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emission originates from the localized emission involving two or
more folded and coupled perylene units. This diagnostic change in
intensity ratios between the first two vibronic transitions is seen
in optical absorption and emission of covalently bound perylene
cyclophanes [73] and folded dimers [18], and is attributed to
π−π
interaction. Broad structureless fluorescence centered at 600
640
nm (Fig. 5.23e) is attributed to delocalized states across extensively
folded and coupled
−
π
-stacks.
h
n
) excitation, perylene-folded cores
receive 58.6 kcal/mol of energy, which is sufficient to disrupt
Upon a single photon (
π−π
interaction energy, determined to be 2
−
7 kcal/mol in organic
solvent (C
). Spectral activity seems to support one average
maximum switching frequency at 6 switch/min (0.1 Hz). This slow
folding/unfolding process is probably due to local energy minima
traps for intermediary folded states, and is indicative of directed
motion involving highly correlated non-Markovian dynamics (Fig.
5.23) [74].
H
Cl
2
2
4
5.7.3
Single-Molecule Studies of Macrocyclic and
Concatenated Foldamers
Compared with the monomer, linear foldamers have rich spectral
dynamic and emit completely different color like red and green.
What is the difference in the behavior between linear dimer (
2A
) and
macrocyclic dimer (
2A
)? How concatenated tetramer (
2
x
2
) behaves
differently from linear-folded tetramer (
)? Next, we present the
four architecturally diverse foldamers chosen for comparison. We
show that the results for macrocyclic dimer (
4A
2A
) and concatenated
−
tetramer (
unfolding model for
linear foldamers and provide further insight into the photoinduced
folding dynamics of linear foldamers.
While contrasted to solution-ensemble measurements,
solventless single-molecule measurements exhibit dramatically
different emission spectra. When using a continuous wave laser to
excite linear foldamers
2
x
2
) strongly support the folding
2A
and
4A
and cyclic compounds
2A
and
2
x
2
their fluorescence spectral trajectories collectively display
various characteristic shapes and vibrant colors. Again, five common
spectral types (Fig. 5.23a-e), including pure monomer-like green
emission (type a) and pure
,
π
-stack red emission (type e), have been
identified as representative of all spectra observed, although many
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