Synthesis and self-assembly of phthalocyanine-tethered block copolymers

Article abstract of DOI:10.1039/c4tc02778g

A series of novel phthalocyanine (Pc)-tethered block copolymers, Pc-poly(methyl methacrylate)-block-polystyrene (Pc-PMMA-b-PS), with various molecular weights (number average molecular weight mass = 41, 66, 86 kg mol^-1), were prepared by atom transfer radical polymerization and click chemistry. The structurally related Pc-tethered homopolymer, Pc-PMMA was also synthesized for comparison. Pc-PMMA forms homogeneous polymer films containing π-assemblies of the terminal Pc groups, whereas Pc-PMMA-b-PS self-assembles into a cylindrical morphology in which the Pc units show π-π interactions inside the confined PMMA cylinders. Such polymer designs have potential applications in optoelectronic devices. This journal is

Full text of DOI:10.1039/c4tc02778g

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Materials Chemistry C
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PAPER
Synthesis and self-assembly of phthalocyanine-
tethered block copolymers†
Cite this: DOI: 10.1039/c4tc02778g
a
b
b
c
c
Junko Aimi,* Motonori Komura, Tomokazu Iyoda, Akinori Saeki, Shu Seki,
a
d
Masayuki Takeuchi and Takashi Nakanishi*
A series of novel phthalocyanine (Pc)-tethered block copolymers, Pc-poly(methyl methacrylate)-block-
polystyrene (Pc-PMMA-b-PS), with various molecular weights (number average molecular weight mass ¼
ꢀ1
4
1, 66, 86 kg mol ), were prepared by atom transfer radical polymerization and click chemistry. The
structurally related Pc-tethered homopolymer, Pc-PMMA was also synthesized for comparison. Pc-
PMMA forms homogeneous polymer films containing p-assemblies of the terminal Pc groups, whereas
Pc-PMMA-b-PS self-assembles into a cylindrical morphology in which the Pc units show p–p
interactions inside the confined PMMA cylinders. Such polymer designs have potential applications in
optoelectronic devices.
Received 4th December 2014
Accepted 7th January 2015
DOI: 10.1039/c4tc02778g
www.rsc.org/MaterialsC
assemblies of Pc molecules in polymer lms in a predictable
manner. Therefore, the development of versatile and robust
Introduction
6
Phthalocyanines are planar aromatic macrocycles with attrac- methodologies for preparing polymer materials with Pc
tive electronic and optical properties; these properties have led assemblies has been the area of research focus.
to the incorporation of phthalocyanines as active components
There have been several recent reports on various designs of
in semiconductors, electrochromic devices, information- p-molecule-containing block copolymers that form well-dened
1
7
storage systems, and liquid-crystal color displays. Pc molecules nanostructures of p-assemblies in their polymer lms. Block
tend to form one-dimensional (1D) columnar structures copolymers show phase-separated morphologies such as
through p–p interactions, exhibiting anisotropic semicon- lamellae, gyroids, hexagonal cylinders, cubes, or spheres,
2
ducting properties. Discotic liquid-crystalline (LC) Pcs, which depending on the components and the relative molecular
can self-assemble into two dimensional (2D) patterned weights of each block. Incorporation of molecular semi-
8
columnar structures, have also been studied extensively in conductors into such block copolymer morphologies is of
recent decades and can be used in many of the applications particular interest because of the potential optoelectronic
3
9
described above. Pc-containing polymers are also attracting applications of the resulting materials. For instance, cylin-
4
attention owing to their high stability and their processability.
drical and/or lamellar morphologies can serve as active layers in
Polymers in which Pc groups are present in the main chains, organic photovoltaic (OPV) devices or organic eld-effect tran-
networks, side chains, or cores, or as terminal groups have been sistors (OFETs) in which the directional p-conjugated pathways
1c
prepared. Among these, stable 1D columnar structures of Pc in the polymer lms are expected to permit efficient transport of
9
can be obtained reasonably directly from main-chain-type Pc charge and excitons. Thelakkat and co-workers reported that
5
polymers. However, the synthesis of such functional polymers perylene bisimide-containing block polymers form p-assem-
remains challenging, mainly because of their low solubilities, blies in block copolymer nanostructures that are useful in
10
and it is even more difficult to prepare highly ordered optoelectronic devices. Fullerene-containing block copoly-
mers have also been synthesized and show unique phase
11
behaviors.
a
Organic Materials Group, Polymer Materials Unit, National Institute for Materials
Here we report our attempts to construct Pc-containing
nanostructures in polymer lms by microphase separation of
block copolymers. Because of the difficulties in predicting the
morphology of newly synthesized functional block copolymers,
we decided to modify the well-studied versatile block copol-
ymer, poly(methyl methacrylate)-block-polystyrene (PMMA-b-
Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. E-mail: AIMI.Junko@
nims.go.jp; Fax: +81 29 8592101; Tel: +81 29 8592031
b
Division of Integrated Molecular Engineering, Chemical Resources Laboratory, Tokyo
Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8503, Japan
c
Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
Osaka 565-0871, Japan
d
International Center for Materials Nanoarchitectonics (MANA), National Institute for PS), with a Pc molecule to minimize the effects of p-assemblies
Materials Science, Ibaraki 305-0047, Japan. E-mail: NAKANIAHI.Takashi@nims.go.jp on the morphology. There are few reports of polymer designs in
†
Electronic supplementary information (ESI) available. See DOI:
which p-molecules are attached to the termini of block
1
0.1039/c4tc02778g
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11a
14
copolymers rather than onto their side chains or main chains.
requirements. A zinc complex of Pc with a terminal hydroxyl
The Pc-tethered block copolymer Pc-poly(methyl methacrylate)- group Pc-OH was synthesized by means of a mixed tetracycli-
block-poly(styrene) (Pc-PMMA-b-PS), in which the Pc unit is zation of 4,5-bis(dodecyloxy)phthalonitrile with 4-benzyloxyph-
attached at the terminus of the PMMA-b-PS, therefore repre- thalonitrile in a 3 : 1 molar ratio in the presence of ZnCl2,
sents a novel type of polymer. PMMA-b-PS was targeted to have followed by deprotection of the benzyl group with Pd/C. The
cylindrical morphology, while the Pc unit is attached at the end hydroxyl group of Pc-OH was reacted with 6-chloro-1-hexyne to
of the cylinder-forming PMMA block. We surmised that if this give the functionalized phthalocyanine 1, which was unambig-
1
block copolymer was capable of self-assembly to form a cylin- uously characterized by means of H NMR and absorption
drical morphology in a thin lm, the Pc end-groups might be spectroscopy along with MALDI-TOF mass spectrometry (see
concentrated inside the conned PMMA columns and that ESI†). Meanwhile, the azide-terminated poly(methyl methacry-
anisotropic alignment might be achievable by manipulating the late) N -PMMA was prepared via ATRP using an azide-bearing
3
0
00 00
orientation of the cylindrical structure of the PMMA-b-PS. Such ATRP initiator and CuBr/CuBr /N,N,N ,N ,N -pentamethyldi-
2
control of the alignment of the cylindrical morphology of ethylenetriamine (PMDETA) as the catalyst system. The result-
PMMA-b-PS has been widely studied in the eld of block ing N
copolymer lithography, where perpendicularly oriented cylin- with styrene by ATRP, to give the azide-terminated block
ders of PMMA-b-PS are used as etch masks to transfer patterns copolymer N -PMMA-b-PS (N -BCP) aer reprecipitation in
onto underlying silicon substrates. The preparation of Pc- methanol. Samples of N -BCP with various molecular weights
tethered block copolymers and the characterization of their lm were prepared to permit investigations on the effects of the size
3
-PMMA macroinitiator was subsequently block-extended
3
3
12
3
morphologies are discussed in this paper.
of the polymer on the morphology of its thin lms. The reaction
conditions, compositions, number-average molecular weights
and polydispersities of the homopolymer and block copolymers
are summarized in Table S1.† The volume fractions of PMMA in
Results and discussion
Synthesis and characterization
the N -BCP (f
MMA
) were estimated by manipulating the integral
3
1
2 2
ratios from the H NMR spectra recorded in CD Cl and mass
The synthetic route to the Pc-tethered block copolymers is
shown in Scheme 1. To functionalize the Pc unit and attach it to
the polymer, we used an azide–alkyne Huisgen cycloaddition,
termed a “click reaction”, in combination with atom transfer
radical polymerization (ATRP). The click reaction is widely
used as a polymer-modication technique owing to its high
ꢀ
3
densities of two components (1.05 and 1.184 g cm for PS and
PMMA, respectively), the values of which were controlled to
obtain a cylindrical morphology.
The Pc-tethered (co)polymers were synthesized by treating
3 3
N -PMMA or N -BCP with an excess of Pc derivative 1 in the
13
presence of copper(I) iodide and diisopropylethylamine (DIPEA)
in tetrahydrofuran (THF) as a solvent (Scheme 1). The course of

delity, quantitative yields, tolerance to a variety of functional
groups, mild reaction conditions, and minimal work-up
Scheme 1 Synthesis of Pc-PMMA and Pc-PMMA-b-PS (PcBCP), where Pc moiety is complexed with a zinc ion.
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(Q-band) and in UV region at 350 nm (Soret band), originating
from a p–p* transition (Fig. 2a). In THF solution, Pc-PMMA
showed a similar spectrum to that of 1 (Fig. 2b, black line).
However, Pc-PMMA in CH Cl solution showed split absorption
2
2
bands at 677 and 693 nm in the Q-band region (Fig. 2b, blue
line). Such split bands are known to result from edge-to-edge
15
2 2
interaction of Pc units. On addition of pyridine to the CH Cl
solution, the longer-wavelength band disappeared and a similar
spectrum to that in THF was observed (Fig. 2b, red dashed line).
1
The H NMR spectrum of Pc-PMMA in CD Cl showed multiple
2
2
signals at d ¼ 6–10 ppm and d ¼ ꢀ3 to 0 ppm in addition to large
signals from PMMA. Upon the addition of a drop of THF-d to
8
2 2
the CD Cl solution, the signals in the downeld region were
simplied and could be assigned to the Pc core protons,
whereas signals in the upeld region were diminished
(Fig. S4†). Considering that the non-equivalent signals were
Fig.
1 GPC profiles during the synthesis of Pc-PMMA by click
chemistry monitored at 0 h (black solid lines) and after 48 hour (black
dashed lines) with RI detector (a) and UV-vis detector at 400 nm (b).
Pc-PMMA was obtained by reprecipitation in diethyl ether (red solid
line).
the reaction was monitored by gel permeation chromatography
(GPC) with a refractive index (RI) detector, along with UV-vis
absorption detector at 400 nm, corresponding to the phthalo-
cyanine Soret absorption band. The product was precipitated in
diethyl ether to remove any catalyst or unreacted 1, giving the
Pc-tethered polymers with unmodied polymers as green
powders (Fig. 1 and S3†). The conversion of the reaction, or the
rate of functionalization of the polymers by Pc estimated from
the absorbance of the Q-band for the molecular absorption
ꢀ
1
ꢀ1
coefficient of Pc derivative 1 (3 ¼ 41 000 M cm , l ¼ 608 nm),
was 83% for Pc-PMMA, and 20–43% for Pc-PMMA-b-PS
(PcBCP1–PcBCP3). The data of the Pc-tethered (co)polymers are
summarized in Table 1. The relatively low degree of conversions
of Pc functionalization of block copolymers with high molecular
weights were probably due to the loss of terminal azide groups
14b
during the block extension with styrene.
Self-assembly behavior in solution
The Pc derivative 1 was readily soluble in THF, chloroform
CHCl ), dichloromethane (CH Cl ), or toluene. These solutions
showed a typical spectrum for a zinc complex of a phthalocya-
Fig. 2 (a) Absorption spectra of phthalocyanine derivative 1 in THF
black line) and CH Cl (blue line). (b) Absorption spectra of Pc-PMMA
in THF (black line), CH
(
3
2
2
(
2
2
2
Cl
2
(blue line) and CH
2
Cl
2
–pyridine (95 : 5 v/v)
nine with sharp peaks appeared in the visible region at 674 nm (dashed red line).
Table 1 Pc-tethered polymers
a
ꢀ1
a
b
c
Entry
Polymer
M
n
(g mol
)
M
w
/M
n
f
MMA
Pc yield (%)
Pc-PMMA
PcBCP1
PcBCP2
PcBCP3
Pc-PMMA
22 200
86 400
65 500
41 400
1.07
1.18
1.12
1.18
—
83
20
30
43
Pc-PMMA220-b-PS553
Pc-PMMA160-b-PS456
Pc-PMMA107-b-PS200
0.27
0.24
0.33
a
b
Number-average molecular weight and polydispersity determined by GPC analysis with polystyrene standards. Volume fraction of PMMA
1
c
determined from H NMR spectroscopy. The conversion of click reaction estimated by absorption spectra.
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diminished upon addition of a drop of coordinating solvent zinc (ArPc) (a ¼ 3.42 nm) (Fig. S9†). In the wide angle region, a
˚
(
THF-d ), axial coordination of the triazole ligand is most diffused halo was observed at about 4.3 A, due to the molten
8
6
1
likely. As shown in Fig. S5,† the triazole group formed in the alkyl chains (Fig. 3a, black arrow), whereas another peak cor-
click reaction can coordinate to a Zn center of a second Pc- responding to a face-to-face distance in the columnar meso-
˚
PMMA macromolecule to form a dimeric structure, that exhibits phase appeared at around 3.4 A (Fig. 3a, red arrow). The SWAXS
ꢁ
split Q-bands in its absorption spectrum and multiple signals in prole at 20 C showed diffuse peaks assignable to (001)
1
its H NMR spectrum as a result of ring-current effect from the through (004), suggesting the presence of a lamellar structure in
neighboring Pc ring. In polar solvents, such as methanol, Pc- the Pc crystal (Fig. 3a, black dots).
PMMA forms aggregates to show a blue shied absorption
spectrum (Fig. S6;† vide infra).
In its DSC prole, Pc-PMMA showed an endothermic tran-
sition at 115 C characterized as the glass transition (devitri-
ꢁ
Similarly, Pc-PMMA-b-PS (PcBCP1–PcBCP3) showed split Q- cation) temperature (T ) of PMMA (Fig. S8b†). Because of no
g
bands in non-coordinating solvents such as CH Cl or toluene, transition characteristic of the LC-Pc was observed in Pc-PMMA,
2
2
whereas the intensity of a shoulder peak at a longer wavelength no large domain of LC-Pc phase is expected to exist inside the
decreased in coordinating solvents such as THF (Fig. S7†). PMMA matrix. POM analysis and tapping-mode atomic force
These phenomena conrm that we had successfully synthesized microscopy (AFM) measurements also provided no evidence of
Pc-tethered (co)polymers through formation of triazole rings via macroscopic phase segregation between LC-Pc domains and
click chemistry.
PMMA in the transparent green polymer lm. On the other
hand, SWAXS proles of Pc-PMMA showed a diffuse scattering
ꢀ
1
at q values of about 0.46 and 2.3 nm , corresponding to
domain sizes of around 13.6 and 2.7 nm, respectively, which
might indicate that the Pc end-groups form nano-size aggre-
gates that are dispersed in the PMMA matrix (Fig. 3b). In the
wide angle region, a large broad PMMA amorphous halo around
Self-assembly behaviors in the solid states
When examined by differential scanning calorimetry (DSC), Pc
derivative
1
exhibits an endothermic transition with
a
ꢁ
maximum at 103 C in a second heating run at a scanning rate
ꢁ
ꢀ1
of 10 C min . This corresponds to a transition from a crys-
talline phase into an LC mesophase (Fig. S8a†). During the
second cooling run, the DSC prole also gives an exothermic
˚
ꢁ
6
.2 A was dominant even at 120 C; therefore, no LC mesophase
was present in the bulk Pc-PMMA (Fig. S10†).
The DSC trace of PcBCP1 showed two endothermic transi-
ꢁ
transition at 54 C originating from crystallization. This is a
typical feature of n-alkoxyphthalocyanines with exible alkyl
chains, which form a major class of LC materials. The sample
decomposed above 320 C before forming an isotropic liquid;
ꢁ
tions at 105 and 120 C, corresponding to the T values of PS
g
and PMMA, respectively (Fig. S8b†). PcBCP3 also shows two
endothermic transitions at slightly lower temperatures than
PcBCP1 owing to its lower molecular weight. These results
indicate that the polymer domains of Pc-PMMA and PS in Pc-
PMMA-b-PS exhibit phase separation. Powdered PS-b-PMMA
17
ꢁ
we could not therefore characterize the mesophase structure by
temperature-controlled polarizing optical microscopy (POM).
LC mesophase was investigated by means of small and wide
angle X-ray scattering (SWAXS) at elevated temperatures using a
3 3
block copolymers (N -BCP1–N -BCP3) with various molecular
weights did not show signicant scattering peaks in SAXS
measurements, probably because of the small difference in the
electron densities of PS and PMMA (Fig. S11†). On the other
hand, the Pc-tethered block copolymers PcBCP1–PcBCP3
showed signicant peaks in the small angle region with q values
2
SAXSess mc instrument (Anton Paar GmbH, Graz, Austria).
Above the transition temperature, a powder sample of 1 sealed
in a glass capillary showed a set of scattering peaks with peak
positions in the ratio 1 : O3 : O4 : O7; this is characteristic of a
hexagonal columnar mesophase (Col ) (Fig. 3a). The lattice
h
parameter a was calculated to be 3.21 nm, a slightly smaller
ꢀ
1
ꢀ1
ꢀ1
of 0.18 nm for PcBCP1, 0.22 nm for PcBCP2, and 0.26 nm
for PcBCP3 (Fig. 3b). PcBCP2 also shows a broad shoulder peak
at a q value of 0.59, corresponding to O7q, tentatively suggesting
that PcBCP2 forms a cylindrical morphology through micro-
value than that of symmetric octakis(dodecyloxy)phthalocyanito
phase separation. On tethering of the Pc unit to the N -BCP by
3
click chemistry, the contrast in the electron density in the SAXS
prole increased to show a signicant primary scattering peak
from microphase separation, although a lack of long-range
order in the polymer powders was implied. In the wide angle
region, large amorphous halos for PS and PMMA appeared at
˚
around 4–10 A, which overlapped the expected peaks from
assembled Pc end-group (Fig. S12†). We therefore investigated
the Pc assembly by means of electronic absorption spectroscopy
measurements.
Self-assembling behaviors in lm states
The absorption spectrum of Pc derivative 1 drop cast on a quartz
Fig. 3 (a) Temperature-dependent SWAXS profiles of Pc derivative 1.
(
b) SAXS profiles of Pc-tethered (co)polymers.
plate from toluene solution showed broad Q-bands at 630 nm
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and 683 nm, along with a shoulder peak at 770 nm. The sharp Q-band corresponding to the monomer structure of 1. On
intensity of the shoulder peak decreased on heating the lm to the other hand, the transparent green polymer lm containing
ꢁ
1
10 C, and a blue-shied peak was observed at 625 nm 1.0 wt% of 1 showed a blue-shied Q-band. This spectrum was
(Fig. S13†). According to the molecular exciton theory, the shape quite similar to that of the Pc-tethered (co)polymers. Therefore,
of the spectrum in the Q-band region is the result of the inter- it is obvious that Pc end-groups in Pc-tethered (co)polymers
actions of two neighboring Pc units in a dimer; these interac- aggregate through p–p interactions inside the polymer lms to
tions can be generalized into four types of dipole transitions in form cofacial or coplanar aggregates.
cofacial, in-line, coplanar or herringbone arrangements,
15a,18
ꢁ
respectively.
At 20 C, 1 showed a split Q-band, indicating a
Morphology of the block copolymers
herringbone arrangement of the Pc molecules, typical of many
ꢁ
With the expectation of observing Pc stacking in the PMMA
microdomains inside the microphase-separated block copoly-
mers, we focused on the lm morphology of the PcBCPs by
analyzing transmission electron microscopy (TEM) images. A 2
wt% toluene solution of the block copolymer was dropped on
the surface of water, and part of the resulting polymer lm was
crystalline Pcs. Upon heating at 110 C, 1 formed Col meso-
h
phase as mentioned above, resulting in a blue-shied spectrum
assigned to cofacial (or coplanar) aggregates (Fig. S13†).
To investigate the assembled structure of the Pc in polymer

lms, toluene solutions of the Pc-tethered (co)polymers were
ꢁ
drop-cast on quartz plates and then annealed at above 150 C
ꢁ
scooped onto a TEM grid and subsequently annealed at 150 C
for 3 h. The lm on the grid was stained by exposure to RuO4
for three hours. The UV-vis spectra of the transparent green lm
of Pc-PMMA shows similar characteristics to that of aggregated
ꢁ
vapor for 60 s before the measurements. This treatment selec-
1
at 110 C, with a blue-shied broad absorption band in the Q-
tively stains PS blocks and provides contrast in terms of electron
density. Dark regions in the bright-eld TEM images corre-
spond to PS domains, whereas bright regions correspond to
PMMA. As can be seen in Fig. 5, the TEM images of PcBCPs
show the presence of phase-separated microdomains. For
instance, the image of PcBCP1 shows white dots in a partially
hexagonal alignment, characteristic of a cylindrical morphology
with perpendicular alignment. The average domain spacing was
estimated to be 37 nm. PcBCP2 and PcBCP3 also showed
wormlike microdomains, assignable to planar-aligned cylin-
drical morphologies with average domain spacings of 32 and 28
nm for PcBCP2 and PcBCP3, respectively. These results show
that the Pc moiety on the end of the block copolymer does not
disturb microphase separation of the block copolymer. Briey,
the Pc units attached to PMMA are concentrated inside the
PMMA cylinders in the PS matrix. More importantly, the
domain size of the microstructure can be tuned by altering the
size of the block copolymer, and therefore the distance between
Pc aggregates inside the PMMA cylinder can be controlled by
changing the molecular weights of the block copolymers.
band region (Fig. S14†), which is also comparable to that of
aggregated Pc-PMMA in MeOH solution mentioned above
(Fig. S6†). Similarly, the lm of PcBCP showed a broad blue-
shied Q-band, revealing the presence of Pc stacking (Fig. 4a
and S14†). The blue-shied band at 630 nm was more apparent
aer sample annealing, suggesting that the Pc end-group in Pc-
PMMA-b-PS also aggregates through p–p interactions in the
polymer lm and that the formation of aggregates proceeds by
soening of polymer matrix on annealing above T of PMMA
g
and PS. It is noteworthy that p–p interactions of Pcs are formed
despite the low concentration of Pc molecules in a large volume
of polymer matrix compared with Pc-PMMA.
To further discuss that Pc forms aggregates in the thin
polymer lms, we investigated the absorption spectra of lms
obtained from mixtures of 1 and N -BCP2 containing various
3
concentrations of Pc. As shown in Fig. 4b, the N -BCP2 lm
3
containing 10 wt% of 1 showed a similar spectrum of that of 1 at
room temperature, indicating that 1 forms a crystalline struc-
ture in the polymer blend. POM observations showed textures of
Pc crystals at the edge of the lm, showing that 1 is not fully
miscible with the polymer at high concentrations (Fig. S15†). At
the lowest concentration of 1 (0.01 wt%), the lm showed a
Fig. 4 (a) Absorption spectra of PcBCP2 immediately after drop-
casting on quartz plate from a toluene solution (dashed line) and after
ꢁ
annealing at 150 C for 3 h (solid line). (b) Absorption spectra of films of Fig. 5 TEM images of thin films of PcBCPs: PcBCP1 (a), PcBCP2 (b)
3
mixtures of 1 and N -BCP2 containing various concentrations of 1.
and PcBCP3 (c).
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We conrmed the phase morphologies of the thin lms of these studies, we had difficulty in controlling the morphology of
block copolymers by means of glazing incidence small-angle X- PcBCP3 compared with that of PMMA107-b-PS200 with no
ray scattering (GI-SAXS) measurements. Fig. 6a shows the in- terminal Pc (N -PB3), indicating a strong inuence of the Pc
3
plane intensity proles of the PcBCP lms. Three scattering end-group on the morphology of N -BCP3, owing to the small
3
signals with values of 1 : O4 : O7 on the q-scale appeared in molecular weight of the block copolymer and high concentra-
PcBCP1, indicating a hexagonally arranged structure, although tion of Pc in the PMMA cylinders. In other words, the balance
no peak corresponding to O3 was observable because of the between the two types of self-assembly, microphase separation
high intensity of the rst-order peak. Furthermore, neither a of the blocks copolymer and noncovalent interactions of p-
peak nor a Debye ring originating from parallel or randomly planes, might play an important role in controlling the
aligned microphase-separated cylinders. This result would morphology of PcBCP3.
indicate that PcBCP1 formed a cylindrical structure normal to
the surface. The domain spacing of the hexagonal cylinder was
Charge transporting property
estimated to be 41.2 nm. Similarly, the second-order peak was
The Pc assemblies formed inside the conned PMMA cylinders
located at O3q relative to the rst-order reection in the case of
might provide a pathway for electronic transport. We therefore
performed ash-photolysis time-resolved microwave conduc-
tivity (FP-TRMC) measurements on PcBCP2, which has a
PcBCP2; this can be tentatively assigned to a hexagonal cylinder
microdomain morphology. On the other hand, because of the
19
lack of long-range ordering of the block copolymer throughout
the lm, PcBCP3 showed only one discernible higher-order
peak in the in-plane scattering. The assumption of a hexagonal
cylindrical structure for PcBCP leads to a domain spacing of the
cylinders of 33.5 nm for PcBCP2 and 31.9 nm for PcBCP3,
showing a similar tendency to the results of the TEM
measurements. Tapping-mode AFM images of the surface
morphologies of the PcBCP lms support the results from the
GI-SAXS measurements. The AFM image of PcBCP2 showed the
presence of hexagonally packed cylindrical microdomains
normal to the substrates, whereas that of PcBCP3 was ambig-
uous in terms of showing phase separation (Fig. 6b). During
cylindrical morphology with Pc assemblies inside PMMA
cylinders (Fig. S16†). Table 2 summarizes the maximum tran-
P
sient photoconductivities (4
mmax) observed for PcBCP2 and
Pc-PMMA as well as for PcBCP2 doped with a Pc derivative
P
ꢀ
6
2
ꢀ1 ꢀ1
(
ArPc). The 4
mmax value for PcBCP2 (4 (ꢂ1) ꢃ 10 cm V
s )
ꢀ
6
was comparatively same with that of Pc-PMMA (2 (ꢂ1) ꢃ 10
2
ꢀ1 ꢀ1
cm
V
s
) despite the much lower content of Pc in the
polymer matrix. To enhance the conductivity, PcBCP2 can be
used as a compatibilizer for Pc molecules and patterned block
copolymers, because Pc tends to be inserted into the Pc end-
group of Pc-PMMA-b-PS through p–p interactions, causing an
increase in the Pc concentration inside the PMMA cylinders.
Addition of ArPc to PcBCP2 in a 1 : 1 molar ratio gave the nearly
P
ꢀ
5
2
ꢀ1 ꢀ1
double 4
m
value of 1.0 (ꢂ0.5) ꢃ 10
cm
V
s ,
max
although the increase is somewhat within the experimental
P
error, due to the small 4
m
max
value of the pristine PcBCP2.
Meanwhile a clear four-fold improvement (4.1 ꢂ 0.8) was found
ꢀ
5
2
ꢀ1 ꢀ1
for 10 : 1 ArPc-PcBCP2 (1.6 (ꢂ0.3) ꢃ 10 cm V
s ). In AFM
measurements on polymer blends, the 10 : 1 blend showed
ambiguous images, suggesting that microphase separation is
partially disturbed by the addition of a large amount of ArPc
(Fig. S17b†). On the other hand, the 1 : 1 blend showed a highly
aligned hexagonal cylindrical morphology arising from micro-
phase separation together with some kind of macrophase
separation (Fig. S17a†). GISAXS proles showed a rst-order
ꢀ1
peak at a q value of 0.2 nm for the 1 : 1 blend lm, whereas no
clear scattering peak was obtained for the 10 : 1 blend lm
(Fig. S17†). These results imply that the appropriate amount of
doped ArPc was introduced into the Pc-containing PMMA
cylinder to increase the conductivity without disturbing the
Fig. 6 (a) GI-SAXS in-plane peak-intensity profiles of PcBCPs. (b) AFM morphology of the block copolymer. The ordering of added ArPc
phase images of PcBCP2 and PcBCP3.
in the cylinders is an important factor as well. A detailed
P
2
ꢀ1 ꢀ1
a
Table 2 Maximum transient photoconductivities (4
m
max) (cm V
s ) of Pc-containing (co)polymers observed by FP-TRMC
Pc-PMMA
PcBCP2
ArPc : PcBCP2 ¼ 1 : 1
ArPc : PcBCP2 ¼ 10 : 1
1.6 (ꢂ0.3) ꢃ 10ꢀ5
(ꢂ1) ꢃ 10ꢀ
6
4 (ꢂ1) ꢃ 10ꢀ6
1.0 (ꢂ0.5) ꢃ 10
ꢀ5
2
a
ꢁ
15
2
Measured at 25 C upon laser-pulse irradiation at 355 nm (photon density, 9.1 ꢃ 10 photons per cm per puls).
J. Mater. Chem. C
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Journal of Materials Chemistry C
analysis of the use of PcBCP2 and advanced engineering as a
compatibilizer is currently underway toward further applica-
tions in optoelectronics.
Y. Iwashima, K. Ohta, K. Hanabusa, H. Shirai and
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268; (d) W. Zhang, K. Ochi, M. Fujiki, M. Naito,
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In conclusion, we prepared a series of novel Pc-tethered (co)
polymers of PMMA and PMMA-b-PS using a combination of
ATRP and click chemistry. The Pc end-groups on the polymer
chains self-assembled through p–p interactions inside the
polymer lms; nevertheless, the Pc-PMMA-b-PS showed micro-
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molecular weights of the block copolymers. The design of a Pc-
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Acknowledgements
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