Self-Assemblies, Folding, and Properties of Perylene Monomers, Oligomers, and Polymers - Molecular Self-Assembly: Advances and Applications - page 155

state. Highly reproducible, elastic folding behavior of foldamers was
observed in high precision.

Pullingdirection

(a)

(b)

(c)

(d)

or

Figure 5.14 The doubly folded foldamer is used to illustrate

nonequilibrium mechanical unfolding. (a) When the AFM tip
approaches the surface, the foldamer far end (5

) hybridizes
with DNA bound to the AFM tip. (b) As the AFM tip retracts
upward, the first

′

π

-stack bursts. (c) Further retraction
induces the second perylene

−

perylene rupturing event. (d)
Finally, the DNA duplex gives up and the foldamer may still
attach to either the substrate or the AFM tip. Repeating this
process reveals either the fully folded states, partially folded,
or unfolded states depending on the refolding kinetics.

Retracting the AFM tip elongated the folded N

π

S, and eventually

−

disengaged the substrate until DNA DNA unzipping occurred. The

observed perylene

−

perylene rupturing force was weaker than

−

DNA ), and consequently perylene

unfolding preceded the DNA unzipping event while being pulled
by AFM. After the DNA duplex rupturing, the foldamer could be
positioned at either the silicon substrate or the AFM tip. When
the AFM tip approached again, complementary DNA hybridized
again to reconnect the substrate and the tip. This engagement
enabled repeated force measurement at the retraction mode. This
AFM pulling process stretched the doubly folded state and created
singly folded state and then to unfolded states in a nonequilibrium
manner.
For foldamer on dendrons, repeated mechanical pulling yielded
force

DNA rupturing force ( vide infra

−

extension curves, which divulged reproducible small peaks