Self-Assemblies, Folding, and Properties of Perylene Monomers, Oligomers, and Polymers - Molecular Self-Assembly: Advances and Applications - page 134

0 SA

entropy is described as (A). It is reasonable to

assume that the folded dimer resembles the self-assembled dimer,
thus their entropies are approximately equal,

∆ S

= S (A:A)

−

2 S

S (A )

≈

S (A:A). Based

2

fold 0 SA

on these approximations, we conclude that

∆ S − ∆ S

= 2 S (A)

fold 0 SA

−

S (A-A) > 0, thus,

∆ S

>

∆ S

. The reason that 2 S (A) is greater

than A bond, which limits its possible

configuration and thus entropy. These analyses summarize that
folding is favored by entropy and thermodynamic analysis argues
that folding precedes self-assembling.

S (A

−

A) originates from the A

−

5.3.2 Foldable Polymer Synthesis

Folding requires that the polymers possess multiple units within the
backbone with mutual attractions. In addition, these units should
be linked with flexible molecular units that function as hinges or
foldable sequence. Owing to these requirements, radical and anionic
polymerizations are currently not suitable to construct foldable
polymers with large chromophores in the backbone. Here, we will
discuss three strategies to develop foldable polymers containing
optically active chromophores in the main chain. The first approach
is solution synthesis of alternating sequences of rigid hydrophobic
chromophores and flexible hydrophilic foldable linkers. This
approach employs the traditional condensation polymerization
technique. The polymer resulting from this method has alternating
sequences originated from the two monomers and its molecular
weight typically has a wide distribution. The advantage of this
method is that the polymerization is convenient and the drawbacks
are that the lengths of the final polymers are ill defined. Individual
folding actions and quantum interactions are overwhelmed by the
ensemble effect.
The second approach shown in Schemes 5.3 and 5.4 is a stepwise
solid-state method [17]. This method employs two key components:
a solid support such as beads or porous glass and one or more
asymmetric building blocks with one end activated and the other end
protected. The foldable polymer can be grown on a solid support by
adding one asymmetric building block at a time. Typically, the growing
end is protected so that only one desired building block is added each
time. To grow the polymer chain, the protected group is removed
after each coupling and the terminal of the polymer chain is available
for extension again. After the desired number of building blocks is