5942
J. Am. Chem. Soc. 2001, 123, 5942-5946
A Nanometer-Sized High-Spin Polyradical:
Poly(4-phenoxyl-1,2-phenylenevinylene) Planarily Extended in a
Non-Kekule´ Fashion and Its Magnetic Force Microscopic Images
Hiroyuki Nishide,* Takahiro Ozawa, Makoto Miyasaka, and Eishun Tsuchida
Contribution from the Department of Polymer Chemistry, Waseda UniVersity, Tokyo 169-8555, Japan
ReceiVed August 7, 2000
Abstract: A π-conjugated, but non-Kekule´- and nondisjoint-type poly(1,2-phenylenevinylene) network bearing
4-substituted di-tert-butylphenoxyls was synthesized through a one-pot polycondensation of the star-shaped
subpart and the subsequent oxidation, which was persistent even at room temperature. The polyphenoxyl radical
with a spin concentration of 0.4 displayed an average S of 10/2. The polyradical with the molecular weight of
3.2 × 104 gave a disklike image of ca. 35 × 0.6 nm with both an atomic and a magnetic force microscopy:
the molecular image was examined as a nanoscale and single-molecular-based magnetic dot.
Introduction
Due to the possibility of obtaining purely organic-derived
magnetic materials, there has been recent interest in the synthesis
of high-spin polyradical molecules based on exchange coupling
through a π-conjugated bond.4,5 Rajca et al. demonstrated a very
high-spin alignment with a spin quantum number (S) of ca. 20/2
by precisely synthesizing dendric-macrocyclic poly(1,3-phe-
nylenephenylmethine)s based on the radicals being cross-
conjugatively formed in the backbones.5a-c An increase in the
molecular size of the polyradicals, however, always accompanies
the formation of a spin defect and a decrease in the through-
bond interactions between a large number of spin sites within
the molecule. Thus multiple coupling pathways of the spin sites
or a two-dimensionally π-conjugated network bring(s) about a
significant increase in S for such polyradical molecules. Rajca
et al. eventually succeeded in reporting the highest recorded
value of spin alignment for purely organic molecules, with an
average S of g80/2 at a low temperature, on the highly cross-
linked network of macrocyclic units; the network with a
molecular weight of 104 was prepared by the condensation of
two elegantly designed and tetrafunctionalized calix[4]arene
derivatives.6
Recent advances in nanotechnology have strongly stimulated
the research efforts focused on new materials with sizes from
one to several tens of nanometer(s). For example, particles with
a nanometer-size and consisting of metals are being developed
as a magnetic dot where, e.g., quantum effects are taken into
account.1 On the other hand, the electronic, optical, and magnetic
functions of organic molecules have been studied and utilized
at a macroscopic bulk level or as condensed materials, while
their functions are essentially ascribed to their activities at the
molecular level. A nanoscale material design by covalently
extending the organic-based functional molecules will be a good
methodology to create nanometer-sized functional materials,2
since their size and shape are controlled, maintaining their well-
defined chemical structure, by conventional organic chemical
approaches. The extended and up-sized molecules, i.e., very high
molecular weight polymers, possess single-molecular-based sizes
in the nanometer-range, and the nanometer-sizes of such
covalently extended molecules are kept even after being
dispersed as an isolated single molecule on a substrate or
embedded in an ultrathin coating. Therefore, they are expected
to open up possibilities that are absent in either conventional
subnanosized molecules or macroscopic materials and, in
nanoscale studies, a scanning probe microscopy3 has been found
to be an effective tool.
In contrast to the backbone conjugatively connected radicals
developed by Rajca et al., a π-conjugated polymer pendantly
bearing multiple radical groups in a non-Kekule´ and nondisjoint4d,7
fashion has only recently been studied as another approach to
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10.1021/ja002944u CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/30/2001