Self-Assemblies, Folding, and Properties of Perylene Monomers, Oligomers, and Polymers - Molecular Self-Assembly: Advances and Applications - page 173

and determine the folded or self-assembled supramolecular
architecture. Nature uses these weak interactions to fold polymers
into nanostructures and subsequently organizes the folded polymers
into supramolecular assemblies as a general strategy to carry out
complex functions. Thus, molecular assemblies allow the capacity
to mimic nature by directing specific reaction pathways that are
otherwise difficult to achieve. Molecular assemblies steer reactions
by modulating the effective concentration of the reactive groups.
Moreover, self-assemblies reduce the entropic barrier for the
chemical reactions by organizing the reactive molecules together to
enhance specific reaction rates.

5.6.1 Chiral Molecular Codes Direct Specific

Cyclolization

In this section, the concept of molecular codes is expanded into chiral
molecular codes. The basis for this is that a chiral molecule will prefer
to interact with another complementary chiral molecule. Planar
perylene molecules are not chiral, but twisted perylene molecules
as those having substitutions at 1-, 6-, 7-, or/and 12-positions,
are chiral. Therefore, tetrachloro perylene has two enantiomers:
R and S enantiomers. At room temperature, the two enantiomers
rapidly convert into each other; therefore, there are two directing
codes in the solution containing one compound. However, a single
tetrachloro-perylene molecule can only adapt one of the two codes
corresponding to the R or S enantiomer at a specific time.
To test the molecular codes capable of chiral recognition,
disulfide chemistry was used to induce the formation of cyclic dimers
(Scheme 5.11). Deacetylating a racemic mixture of the twisted
chiral monomer 1,6,7,12-tetrachloro perylene initially yielded the
homochiral cyclic product 2B and the heterochiral linear dimer 2D

as indicated by TLC. Quenching the reaction early captured these
two products, which were separated by column chromatography and
characterized by NMR and mass spectrometry. When the reaction
was allowed to proceed to completion, was the only main product.

Unlike the achiral planar monomers, no concatenated or monomer
ring compounds were detected. Interestingly, the heterochiral cyclic
dimer

2B

was not detected in reasonable amount.
It is instructive to compare the achiral planar molecules with the
twisted chiral monomers. The planar perylene readily

2K

π

-stacks with