CNMS Research and User Research
New Class of Supramolecular Wires
G. Sumpter1, V. Meunier1, E. F. Valeev2, A. J. Lampkins3,
A. Vazquez-Mayagoitia4, and
R. K. Castellano3
for Nanophase Materials Sciences, Oak Ridge National Laboratory
2Department of Chemistry, Virginia Tech; 3Department
of Chemistry, University of Florida;
4Computer Science and Mathematics
Division, Oak Ridge National Laboratory
A new approach, emerging from experimental and theoretical studies
of donor-σ-acceptor molecules, has been developed to construct
one-dimensional supra-molecular wires that have easily tunable
electronic and physical properties . This concept is established
using one class of these systems, 1-aza-adamantanetriones (AATs),
which are well characterized in terms of their solution and solid-state
self-assembly and chemical manipulation, (see Fig. 1). Following
self-assembly of the molecules into 1-D periodic arrays  --
a process driven by dipolar and dispersion forces -- the frontier
molecular orbitals are delocalized, spanning the entire system,
through the saturated tricyclic cores of the monomers, (see Fig.
2, Top). The electronic band structure for the wire reveals significant
dispersion and can be tuned from the insulating regime to the semiconducting
regime by suitable chemical functionalization of the core ,
(Compare top and bottom images in Fig. 2)
Understanding and controlling the forces that drive self-assembly processes
provides a viable route for the design of functional materials
with desired properties. Moving toward this goal, π-conjugated
systems are at the forefront of the organic electronics field due
to their synthetic accessibility, tunable electronic properties
with substitution and conjugation length, and predictable
self-assembly into nanoscale architectures through π-stacking (often together
with other non-covalent interactions). Our new theoretical understanding,
highlighting the fundamental importance of the intrinsic dipolar
and dispersion interactions in the self-assembly process, for a
new class of supra-molecular structures based on unconventional
donor-σ-acceptor molecules [1-3] and the theoretical characterization
of the subsequent electronic structure and properties, sets the
stage for the tailored design of novel functional materials that
are an alternative to those comprised of traditional π-conjugated
systems. Continued recognition that electronic, optical, and transport
properties similar to traditional π-conjugated materials may be
accessible to alternative organic architectures, particularly those
that spontaneously organize, should encourage the development of
new approaches to functional materials design such as materials
for organic-based optoelectronic devices.
resulting structure from subsequent self-assembly of multiple molecules
of these two AATs into stable periodic wires is
shown in the Fig. 2. The binding energy (dimer dissociation energy)
and the full electronic band structure are also highlighted in these
frames, showing surprisingly strong intermolecular interactions and
electronic states with relatively large dispersion. As can be seen,
the electronic bandgap for the two different AATs is highly dependent
on the substitution of the AAT core, ranging from 2.3 eV for the tribenzyl
AAT (Top, Fig. 2) to 1.5 eV for the triamide AAT (Bottom, Fig. 2),
demonstrating the ability to control the electronic structure. The
nature of the dispersion can be seen from the frontier molecular orbitals,
which show delocalization through the saturated tricyclic cores of
the monomers (insert on the band structure plot in Fig. 2, Top). The
simulated XRD pattern obtained from the optimized wire structure for
the tribenzyl AAT compares favorably to the experimentally measured
XRD pattern and this agreement provides strong support for the concept
of the formation of the 1-D supramolecular wires . Additional support
is available from NMR, IR, DSC and SEM images.
Acknowledgment of Support
This work was a culmination of research from both the science and user
programs. BGS and VM were supported by the Center for Nanophase Materials
Sciences (CNMS), sponsored by the Division of Scientific User Facilities,
U.S. Department of Energy. This research was part of a CNMS User
Program (CNMS2004-016 and CNMS2007-029). AJL, HL, RKC were supported
by the National Science Foundation (CHE-0548003). EFV was supported
by the National Science Foundation CRIF Grant CHE-0443564.
B. G. Sumpter, V. Meunier, E. F. Valeev, A. J.
Lampkins, H. Li, and R. K. Castellano, J. Phys. Chem.
C 111(5), 18912-18916 (2007).
G. Sumpter, V. Meunier, A. Vazquez-Mayagoitia, R.
K. Castellano, Int. J. Quant. Chem. 107, 2233-2242 (2007).
Yuan, B. G. Sumpter, K. A. Abbound, R. K. Castellano, New
J. Chem. 32, 1924-1934 (2008).