Synthesis and solid-state polymerization of diacetylene derivatives with an N-carbazolylphenyl Group

Article abstract of DOI:10.1246/bcsj.20150019

Four diacetylene derivatives with an N-carbazolylphenyl group as a donor moiety have been synthesized and subsequently characterized. These diacetylene derivatives undergo solid-state polymerization via UV irradiation, although these compounds have relatively large π-conjugated aromatic groups. The polymerization behaviors of these derivatives were confirmed by distinct absorption bands for polydiacetylenes. The reactive process is strongly influenced by the slightly differing side groups. Single crystal growth of the two compounds was successful and their crystal structure analyses revealed large differences in the molecular conformations and intermolecular geometries caused by a methylene unit. The HOMO population of the monomers is predominantly expressed in the phenyl carbazole unit, while each polymer showed differing HOMO energies with some polymers exhibiting high-lying HOMO levels.

Full text of DOI:10.1246/bcsj.20150019

Synthesis and Solid-State Polymerization of Diacetylene Derivatives
with an N-Carbazolylphenyl Group
Masataka Ikeshima, Masashi Mamada, Hiroshi Katagiri,
Tsuyoshi Minami, Shuji Okada, and Shizuo Tokito*
Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata 992-8510
E-mail: tokito@yz.yamagata-u.ac.jp
Received: January 15, 2015; Accepted: February 27, 2015; Web Released: March 6, 2015
Four diacetylene derivatives with an N-carbazolylphenyl group as a donor moiety have been synthesized and
subsequently characterized. These diacetylene derivatives undergo solid-state polymerization via UV irradiation, although
these compounds have relatively large π-conjugated aromatic groups. The polymerization behaviors of these derivatives
were confirmed by distinct absorption bands for polydiacetylenes. The reactive process is strongly influenced by the
slightly differing side groups. Single crystal growth of the two compounds was successful and their crystal structure
analyses revealed large differences in the molecular conformations and intermolecular geometries caused by a methylene
unit. The HOMO population of the monomers is predominantly expressed in the phenyl carbazole unit, while each
polymer showed differing HOMO energies with some polymers exhibiting high-lying HOMO levels.
Polydiacetylenes (PDAs), which can be obtained through the
topochemical solid-state polymerization of diacetylene (DA)
monomers, have been studied extensively as materials for use
in third-order nonlinear optics (NLO),1,2 Langmuir-Blodgett
(LB) films,3 optical sensors,4 and solid hole conductors.5,6
Their extended π-systems along the polymer backbone explain
their unique characteristics, such that the conduction paths
through the polymer main chain have very fast charge transport
properties. In fact, the charge carrier mobility of PDAs have
molecules can show strong π-stacking, although its slightly
twisted conformation may increase intermolecular interactions
in two dimensions.16 Moreover, carbazole derivatives are sta-
ble, easy to handle, and therefore widely used as side chains in
conjugated polymers.17 However, by directly introducing rigid
aromatic groups to both sides creates the potential loss of the
polymerization capability and solubility.18,19 Thus, flexibility
should be maintained in the other side group in order to provide
for the appropriate orientation of DA monomers. We have
chosen an alkyl chain with a carbamate (urethane) group,
which proves to be effective in orientation through hydrogen
bonding.20 Here, we report the synthesis and solid-state poly-
merization behavior of asymmetric DA monomers substituted
by N-CzPh and carbamate groups at each side (Figure 1). The
DA monomers have been characterized by spectroscopic
studies and some were further characterized with X-ray single
crystal analysis. The relationship between their molecular
packing and polymerization reactivity is also discussed.
¹1
been found to be ca. 10000 cm2 V¹1 s in a theoretical study,7
¹1
ca. 10 cm2 V¹1 s as estimated by the time-of-flight method,8
and up to 3.8 cm2 V¹1 s¹1 in field-effect transistors.9 Such prop-
erties were achieved through single dimensional conjugation in
the polymer chain because aliphatic side groups do not increase
π-delocalization. Meanwhile, DA monomers with conjugated
substituents, such as aromatic and heteroaromatic rings, can
give PDAs with π-extension to the side groups in each repeat-
ing unit. In addition, the interactions between side groups may
enhance the dimensionality of the charge transport paths. More-
over, this enables fine-tuning of the electronic properties of
PDAs. Therefore, we designed new DA monomers with an N-
carbazolylphenyl (N-CzPh) unit, which is an electron donor
and has hole transport properties.10,11 There have been several
reports on PDAs with carbazole moieties such as 1,6-di-
(N-carbazolyl)-2,4-hexadiyne (DCH),12 1-(9-carbazolyl)-6-
iodohexa-2,4-diyne (CIHD),13 1-(N-carbazolyl)penta-1,3-diyn-
5-ol (CPDO),14 and 1-(N-carbazolyl)penta-1,3-diyn-5-acetoxy
(CPDA).15 However, PDAs from DCH and CIHD have no
conjugation between the carbazole moieties and the PDA
backbone. Although the carbazole moieties are directly bound
to the PDA backbone in the PDAs from CPDO and CPDA,
more extended π-conjugation in the side chains is expected for
PDAs having direct conjugation with N-CzPh units. The struc-
ture of N-CzPh is more planar than triphenyl amine, where the
Experimental
General. 1H NMR and 13C NMR spectra were recorded on
a JEOL 500 MHz JNM-ECX instrument. Chemical shifts were
1
calibrated by Me4Si for H NMR and by deuterated solvents
for 13C NMR. The elemental analyses were performed with a
Perkin-Elmer 2400 series II CHNS/O elemental analyzer.
Differential scanning calorimetry (DSC) was preformed using a
TA Instruments DSC Q2000. UV-vis diffuse reflectance spectra
were measured using a JASCO V-570 spectrophotometer with
an integrated sphere. The highest occupied molecular orbital
(HOMO) energies of DA monomers and the corresponding
polymers were examined using photoelectron yield spectros-
copy (PYS) in air obtained by a Riken Keiki AC-3 spectrometer.
Thin films of the samples were prepared on glass substrates by
drop-casting. For monomers, their 1,2-dichloroethane solutions
Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan | 843

R
R
R
R
R
R
hν
1,4-addition
D
D
D
D
D
D
Figure 1. Solid-state polymerization of diacetylene (DA) with a donor moiety. D is N-CzPh as a donor and R contains a carbamate
group.
were just cast and dried while dispersions of UV-irradiated
samples in 1,2-dichloroethane were cast and dried for the
polymer samples.
Materials and Reagents. All the commercially available
chemicals were used as received. Compound 1 (9-(4-ethynyl-
phenyl)-9H-carbazole) was synthesized from commercially
available 9-(4-bromophenyl)-9H-carbazole according to the
literature.10
126.9, 126.2, 123.7, 121.0, 120.5, 120.5, 109.8, 84.8, 75.3,
74.3, 65.7, 64.5, 45.2, 28.4, 24.9, 19.5. Anal. Calcd. For
C34H28N2O2: C, 82.23; H, 5.68; N, 5.64%. Found: C, 82.23; H,
5.77; N, 5.67%.
Synthesis of 8-[4-(9H-Carbazol-9-yl)phenyl]octa-5,7-
diyn-1-yl Phenethylcarbamate (DA2). DA2 was synthesized
(73% yield) by a similar method to that for DA1. Mp: 125.7-
1
127.7 °C. H NMR (500 MHz, CDCl3, Me4Si): ¤ 8.14 (d, 2H,
Synthesis of 8-[4-(9H-Carbazol-9-yl)phenyl]octa-5,7-
diyn-1-ol (2). Copper(I) chloride (39.6 mg, 0.400 mmol) was
added to a solution of 1 (2.67 g, 10.0 mmol) and n-butylamine
(30 ml) in methanol (10 ml) at room temperature under N2
atmosphere. The solution immediately turned blue, but the
solution was quenched by the addition of a spatula tip’s worth
of hydroxylamine hydrochloride (H2NOH¢HCl) giving a pale
yellow solution. 6-bromo-5-hexyn-1-ol (1.42 g, 8.00 mmol) was
added in a single portion as a solution in methanol (ca. 1 mL).
The reaction solution was stirred vigorously at room tem-
perature under N2 atmosphere. Approximately every 2 min a
spatula tip’s worth H2NOH¢HCl was added for 2 h. After
stirring for 12 h, a yellow color developed and the reaction
completion was confirmed by TLC. The reaction solution was
concentrated in vacuo. The crude oil was purified by column
chromatography on silica gel using dichloromethane to give
compound 2 (1.91 g, 66%) as a yellow solid. Mp: 101.7-
J = 7.8 Hz), 7.70 (d, 2H, J = 8.3 Hz), 7.54 (d, 2H, J = 8.3 Hz),
7.32 (dd, 2H, J = 7.4 Hz, J = 7.2 Hz), 7.32-7.29 (m, 2H), 7.25
(t, 1H, J = 7.4 Hz), 7.21 (d, 2H, J = 7.2 Hz), 4.70 (br, 1H),
4.12 (t, 2H, J = 6.2 Hz), 3.47 (td, 2H, J = 6.9 Hz), 2.84 (t, 2H,
J = 6.9 Hz), 2.44 (t, 2H, J = 6.8 Hz), 1.78 (m, 2H), 1.68 (m,
2H). 13C NMR (125 MHz, CDCl3, Me4Si): ¤ 156.6, 140.5,
138.9, 138.3, 134.2, 128.9, 128.8, 126.9, 126.7, 126.2, 123.7,
121.0, 120.5, 120.5, 109.8, 84.8, 75.3, 74.3, 65.7, 64.3, 42.3,
36.3, 28.4, 24.9, 19.5. Anal. Calcd. For C35H30N2O2: C, 82.33;
H, 5.92; N, 5.94%. Found: C, 82.44; H, 5.97; N, 5.59%.
Synthesis of 8-[4-(9H-Carbazol-9-yl)phenyl]octa-5,7-
diyn-1-yl Hexylcarbamate (DA3).
DA3 was synthesized
(86% yield) by a similar method to that for DA1. Mp: 102.5-
1
104.2 °C. H NMR (500 MHz, CDCl3, Me4Si): ¤ 8.14 (d, 2H,
J = 7.7 Hz), 7.70 (d, 2H, J = 8.3 Hz), 7.54 (d, 2H, J = 8.3 Hz),
7.44-7.40 (m, 4H), 7.32-7.28 (m, 2H), ¤ 4.64 (br, 1H), 4.11 (t,
2H, J = 6.2 Hz), 3.18 (td, 2H, J = 6.6 Hz), 2.45 (t, 2H, J =
6.9 Hz), 1.81-1.76 (m, 2H), 1.71-1.66 (m, 2H), 1.52-1.48 (m,
2H), 1.34-1.30 (m, 6H), 0.89 (t, 3H, J = 6.7 Hz). 13C NMR
(125 MHz, CDCl3, Me4Si): ¤ 156.7, 140.5, 138.3, 134.1, 126.9,
126.2, 123.7, 121.0, 120.5, 120.4, 109.8, 84.8, 75.3, 74.3, 65.6,
64.1, 41.2, 31.6, 30.1, 28.4, 26.5, 24.9, 22.7, 19.5, 14.2. Anal.
Calcd. For C33H34N2O2: C, 80.78; H, 6.98; N, 5.71%. Found:
C, 80.95; H, 6.96; N, 5.70%.
1
103.4 °C. H NMR (500 MHz, CDCl3, Me4Si): ¤ 8.14 (d, 2H,
J = 7.7 Hz), 7.70 (d, 2H, J = 8.2 Hz), 7.54 (d, 2H, J = 8.2 Hz),
7.44-7.39 (m, 4H), 7.30 (m, 2H), 3.72 (q, 2H, J = 5.6 Hz), 2.46
(t, 2H, J = 6.6 Hz), 1.79-1.68 (m, 4H), 1.28 (t, 1H, J = 5.0 Hz).
13C NMR (125 MHz, CDCl3, Me4Si): ¤ 140.5, 138.3, 134.2,
126.9, 126.2, 123.7, 121.0, 120.5, 120.4, 109.8, 85.1, 75.3,
74.3, 65.6, 62.4, 31.9, 24.7, 19.6. Anal. Calcd. For C26H21NO:
C, 85.92; H, 5.82; N, 3.85%. Found: C, 86.08; H, 5.96; N,
3.88%.
Synthesis of Butyl 2-{[({8-[4-(9H-Carbazol-9-yl)phenyl]-
octa-5,7-diyn-1-yl}oxy)carbonyl]amino}acetate
(DA4).
Synthesis of 8-[4-(9H-Carbazol-9-yl)phenyl]octa-5,7-
DA4 was synthesized (80% yield) by a similar method to that
for DA1. Mp: 82.3-85.6 °C. 1H NMR (500 MHz, CDCl3,
Me4Si): ¤ 8.14 (d, 2H, J = 7.7 Hz), 7.70 (d, 2H, J = 8.5 Hz),
7.54 (d, 2H, J = 8.5 Hz), 7.44-7.39 (m, 4H), 7.32-7.28 (m,
2H), 5.16 (br, 1H), 4.17 (t, 2H, J = 6.6 Hz), 4.15 (t, 2H, J =
6.3 Hz), 3.98 (d, 2H, J = 5.5 Hz), 2.45 (t, 2H, J = 7.0 Hz),
1.84-1.78 (m, 2H), 1.72-1.61 (m, 4H), 1.42-1.36 (m, 2H),
0.94 (t, 3H, J = 7.3 Hz). 13C NMR (125 MHz, CDCl3, Me4Si):
¤ 170.3, 156.6, 140.5, 138.3, 134.2, 126.9, 126.2, 123.7,
121.0, 120.5, 120.4, 109.8, 84.7, 75.3, 74.3, 65.7, 65.5, 64.8,
42.8, 30.7, 28.3, 24.8, 19.4, 19.2, 13.8. Anal. Calcd. For
C33H32N2O4: C, 76.13; H, 6.20; N, 5.38%. Found: C, 76.18; H,
6.37; N, 5.38%.
diyn-1-yl Benzylcarbamate (DA1).
To a solution of 2
(218 mg, 0.60 mmol), triethylamine (3 drops), and dibutyltin
dilaurate (3 drops) in 1,2-dimethoxyethane (20 ml), benzyl
isocyanate (107 mg, 0.800 mmol) was added dropwise with
vigorous stirring at 50 °C under N2 atmosphere. After stirring
for 12 h, the reaction solution was concentrated in vacuo. The
crude solid was purified by column chromatography on silica
gel using dichloromethane followed by recrystallization from
hexane/dichloromethane (10/1) to give DA1 (240 mg, 80%)
1
as a colorless solid. Mp: 120.4-122.3 °C. H NMR (500 MHz,
CDCl3, Me4Si): ¤ 8.14 (d, 2H, J = 7.6 Hz), 7.70 (d, 2H, J =
8.3 Hz), 7.54 (d, 2H, J = 8.3 Hz), 7.44-7.40 (m, 4H), 7.37-7.32
(m, 2H), 7.32-7.27 (m, 4H), 4.98 (br, 1H), 4.39 (d, 2H, J = 5.8
Hz), 4.16 (t, 2H, J = 6.3 Hz), 2.45 (t, 2H, J = 6.7 Hz), 1.84-
1.78 (m, 2H), 1.72-1.66 (m, 2H). 13C NMR (125 MHz, CDCl3,
Me4Si): 156.8, 140.5, 138.6, 138.3, 134.2, 128.8, 127.7, 127.6,
X-ray Crystal Structure Analysis. X-ray diffraction data
for DA1 and DA2 were collected on a Rigaku Saturn 724
CCD diffractometer with Mo Kα radiation (- = 0.71075 ¡) at
93 K. Data collection, cell refinement, and data reduction were
844 | Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan

carried out using the CrystalClear-SM software.21 The struc-
tures were solved by direct methods using the program
SHELXS-97 and refined by full-matrix least-squares methods
on F2 using SHELXL-97.22 All non-hydrogen atoms were
refined anisotropically. All materials for publication were
prepared by Yadokari-XG 2009 software.23
ethyl acetate for DA2, for which the asymmetric unit is com-
prised of two independent molecules.25 In order to clarify the
reactivity of the polymerization process, the relative orienta-
tions of diacetylene moieties between the molecules are most
important, whereby the stacking interval d and the inclination
angle ª of the DA moiety to the stacking direction should be in
the range of 4.2-5.7 ¡ and 40-60° (around 45° in most cases),
respectively, according to the Baughmann criterion.26 DA1 has
d of about 5.09 ¡ and ª of about 61.8° between the acetylene
moieties along the direction of the a axis (Figure 2). The angle
ª is large compared to the ideal orientation for polymerization.
On the other hand, DA2 has more preferable angles of about
50°, which better enables the polymerization process. Although
the molecular structures for compounds DA1 and DA2 are
quite similar with the exception of the end groups, they resulted
in different packing motifs. Those two compounds DA1 and
DA2 have similar π-stacking intermolecular interactions in
the N-CzPh moiety, where the torsion angles between carbazole
and phenyl rings are about 48° for both compounds. In the
carbamate groups, conformation of the molecules is fixed by
classical N®H£O hydrogen bonds (Table 1), which are nearly
the same geometry for both compounds. However, the con-
formation of the butylene chain showed obvious differences,
whereby DA1 has trans-trans conformation and DA2 has
gauche-gauche conformation. This flexibility caused a differ-
ence of relative orientations of the acetylene units. These
results indicate that the conformation of DAs is a relatively
unpredictable and uncontrollable event. On the other hand,
the rigid N-CzPh groups with strong π-interactions seem to
be advantageous to aligning molecular orientations. Unfortu-
nately, single crystals of DA3 and DA4 appropriate for X-ray
crystallographic analysis could not be obtained after many
trials so far. However, these compounds are likely to satisfy
Baughmann’s criterion due to higher flexibility of the side
chains.
Solid-State Polymerization.
Solid-state polymerization
of DA1-DA4 was performed by UV irradiation at room
temperature. The UV source was a 16 W low-pressure mercury
lamp emitting at 254 nm (R-52G, UVP). Conversion (%) to the
corresponding polymer was determined by two methods. One
is to calculate monomer ratio by DSC heat flow per unit mass
during the monomer melting process before and after UV
irradiation (DSC method). Since the monomers in this study are
thermally inactive as mentioned later, no polymerization occurs
during heating in the DSC measurement. In this method,
reduction of heat flow is thought to originate from polymer
production. The other is a gravimetric method, in which mass
ratio of the insoluble portion after extraction to the original
mass before extraction is considered to be the conversion.
Solvent used for extraction was acetone, which is a good sol-
vent for DA1-DA4. Collection of the insoluble portions was
performed using Duraporeμ membrane filters (1.0 ¯m, VVHP).
Results and Discussion
The approach to the synthesis of these asymmetric DA mono-
mers involves the use of Sonogashira coupling and Cadiot-
Chodkiewicz coupling, which are often used to synthesize
asymmetrical DA monomers,24 and the formation of carbamates
group from isocyanate. The synthetic routes are outlined in
Scheme 1. Compounds DA1 (benzyl group), DA2 (phenethyl
group), DA3 (hexyl group), and DA4 (buthoxycarbonylmethyl
group) were readily and successfully synthesized in good yields
and then characterized. All of the compounds showed good
solubility in common organic solvents at room temperature.
DSC measurements of DA1-DA4 exhibited a sharp melting
point at around 120 °C without mesophase transition and no
exothermic peak at higher temperatures until decomposition had
begun for all of the compounds, indicating potential difficulty
in polymerization through heating. These results are consistent
with previously reported DA monomers using carbamate
groups, which also do not exhibit thermal polymerization.2
Single crystals suitable for X-ray analysis were grown by
slow evaporation of 1,2-dimethoxyethane (DME) for DA1 and
Upon irradiation by UV light, the colorless solids of the
DA monomers turned to colored solids, suggesting solid-state
polymerization. The color of the PDAs, which is caused by
the linear π-conjugation of the polymer main chain, generally
appears from absorption bands at around 500-700 nm.27
Figure 3 (upper portion) shows the changes of UV-vis diffuse
reflectance spectra vs. UV irradiation time for compounds
DA1-DA4. The ordinate of these figures is for the values con-
ducted from diffuse reflectance by using the Kubelka-Munk
Br
OH
N
N
OH
NH2OH•HCl
CuCl, n-BuNH2
1
2 (66%)
MeOH
R =
DA1 (80%)
RNCO
H
N
N
O
DA2 (73%)
DA3 (86%)
DA4 (80%)
R
Bu2Sn(OCOC11H23 2
)
O
DME
C6H13
O
Bu
O
Scheme 1. Synthesis of diacetylene (DA) monomer derivatives DA1-DA4.
Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan | 845

(a)
(b)
(c)
(d)
5.04 Å 5.18 Å
48.4° 49.1°
5.09 Å
61.8°
Figure 2. Molecular packing of (a) DA1 and (b) DA2 along with the a axis (thermal ellipsoids 50% probability). The geometry for
monomers (c) DA1 and (d) DA2.22
Table 1. Hydrogen-Bond Geometry (¡, °)
Compd. D®H£Aa)
D®H H£A
580 nm with UV irradiation, which should be assigned to a
less-ordered PDAs showing red color.29 Some PDAs are known
to exhibit thermochromism, where the color transforms from
blue to red upon heating. The mechanism behind the chromatic
transition has been discussed but is not fully understood. A
possible explanation is the changing interplay between the
conformation of the side groups and the backbone.30 Com-
pound DA2 originally polymerized into a red color at room
temperature, which means the relatively rigid side groups
of DA2 strongly constrain the conformation of the polymer
backbone. In contrast, compounds DA3 and DA4 having more
flexible side groups exhibited absorption bands at lower
energies. The lowest energy absorption maximum of com-
pounds DA3 and DA4 are 598 and 626 nm, respectively. The
blue color of polymer DA4 indicates the formation of con-
jugated backbone with an ordered structure, which may also be
related to a faster conversion reaction in DA4. The violet color
of polymer DA3 may be the result of an intermediate state
between the blue-colored and red-colored states. Interestingly,
slight differences in the side groups, especially on the outside
of the hydrogen bond, dramatically affect the conjugated
polymer main chains, as well as the conformational changes of
four methylene groups. As a result, the solid-state polymeriza-
tion could be achieved despite the existence of a large π-
conjugated N-CzPh group. Unfortunately, thermochromic tran-
sition behavior of polymers was not observed at heating
temperatures below the melting points. However, the results
provide valuable information for the design of DA monomers
D£A
D®H£A
DA1
DA2
N2®H2A£O2i
0.83 2.17 2.968(6)
N2®H2A£O4ii 0.86 2.10 2.914(5)
N4®H4A£O2iii 0.78 2.19 2.959(5)
163
159
166
a) Symmetry codes: (i) x ¹ 1, y, z; (ii) ¹x, 1 ¹ y, 1 ¹ z; (iii)
1 ¹ x, 1 ¹ y, 1 ¹ z.
function,28 and the values are roughly proportional to the
absorbance. The lower portions of each figure show the time
dependence of absorbance near the absorption maxima of the
polymers, i.e., 580 nm for DA2, 600 nm for DA3 and 630 nm
for DA4. From these figures, the order of time to reach the
saturation of absorbance at the maximum is determined to
be DA4 < DA3 < DA2, which should be related to the initial
reaction rate. These results clearly show a different means of
polymerization for DA monomers. Accordingly, each mono-
mer showed different colors: yellow for DA1, red for DA2, red-
violet for DA3, and blue for DA4.
The UV-vis diffuse reflectance spectra of compound DA1
exhibited red-shift at the absorption edge without an increase in
the absorption maxima for standard PDAs (Figure 3a). There-
fore, compound DA1 may react in distorted structure instead
of via the regular 1,4-addition to form a fully conjugated
backbone.6 This is consistent with the result that the crystal
structure of DA1 does not meet Baughmann’s criterion. On the
other hand, DA2 developed absorption bands around 540 and
846 | Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan

(a)
(b)
0 min
0 min
2 min
2 min
5 min
5 min
10 min
20 min
40 min
90 min
10 min
20 min
40 min
60 min
400 450 500 550 600 650 700
Wavelength/nm
400 450 500 550 600 650 700
Wavelength/nm
0.01
0.008
0.006
0.004
0.002
0
0.5
i = 580 nm
0.4
0.3
0.2
0.1
0
i = 580 nm
i = 600 nm
i = 600 nm
i = 630 nm
i = 630 nm
0
10 20 30 40 50 60 70 80 90100110120
Time/min
0 10 20 30 40 50 60 70 80 90100110120
Time/min
(c)
(d)
0 min
0 min
2 min
5 min
0.5 min
1 min
10 min
20 min
40 min
60 min
2 min
5 min
10 min
20 min
400 450 500 550 600 650 700
Wavelength/nm
400 450 500 550 600 650 700
Wavelength/nm
0.5
0.4
0.3
0.2
0.1
0
0.5
0.4
0.3
0.2
0.1
0
i = 600 nm
i = 580 nm
i = 630 nm
i = 580 nm
i = 600 nm
i = 630 nm
0
10 20 30 40 50 60 70 80
Time/min
0
5
10
15
Time/min
20
25
30
Figure 3. The diffuse reflectance spectra for each monomer: (a) DA1, (b) DA2, (c) DA3, and (d) DA4, as obtained from the diffuse
reflection measurements; the lower portion shows KM in the range i from 580 to 630 nm, KMi, normalized to that at absorption
maximum wavelength of monomer (KMi=KM
) plotted vs. UV irradiation time.
monomer--max
and the factors relating to the thermochromic properties of their
PDA derivatives.
12% for DA4, respectively. Generally, the former conversion
becomes larger than the latter one because of the following
reasons. The conversion by the DSC method may be over-
estimated when deterioration of crystallinity during polymer-
ization and/or side reaction other than polymerization occur. In
the gravimetric method, the conversion may be underestimated
if the polymers disperse in the solvent for extraction and
pass through the filter. Actually, after acetone extraction and
filtration in the gravimetric method, yellow to orange filtrates
were obtained for all the compounds. Especially for DA1,
which did not show regular 1,4-addition polymerization, the
The heat flows for the UV-irradiated samples decreased with
a decrease in the monomers. None of the monomers reached
100% conversion, even for the relatively reactive monomer
DA4. The conversions obtained by the DSC method were 20%
for DA1, 32% for DA2, 51% for DA3, and 68% for DA4,
respectively. A percentage conversion level of 60% is not con-
sidered low level as compared to other reported polymers.2,14
On the other hand, the conversions obtained by the gravimetric
method were ca. 0% for DA1, 7% for DA2, 9% for DA3, and
Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan | 847

Table 2. Ionization Potentials of DA1-DA4 before and after
UV-Irradiation
differences in molecular structure have a large impact on
molecular conformation, which was validated by X-ray single
crystal analysis, and are strongly related to the solid-state
polymerization reactivity and the physical properties of the
polymers. The blue-colored polymer is expected to have good
hole conducting properties due to their suitable HOMO energy,
which are being investigated.
Ionization potential/eV
DA1
DA2
DA3
DA4
Monomer
After UV irradiation
5.96
6.01
6.04
6.02
6.01
5.68
5.85
5.39
We thank Prof. C. Shepherd for helpful discussions. This
work was financially supported by the Grant-in-Aid for Young
Scientists (B) (No. 26810106) from the Japan Society for the
Promotion of Science (JSPS), the Japan Regional Innovation
Strategy Program by the Excellence (creating international
research hub for advanced organic electronics) of Japan
Science and Technology Agency (JST), and by the Ministry
of Education, Culture, Sports, Science and Technology, Japan.
insoluble polymers were hardly obtained. Thus, real conver-
sions should be intermediate between the two values obtained
by the two methods. It should be noted that the order of
conversions is the same between two method, i.e., DA1 <
DA2 < DA3 < DA4. Thus, the photopolymerizability of the
monomers must be in this order. Among the monomers in this
study, the polymers showing lower energy absorption maxima
tend to have higher levels of polymer conversion.
Supporting Information
Preparation of thin films is an important step for electronic
device fabrication. Therefore, we prepared thin films of the
monomers and the UV-irradiated samples, whose structures
may be different from the bulk crystals, and their electronic
states were verified by PYS. PYS measurements showed nearly
the same ionization potentials of around 6 eV for all monomers,
as shown in Table 2. This is attributed to a localized-HOMO
population on the N-CzPh moiety, whereby some simple N-
CzPh derivatives have similar HOMO levels.31 Slight dif-
ferences among monomers are caused by variations in the
solid state intermolecular interactions, which enable a shift in
the HOMO-LUMO levels, rather than through intramolecular
effects. In fact, the DFT calculations showed nearly the same
HOMO energies for all monomers and an N-CzPh molecule
(¹5.7 eV), where the molecular geometries were optimized
using the crystal structures as an initial geometry.32 The poly-
merized DA3 and DA4 showed lower ionization potentials
than monomers, which indicates formation of a π-conjugated
chain. In addition, the polymer from DA4 showed a large shift,
suggesting a higher degree of conjugation. Interestingly, the
ionization potentials of polymers from DA1 and DA2 remained
nearly unchanged, nevertheless DA2 turned reddish with a
polymerization. These results indicate that less-ordered con-
formations in the red-colored state significantly prevent effec-
tive π-conjugations of the polymer backbone and the N-CzPh
moieties. HOMO energies ranging from 5.0 to 5.5 eV are suita-
ble as a hole conductor owing to their good contact with the
work function of a gold electrode. Accordingly, these energy
levels indicate potential for use of polymer DA4 in organic
electronic device applications.
Characterization, DFT calculations, and NMR spectra for all
new compounds, and crystallographic information files (CIFs)
for DA1 and DA2 are available free of charge on J-STAGE.
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Bull. Chem. Soc. Jpn. 2015, 88, 843–849 | doi:10.1246/bcsj.20150019
© 2015 The Chemical Society of Japan | 849