XRD section. However, 4b single
crystals were very simple to obtain. When pure 4b is
recrystallized from an acetone/water, crystals formed
that showed an unexpected appearance in blue color.
We found it more difficult to form large crystals
of 4b. Nevertheless, colorless long needle-shaped
crystals formed by re-precipitation with slow
vaporation/crystallization over several days and

Page 5 of 11
Organic & Biomolecular Chemistry
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DOI: 10.1039/C5OB00435G
A well-formed crystal was selected, and a structure
determination revealed that the molecule had
crystallized as a triclinic with alignment of the
diacetylene functionalities in
a
bit reasonable
agreement with the requirements for a topochemical
polymerization.
The crystal structure of 4b monomers was
investigated on the basis of the results of the X-ray
single-crystal structure analysis (Figure S3). Single
crystal X-ray diffraction reveals that 4b monomers
crystallizes in the triclinic space group P-1 and
exhibits an alignment of the DA functionalities. As
shown in Figure 3a, the carbon-carbon distance for 1,
4-propagation during polymerization is 3.65Å [35]. It
should be pointed out that there are aromatic ring
systems and heteroatoms in 4b which may form
various hydrogen bonds stacking interactions.
Analysis of the crystal packing of 4b revealed that an
infinite 2-D supramolecular network was formed by
two intermolecular hydrogen bonds interactions
(Figure 3b). One is the O–H…O hydrogen bonds
interactions. The O…O distances are 2.980Å, the
bond angles around O–H…O are 167°. The other is
the C–H…O hydrogen bonds, which play important
roles in biological carbohydrate-protein recognition
systems[36-38]. The H…O distances of hydrogen bonds
are 2.362Å (bond angles around C–H…O are 162.95°)
between the activated C-H groups of benzene rings
and the hydroxy O-atoms, which are shorter than the
approximate distance (d, 2.49-2.74Å) of the H…O
reported by Desiraju et al.[39, 40]. These 2-D layers are
further connected to 3-D supramolecular network
(Figure 3d) by the edge-to-face C–H…π interactions
(distance 3.365Å, dihedral angel 91.3°, H/π-plane
separation: 3.323Å) between adjacent phen ring of 4b
which leaded to a layered stacking along the a-axis of
the crystal (Figure 3c)[41,42]. These foregoing facts
specified that the weak interactions are very important
in 4b, where they contributed significantly to
molecular self-assembly processes.
Fig. 3 (a) Stacking diagram of 4b drawn at 20% probability. (b)
Two-dimensional layered supramolecular network of 4b. The
dashed lines represent hydrogen bonds interactions. (c) The
edge-to-face C–H…π interactions along the a-axis. (d) Stacking
diagram of 4b. Part hydrogen atoms are omitted for clarity.
Data of the molecule crystal revealed that it was
in a bit reasonable agreement with the requirements
for a topochemical polymerization and slow formation
of an amount of insoluble material was observed.
Solid-state Polymerization of 4b cast film and bulk
crystal
The photopolymerization of the DA monomers
was carried out in the solid state under UV irradiation
at
250nm
or
365nm.
The
process
of
photopolymerization was confirmed by a color change
in the appearance of the crystal, in which the color of
PDAs is due to
a
π-π* transition of the
linear-conjugated polymer backbone. Unpolymerized
DAs do not exhibit absorption in the visible region,
but upon polymerization a blue color appears from
two absorption band with maximum around 590nm
and 540nm shown in Figure 4. In the case of
irradiation at 365nm, the absorption had developed an
intense absorption band with a maximum at about
590nm (Figure 4). The relatively sharp absorption
band at 590nm can be attributed to a band of a “purple
form”, intermediate in order between the blue phase
and the red phase[43]. The position and width of the
second, broader band at about 540nm is likely that this
should be assigned to PDA groups in a less ordered
environment, in a so-called “red phase”[44]. In order to
investigate the irradiation dependence of the
absorption spectra, 4b cast film irradiated at 365nm
was carried out for different time, and then the UV-vis
absorption spectra were recorded at ambient without

Organic & Biomolecular Chemistry
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the separation of the resulting polymer and the
remaining monomer as shown in Figure S4, in which
the absorbance of typical peaks of conjugated
backbone increased with increasing irradiation time
and became broader with new shoulder peak at about
650nm. It is indicating that regular 1, 4-addition
thermochromism properties, the achieveDmOeIn: 1t0.o10f39a/C5OB00435G
controlled transformation between red and blue state
is worth investigating as future works.
To confirm the formation of PDAs on the quartz
substrate, we used Raman spectrum to probe the
changes before and after UV irradiation. As shown in
Figure 5a, the acetylene stretching band appeared at
2239cm-1. After UV irradiation of 4b cast film, two
new peaks at 1458cm-1 and 2089cm-1 at a much
greater intensity assigned to the typical conjugated
alkyne−alkene structures of PDA (Figure 5b)[47]. The
result evidenced that 4b cast film transformed to
PDAs by UV irradiation.
occurred[45]
.
Fig. 4 UV-vis spectrum of cast film on quartz before (black) and
after (red, blue) irradiation at 250nm and 365nm for 10min,
respectively.
This also can be confirmed by FL spectra.
Fluorescence spectra of 4b solution, cast film and cast
film irradiated by deep UV light were also
investigated. In the case of 4b solution, the
fluorescence emission spectra at λexc=380nm as shown
in Figure S5(d), in which the emission band was at
about 440nm. There is inconspicuous emission peak at
λexc=250nm as shown in Figure S5(e). However,
stronger emission peak of 4b cast film irradiated by
deep UV light at 400 nm and 580nm at λexc = 250nm
could be observed in Figure S5(f). After UV
Fig. 5 Raman spectra of cast film on quartz before (a) and after
(b) irradiation at 365nm for 100min.
There are little changes in 2212cm-1, 2217cm-1
corresponding to stretching vibration of acetylene and
double bond when irradiated by 250nm in its IR
spectra of 4b cast film on CaF2 substrate (Figure S6b).
The bands at 1353cm-1 of the symmetric -NO2
stretching became weak and extended to the long
wavelength region, in which it proved that
polymerization took placed with extension of
π-conjugation, leading to the change of nitro group
(Figure S6c). It can be plausibly explained that the
orientation of molecular in crystal changed by
polymerization procession which resulting in the
orientation of nitro-group.
irradiation for
a long time, the fluorescence
disappeared. Nevertheless, the bulk crystals obtained
by re-precipitation method had no fluorescence
throughout UV irradiation process, which may result
from the fluorescence quenching effect of
nitrobenzene group. It is well known that PDAs have
different fluorogenic properties between
a red
fluorescent state and a blue non-emissive state[46]. It
might seem that different preparation methods led to
different polymer forms. The difference of compound
structure may have an effect on fluorescence
properties. Thus, unlike most PDAs that exhibit
Those results which are consistent with structure
analysis of 4b single crystal showed that a prerequisite
of the regular polymerization is highly ordered
packing of monomers. That is to say that the
polymerization successfully proceeds because the

Page 7 of 11
Organic & Biomolecular Chemistry
monomer spacing, imposed by the hydrogen bond
X-ray diffraction (XRD) patterns ofDcOoI:m10p.o10u3n9Vdi/eCw5AOrtBic0le0O4n3l5inGe
4a, 4b were measured to study the packing
configuration and the distances within the
supramolecular structure and compare different
solidified forms. Samples were obtained through usual
solidified form (4a-u, 4b-u), cast film (4b-c) and
re-precipitation (4b-r) (Figure 7).
forces between the hydroxyl with nitro groups in
different molecules, which made molecular close
enough to the spacing required for the DA backbone
to form PDA.
Heat experimental
Heating the same fresh single crystal to a
temperature of 60℃ by a slow annealing treatment
without light for 1h gave no polymer. However, when
crystals were kept under ambient light at room
temperature, appropriately aligned monomer crystals
will polymerize spontaneously. As the heating
temperature is increased until at 70℃ under the light,
the crystal began to melt and expanded, but the
polymerized part is still maintaining the same shape
like crystal as shown in Figure S7.
Fig. 7 X-ray diffraction patterns of a) 4a obtained through usual
solidified form. The black and red lines are for 4a-u before and
after UV irradiated at 250nm, respectively. b) 4b cast film. The
red, blue, and black lines are for 4b-c, 4b-c after UV irradiation
and 4b-c after washed by acetone, respectively. c) 4b bulk crystal
prepared by re-precipitation. The black and blue lines are for
4b-r prepared by re-precipitation before and after irradiated at
250nm, respectively. The red line in (c) is for 4b-u.
Water contact angle analysis
Fig. 6 Static water contact angle of 4b cast film irradiated at
different time. (a), 0min;(b), 10min;(c), 20min;(d), 30min;(e),
45min.
The crystallinity of 4a obtained through usual
solidified form was low while 4b obtained by same
way showed several sharp peaks, which also
confirmed that 4b had more regular intermolecular
interactions(Figure 7a, 7c). The insufficient
crystallinity of 4a (Figure 7a) may cause irregular
alignment of the butadiyne group resulting in a low
polymerization degree (Table S1), which may be
associated with its weak C–H…π interactions. As
shown in Figure 6b, although 4b cast film were
confirmed to be amorphous by the broad diffraction
peaks at 2θ=22°, several peaks implied partial regular
structures[28]. After UV irradiation and washed by
acetone, the crystallinity of 4b cast film was almost
lost and completely amorphous, respectively. Similar
sharp peaks at 2θ=24° (3.67Å) attributed to the π−π
distance between the molecules have been observed in
A CAMERAY digital color CCD camera was
used for the measurement of the contact angle of
water droplets on the surface of 4b cast film irradiated
by UV light. A small droplet was placed on the
surface of substrate and vibrated gently to overcome
any contact line pinning effects. Then it gave a
uniform contact angle at all points along the three
phase contact line. Water droplets deposited on solid
surfaces were shown in photo images (Figure 6). The
contact angle was as low as 5° for the hydrophilic
glass substrate by hydrophilicity treated, which
showed that the glass substrate had good hydrophilic
activity. On the case of cast film of 4b, the contact
angle increased from 61° to 82° (Figure 6 a-e),
indicating that the surface configuration had
a
different solidified forms (Figure 7b, 7c)[48]
Distinctively, 4b bulk crystal prepared by
re-precipitation showed particularly sharp and
.
significant change due to the photopolymerization of
4b, which is consistent with the results of SEM
(Figure S8). As shown in Figure S8, the surface of 4b
cast film became rough after UV irradiation for 20
minutes.
a
intense peak at 2θ=8° (11.05Å), which is very close to
a lattice constant c (11.29Å) of 4b single crystal. The
similar peak before and after UV irradiation also
XRD analysis

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DOI: 10.1039/C5OB00435G
revealed that the bulk crystals have not undergone a
phase change to a new form (Figure 7c).
Electrochemical analysis
Analysis by UV-vis spectra and Raman
spectroscopy has been able to reveal the topochemical
polymerization of compound 4b. The introduction of
the redox-active nitrobenzene groups further allows us
to perform a cyclic voltammetry (CV) study to
provide more detailed insight into the relationship
between regular topochemical polymerization and
irregular polymerization. The 80wt% prepared
samples were mixed with 15wt% acetylene black and
5wt% polytetrafluoroethylene (PTFE) in aqueous
solution to form slurry and then cast onto nickel
Fig. 9 Nyquist plots of nickel foams (Blank), 4b crystal before
(4b) and after (p-4b) UV irradiation. The inset is the equivalent
circuit model. R1 and R2 are system resistances and
charge-transfer resistances, respectively. CPE is the constant
phase element.
foams followed by drying at 30℃ for about 12h[49][50]
.
After compressed, nickel foams containing samples
were used as working electrode.
To gain insight into the prominent change of
electrochemical behavior of 4b observed from CV, ac
impedance measurements were performed. As shown
in Figure 9, a frequency range of 0.1-105Hz with
signal amplitude of 20mV was employed and nyquist
spectra showed a semicircle in the high-frequency
range and
a
straight ascending line in the
low-frequency range. The equivalent circuit model of
the studied system is also shown in Figure 9 according
to the works of others[52][53]. R1 corresponds to the
resistance of the surface coating formed on the nickel
foams and R2 represents the ability to impede ion
transport at the electrode/electrolyte interface[54]. It
can be seen that P-4b exhibits a smaller R1 (4.245Ω)
and R2 (9.654Ω) than 4b (5.953Ω, 10.62Ω), which
may be caused by the extended conjugation after
Fig.
8 Cyclic voltammograms of nickel foams(Blank), 4a
powders before(4a) and after(P-4a) UV irradiation, and 4b
crystal before(4b) and after(p-4b) UV irradiation in aqueous
solution with 0.2 M KCl. Initial and final potentials, 0V; reversal
potential, -0.6V; scan rate, 50 mV s−1
.
polymerization
(Table
S2).
Topochemical
As shown in Figure 8, the initial scan in the CV
from 0 to -0.6V show the only one well-defined and
stable redox waves, which correspond to the reduction
of the nitrobenzene group and the reoxidation of the
nitrobenzene radical anion[51]. The CV curves of 4a
powders before and after UV irradiation (4a and P-4a)
only showed a negligible change. However, The peak
current and peak potential of 4b crystal before and
after UV irradiation (4b and P-4b) showed the
dramatical change, which may be associated with the
changes of electroactivity and crystal structure.
polymerization process significantly influences the
electrochemical behavior, which is different from
irregular polymerization based on our results of
electrochemistry analysis.
Conclusions
6-(p or m-nitrophenyl)-3, 5-heaxdiyne-1-ol (4a,
1
4b) were designed and characterized with H NMR,
13C NMR, IR, and GC/MS spectra. The mono-aryl
containing electro-withdrawing group (host) and
2-hydroxyethyl group (guest) on different terminals of
compound 4a, 4b made them easy to self-assembly to
form crystals by numerous O–H…O and C–H…π

Page 9 of 11
Organic & Biomolecular Chemistry
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interactions, while the obtained poly(diacetylene)s
3
Isabelle Levesque; Simon Rondeau-Gagné;
DOI: 10.1039/C5OB00435G
with aromatic rings as a host group directly bound to
Jules Roméo Néabo and Jean-François Morin.
the alternating ene–yne main chain gave an extension
Org. Biomol. Chem. 2014, 12, 9236–9242.
Jianzhao Liu; Jacky W. Y. Lam; Ben Zhong
Tang. Chem. Rev. 2009, 109, 5799–5867.
Li Liu; Zuxing Chen; Shizhong Liu. Acta Chim
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of
the
π-conjugation
system.
Solid-state
4
5
6
polymerization properties of compound 4a and 4b
were also systematic investigated by deep UV
irradiation and annealing, in which only compound 4b
showed that it could polymerize to give a blue-colored
polymers insoluble in common laboratory solvents.
Cast film and re-precipitation methods were applied to
align crystal structure appropriately for the
topochemical polymerization. Crystal film and bulk
crystal of compound 4b were obtained successfully.
They both could photopolymerize to the
corresponding regular poly(diacetylene) polymer, as
evidenced by UV-vis, IR, FL spectra and Raman
spectroscopy, as well as single-crystal structure
analysis of 4b single crystals in which a crystalline
lattice nearly commensurate with the repeat distance
of the desired structure for regular polymerization.
Electrochemical properties and behaviors of 4a and
4b were also investigated, and it shows that the
differences between para and meta position of
mono-phenylacetylene substituent probably results
from the topochemical polymerization. Thus,
m-nitrophenylbutadiyne derivatives with sizeable
C–H…π interactions seemed to be effective to form a
polymerizable packing which is appropriate for the
topochemical polymerization.
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Table of contents entry
Synthesis and solid-state polymerization of
unsymmetrical aryldiacetylenes supramolecule with
nitrophenyl substituents