Chemistry Reference
In-Depth Information
R
1
R
1
R
1
R
2
R
2
R
2
R
2
R
1
R
1
R
1
R
1
= Bu
R
2
= dodecyl
27
28
Scheme 10 Macrocycles with many 1,8-anthracene units
[
64
,
65
]. The hydrophilic hydroxyl groups at the terphenyl side assisted the forma-
tion of a monolayer at the air-water interface. Recently, 1,3,5-
benzenetricarboxylate triester derivative of 26 was utilized for the photochemical
formation of a 2D monolayer polymer, where the cyclic structure was fixed into a
trigonal prism shape by the extra benzene capping [
66
].
Larger 1,8-A oligomers were synthesized in a similar manner. Nonamer 27 has
six 1,8-A units and three 1,5-units (Scheme
10
)[
67
]. The X-ray analysis revealed a
flat and slightly bent structure with two pairs of partially stacked anthracene units.
Dodecamer 28 with 12 1,8-A units was obtained with hexamer 25 on cyclization of
a hexameric precursor [
63
]. This macrocycle tends to take highly folded structures
according to the DFT calculation. The most stable structure has some internally
folded units to yield two pairs of four-layered stackings. The VT
1
H NMR spectra
showed slow interconversion between folded conformations at low temperature.
These compounds offer a new motif of belt-shaped molecules with anthracene
units.
Macrocyclic compounds 29-31 have three 9,10-A units in the nearly planar
triangle, circle, and hexagon frameworks, respectively (Scheme
11
). In 29 and 30,
9,10-A units are twisted from the macrocyclic plane due to steric hindrance to yield
nonplanar structures [
68
,
69
]. It is interesting that compound 29 showed a liquid-
crystal phase at high temperature. Because compound 31 has a large macrocyclic
framework, three 9,10-A units are coplanar to the macrocyclic plane in the global
minimum structure [
70
]. However, the rotational barrier is so low that this molecule
can take nonplanar conformations such as a tube-like shape by rotation of the three
units.
5 Cage Type Aromatic Networks
Cage compounds have 3D polycyclic frameworks resembling a cage in structure.
When aromatic units are incorporated into the cage structure, these planar units
have a function of walls or panels to separate inner and outer space. A large cage
