lengths, with few systems providing well-aligned columns.
Strategies for controlling both the length of a stack and the
alignment of the constituent discs or rings not only provide
new insights into the organization of the corresponding
assemblies but also enhance the ability to construct new
structures and to manipulate various materials properties
associated with the generated structures.6 A particularly
effective strategy for curbing the growth of a self-assembling
stack is to introduce oligomeric tethers7 that define the
number of stacking units, which, in many cases, may lead
to new foldamers.8 Polymeric tethers9 have also been
adopted to enhance the alignment and stability of colum-
nar structures consisting of stacked discs. Herein we
describe the creation of folded helical structures consisting
of multiply H-bonded aromatic rings that are covalently
grafted to tethers derived from oligoamines.
1a or 1b, serves as a control. These structures are designed
based on these considerations: (1) analogous 1,3,5-benze-
netricarboxamides were reported to self-assemble into
H-bonded columns of undefined lengths in the solid state
and to undergo H-bond-mediated assembly in organic
solvents (e.g., hydrocarbon) of very low polarity;3 (2)
chiral side chains based on the n-octyl ester of alanine
allow the chirality of covalently tethered stacks to be
probed; (3) the synthesis of the oligoamine tethers consist-
ing of the ꢀNH(CH2)3ꢀ units and other analogous tethers
is known,10 which allows the total length, and thus the
number of NH groups, of an oligoamine tether to be
controlled and adjusted. In addition to defining the num-
ber of “discs”, the presence of the covalent tethers serves to
greatly enhance the otherwise weak intermolecular
H-bonds between the discs into much more favorable
intramolecular ones, leading to discrete stacks with sig-
nificantly enhanced stabilities.
Compounds 1a and 1b, consisting of 1,3,5-benzenetria-
mide (“disc”) units attached to oligoamine tethers, were
designed. Compound 2, corresponding to a single disc of
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Figure 1. Side (left) and top (right) views of the structures of (a)
1a0 and (b) 1b0 optimized using the density functional theory
(DFT) within generalized-gradient approximation in the form
of a BLYP functional.11 For clarity, hydrogen atoms other than
those of the amide groups are not shown. Hydrogen bonds are
shown as green dashed lines.
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the structures of1a0 and 1b0, whichcorrespond to1aand 1b
with R1 and R2 being replaced by methyl groups, were
computationally optimized. As shown in Figure 1a, the
two parallel discs of 1a0 associate with each other via three
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