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nuclear magnetic resonance (NMR) and photophysical measurements
(UV
−
vis). The issue here is how to determine whether the dimer-
based macrocyclic disulfide
2A
is a monocyclic structure rather
than a monomer-based catenane
1
x
1
, and whether the dimer-based
bicyclic disulfide catenane
2
x
2
is formed rather than a tetramer-
based monocycle
4
or other concatenated structure such as
1
x
3
.
The observation of a parent mass peak at
m
/
Z
= 1544.5 (Fig.
5.16a), and fragmentations at 1484.0 (
−
SC
H
), 1380.6 (
−
S(C
H
O)
),
2
4
2
4
3
−
−
1320.3 (
SS(C
H
O)
C
H
), and 1215.3 (
(OC
H
)
SS(C
H
O)
) are
2
4
3
2
4
2
4
3
2
4
3
consistent with the macrocyclic dimer structure
2A
. The evidence
for concatenated perylene dimer
comes from
MALDI-TOF measurements (Fig. 5.16b) because there are no ions
found between the tetramer parent ion with Na
−
dimer rings
2
x
2
+
(
m
/
Z
= 3113.1) and
the dimer daughter ions (
= 1544.5). A characteristic feature in
the mass spectra of catenanes is the total absence of ions between
the molecular peak and the peak corresponding to one individual
macrocycle [54]. In other words, residues existing between the
molecular peak and the peak corresponding to half (or part) of the
ring structure indicate that monocyclization rather than catenation
took place. The MALDI PSD (post source decay) data is consistent with
the proposed catenane structure. Only in dimer
m
/
Z
dimer concatenated
rings, breaking of any bond will lead to linear and cyclic daughter
fragments of half of the parent ion mass. The further fragmentation
pattern of the monocyclic daughter ion is identical to that of a
macrocyclic perylene dimer
−
2A
, indicating the original parent ion is
the dimer
−
dimer catenane
2
x
2
. The monocyclic perylene monomer
1
is also validated by MALDI-TOF mass spectrometry with a strong
parent ion at 772.39 having the expected isotope ratios (Fig. 16c).
Unlike linear oligomer structures, all the observed cyclic
structures (
) have eight sets of symmetric ethylene
chemical resonances in the NMR spectra as shown in Fig. 5.17. The
upfield shift and large separation of aromatic protons (H
2A
,
1
, and
2
x
2
α
β
and H
in Fig. 5.5) indicate a perylene
-stack in the ring; this behavior is
characteristic of the linear folded perylene dimer and tetramer, in
agreement with the early report [17,18]. Similar to the linear folded
perylene dimer (
π
), the upfield chemical shifts
and separation of the bay protons (assigned as H
2A
) and tetramer (
4A
β
) and outer protons
(assigned as H
α
) in ring structures are dependent on the degree of
π
perylene
-stacking. Consequently, the increased upfield shift and
separation of the aromatic protons H
α
β
and H
should be larger for
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