Self-Assemblies, Folding, and Properties of Perylene Monomers, Oligomers, and Polymers - Molecular Self-Assembly: Advances and Applications - page 131

defined as intermolecular association. Intermolecular association
can involve molecules of the same type like homodimers or
molecules of different types such as heterodimers. Both folding and
self-assembly play vital roles in molecular science. Indeed, folded
proteins and their self-assemblies can accomplish remarkable
functions including catalysis [13], DNA repair [14], and information
translation [15]. Obviously, the weak secondary interactions
between the molecular units drive both folding and self-assembly.
Typical such secondary interactions include hydrogen bonding,
charge interactions, and solvophobic effects. Driven by the same
secondary forces, will a linear polymer fold or self-assemble first? We
first answer this question using a class of oligomers, which consist
of rigid chromophores linked by flexible ethylene glycols. Because
such folding or self-assembling involves

π

-stacking, diagnostic

1

vis, and fluorescent spectra when the
chromophores come into close contact.
One strategy to prepare foldable polymers is to alternate a
flexible region and a rigid hydrophobic chromophore region. Both
regions should have a well-defined sequence and length, preferably
in the nanometer regime, so that the folded polymers form “smart”
nanostructured materials. The requirements for the foldable regions
are such that they possess flexibility, hydrophilicity, and solubility
in water or organic solvents. Suitable sequences for the foldable
regions are oligo(ethylene glycol) (OEG) and oligo deoxyribonucleic
acid (DNA). OEGs are soluble in both organic and aqueous solutions
and hence suitable for folding studies in both organic and aqueous
phases, whereas DNA is only soluble in aqueous solutions and foldable
polymers with extensive DNA sequences can only be investigated in
water. However, the requirements for the hydrophobic regions are the
ability to pack into ordered structures. The hydrophobic sequences
should also have interesting optical properties, absorption and/
or fluorescence, which serve to report structural changes during
folding.
One of the central ideas in designing foldable polymers is to
use attractive forces between chromophores to create folded
nanostructures. These forces could be molecular orbital overlaps
such as

changes occur in H NMR, UV

−

interaction or could come from hydrophobic effects. To
illustrate this principle, we will use OEG to minimize appreciable
molecular interactions in the foldable regions and focus on the

π−π