CMDITR Review of Undergraduate Research - Pluto - University of ...

molecular orbitals of thiophene oligomers and
polymers form two continuous energy bands as
opposed to discrete energy levels. 1 The energy
gap (band gap) between the filled and vacant
bands is approximately 4eV (~100 kcals), 1 which
lies in the semiconductor regime. The 4eV band
gap of thiophene oligomers and polymers, in
conjunction with their stability and structural
planarity, 1 allows quinquethiophene and other
higher-order oligomers to mimic conventional
semiconductors, such as silicon. In complement,
the use of BNN radicals for the radical
constituent of (1) was primarily motivated by the
stability of these radicals 2 and their ability to be
incorporated into a polymer backbone.
Furthermore, the unpaired electron of the BNN
radical is delocalized onto the annelated phenyl
moiety in addition to the two NO groups, 2 thus
providing multiple pathways for magnetic
coupling between the radicals in three
dimensions, in the solid state that can potentially
translate into bulk ferromagnetic ordering of
electron spins 3 (which describes a magnetic
material). Hence, a polythiophene polymer
covalently “doped” with BNN radicals is
inherently multifunctional and can, therefore,
serve as a model system for investigating spincorrelated
conductivity.
In order to lay the initial steps to assembling
(1), the synthesis and characterization of certain
key “monomers” (2-4) was attempted and the
results discussed herein. The first of the three
monomers, (2), was synthesized because it
serves as a building block for (1); the second
monomer, (3), can be used to ascertain the extent
of the electronic perturbation caused to the
parent BNN radical by one thiophene moiety;
and, finally, the magnetic properties of the third
monomer, (4), can provide a foundation for
predicting the magnetic exchange interactions in
(1).
16 CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004