Self-Assemblies, Folding, and Properties of Perylene Monomers, Oligomers, and Polymers - Molecular Self-Assembly: Advances and Applications - page 160

and resulted in the most favorable structures, monocycle 2 and

catenane . At a more dilute concentration (0.03 mM), unimolecular

self-cyclization occurred and the monocyclic ring

2 x 2

was obtained as
the third major product. These results revealed that at or above the
critical concentration, the bimolecular reaction product

1

2A formed

before the unimolecular product because of the acceleration

effect of dynamic self-assembly. Below the critical concentration,
C

1

, the unimolecular reaction became competitive, especially under
the influence of other directing or templating effects [52,53]. The
presence of methanol in the self-assembly system of

c

is a driving
factor toward organization, thus potentially lowering the

1I

C value.

c

−

, other
ring compounds are not directed by DSA. In other words, the two
specific sulfur atoms required to form a disulfide bond are not
brought together by dynamic self-assembly. For example, formation
of concatenated rings

Unlike dimer ring 2A and the dimer dimer catenane 2 x 2

1 x 1 , 1 x 2 , and 1 x 3 requires the two adjacent

π °

perylene units to form -stacking with an angle close to 90 . However,

ab initio calculations at the MP2 level suggest that the perylene

units prefer a more parallel conformation with a 30

°

rotation as the
minimum energy conformation; other angles are even less favorable.
Owing to the lack of a self-assembly driving effect, the formation of
catenanes having an -perylene cycle concatenated with a single

perylene cyclic monomer should be entropically discouraged.
Monocyclic trimer

N

is kinetically disfavored because it requires a
sterically inhibited reaction between two thiol groups of the next
nearest neighbor atoms (Scheme 5.7: blue arrows on

3

) that reside
on opposite sides of perylene assemblies (sterically prohibited and
high transition state energy). Thermodynamically, cyclic trimer

3

3 is

π−π

also not favored owing to disruption of stacking. The monocyclic

tetramer is not favored by dynamic self-assembly and only a trace

amount was detected by mass spectrometry because it requires
reaction of a sulfur atom with another sulfur atom at the third
nearest neighbor position (Scheme 5.7: blue arrows on

4

4 ), a difficult

situation to achieve but still possible.

5.5.2 Characterizing Macrocyclic Rings and

Concatenated Rings

The ring structures linked by disulfide bonds were characterized
using both structural methods such as mass spectrometry (MS) and