Room-temperature high-spin organic single molecule: Nanometer-sized and hyperbranched poly[1,2,(4)-phenylenevinyleneanisylaminium]

Article abstract of DOI:10.1021/ja0569611

Poly[1,2,(4)-phenylenevinyleneanisylaminium] 1 was synthesized by one-pot palladium-catalyzed polycondensation of N-(3-bromo-4-vinylphenyl)-N-(4- methoxyphenyl)-N-(4-vinylphenyl)amine 3 and subsequent oxidation with the thianthrene cation radical tetraflu

Full text of DOI:10.1021/ja0569611

Published on Web 12/27/2005
Room-Temperature High-Spin Organic Single Molecule:
Nanometer-Sized and Hyperbranched
Poly[1,2,(4)-phenylenevinyleneanisylaminium]
Eiji Fukuzaki and Hiroyuki Nishide*
Contribution from the Department of Applied Chemistry, Waseda UniVersity,
Tokyo 169-8555, Japan
Received October 12, 2005; E-mail: nishide@waseda.jp
Abstract: Poly[1,2,(4)-phenylenevinyleneanisylaminium] 1 was synthesized by one-pot palladium-catalyzed
polycondensation of N-(3-bromo-4-vinylphenyl)-N-(4-methoxyphenyl)-N-(4-vinylphenyl)amine 3 and sub-
sequent oxidation with the thianthrene cation radical tetrafluoroborate: compound 1 three-directionally
satisfies a non-Kekule´-type π-conjugation and the ferromagnetic connectivity of the unpaired electrons of
the triarylaminium cationic radical. The average molecular weight of the polymer was 4700-5900 (degree
of polymerization ) 11-14), which gave a single molecular-based and globular-shaped image of ca. 15
nm diameter by atomic and magnetic force microscopies under ambient conditions. The aminium polyradical
1 with a spin concentration (determined by iodometry) of 0.65 spin/unit displayed an average S (spin quantum
7
number) value of /2 even at 70 °C according to NMR and magnetization measurements.
Introduction
temperature range of magnetic ordering and possibly provide a
molecular-based purely organic magnetic material.
Due to the possibility of obtaining purely organic-derived
magnetic materials, there has been current interest in the
synthesis of very high-spin polyradical molecules based on a
ferromagnetic spin alignment through the π-conjugated skeleton
of a molecule.1 These high-spin molecules are designed to satisfy
a π-conjugated but non-Kekule´ and nondisjoint connectivity2
among the nonbonding molecular orbitals of the unpaired
electrons.3,4 Along with this molecular designing, they have been
extended to cross-linked or networked π-conjugation systems.3a,4a
Rajca et al.5 eventually synthesized two-dimensionally dendritic
macrocyclic poly(1,3-phenylenephenylmethine)s with magnetic
ordering and a huge magnetic moment corresponding to S (spin
quantum number) > 5000. However, the triarylmethane radical
survives only below 200 K. Chemically stable radical species
are desired in such a network high-spin polyradical to raise the
On the other hand, we have recently succeeded in applying
magnetic force microscopy (MFM) to effectively study the
molecular image and very weak magnetic response of an organic
radical macromolecule with molecular size from 10 to 1000
nm.6 The MFM images of the magnetic particles showed a
magnetic gradient response with a fairly high resolution on a
10 nm scale at the position of the radical molecule dispersed
on a substrate surface at room temperature. The MFM molecular
image has been examined as a magnetic dot, by use of organic
radical samples with different molecular weights and spin
concentrations.6b However, the magnetic response upon MFM
was also ascribed to paramagnetic radical macromolecules,7 and
there still remains the pending subject of a nanometer-scale study
on a high-spin organic molecule under ambient conditions. From
such a viewpoint, one of the unrealized benchmarks for
exploring a single molecular-based and purely organic magne-
tism is to synthesize a practically available high-spin organic
molecule with good stability under ambient conditions.
(1) (a) Magnetic Properties of Organic Materials; Lahti, P. M., Ed.; Marcel
Dekker: New York, 1999. (b) π-Electron Magnetism From Molecules to
Magnetic Materials; Veciana, J., Ed.; Springer: Berlin, 2001. (c) Rajca,
A. Chem. Eur. J. 2002, 8, 4834. (d) Baumgarten, M. In Progress in
Theoretical Chemistry and Physics; Lund, A., Shiotani, M., Eds.; Kluwer
Academic Publishers: Dordrecht, The Netherlands, 2003; Vol. 10, Chapt.
12. (e) Rajca, A. AdV. Phys. Org. Chem. 2005, 40, 153.
While a number of the ground-state high-spin organic radical
molecules synthesized along the molecular designing of non-
Kekule´ and nondisjoint fashion are known, as far as we know,
only a few of these radical molecules, such as the tri-
(chlorophenyl)methyl radical synthesized by Veciana et al.8 and
the triplet Yang’s biradical,9 display high-spin magnetic pa-
(2) Borden, W. T.; Davidson, E. R. J. Am. Chem. Soc. 1977, 99, 4587.
(3) (a) Rajca, A.; Rajca, S.; Wongsriratanakul, J. J. Am. Chem. Soc. 1999,
121, 6308. (b) Teki, Y.; Miyamoto, S.; Nakatsuji, M.; Miura, Y. J. Am.
Chem. Soc. 2001, 123, 294. (c) Nishide, H.; Nambo, M.; Miyasaka, M. J.
Mater. Chem. 2002, 12, 3578. (d) Kaneko, T.; Makino, T.; Miyaji, H.;
Teraguchi, M.; Aoki, T.; Miyasaka, M.; Nishide, H. J. Am. Chem. Soc.
2003, 125, 3554. (e) Rajca, A.; Wongsriratanakul, J.; Rajca, S. J. Am. Chem.
Soc. 2004, 126, 6608. (f) Rajca, A.; Wongsriratanakul, J.; Rajca, S.; Cerny,
R. L. Chem. Eur. J. 2004, 10, 3144. (g) Fukuzaki, E.; Takahashi, N.; Imai,
S.; Nishide, H.; Rajca, A. Polym. J. 2005, 37, 284. (h) Rajca, A.; Shiraishi,
K.; Vale, M.; Han, H.; Rajca, S. J. Am. Chem. Soc. 2005, 127, 9014.
(4) (a) Bushby, R. J.; Gooding, D. J. Chem. Soc., Perkin Trans. 2. 1998, 1069.
(b) Selby, T. D.; Blackstock, S. C. Org. Lett. 1999, 1, 2053. (c) van Meurs,
P. J.; Janssen, R. A. J. J. Org. Chem. 2000, 65, 5712. (d) Murata, H.;
Takahashi, M.; Namba, K.; Takahashi, N.; Nishide, H. J. Org. Chem. 2004.
69. 631.
(6) (a) Nishide, H.; Ozawa, T.; Miyasaka, M.; Tsuchida, E. J. Am. Chem. Soc.
2001, 123, 5942. (b) Miyasaka, M.; Saito, Y.; Nishide, H. AdV. Funct.
Mater. 2003, 13, 113.
(7) Michinobu, T.; Inui, J.; Nishide, H. Polym. J. 2003, 35, 71.
(8) Veciana, J.; Rovira, C.; Ventosa, N.; Crespo, M. I.; Palacio, F. J. Am. Chem.
Soc. 1993, 115, 57.
(9) (a) Yang, N. C.; Castro, A. J. J. Am. Chem. Soc. 1960, 82, 6208. (b) Mukai,
K.; Ishizu, K.; Deguchi, Y. J. Phys. Soc. Jpn. 1969, 27, 783.
(5) Rajca, A.; Wongsriratanakul, J.; Rajca, S. Science 2001, 294, 1503.
9
996
J. AM. CHEM. SOC. 2006, 128, 996-1001
10.1021/ja0569611 CCC: $33.50 © 2006 American Chemical Society

Room-Temperature High-Spin Organic Polymer
A R T I C L E S
Scheme 1
Scheme 2
rameters at high temperatures such as room temperature. The
radical species involved in these molecules possess a tradeoff
relation between sufficient exchange interaction for spin align-
ment and chemical stability. Among the list of radical species,
the triarylaminium radical is a favorable candidate for the spin
source to be utilized in robust high-spin purural-radical mol-
ecules at room temperature. From such a viewpoint, a series of
aminium polyradicals has been synthesized and their magnetic
behaviors have been reported. However, they often lacked
solvent solubility that lead to both a limitation of radical (spin)
generation yield and a lack of chemical structure identification.
To the best of our knowledge, no high-spin molecules at room
temperature have been studied by use of aminium radical
polymers with well-defined chemical structure.
This paper describes the first example of room-temperature
high-spin purely organic molecules possessing a nanometer-
range single molecular size. The high-spin molecule poly[1,2,-
(4)-phenylenevinyleneanysilaminium] 1 was designed to be
hyperbranched in a π-conjugated but non-Kekule´ and nondis-
joint fashion. The aminium polyradical 1 was synthesized via
the one-pot polycondensation of an asymmetric trifunctional
monomer 3 and subsequent careful oxidation. Compound 1 was
soluble in common solvents and durable under ambient condi-
tions. The single molecular-based high-spin behavior of 1 was
examined by NMR and magnetization measurements and
magnetic force microscopy at room temperature.
and fluorescence spectroscopies. For example, the NMR inte-
gration ratio of two vinyl groups was almost unity, indicating
a highly branched polymer structure. The end vinyl groups of
the polymer were capped by reaction with excess p-bromoani-
sole to give 2, to avoid all side reactions of the vinyl groups in
the following radical generation.
The head-to-tail linkage and the branched structure were
further supported by the model reaction of N-(4-methoxyphe-
nyl)-N-(3-methyl-4-vinylphenyl)-N-(4-vinylphenyl)amine 4 and
p-bromobenzene by use of the same Pd catalyst and condensa-
tion reaction conditions; the model reaction represented in
Scheme 2 gave N-(4-methoxyphenyl)-N-(3-methyl-4-styrylphe-
nyl)-N-(4-styrylphenyl)amine 5 (for details, see the Experimental
Section). The branched structure and the degree of branching11
were examined on the basis of the NMR integral ratios of the
vinyl and methoxy groups of the terminal unit 4, the linear units
6 and 6′, and the dendritic unit 5. The branching unit 5 was
predominantly favored in comparison with the linear 6 and 6′
unit formation.12 The degree of branching for the model reaction
was ca. 0.5. These results indicated that poly[1,2,(4)-phenyle-
nevinyleneanisylamine] 2 with a highly branched structure was
formed under these experimental conditions (Figure 1).
The UV/vis absorption and fluorescence of the hyperbranched
polymer 2 (λmax ) 300, 385 nm and λem ) 505 nm, respectively)
were comparable with those for the linear corresponding
polymer poly{4-[bis(4-methoxyphenyl)amino]-1,2-phenylenevi-
Results and Discussion
The hyperbranched and head-to-tail linked poly(phenylenevi-
nylene), poly[1,2,(4)-phenylenevinyleneanisylamine] 2, was
synthesized via one-pot palladium-catalyzed10 polycondensation
of an asymmetric trifunctional (the bromo, two kinds of vinyl
groups) monomer, N-(3-bromo-4-vinylphenyl)-N-(4-methox-
yphenyl)-N-(4-vinylphenyl)amine 3, which was prepared by
coupling 4-[N-(4-methoxyphenyl)amino]benzaldehyde and 2-bro-
mo-4-iodobenzaldehyde and the following Wittig reaction
(Scheme 1). A gel-permeation chromatographic (GPC) profile
of the polymer (uncapped) 2 was unimodal. Bromine was
detected at less than 2 wt % in the elemental analysis. Further
reaction of the isolated polymer by the Pd catalyst resulted in
recovery of the starting polymer. These results denied a coupling
reaction between the oligomers during the polymerization
because the surface of the oligomer and polymer is occupied
by the vinyl groups of the monomer. The hyperbranched and
(11) (a) Thompson, D. S.; Markoski, L. J.; Moore, J. S. Macromolecules 1999,
32, 4764. (b) Dendrimers and Other Dendritic Polymers; Fre´chet, J. M.
J.; Tomalia, D. A., Eds.; John Wiley & Sons: Chichester, U.K., 2001. (c)
Jikei, M.; Kakimoto, M. Prog. Polym. Sci. 2001, 26, 1233.
(12) NMR spectrum of the reaction mixture showed multiple peaks at 5.7-5.1
and 3.8 ppm, which were ascribed to the vinyl and methoxy groups of the
compounds formed in the model reaction. Each peak was attributed to the
terminal unit 4, the linear units 6 and 6′, and the dendritic unit,
N-(4-methoxyphenyl)-N-(3-methyl-4-styrylphenyl)-N-(4-styrylphenyl)-
amine 5, by the following HPLC separation, and mass, and 1H NMR
spectroscopies. The ratio of the vinyl groups [linear (L)/terminal (T) )
2.02/1] and the ratio of the methoxy groups [dendritic (D)/L/T ) 0.91/
2.08/1] in the NMR spectrum gave the degree of branching [) (D + T)/(L
+ D + T) ) 2T/(L + 2T)] for the products of the model reaction to be
0.50 and 0.48, respectively. N-(4-Methoxyphenyl)-N-(3-methyl-4-styrylphe-
nyl)-N-(4-styrylphenyl)amine 5: IR (KBr pellet) 2932 (νAr C-H), 1241
(νC-O-C), 961 cm-1 (δAr C-H); 1H NMR (CDCl3, 500 MHz) δ ) 7.51-
6.85 (m, 13H, aryl), 7.38 (d, J ) 8.4 Hz, 2H, aryl), 7.31 (d, J ) 18 Hz,
1H, vinylene), 7.25 (d, J ) 19 Hz, 1H, vinylene), 7.10 (d, J ) 8.8 Hz, 2H,
aryl), 7.03(2) (d, J ) 19 Hz, 1H, vinylene), 7.02(7) (d, J ) 8.4 Hz, 2H,
aryl), 6.90 (d, J ) 18 Hz, 1H, vinylene), 3.82 (s, 3H, methoxy), 2.33 (s,
3H, methyl); mass calcd for M 493.6, found (m/z) 494 (M+). For 6 and 6′,
see Supporting Information.
l
head-to-tail structure was characterized by H NMR, UV/vis,
(10) Heck, R. F. Org. React. 1982, 27, 345.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 997

A R T I C L E S
Fukuzaki and Nishide
Figure 3. Electrolytic UV/vis spectrum of the CH2Cl2 solution of the
hyperbranched polymer 2 (DP ) 12) with 0.1 M (C4H9)4NBF4 under the
given potential. Inset: Absorption change of the CH2Cl2 solution of 0.1
mM 2 after mixing with the CH2Cl2 solution of 2 mM NOSbF6.
chemically persistent even in a solution at room temperature
without any subsequent chemical side reactions. The differential
pulse voltammogram displayed two oxidation peaks at 0.9 and
1.1 V. The cyclic voltammetry of 2 at the slow scan rate of 25
mV s-1 also showed a new redox wave at ca. 0.9 V or a two-
stepped quasi-reversible wave. On the other hand, the cyclic
voltammogram for 2 with the lower molecular weight of 1700
(degree of polymerization ) 4) (Figure 2b) showed a unimodal
oxidation wave at 0.9 V. These results suggest that the oxidation
of the amine moiety or the cationic radical generation inside
the hyperbranched polymer 2 is kinetically shielded by the outer
layer and that the oxidation potential for the dendritic amine
moiety inside the polymer is lower (0.9 V) than that (1.1 V)
for the terminal amine moiety.13
Figure 1. Structure of the hyperbranched poly(1,2,(4)-phenylenevinyle-
neanisylamine) 2.
The CH2Cl2 solution of the hyperbranched polymer 2 was
electrochemically oxidized under the given potential up to 1.3
V and the UV/vis spectrum was recorded. An absorption peak
appeared at λmax ) 529 nm with an isosbestic point at 447 nm
in the range of 0.7-1.0 V and a new peak occurred at λmax
)
733 nm with an isosbestic point at 565 nm at greater than 1.0
V. This result indicated that the hyperbranched polymer 2
possesses two amine moieties oxidized at each potential, 0.8-
1.0 and 1.1-1.3 V, and these two amine moieties were oxidized
to two aminium radicals with visible absorption maxima at 529
and 733 nm.
The hyperbranched polymer 2 was oxidized with nitrosonium
hexafluoroantimonate (NOSbF6) in a stopped-flow UV/vis
spectrophotometer (inset of Figure 3). NOSbF6 was selected as
the oxidizing agent because it has no absorption in the UV/vis
region and a bulky counteranion, SbF6-, to stabilize the formed
aminium cation radical. After the oxidation of the inside and
dendritic amine moiety with the lower oxidation potential, the
oxidation of the amine moiety located on the outside of the
polymer with the higher potential was observed with the
absorbance increase at 733 nm.
Figure 2. Cyclic and differential pulse voltammograms of 2 with DP )
12 (a) and DP ) 4 (b) in CH2Cl2 with 0.1 M (C4H9)4NBF4.
nylene} (λmax ) 302, 368 nm and λem ) 528 nm), which
suggested a developed π-conjugation in 2. The molecular weight
of 2 was, for example, 5200 [degree of polymerization (DP) )
12]. Compound 2 was a yellow powder and quite soluble in
the common solvents such as benzene, CHCl3, and tetrahydro-
furan (THF). The solution viscosity of 2 (DP ) 12) was 1 order
of magnitude lower (intrinsic solution viscosity [η] ) 0.014
g/dL) than that of the corresponding linear polymer (DP ) 13,
[η] ) 0.12 g/dL). An extremely low solution viscosity is one
of the characteristics of hyperbranched polymers, which is
ascribed to the highly branched and globular structure.
Cyclic voltammetry of 2 showed a redox wave with the
oxidation peak at 1.0 V vs Ag/AgCl and the redox peak
separation of 120 mV at a sweep rate of 100 mV s-l (Figure
2): The voltammogram was repeatedly recorded for potential
sweeps of 100 times at room temperature. The electrolytic
electron spin resonance (ESR) spectrum was recorded under
the potential at 1.2 V. A strong absorption appeared at g )
2.0028, indicating a nitrogen-centered radical generation. The
ESR absorption disappeared under the potential at 0.6 V. These
results mean that the triarylamine moiety is electrochemically
oxidized to the triarylaminium cationic radical and reversibly
reduced to the starting amine and that the aminium radical is
(13) The basicity gradient and the metal complexation rate of the amine moieties
for the dendritic poly(phenylazomethine)s suggested the following two
features of the dendritic and hyperbranched aromatic polymers: (a)
Yamamoto, K.; Higuchi, M.; Shiki, S.; Tsuruta, M.; Chiba, H. Nature 2002,
415, 509. (b) Satoh, N.; Nakashima, T.; Yamamoto, K. J. Am. Chem. Soc.
2005, 127, 13030. (i) The basicity of the amine moieties inside the polymer
is higher than that outside, because a Coulombic repulsion among the
sterically crowded amine moieties outside the polymer retards the aminium
cation formation. (ii) The reaction on the amine moieties inside the polymer
is slower than that outside due to a steric shielding with the outer shell.
These could be also the case for the oxidation of the hyperbranched polymer
2. The corresponding linear-type poly(4-dianisylamino-1,2-phenylenevi-
nylene) showed a unimodal oxidation wave during cyclic voltammetry even
at a slow scan rate and the relatively low oxidation potential of 0.81 V vs
Ag/AgCl.4d
9
998 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Room-Temperature High-Spin Organic Polymer
A R T I C L E S
Figure 4. AFM (tapping mode) image (a) and MFM (noncontact mode)
image (b) of the polyradical 1 with DP ) 12 at room temperature.
Figure 5. ømolT vs T plots for 1 with DP ) 12 and spin concentration )
0.65 (b) and Yang’s biradical19 (O). The ømolT values were estimated by
the NMR shift method. Inset:
ømolT plots obtained by the SQUID
The hyperbranched polymer 2 was also chemically converted
to the aminium polyradical 1 with an equivalent amount of
thianthrene radical tetrafluoroborate14 in an acidic solvent (CH2-
Cl2/trifluoroacetic acid/trifluoroacetic anhydride ) 81/17/2 v/v/
v).15 Upon oxidation, the solution color turned to deep purple.
The ESR spectrum of the solution of 1 showed a strong
unimodal signal (g ) 2.0028) without any absorption at g )
2.0078 ascribed to the oxidizing agent of the thianthrene radical.
The half-life of the polyradical 1 was estimated by the ESR
signal intensity to be 3.1 weeks at room temperature. The
aminium radical integrated in the highly branched phenylenevi-
nylene structure was chemically stable in comparison with that
(1.8 weeks) for the linear-type aminium polyradical, poly(4-
diphenylaminium-1,2-phenylenevinylene), under the same con-
ditions.
magnetization measurement for the 1 sample with the spin concentration
) 0.45.
week, which corresponded to inactivation of the radical in the
solid state under ambient conditions.17
The magnetic susceptibility (ø) of the aminium cation
polyradical 1 in the frozen acidic CH2Cl2 solution was measured
on a superconducting quantum interference device (SQUID) in
the low-temperature range of 1.8-170 K. The inset of Figure
5 shows the ømolT vs T plots obtained for the 1 sample (spin
concentration ) 0.45). The constant ømolT value of ca. 0.8
indicated a high-spin state or a strong spin-exchange interaction
in the polyradical 1.
Magnetization of the aminium cation polyradical 1 was also
measured by the NMR shift method and Evans equation18 in
acidic CD2Cl2 solution: The ø value was estimated by measur-
ing the standard peak shift of cyclohexane for a concentration
series of the polyradical solution.19 The ømolT value for the 1
sample with DP ) 12 and a spin concentration of 0.65 at room
The content of the aminium cation radical or spin concentra-
tion (spin per the amine site) was chemically determined by
the titration of 1 with n-tetrabutylammonium iodide (a chemical
quenching or reduction of the radical with the reductant iodide
ion.14c,16). Aminium radicals are known to be reduced to amines
with iodide ion. The spin concentration based on the titration
was 0.65 for 1 with DP ) 12 (herein after, the reported spin
concentration is based on the iodometric titration of the sample).
temperature (303 K) corresponded to spin quantum number (S)
7
)
/
(Figure 5). The 1 sample with DP ) 12 and spin
2
concentration ) 0.35 was prepared by oxidation with 0.5 equiv
of thianthrene tetrafluoroborate, which gave an ømolT value of
4
0.355 that corresponded to ca. S ) /2 at room temperature.
After the iodometric reduction of the polyradical 1, the
(quenched) polymer sample was sufficiently washed and
examined by lH NMR spectroscopy. The NMR spectra were in
fair agreement with those of the starting amine polymer (see
Supporting Information), indicating the appreciable retention
of the chemical (especially π-conjugated) structure during the
radical generation in 1.
These results suggested that the multiplet state is a stable ground
state with a large multiplet-singlet gap or a very strong spin
exchange interaction between the unpaired electrons for 1
(however, it does not rule out the possibility of a degenerate
singlet-multiplet state). Although the spin (radical) concentra-
tion of the 1 sample was not high, the generated radicals’ spins
did accumulate on the inside of the dendritic amine moiety of
the hyperbranched polymer to realize the relatively high S
values. The high-spin state of 1 was maintained in the high-
temperature range of 303-343 K, as shown in Figure 5. These
demonstrated both the chemical stability and the strong spin-
exchange interaction of 1.
The diluted solution of the polyradical 1 was transferred to
a mica surface and subjected to atomic and magnetic force
microscopies (AFM and MFM, respectively). A globular image
was detected on the mica, and the single-molecular size
corresponded to the molecular weight of the polyradical; a
horizontal distance of ca. 15 nm and a vertical distance of ca.
2 nm were estimated for 1 with DP ) 12 (Figure 4). The
following MFM clearly indicated a magnetic gradient response
exactly on the AFM molecular position. The MFM image of
the polyradical molecule disappeared after measurement for 1
The results in this paper concluded that the aminium
7
polyradical 1 behaves as a multiplet molecule (S ) /2 for 1,
with DP ) 12 and spin concentration of 0.65) even at room
temperature.
(17) Although the MFM image of the polyradical disappeared after 1 week, the
AFM molecular image remained intact even after the complete disappear-
ance of the MFM image. Such a magnetic response could not be detected
(14) Thianthrene radical is soluble in organic solvents, is a strong oxidizing
agent (E°′ ) 1.38 V vs Ag/AgCl), and is widely utilized to oxidize
triarylamines. (a) Boduszek, B.; Shine, H. J. J. Org. Chem. 1988, 53, 5142.
(b) Murata Y.; Shine, H. J. J. Org. Chem. 1969, 34, 3368. (c) Connelly, N.
G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.
for the polyradical 1 sample with the lower spin concentration and S by
7
applying the same procedure. The polyradical 1 with S )
magnetization enabled the MFM detection.
/ and a large
2
(15) It is known that trifluoroacetic acid stabilizes organic cation radicals; for
example, Hammerich, O.; Nils, S. M.; Parker, V. D. J. Chem. Soc., Chem.
Commun. 1972, 156.
(18) (a) Evans, D. F. J. Chem. Soc. 1959, 2003. (b) Cotton, F. A.; Murillo, C.
A.; Wang, X. Inorg. Chem. 1999, 38, 6294.
(19) As the control, the ømolT value for a well-known triplet molecule, Yang’s
(16) Eberson, L.; Larsson, B. Acta Chem. Scand. 1987, B41, 367.
biradical,9 was used under the same measurement conditions.
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 999

A R T I C L E S
Fukuzaki and Nishide
mmol), and N,N-dimethylformamide (DMF; 2.49 mL) were heated to
100 °C for 1 h. The THF-soluble part was purified on a polystyrene
gel column. Reprecipitation from the chloroform solution into methanol
and freeze-drying produced a yellow powder of poly(1,2,(4)-phenyle-
nevinyleneanisylamine) (79 mg yield 39 wt %): IR (KBr pellet) 1242
(νC-O-C), 1038 (νC-O-C), 961 cm-1 (δCdC); 1H NMR (CDCl3, 500 MHz)
δ ) 7.36-6.39 (m, 13H, aryl), 5.69-5.48 (m, 0.96H, vinyl), 5.30-
5.18 (m, 0.54H, vinyl), 5.18-5.08 (m, 0.42H, vinyl), 3.81 (s, 3H,
methoxy); UV/vis (dichloromethane) λmax ) 362 nm (ꢀ ) 1.0×104 cm-1
M-1, 315 nm (ꢀ ) 9.4 × 103 cm-1 M-1); fluorescent (dichloromethane)
λem ) 492 nm (λex ) 313 nm); GPC (calibrated with polystyrene
standard) Mw ) 4000, Mw/Mn ) 2.0. Calcd for C276H229BrN12O12 (DP
) 12): C, 83.1; H, 5.8; Br, 2.0; N, 4.2. Found: C, 83.3; H, 5.8; Br,
1.9; N, 4.0.
Experimental Section
The ABB′ type monomer N-(3-bromo-4-vinylphenyl)-N-(4-meth-
oxyphenyl)-N-(4-vinylphenyl)amine 1 was synthesized via six steps,
as described below.
4-[N-(4-Methoxyphenyl)amino]benzaldehyde. p-Bromobenzalde-
hyde (4.45 g, 24.5 mmol), p-anisidine (3.55 g, 28.9 mmol), Pd2(dba)3
[dba ) dibenzylideneacetone; 275 mg, 0.300 mmol], BINAP [2,2′-
bis(diphenylphosphino)-1,1′-binaphthalene; 562 mg, 0.902 mmol], Cs2-
CO3 (11.8 g, 36.1 mmol), and toluene (48.1 mL) were placed in a 50
mL ampule. The ampule was degassed and sealed. The mixture was
heated to 100 °C for 16 h, poured into dilute aqueous ammonia, and
extracted with chloroform. The extract was washed with water, dried,
evaporated, and then purified by silica gel column separation with
hexane/CHCl3 (5/1) as the eluent. The recrystallization from hexane-
CHCl3 gave an orange plate crystal of 4-[N-(4-methoxyphenyl)amino]-
benzaldehyde (3.69 g, yield 67%): mp ) 113 °C; IR (KBr pellet) 3585
p-Bromoanisole (0.281 mL, 2.26 mmol) was mixed with poly(1,2,-
(4)-phenylenevinyleneanisylamine) (79 mg), Pd(OAc)2 (10.1 mg, 4.52
× 10-5 mol), P(o-tolyl)3 (55.1 mg, 1.81 × 10-4 mol), LiCl (95.6 mg,
2.26 mmol), triethylamine (0.756 mL, 5.42 mmol), and DMF (2.5 mL)
and then heated to 100 °C for 3 h. The THF-soluble mixture was
purified by a polystyrene gel column. Reprecipitation from the
chloroform solution into methanol and freeze-drying produced a yellow
powder of the end-capped poly(1,2,(4)-phenylenevinyleneanisylamine)
(2) (79.7 mg, yield 100 wt %): IR (KBr pellet) 1244 (νC-O-C), 1036
1
(νN-H), 1726 (νCdO); H NMR (CDCl3, 500 MHz) δ ) 9.76 (s, 1H,
aldehyde), 7.71-6.84 (m, 8H, aryl), 6.05 (s, 1H, amine), 3.83 (s, 3H,
methoxy); 13C NMR (CDCl3) δ ) 190.25, 157.03, 151.43, 132.59,
132.20, 127.83, 125.10, 114.84, 133.38, 55.52; mass calcd for M 227.3,
found (m/z) 227 (M+). Calcd for C14H13NO2; C, 74.0; H, 5.8; N, 6.2.
Found: C, 74.6; H, 5.7; N, 6.3.
1
(νC-O-C), 960 cm-1 (δCdC); H NMR (CDCl3, 500 MHz) δ ) 7.52-
4-[N-(3-Bromo-4-formylphenyl)-N-(4-methoxyphenyl)amino]ben-
zaldehyde. 2-(2-Bromo-4-iodo)-1,3-dioxolane4d (5.52 g, 17.8 mmol),
4-[N-(4-methoxyphenyl)amino]benzaldehyde (3.67 g, 16.2 mmol), Pd2-
(dba)3 (185 mg, 0.202 mmol), BINAP (371 mg, 0.606 mmol), Cs2CO3
(7.89 g, 24.2 mmol), and toluene (32 mL) were sealed in an ampule
and heated to 100 °C for 64 h. The mixture was poured into dilute
aqueous ammonia and extracted with chloroform. The extract was
washed with water, dried, evaporated, and then purified by silica gel
column separation with hexane/CHCl3 (5/1) as the eluent. Recrystal-
lization from methanol gave a yellow powder of 4-[N-(3-bromo-4-
formylphenyl)-N-(4-methoxyphenyl)amino]benzaldehyde (3.48 g, yield
53%): mp ) 138.0 °C; IR (KBr pellet) 1576 (νCdO), 1324 (νC-N), 1246
(νC-O-C), 1028 cm-1 (νC-O-C); 1H NMR (CDCl3, 500 MHz) δ ) 10.18
(s, 1H, aldehyde), 9.90 (s, 1H, aldehyde), 7.80-6.95 (m, 11H, aryl),
3.85 (s, 3H, methoxy); 13C NMR (CDCl3) δ ) 190.40, 190.12, 158.43,
152.59, 151.31, 137.37, 131.70, 131.28, 130.77, 128.84, 128.46, 128.43,
124.92, 122.95, 120.12, 115.63, 55.52; mass calcd for M 410.3, found
(m/z) 410 (M+). Calcd for C21H16BrNO3: C, 61.5; H, 3.9; N, 3.4.
Found: C, 61.4; H, 3.9; N, 3.4.
6.15 (m, aryl), 3.78 (s, methoxy); UV/vis (dichloromethane) λmax
)
300 nm (ꢀ ) 2.1 × 104 cm-1 M-1), 385 nm (ꢀ ) 2.3 × 104 cm-1
M-1); fluorescent (dichloromethane) λem ) 505 nm (λex ) 430 nm);
GPC Mw ) 5200, Mw/Mn ) 2.1.
Model Reaction. N-(4-Methoxyphenyl)-N-(3-methyl-4-vinylphenyl)-
N-(4-vinylphenyl)amine 4 (10 mg, 29.3 µmol), p-bromobenzene (460
mg, 29.3 µmol), Pd(OAc)2 (0.13 mg, 0.579 µmol), P(o-tolyl)3 (0.72
mg, 2.37 µmol), LiCl (12.4 mg, 0.93 mmol), triethylamine (7.15 mg,
0.703 µmol), and DMF (0.15 mL) were heated to 100 °C for 48 h. The
mixture was extracted with chloroform, and the extract was washed
with water, dried, and evaporated to yield the purified reaction mixture.
Preparation of the Polyradical. The thianthrene cation radical
tetrafluoroborate (4.00 mg, 13.2 µmol) was dissolved in a mixed solvent
(0.92 mL) of CH2Cl2/trifluoroacetic acid/trifluoroacetic anhydride )
97/0.6/2.6 (v/v/v). The solution was dropped into the trifluoroacetic
acid (40.9 µL) solution of 2 (1 mg, 2.36 µmol), and stirred for 5 min
at room temperature (the resultant solution composition was CH2Cl2/
trifluoroacetic acid/trifluoroacetic anhydride ) 81/17/2 v/v/v).
Cyclic and Differential Pulse Voltammetry. Cyclic voltammetry
and differential pulse voltammetry were recorded for the 1 mM 2 in
the 0.1 M tetrabutylammonium tetrafluoroborate-CH2Cl2 solution by
use of a BAS 100B/W electrochemical analyzer (Bioanalytical Systems,
Inc.). The working electrode, the counterelectrode, and the reference
electrode were a platinum disk, a platinum wire, and a saturated Ag/
AgCl calibrated versus a ferrocene couple, respectively.
Stopped-Flow and Electrolytic ESR and UV/Vis Spectroscopies.
Anhydrous CH2Cl2 solutions of 0.1 mM 2 and 2 mM NOSbF6
solubilized with 18-crown-6 were mixed in the spectrophotometer. The
time-resolved UV/vis spectrum was recorded on a rapid-scan stopped-
flow spectrophotometer RSP-501 (Unisoku Co., Osaka, Japan). Com-
pound 2, 0.1 mM in the CH2Cl2 solution containing 0.1 M (C4H9)4NBF4,
was oxidized with a platinum gauze (100 mesh) electrode at a given
potential by use of a potentiogalvanostat NPGS-301 (Nikko Keisoku
Co., Kanagawa). The ESR and UV/ vis spectra were recorded on a
JEOL JES-2XG ESR spectrometer and a Jasco V-550 UV/vis spec-
trophotometer. The ESR signal was calibrated with an external standard
of Mn2+/MgO (g ) 1.981).
N-(3-Bromo-4-vinylphenyl)-N-(4-methoxyphenyl)-N-(4-vinylphe-
nyl)amine (3). Methyltriphenylphosphonium bromide (586 mg, 1.64
mmol) was placed in a Schlenk tube, and n-butyllithium (0.513 mL,
0.820 mmol) was injected to form an ylide after the addition of
anhydrous THF (0.4 mL). 4-[N-(3-Bromo-4-formylphenyl)-N-(4-meth-
oxyphenyl)amino]benzaldehyde (67.4 mg, 0.164 mmol) was added and
stirred for 30 min. The mixture was extracted with chloroform, and
the extract was washed with water, dried, and evaporated. Flash
chromatography (silica gel, hexane/CHCl3 7/1) gave a pale yellow oil
of N-(3-bromo-4-vinylphenyl)-N-(4-methoxyphenyl)-N-(4-vinylphenyl)-
amine (46.1 mg, yield 69%): IR (KBr pellet) 1325 cm (νC-N), 1242
(νC-O-C), 1036 cm-1 (νC-O-C); 1H NMR (CDCl3, 500 MHz) δ ) 7.39-
6.84 (m, 11H, aryl), 6.98 (dd, J ) 11 and 17 Hz, 1H, vinyl), 6.65 (dd,
J ) 11 and 18 Hz, 1H, vinyl), 5.64 (d, J ) 18 Hz, 1H, vinyl), 5.57 (d,
J ) 17 Hz, 1H, vinyl), 5.23 (d, J ) 11 Hz, 1H, vinyl), 5.16 (d, J ) 11
Hz, 1H, vinyl), 3.80 (s, 3H, methoxy); 13C NMR (CDCl3) δ ) 156.81,
148.44, 146.76, 139.56, 136.10, 135.11, 132.31, 130.27, 127.62, 127.15,
126.73, 125.18, 124.03, 123.44, 120.95, 114.99, 114.40, 112.45, 55.46;
mass calcd for M 406.3 found (m/z) 406 (M+). Calcd for C23H20-
BrNO: C, 68.0; H, 5.0; N, 3.5. Found: C, 67.7; H, 4.8; N, 3.3
AFM and MFM Measurements. A drop of 1-5 µM dichlo-
romethane solution of the polyradical 1 was transferred onto freshly
cleaved mica with a microsyringe, and then the solvent was carefully
removed by air-drying. If a concentrated solution was used, the polymer
was aggregated on the surface. The AFM and MFM experiments were
Poly(1,2,(4)-phenylenevinyleneanisylamine) (2). N-(3-Bromo-4-
vinylphenyl)-N-(4-methoxyphenyl)-N-(4-vinylphenyl)amine (202 mg,
0.497 mmol), Pd(OAc)2 (2.23 mg, 1.60 µmol), P(o-tolyl)3 (12.1 mg,
39.8 µmol), LiCl (210 mg, 4.97 mmol), triethylamine (0.166 mL, 1.19
9
1000 J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006

Room-Temperature High-Spin Organic Polymer
A R T I C L E S
performed on a Nanoscope III (Digital Instruments, Inc.). A single-
crystal silicon cantilever for AFM (Digital Instruments; NCH; tip height
10-15 µm, radius curvature at front ca. 5 nm, length 125 µm, width
30 µm, and thickness 3-5 µm, with a spring constant between 20 and
100 Nm-1) was used. Resonance peaks in the frequency response of
the cantilever were selected in the range between 280 and 320 kHz for
the tapping-mode oscillation. A commercially available and standard
MFM tip coated with a ferromagnetic CoCr alloy with a length of 225
µm and a magnetic moment of 10-13 emu (purchased from Digital
Instruments, Nanoprobe SPM Tips type MESP) was used. All tips were
magnetized in the z-direction, which is along the long tip axis. The
MFM images in the noncontact mode were obtained after the AFM
imaging in the tapping mode in the same scan area with a scan rate of
2 Hz, a drive resonance frequency of ca. 78 kHz, and a scan lift height
of 20 nm, which were selected upon tuning.
Magnetic Susceptibility Measurement with NMR. Thin NMR
tubes filled with 2 vol % cyclohexane-mixed sample solution were
placed in the center of a thick standard NMR tube (a 5 mm i.d. glass
tube) which was filled with the mixture of the deutrated solvent C6D6
and cyclohexane for the external reference, and the NMR spectrum
was recorded at 499.10 MHz on a JEOL NMR 500 Λ spectrometer.
The chemical shift of cyclohexane was measured, and the magnetic
susceptibility was calculated on the basis of the Evans equation18 from
∆ν, which is the frequency separation of cyclohexane between those
of the internal sample solution and the external reference for the radical
solutions at concentrations of 9.5, 6.3, 3.2, and 0 mM. The accuracy
of these methods was confirmed by measurement of Cr(acac)3, in which
the solution composition and concentration were equivalent to the other
measurements [the external reference was C6D6 containing 2 vol %
cyclohexane; the internal reference was the mixed solution CH2Cl2/
trifluoroacetic acid/trifluoroacetic anhydride (81/17/2 v/v/v) containing
2 vol % cyclohexane].
SQUID Measurement. The magnetization and static magnetic
susceptibility were measured on a Quantum Design MPMS-7 SQUID
magnetometer. The static magnetic susceptibility was measured from
1.8 to 200 K in a 0.5 T field. The magnetization was measured from
0.5 to 7 T at 1.8, 2, 2.5, and 5 K. Ferromagnetic impurities and
diamagnetic susceptibility of the matrix and the capsule were determined
by Honda-Owen and Curie plots, respectively, and were subtracted from
the measured magnetization.
Acknowledgment. This work was partially supported by
Grants-in-Aids for Scientific Research on the Priority Area
Super-Hierarchical Structures, for the COE Research Programs
Practical Nano-Chemistry and Molecular Nano-Engineering
from MEXT, Japan, and by the Research Project Radical
Polymers at Advanced Research Institute for Science &
Engineering, Waseda University.
Supporting Information Available: Data of the model
reaction, chemical reduction of 1, ESR spectrum of 1, data of
the NMR shift measurement, and other measurements. This
material is available free of charge at http://pubs.acs.org.
JA0569611
9
J. AM. CHEM. SOC. VOL. 128, NO. 3, 2006 1001