Synthesis of oligo(thiophene)-coated star-shaped ROMP polymers: Unique emission properties by the precise integration of functionality

Article abstract of DOI:10.1021/ja301526v

A facile synthesis of oligo(thiophene)-modified (coated) soluble star (ball)-shaped polymers has been achieved via sequential living ring-opening metathesis polymerization (ROMP) of norbornene and a cross-linking reagent using Mo(CHCMe₂Ph)(N-2,6-ⁱPr ₂C₆H₃)(O^tBu)₂ as the initiator and oligo(thiophene) carboxaldehydes for termination. The resultant star-shaped ROMP polymers containing ter- and tetrathiophene moieties exhibit unique emission properties due to an integration of the ROMP polymers (arranged functionalities): the blue emission was tuned to the white emission upon addition of 2-[2-[(E)-4-(dimethylamino)styryl]-6-methyl-4H-pyran-4-ylidene] malononitrile.

Full text of DOI:10.1021/ja301526v

Article
pubs.acs.org/JACS
Synthesis of Oligo(thiophene)-Coated Star-Shaped ROMP Polymers:
Unique Emission Properties by the Precise Integration of
Functionality
Kenji Takamizu and Kotohiro Nomura*
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami Osawa,
Hachioji, Tokyo 192-0397, Japan
*
S Supporting Information
ABSTRACT: A facile synthesis of oligo(thiophene)-modified (coated) “soluble” star
ball)-shaped polymers has been achieved via sequential living ring-opening metathesis
polymerization (ROMP) of norbornene and a cross-linking reagent using Mo-
(
i
t
(
CHCMe Ph)(N-2,6- Pr C H )(O Bu) as the initiator and oligo(thiophene) carbox-
2 2 6 3 2
aldehydes for termination. The resultant star-shaped ROMP polymers containing ter-
and tetrathiophene moieties exhibit unique emission properties due to an integration of
the ROMP polymers (arranged functionalities): the blue emission was tuned to the
white emission upon addition of 2-[2-[(E)-4-(dimethylamino)styryl]-6-methyl-4H-
pyran-4-ylidene]malononitrile.
INTRODUCTION
1,4,5,8-exo-endo-dimethanonaphthalene (CL, exo:endo =
■
1
4
0
.17:1.00) was chosen as a cross-linking reagent. The
Star-shaped polymers containing multiple linear arms con-
nected at a central branched core represent one of the simplest
polymerization was terminated with various aldehydes
[ArCHO, Ar = oligo(thiophene)s such as 2,2′:5′,2″-terthio-
phene (3T), 5-(2,4,6-trimethoxyphenyl)-2,2′:5′,2″-terthiophene
1
,2
nonlinear polymers,
and synthetic studies using living
polymerizations (with the absence of undesirable side reactions
such as chain transfer and termination), especially atom transfer
(
(
MP3T), and 3,3‴-dihexyl-2,2′:5′,2″:5″,2‴-quaterthiophene
15
3
DH4T); Scheme 1]. The results are summarized in Table 1.
It turned out that the resultant polymers terminated with
radical polymerization (ATRP), have thus been reported
2
d,f,g,4
recently.
The synthesis of cross-linked polymers by ring-
5
various aldehydes (3T-CHO, MP3T-CHO, DH4T-CHO)
opening metathesis polymerization (ROMP) has also been
6
−9
were high-molecular-weight ring-opened polymers with uni-
known, and we recently demonstrated a controlled synthesis
of “soluble” star polymers by the living ROMP technique using
a molybdenum−alkylidene initiator by simple sequential
4
form molecular weight distributions [M = (7.05−9.02) × 10 ,
n
15
M /M = 1.20−1.36; runs 1, 2, 4, and 5), that were highly
soluble in ordinary organic solvents such as toluene,
tetrahydrofuran (THF), dichloromethane, and chloroform.
w
n
8
additions of norbornene (NBE) and a cross-linker; the
exclusive introduction of a functionality into the chain end
can easily be achieved by adopting this approach.
8
,10,11
The M values were similar to those for previously reported
We also
n
polymers terminated with 4-pyridinecarboxaldehyde (4-
demonstrated that poly(9,9-di-n-octylfluorene-2,7-vinylene)s
containing oligo(thiophene) moieties at the chain ends show
unique emission properties resulting from intramolecular
C H NCHO) and 4-trimethylsiloxybenzaldehyde (4-
5
4
Me SiOC H CHO) obtained under the same conditions
3
6
4
8a
1
2
(
runs 6 and 7). These facts suggest that preparations of
energy transfer. Since unique emission properties would be
expected to arise from placement of functionalities in a precise
manner through weak interactions, we herein present a facile
synthesis of oligo(thiophene)-modified star (ball)-shaped
ROMP polymers that exhibit unique emission properties
resulting from the precise assembled arrangement (Scheme
end-functionalized polymers (introduction of functionalities
onto the surface of the star-shaped polymers) were achieved
using this approach. The M values in the resultant ROMP
n
polymers increased when the amount of NBE in the third
polymerization was increased (25 → 50 equiv relative to Mo;
1
6
1
3
runs 1−3). The increase in the M value was larger than that
1).
n
for linear poly(NBE), strongly suggesting the formation of star-
shaped polymers.
16
RESULTS AND DISCUSSION
According to our previous communication, the method
consists of the three key steps outlined in Scheme 1.
■
8a
Figure 1 shows UV−vis and fluorescence spectra (in THF at
5 °C) for the resultant star-shaped polymers containing
2
i
t
oligo(thiophene)s. The absorption bands in star-3T (388 nm)
Mo(CHCMe Ph)(N-2,6- Pr C H )(O Bu) (Mo) was chosen
2
2
6
3
2
as the initiator because of its ability to prepare the multiblock
ring-opened copolymers in a precise manner with complete
Received: February 15, 2012
Published: April 11, 2012
10,11
conversion of monomers,
and 1,4,4a,5,8,8a-hexahydro-
©
2012 American Chemical Society
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dx.doi.org/10.1021/ja301526v | J. Am. Chem. Soc. 2012, 134, 7892−7895

Journal of the American Chemical Society
Article
Scheme 1. Synthesis of Oligo(thiophene)-Modified Star-Shaped Polymers by Living ROMP of Norbornene
Table 1. Selected Results for Syntheses of Modified Star
(
Ball)-Shaped Polymers by Sequential Additions of NBE and
a
CL in ROMP using Mo in Toluene
b
c
10−4Mn
d
d
n
e
run
Ar−CHO
3T-CHO
n
M /M
yield (%)
w
1
2
3
4
5
25
25
50
25
25
25
25
9.00
9.02
13.8
7.05
7.80
8.47
8.97
1.36
1.20
1.41
1.30
1.23
1.42
1.31
92.1
92.1
>99.9
90.2
81.3
95
3T-CHO
3T-CHO
MP3T-CHO
DH4T-CHO
f
6
4-C H NCHO
5 4
f
7
4-Me SiOC H CHO
95
3
6
4
a
Conditions for the first reaction in Scheme 1: Mo cat. (1.82 × 10−5
mol), NBE (25 equiv relative to Mo), toluene (10.0 g), 25 °C, 5 min.
1
5 b
Detailed procedures are described in the SI.
Aldehyde for
Figure 2. Fluorescence spectra of 3T, star-3T , 3T-Ph, 3T-vinyl, and
n
termination; structures of 3T, MP3T, and DH4T are shown in
3T-attached poly(NBE) (NBE -3T) [n = 25, 50; concentration 5.0 ×
n
c
−7
Scheme 1. Starting feedstock ratio in the third step in Scheme 1.
10 M on the basis of oligo(thiophene) units as estimated by the
d
e
17
Obtained from GPC in THF vs polystyrene standards. Isolated
molar ratio] in THF at 25 °C with excitation at 380 nm.
f
yields. Cited from ref 8a.
and star-DH4T (400 nm) were shifted to longer wavelength
relative to those in 3T (354 nm) and DH4T (376 nm),
respectively. The emission-peak maxima in star-DH4T (479
and 508 nm) were shifted to longer wavelength relative to
those in star-3T (442 and 472 nm) and were relatively close in
region to those in star-MP3T (486, 504, and 527 nm).
As shown in Figure 2, a notable increase in the emission
sponding to the end fragment by termination with aldehyde.
Marked differences in the emission spectra of star-3T were not
17
observed upon variation of the solvent or temperature. In
contrast, it should be noted that a significant decrease in the
emission intensity in star-3T was observed when the number of
NBE repeat units in the third polymerization step was increased
from 25 to 50 (star-3T25 vs star-3T50 in Figure 2).
intensity of star-3T relative to 3T was observed (5.0 × 10−7
M
It is noteworthy that the absorption band observed in the
UV−vis spectrum and the emission pattern observed in the
fluorescence spectrum of star-3T were close to those of the
phenyl-substituted terthiophene 5-phenyl-2,2′:5′,2″-terthio-
in THF at 25 °C), and the emission bands of star-3T observed
at 442 and 472 nm in addition to shoulders at 497, 510, and
5
2
38 nm were apparently different from those in 3T and 5-vinyl-
,2′:5′,2″-terthiophene (3T-vinyl) (434 and 455 nm), corre-
17
phene (3T-Ph). Moreover, as exemplified in Figures 2 and
Figure 1. (left) UV−vis spectra of 3T, star-3T, DH4T, and star-DH4T and (right) fluorescence spectra of star-3T, star-MP3T, and star-DH4T
−6
(
excitation at 380 nm). The concentration was 1.0 × 10 M [on the basis of oligo(thiophene) units as estimated by the molar ratio] in THF at 25
°C.
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Journal of the American Chemical Society
Article
Figure 3. Fluorescence spectra of star-3T , 3T-attached poly(NBE) (NBE -3T), star-DH4T , and DH4T-attached poly(NBE) (NBE -DH4T)
2
5
25
25
25
1
7
at different concentrations in THF at 25 °C with excitation at 380 nm.
1
9
3
, the emission bands in star-3T and star-DH4T were close to
those of the corresponding linear ring-opened polymers NBEn-
T (n = 25, 50) and NBE -DH4T. The emission intensities in
potential applications in full-color flat panel displays, etc., and
in particular, white polymer light-emitting diodes (WPLEDs)
are promising because of their great potential of flexibility and
3
2
5
20
these linear polymers were dependent upon the number of
NBE repeating units (NBE -3T vs NBE -3T). Moreover,
the emission intensities of NBE -3T and NBE -DH4T were
easy solution processing. Although studies of the efficiency of
the resultant polymers and the detailed mechanism are still in
progress, this might be a unique candidate for the preparation
of white-light-emitting materials based on star-shaped poly-
19
2
5
50
2
5
25
strongly affected by the concentration, and trends in the relative
intensities opposite to those for star-3T were observed as the
concentration was varied (Figure 3): the intensities of the linear
polymers remarkably increased at higher concentration (Figure
3
3
intensity (and shifts in both the emission maxima and the
absorption bands) in star-3T would be due to a (weak)
interaction of the 3T fragment with the phenyl group (existing
in the ROMP polymer as the initiating fragment) in solution. A
similar observation was also realized for star-DH4T, although
an interaction with the phenyl group may not be as strong as
for the terthiophene analogues (star-3T and NBE-3T),
probably because of the n-hexyl substituent. Taking into
account these facts, it is thus suggested that a precise placement
21
mers.
CONCLUSION
■
right) and decreased drastically at low concentration (Figure
left). This fact would suggest that an increase in the emission
We have demonstrated that a facile synthesis of “soluble” star-
shaped polymers containing oligo(thiophene)s has been
accomplished in a precise manner by adopting the living
ROMP technique using a molybdenum−alkylidene initiator by
simple sequential additions of norbornene and the cross-linker.
The resultant polymers, especially star-3T, exhibited unique
emission properties that were observed by integration of the
ROMP polymer (especially by placement of the initiating and
end functionalities) in a precise manner. As far as we know, this
is the first example of not only the precise synthesis of star-
shaped polymers modified with conjugated molecules but also
the demonstration of unique emission properties through
integration of functionalities. We thus believe that the method
would provide new possibilities for applications of the star-
shaped polymers as new performance materials.
(
arrangement) of both the initiating fragment and the end-
functional group are prerequisites for exhibiting the present
unique emission (by a through-space energy transfer).
It is interesting to note that the blue-light emission of the
−5
THF solution containing star-3T (1.0 × 10 M) was simply
tuned to white-light emission upon addition of a THF solution
3.2 × 10−6 M) containing the orange-red-emitting dye 4-
dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-
ASSOCIATED CONTENT
(
(
■
*
S
Supporting Information
18
pyran (DCM) (Figure 4). The white emission was not
observed from THF solutions containing 3T and 3T-Ph and
was difficult to tune by using linear polymers containing 3T at
Experimental details and additional UV−vis and fluorescence
spectra for the resultant star polymers. This material is available
free of charge via the Internet at http://pubs.acs.org.
the chain end (NBE -3T). White-light-emitting diodes
n
(
WLEDs) have received considerable interest because of their
AUTHOR INFORMATION
■
Corresponding Author
ktnomura@tmu.ac.jp
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This project was partially supported by a Grant-in-Aid for
Challenging Exploratory Research (21656209). K.N. expresses
́
his thanks to Prof. Yves H. Geerts (Universite Libre de
Bruxelles) and Prof. Michiya Fujiki (Nara Institute of Science
and Technology) for helpful discussions.
Figure 4. Fluorescence spectra of star-3T upon addition of DCM in
THF at 25 °C with excitation at 380 nm.
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Journal of the American Chemical Society
Article
2
003; Vol. 3, p 226. (d) Buchmeiser, M. R. Chem. Rev. 2009, 109, 303.
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