Chemistry Reference
In-Depth Information
In 2010, Wang and Michinobu proposed a one-step synthesis of conjugated
ladder polymers based on the Pd-catalyzed methodology developed by Tilley [
105
].
Symmetrical 96a/d and unsymmetrical 96b/c bisfunctionalized monomers were
synthesized by sequential Sonogashira couplings of 1,4-diiodo-2,5-dibromo-
benzene and then submitted to the Tilley conditions (Scheme
26
). All of the
monomer was consumed after heating for 48 h to give highly soluble polymers
P96a-d of moderate lengths (Table
10
).
The optical and electrochemical properties of polymers P96a-d are
also summarized in Table
10
.Aswith66c, a bathochromic shift is seen in the
absorbance spectra of the polymers with the strongest electron-donating
substituents, decreasing down the series from P96a-d. All of the polymers were
weakly fluorescent and exhibited irreversible redox properties that were also
tunable depending on the electron-withdrawing or accepting ability of
the
substituents.
4 Conclusions and Outlook
Much can be learned by studying the interplay of aromaticity and antiaromaticity,
and how these dueling theories affect synthetic access to and properties of organic
materials. Fully-conjugated ladder structures, both small molecules and polymers,
are interesting candidates for optoelectronic applications in that they provide
conformationally-rigid systems that promote electron delocalization. The chemistry
and properties surrounding the [N]phenylenes are quite well-established. However,
the synthesis of polymeric and graphitic materials that reflect those properties still
remains a challenge. For the case of diaryl[
a,e
]pentalenes, access to a large toolbox
of synthetic methodology has allowed researchers the opportunity to develop a
diverse array of PAHs containing this framework, as well as extending to the
synthesis of ladder polymers. Continued development of synthetic methodology
for both systems will allow researchers to confirm experimentally some of the
theoretical predictions, and to expand our understanding of the effects of electron
delocalization in ladder systems.
Acknowledgements The support of the National Science Foundation DMR-1005810 and the
Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001088,
is greatly appreciated.
References
1. Minkin VI, Glukhovtsev MN, Simkin BY (1994) Aromaticity and antiaromaticity. Electronic
and structural aspects. Wiley, New York
2. Garratt PJ (1986) Aromaticity. Wiley, New York
