is hydrogen binding in the POSS(Tp) 8 supermolecules due to 16 amide groups,
we found by FTIR study that hydrogen bonding existed both below and above the
isotropization temperatures, regardless of the disordering of the supramolecular
self-assemblies. Therefore, we consider that molecular shape and topology is
more important for the supramolecular self-assembly of POSS(Tp) 8 . When the
spacer length, e.g., C 2 in sample 16, is much shorter than the C 12 alkyl chains, the
Tp arms are tightly attached to the POSS core, and thus the supermolecules adopt
a disklike overall molecular shape when they stack in parallel together. Finally, a
column-within-column nanostructure is obtained; four Tp columns inside a supercolumn formed by the entire supermolecules (see the top panel of Fig. 21).
Assuming one molecule per unit cell (area = 20.96 nm
2 ) and the thickness per
molecule = 0.72 nm (i.e., 2 Â 0.36 nm), the density of sample 16 is estimated to
be 1.218 g/cm
3 . When the spacer length increases to C 6 in sample 17, Tp arms are
decoupled from the POSS core to a certain extent. The supermolecules therefore
adopt a board-like overall molecular shape, and a lamellar structure with a 2D
rectangular symmetry is obtained. Assuming one molecule per unit cell
(area = 22.18 nm
2 ) and the thickness per molecules = 0.72 nm, the density of
sample 17 is estimated to be 1.198 g/cm
3 . When the spacer length further
increases to C 10 in sample 18, Tp arms become fairly mobile, and thus four Tp
columns aggregate together (i.e., segregated from the POSS core) to form a
supercolumn. Assuming one molecule per unit cell (area = 24.83 nm
2 ) and the
thickness per molecule = 0.72 nm, the density of sample 18 is estimated to be
1.112 g/cm
3 . All these estimated densities are consistent with experimental
densities; 1.16 g/cm
3 for sample 16, 1.147 g/cm
3 for sample 17, and 1.055 g/
cm
3 for sample 18. In these schematic drawings, terminal alkyl chains in Tp arms
occupy the rest of spaces other than the Tp columns and the POSS core. Meanwhile, these alkyl chains of adjacent supermolecules can interdigitate, thus
forming a uniform alkyl chain environment.
Conclusion
In this entry, we have demonstrated the supramolecular self-assembly of doubly
discotic liquid crystalline LEGOs. Without hydrogen bonding, randomly mixed
columnar liquid crystalline phases are obtained for Pc(Tp) 4 supermolecules. With
hydrogen bonding, organized Py(Tp) 2 crystals and Py(Tp) 4 liquid crystals are
obtained. Finally, topology of discotic liquid crystalline supermolecules is also
important in POSS(Tp) 8 . Microphase-separated POSS and columnar structures are
observed as a result of topological confinement. There are other ways to combine
discotic liquid crystalline supermolecules with perylene, POSS, C 60 , and many other
cores. They may find future potentials in organic electronics applications.
Acknowledgment This work was supported by the National Science Foundation CAREER Award
(DMR-0348724), DuPont Young Professor Award, and 3M Nontenured Faculty Award.
244
L. Zhu
we found by FTIR study that hydrogen bonding existed both below and above the
isotropization temperatures, regardless of the disordering of the supramolecular
self-assemblies. Therefore, we consider that molecular shape and topology is
more important for the supramolecular self-assembly of POSS(Tp) 8 . When the
spacer length, e.g., C 2 in sample 16, is much shorter than the C 12 alkyl chains, the
Tp arms are tightly attached to the POSS core, and thus the supermolecules adopt
a disklike overall molecular shape when they stack in parallel together. Finally, a
column-within-column nanostructure is obtained; four Tp columns inside a supercolumn formed by the entire supermolecules (see the top panel of Fig. 21).
Assuming one molecule per unit cell (area = 20.96 nm
2 ) and the thickness per
molecule = 0.72 nm (i.e., 2 Â 0.36 nm), the density of sample 16 is estimated to
be 1.218 g/cm
3 . When the spacer length increases to C 6 in sample 17, Tp arms are
decoupled from the POSS core to a certain extent. The supermolecules therefore
adopt a board-like overall molecular shape, and a lamellar structure with a 2D
rectangular symmetry is obtained. Assuming one molecule per unit cell
(area = 22.18 nm
2 ) and the thickness per molecules = 0.72 nm, the density of
sample 17 is estimated to be 1.198 g/cm
3 . When the spacer length further
increases to C 10 in sample 18, Tp arms become fairly mobile, and thus four Tp
columns aggregate together (i.e., segregated from the POSS core) to form a
supercolumn. Assuming one molecule per unit cell (area = 24.83 nm
2 ) and the
thickness per molecule = 0.72 nm, the density of sample 18 is estimated to be
1.112 g/cm
3 . All these estimated densities are consistent with experimental
densities; 1.16 g/cm
3 for sample 16, 1.147 g/cm
3 for sample 17, and 1.055 g/
cm
3 for sample 18. In these schematic drawings, terminal alkyl chains in Tp arms
occupy the rest of spaces other than the Tp columns and the POSS core. Meanwhile, these alkyl chains of adjacent supermolecules can interdigitate, thus
forming a uniform alkyl chain environment.
Conclusion
In this entry, we have demonstrated the supramolecular self-assembly of doubly
discotic liquid crystalline LEGOs. Without hydrogen bonding, randomly mixed
columnar liquid crystalline phases are obtained for Pc(Tp) 4 supermolecules. With
hydrogen bonding, organized Py(Tp) 2 crystals and Py(Tp) 4 liquid crystals are
obtained. Finally, topology of discotic liquid crystalline supermolecules is also
important in POSS(Tp) 8 . Microphase-separated POSS and columnar structures are
observed as a result of topological confinement. There are other ways to combine
discotic liquid crystalline supermolecules with perylene, POSS, C 60 , and many other
cores. They may find future potentials in organic electronics applications.
Acknowledgment This work was supported by the National Science Foundation CAREER Award
(DMR-0348724), DuPont Young Professor Award, and 3M Nontenured Faculty Award.
244
L. Zhu