Supramolecular structural diversity among first-generation hybrid dendrimers and twin dendrons

Article abstract of DOI:10.1002/chem.200701658

Hybrid dendrimers, obtained by complete monofunctionalization of the peripheral amines of a zero-generation polyethyleneimine dendrimer, provide structurally diverse lamellar, columnar, and cubic self-organized lattices that are less readily available from other modified dendritic structures. The reaction of tris(2-aminoethyl)amine (TREN) with 4-dodecyloxybenzimidazolide provides only the corresponding zero-generation TREN dendrimer. From the mixture of triand disubstituted TREN derivatives obtained from first-generation self-assembling dendritic imidazolides, the hybrid dendrimer and a twin dendron could be separated, purified, and characterized. The hybrid dendrimers display smectic, columnar hexagonal (φ_h), and cubic (Pm3n) lattices. The TREN twin dendrons, on which only two peripheral amines have been acylated, exhibit centered-rectangular columnar (φ_r-c), φ_h, and Pm3n lattices. The existence of a thermoreversible φ_h-to-Pm3n phase transition in the first-generation hybrid dendrimers and twin dendrons is exploited to elucidate an epitaxial relationship between the two mesophases. We postulate a mechanism by which the transition proceeds. The thermoreversible φ_h-to- Pm3n phase change is accompanied by optical property changes that are suitable for rudimentary signaling or logic functions. This structural diversity reflects the quasiequivalence of flat-taper and conical self-assembling dendrons and the ability of flexible dendrimers to accommodate concomitant conformational and shape changes.

Full text of DOI:10.1002/chem.200701658

FULL PAPER
DOI: 10.1002/chem.200701658
Supramolecular Structural Diversity among First-Generation Hybrid
Dendrimers and Twin Dendrons
Virgil Percec,*[a] Jonathan G. Rudick,[a] Mihai Peterca,[a, b] Michael E. Yurchenko,[a]
Jan Smidrkal,[a] and Paul A. Heiney[b]
Abstract: Hybrid dendrimers, obtained
by complete monofunctionalization of
the peripheral amines of a “zero-gener-
ation” polyethyleneimine dendrimer,
provide structurally diverse lamellar,
columnar, and cubic self-organized lat-
tices that are less readily available
from other modified dendritic struc-
tures.The reaction of tris(2-amino-
ethyl)amine (TREN) with 4-dodecylox-
ybenzimidazolide provides only the
corresponding zero-generation TREN
dendrimer.From the mixture of tri-
and disubstituted TREN derivatives
obtained from first-generation self-as-
sembling dendritic imidazolides, the
hybrid dendrimer and a twin dendron
could be separated, purified, and char-
acterized.The hybrid dendrimers dis-
play smectic, columnar hexagonal (Fh),
eration hybrid dendrimers and twin
dendrons is exploited to elucidate an
epitaxial relationship between the two
mesophases.We postulate a mechanism
by which the transition proceeds.The
¯
and cubic (Pm3n) lattices.The TREN
¯
twin dendrons, on which only two pe-
ripheral amines have been acylated, ex-
hibit centered-rectangular columnar
thermoreversible Fh-to-Pm3n phase
change is accompanied by optical prop-
erty changes that are suitable for rudi-
mentary signaling or logic functions.
This structural diversity reflects the
quasiequivalence of flat-taper and coni-
cal self-assembling dendrons and the
ability of flexible dendrimers to accom-
modate concomitant conformational
and shape changes.
¯
(Fr-c), Fh, and Pm3n lattices.The exis-
tence of thermoreversible Fh-to-
Pm3n phase transition in the first-gen-
a
¯
Keywords:
liquid crystals
dendrimers
self-assembly
·
·
·
supramolecular chemistry
Introduction
and novel functions that arise through hierarchical self-as-
sembly and self-organization are the basis for the elabora-
tion of new concepts relevant for macromolecular and su-
pramolecaular chemistry, as well as the nanosciences.Fur-
thermore, structural and retrostructural analysis of the self-
organized arrays facilitates elucidation of the design princi-
ples that underlie the hierarchical self-assembly process.[3c]
Several architectural classes can be identified among den-
drons and dendrimers that form liquid-crystalline mesophas-
es.[4] We have pioneered the use of mesogenic repeat units
to prepare dendrons and dendrimers[5] and the use of amphi-
philic self-assembling dendrons to generate supramolecular
dendrimers[6] and self-organizable dendronized polymers.[7]
An alternative approach is to append mesogens to the pe-
riphery of nonmesogenic dendrimers.[8] We have further ex-
tended this approach to the functionalization of FrØchet-
Self-assembling dendrons and dendrimers available through
divergent[1] and convergent[2] synthetic strategies are power-
ful monodisperse architectures with which to investigate
how primary structure manifests in the formation of three-
dimensional (3D) superstructures.[3] Dendrons and dendrim-
ers that form liquid crystalline phases,[3c,4] in particular, have
shown tremendous potential for the control of molecular
and supramolecular properties.The emergent mesophases
[a] Prof.Dr.V.Percec, Dr.J.G.Rudick, Dr.M.Peterca,
Dr.M.E.Yurchenko, J.Smidrkal
Roy & Diana Vagelos Laboratories
Department of Chemistry
University of Pennsylvania
Philadelphia, PA 19104–6323 (USA)
Fax : (+1)215-573-7888
[9]
type,[2a] AB4,[9] and AB5 dendrons with amphiphilic self-as-
sembling dendrons.[9,10] Nonmesogenic dendrons and den-
drimers appended with peripheral mesogens display limited
structural diversity,[4,8,10] especially when contrasted with the
rich structural complexity available from the supramolecular
dendrimers[6] and self-organizable dendronized polymers[7]
E-mail: percec@sas.upenn.edu
[b] Dr.M.Peterca, Prof.Dr.P.A.Heiney
Department of Physics and Astronomy
University of Pennsylvania
Philadelphia, PA 19104–6396 (USA)
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3355

derived from amphiphilic self-assembling dendrons.Lamel-
lar, various two-dimensional (2D) columnar, and 3D cubic,
tetragonal, and 12-fold liquid-quasicrystal arrays have been
identified.[6,7]
Hybrid dendrons and dendrimers combine two constitu-
tively different building blocks.This expands our previous
definition of “hybrid” dendrons as those composed of non-
dendritic ((AB)y) and dendritic (ABn) building blocks.[11] As
such, this term now includes dendrons composed of combi-
nations of (AB2) with (AB3) building blocks[6a–d,10] and of
(AB2) or (AB3) with (AB4) or (AB5) building blocks.[9] Ex-
amples of branched compounds that are not amenable to
elaboration with dendrimers have been appended with self-
assembling dendrons and exhibit liquid-crystalline phases.[12]
These too constitute hybrid dendrimers.Self-assembling
hybrid dendrons and dendrimers are distinct from dendritic
molecules functionalized at their periphery with traditional
mesogens.[4]
tural congeners to liquid-crystalline cyclic oligomers[17] and
linear polymers.[15] The dendrimers were prepared by the re-
action of the PEI dendrimer with the dendritic benzoyl
chloride.[8b,c] While the first-generation dendrimer does not
display any mesophases,[8b] the second-generation dendrimer
was found to form a Fh phase.[8c] Both first- and second-gen-
eration dendrimers exhibit mesophases upon complexation
Herein, we present a strategy by which to increase the
supramolecular structural diversity available with dendrim-
ers by using hybrid dendrimers.Hybrid dendrimers are com-
posed of two or more constituent elements, each of which is
capable of elaborating a perfectly branched molecular struc-
ture independent of the other.The present hybrid dendrim-
ers are obtained by acylation of the prototypical “zero-gen-
eration” polyethyleneimine (PEI) dendrimer, tris(2-amino-
ethyl)amine (TREN), with 4-dodecyloxybenzimidazolide,[13]
or first-generation self-assembling dendritic imidazolides.[13]
Either trisubstituted dendrimers or disubstituted twin den-
drons[14] are obtained.The hybrid dendrimers display smec-
of transition-metal salts.[8c]
A lamellar phase is most
common among the transition-metal complexes of 1.
We have employed larger first-generation self-assembling
dendrons, which are acid sensitive, to explore supramolec-
ular structural diversity within low-generation hybrid den-
drimers.Consequently, we sought a synthetic strategy that
would avoid the benzoyl chloride intermediate.Imidazolides
2a–c (Scheme 1) have recently been prepared through reac-
tion of 1,1-carbodiimidazole (CDI)[18] with the correspond-
ing dendritic carboxylic acid.[13] The imidazolides can be iso-
lated and stored in the absence of moisture.Reaction of the
imidazolide with TREN provided a mixture of di- and tria-
cylated products (Scheme 1).The structures and purities of
dendrimers 3a–3c and the twin-dendritic compounds 4b
and 4c were confirmed by a combination of 1H and
13C NMR spectroscopy, HPLC, and MALDI-TOF mass
spectrometry.
¯
tic, columnar hexagonal (Fh), and cubic (Pm3n) lattices.
Similarly, the twin dendrons exhibit centered-rectangular
¯
(Fr-c), Fh, and Pm3n lattices.Furthermore, we observe ther-
moreversible phase changes accompanied by changes in op-
tical properties that are suitable for rudimentary signaling
¯
or logic functions.A Fh-to-Pm3n phase transition reported
herein reveals an epitaxial relationship between the Fh and
Pm3n lattices.Based on this relationship, we have postulat-
Differential scanning calorimetry (DSC) and thermal opti-
cal polarized microscopy (TOPM) were used to identify
¯
ed a mechanism by which the
transition between the two
mesophases can occur.This
mechanism may be relevant to
other supramolecular dendri-
mers,[10b] dendronized poly-
mers,[15d–g] and metallomeso-
gens[16] exhibiting a similar col-
umnar-to-cubic phase transi-
tion.
Results and Discussion
Zero- and first-generation PEI
dendrimers have previously
been functionalized with 3,4-
bis
ACHTREUNG(decyloxy)benzoate groups
(for example, 1)[8b,c] as architec-
Scheme 1.Synthesis of hybrid dendrimers and twin dendrons.a) THF.
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Hybrid Dendrimers and Twin Dendrons
FULL PAPER
phase transitions and establish preliminary phase assign-
ments.The phase assignments were confirmed by X-ray dif-
fraction (XRD) (Figure 1).Table 1 presents phase-transition
temperatures and corresponding enthalpy changes for each
of the hybrid dendrimers and twin dendrons.The zero-gen-
eration hybrid dendrimer 3a exhibits a narrow smectic
phase, which is consistent with the previous observation for
transition-metal salts of 1.[8] The first-generation hybrid den-
drimers and twin dendrons exhibit columnar or cubic meso-
phases, or both.
Table 2 provides the structural and retrostructural analysis
of the self-organized lattices generated by the hybrid den-
drimers and twin dendrons.Both first-generation hybrid
dendrimers self-assemble into supramolecular spheres that
¯
self-organize into a Pm3n lattice.We have previously show-
n[6a,e,f] that this lattice is composed of micellar spherical
supramolecular dendrimers resulting from the self-assembly
and self-organization of the hybrid dendrimers and twin
dendrons.Furthermore, we can contrast this mesophase with
the gyroid mesophase formed by other self-assembling den-
drons.[19] The appearance of the Pm3n lattice is remarkable
¯
given that the constituent dendrons typically form Fh
phases.[10] Nonetheless, retrostructural analysis of 3b and 3c
¯
in the Pm3n lattice confirms relationships observed for the
constituent dendrons in the Fh lattice.The former dendron
generates larger supramolecular objects and each supra-
molecular object is comprised of more molecules.These are
seen by comparing the sphere diameters (D) and number of
dendrimers per supramolecular sphere (m; Table 2).We
have previously explained this based on the projected mo-
lecular solid angle (a’), whereby the (4-3,4)12G1-X self-as-
sembling dendrons occupy a smaller projected solid angle
than the (4-3,4,5)12G1-X self-assembling dendrons (see
Scheme 1 for structures).The relationship between the den-
dron primary structure and features of the tertiary structure
are also found for the twin dendrons in the Fh phase
(Table 2).
Quasiequivalence[7a,c] of flat-taper and conical self-assem-
bling dendrons results from their conformational flexibility
and allows them to behave interchangeably.Self-organizable
dendronized polymers take advantage of this by adopting
different shapes depending on their degree of polymerizatio-
n.[7a,c] We infrequently observe quasiequivalence[7a,c] that re-
sults in reversible shape changes.The first-generation liquid-
crystalline PEI dendrimers and twin-dendritic compounds
provide two new examples in this small library.We can sur-
mise that the flexible PEI core assists in accommodating the
conformational changes that accompany the change in
shape.
Figure 1.Small-angle XRD powder plots for a) 3b and 4b and b) 3c and
4c.The structure, temperature, diffraction-peak indexing, and lattice pa-
rameters are indicated.
Models based on the experi-
Table 1.Thermal transitions [ 8C] and corresponding enthalpy changes [kcalmolÀ1] for the hybrid dendrimers
mental structural and retro-
structural analysis of 3c and
4c are shown in Figure 2.The
models reflect conformations
consistent with those expected
in the Fh lattice.Close inspec-
tion of the models reveals that
we have intentionally included
fewer molecules per column
stratum than the number re-
ported for m in Table 2.The
and twin dendrons.[a]
Compound
First and second heating scans
First cooling scans
3a
k[b] 104 (0.8) S[c] 106 (1.0) i[d]
i 51 (0.6) S 45 (1.5) k
k 101 (0.6) S 104 (6.8) i
3b
3c
4b
4c
k 82 (4.8) x[e] 103 (3.2) x 131 (À3.7) x 152 (9.4) Cub[f] 212 (0.6) i
Cub 211 (0.5) i
i 208 (0.4) Cub
Cub 58 (0.9) Fh
[h]
Fh,g[g] 55 Fh 78 (0.7) Cub
Fh 78 (0.8) Cub
[i]
k 86 (1.0) x 102 (3.3) x 123 (2.0) x 156 (0.7) Fh
Fr-c 67 (À3.9) k 103 (2.5) Fr-c 156 (0.7) Fh
Fh 56 (17.9) Cub 160 dec[j]
Fh 153 (0.7) Fr-c
[a] Thermal transitions [8C] and enthalpy changes [kcalmolÀ1] in parentheses were determined by DSC (rate:
108CminÀ1).Data from first heating and cooling scans are on the first line, and data from the second heating
scans are on the second line.[b] k: crystalline phase.[c] S: smectic phase.[d] i: isotropic liquid phase.[e] x: un-
calculation of
m in Table 2
refers to a 4.7 Š-thick column
stratum, which is based on the
peripheral alkyl chain packing.
¯
identified phase.[f] Cub: Pm3n cubic lattice.[g] Fh,g: glassy p6mm hexagonal columnar lattice.[h] Fh: p6mm
hexagonal columnar lattice.[i] Fr-c : c2mm centered-rectangular columnar lattice.[j] dec: sample decomposes.
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3357

V.Percec et al.
Table 2.Structural and retrostructural analysis of the hybrid dendrimers and twin dendrons.
tum.Recalculation of m bears
out the number of dendrons
shown in Figure 2.
[a]
[b]
Compound
T
[8C]
Phase a[a,b,c] or
d10, d20 or d110, d200, d210, d211, d220, d310, d321, d400 or d10, D [Š]
m
[c]
[d]
a, b[d]
d11, d20 or d20, d11, d02, d22, d13, d40, d31, d42, d24 [Š]
[Š]
Closer packing at the core of
3a
3b
3c
50
S
36.5[a]
36.5, 18.3[a]
–
–
the
hybrid-dendrimer
and
180 Pm3n 102.5[b]
72.6, 51.4, 45.0, 41.9, 36.3, 32.4, 27.4, 25.6[b]
38.5, 22.2, 19.2[c]
63.6[e] 36.8[f]
44.4[g] 1.6[h]
54.1[e] 16.2[f]
53.6[g] 4.6[h]
92.8,[i] 14.4[k]
104.5[j]
¯
twin-dendron supramolecular
columns facilitates hydrogen
bonds along the length of the
column.A network of possible
intermolecular hydrogen bonds
is identified at the core of the
supramolecular column com-
prised of the first-generation
hybrid dendrimer 3c (Fig-
ure 2d).On the other hand,
both intramolecular and inter-
molecular hydrogen bonds are
possible between the twin den-
drons.Such a network can be
accommodated at the core of
the resulting supramolecular
column (Figure 2 h).
55 Fh
44.4[c]
95 Pm3n 87.2[b]
61.5, 43.6, 39.1, 35.5, 30.8, 27.5, 23.3, 21.7[b]
46.4, 26.8, 23.2[c]
¯
4b
4c
160 Fh
50 Fr-c
53.6[c]
145.8,
104.5[d]
50.3[c]
–, –, 52.4, 42.6, –, –, 44.3, 29.9, 24.6[d]
40 Fh
43.6, 25.2, 21.8[c]
50.3[g] 3.0[h]
58.7[e] 30.4[f]
70 Pm3n 94.6[b]
67.1, 47.3, 42.5, 38.6, 33.5, 29.9, 25.3, 23.7[b]
¯
[a] Layer spacing (a=0.5
[d10+2d20]) and
d
spacings of the smectic phase.[b] Lattice parameter
(
a=
0.5
[20.5d110+2d200+50.5d210+60.5d211+80.5d220+100.5d310+140.5d321+16
d
]/8) and d spacings for the Pm3n cubic latti-
¯
400
ces.[c] Lattice parameter ( a=2/3[d10+30.5d11+2d20]3À0.5) and d spacings in the ratio d10:d11:d20 =1:30.5:2 for the
p6mm lattice of the Fh phase.[d] Lattice parameters ( a and b) and d spacings for the c2mm lattice of the Fr-c
phase.In general, a=d10 and b=d01.The ratio of the d spacings can be calculated from the general equation
hk =((haÀ1)2+
A
(
D=8
A
)
in the Pm3n lattices.
¯
d
[f] Number of dendrimers or twin-dendritic molecules per sphere (m=a3NA1/8M, where NA is Avogadroꢁs
number (6.0220455”1023), 1 is the density of the polymer (assumed to be 1 gcmÀ3), and M is the molecular
weight of the compound).[g] Experimental column diameter ( D=a) in the p6mm lattices.[h] Number of den-
drimers or twin-dendritic molecules per 4.7-Š-thick column stratum (m=3À0.5aNAt1/2M, where t is the column-
stratum thickness.[i] Experimental column diameter along the a direction of the c2mm lattice (D=2a/p).
[j] Experimental column diameter along the b direction of the c2mm lattice (D=b).[k] Number of dendrimers
or twin-dendritic molecules per elliptical 4.7-Š-thick column stratum in the c2mm lattice of the Fr-c phase (m=
abNAt1/2M).
The existence of both Fh
¯
and Pm3n mesophases in the
Packing of the interior benzyl ether segments is typically
much closer, so the models reflect a 3.5 Š-thick column stra-
phase sequence of a singe liquid crystalline dendron or den-
drimer remains a rare phenomenon.[10b,15d–g,16,20] Such behav-
Figure 2.Molecular models of a)–d) 3c and e)–h) 4c shown in the all-trans flat dendrimer conformation
ACHTRE(UNG a and e), from the top and side stick views of
the column strata (b and f), with the hydrogen-bonding network highlighted (c and g), and as a stick side view of the column core region (d and h).
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Hybrid Dendrimers and Twin Dendrons
FULL PAPER
¯
ior can be valuable in elucidating the pathway by which the
two phases are related.[21] Epitaxial relationships between
2D hexagonal and 3D cubic mesophases in lyotropic liquid
crystals[21a,b] and block copolymers[21c,d] suggest that cylindri-
cal objects in the 2D hexagonal lattice form undulating col-
umns, which subsequently form spherical objects through
break points along the cylinder axis.Monodomains of the
Fh lattice generated by 3c have been prepared by extrusion
of oriented fibers.These samples are amenable to XRD.
XRD patterns from oriented fiber samples of 3c at vari-
ous temperatures are presented in Figure 3a.The phase se-
quence described in Table 1 can be observed in the XRD
patterns.Both the glass ( Fh,g) and the Fh mesophase show
evidence of being well oriented with the q10, q11, and q20 re-
flections perpendicular to the fiber axis.Heating of the
phase is not recovered upon cooling from the Pm3n meso-
phase.[21c] Upon cooling oriented fiber samples from the
¯
Pm3n mesophase to the Fh mesophase, we observed no ori-
entational order in the sample (Figure 3a).As the phase
transition is reversible, the pathway by which spheres
become cylinders should be the reverse of that by which cyl-
inders become spheres (Figure 3b).Nonetheless, the 3D
cubic lattice does not retain memory of the orientational
order of the 2D columnar lattice.Consequently, domains of
cylinders formed during cooling do not have a preferred ori-
entation.
The models in Figure 2 allude to a possible molecular
mechanism for pinch-point formation in the undulating col-
umns in the proposed phase transformation.Necessarily, the
columns shrink between two column strata.Transformation
from the flat-taper conformation to the conical conforma-
tion can be rationalized as small reorientations of the
TREN moiety.During this process, the self-assembling den-
dron fragments are forced into closer proximity.The net
effect is similar to that observed for self-assembling den-
drons comprised of 3,4- or 3,4,5-branching units; conical-
shaped supramolecular building blocks emerge.[6a,e,f,10b] The
conical dendrons involve more extended molecular confor-
mations (that is, with smaller a’ values) than the flat-taper
dendrons.[22] Thus, at the peak of the undulation, which cor-
responds to the diameter of the newly forming spheres, the
undulating column gets larger than the original column.
Moving away from this location toward the pinch point, the
conical molecules tilt away from their orientation in the
column and this results in a constriction of the undulating
column diameter below that of the original column.Eventu-
ally, the spheres separate into individual micellar aggregates.
¯
sample to generate the Pm3n mesophase transforms the dif-
fraction pattern and indicates coincidence of the Fh q10 re-
¯
flection and the Pm3n q211 reflection.This is indicative of a
possible epitaxial relationship.[21a] Figure 3b presents a sche-
matic representation of the epitaxial relationship between
the columns of the Fh lattice and the (111) direction of the
¯
Pm3n lattice.The six-fold axis of symmetry of the Fh lattice
¯
becomes the three-fold symmetry of the Pm3n lattice.In
keeping with previous explanations for such a relationship,
we illustrate the transformation of the supramolecular cylin-
ders into supramolecular spheres as proceeding through un-
dulating columns.Recently a similar mechanism for colum-
nar-to-cubic phase transitions was proposed for metallomes-
ogens[16] and “Janus-like” diblock codendrimers,[20] although
oriented fiber diffraction experiments were not reported.
Given the fast dynamics of the phase transition, it is not
surprising that the preferred orientation of the Fh meso-
Figure 3.Epitaxial transition from the hexagonal to cubic phase observed for the 3c.a) Small-angle XRD fiber patterns collected in the thermal cycle in-
dicated by arrows; the lattice, temperatures, fiber orientation, and diffraction-peak indexing are marked.b) Schematic representation of the epi taxial re-
lationship between the column axis in the hexagonal phase and the (111) direction of the cubic phase; the six-fold axis of symmetry of the columns be-
comes the three-fold axis of symmetry of the cubic phase.It is most likely that the weaker interactions present between the supramolecular spheres an d
the rearrangement of the face spheres (light gray) upon the transition from the oriented cubic to the hexagonal phase prohibit any epitaxial relationship.
A set of corner/center spheres from the shown cubic lattice in (b) are colored in dark gray to show the connectivity.
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V.Percec et al.
vacuum was maintained along the length of the flight tube and within the
sample chamber. Samples were held in quartz capillaries (0.7–1.0 mm in
diameter), mounted in a temperature-controlled oven (temperature pre-
cision: Æ0.18C; temperature range from À120 to 2708C).The distance
between the sample and the detector was 12.0 cm for wide-angle diffrac-
tion experiments and 54.0 cm for intermediate-angle diffraction experi-
ments.Aligned samples for fiber XRD experiments were prepared by
using a custom-made extrusion device.Thus, powdered sample ( ꢀ10 mg)
was heated inside the extrusion device above the melt temperature.The
fiber was extruded in the mesophase and cooled to 238C.Typically, the
aligned samples had a thickness of ꢀ0.3–0.7 mm and a length of ꢀ3–
7 mm.All XRD measurements were done with the aligned-sample axis
perpendicular to the beam direction.XRD peak position and intensity
analysis was performed by using the Datasqueeze software (Ver-
sion 2.01), which allows background elimination and Gaussian, Lorent-
zian, Lorentzian squared, or Voigt peak-shape fitting.
Conclusion
First-generation hybrid dendrimers and their twin-dendron
congeners comprised of self-assembling dendrons facilitate
structural diversity at low generations.The dendrimers and
twin dendrons have been prepared by coupling dendritic
imidazolides and TREN.Structural and retrostructural anal-
ysis demonstrated that smectic, 2D Fr-c, and Fh, as well as
3D cubic, lattices are formed.Just as for supramolecular
dendrimers prepared from self-assembling dendrons, the pri-
mary structure of the constituent dendron manifests in the
tertiary structure of the supramolecular object and the self-
organized lattice.Quasiequivalence
[7a,c]
of the self-assem-
bling dendrons is further exploited by the flexibility of the
dendrimer core, as we observe two new examples of ther-
moreversible shape change accompanied by optical property
changes.Such behavior is demonstrative of rudimentary sig-
naling or binary logic functions.Furthermore, the phase se-
quences reported herein have revealed an epitaxial relation-
Typical procedure for coupling of imidazolides with TREN: Tris{2-[(4-
dodecan-1-yloxy)benzamido]ethyl}amine (3a): Imidazolide 2a (0.712 g,
2.0 mmol) was dissolved in anhydrous THF. TREN (0.097 mL,
0.60 mmol) was added to the mixture through a syringe. The reaction
mixture was stirred for 2 h at 228C under an argon atmosphere.After
completion of the reaction, the mixture was poured into water and the
white precipitate was filtered off.Several recrystallizations from ethyl
acetate afforded pure 3a (0.539 g, 80%) as a white colorless powder:
1H NMR (CDCl3, TMS): d=0.87 (t, 9H), 1.26 (m, 48H), 1.42 (m, 6H),
1.75 (m, 6H), 2.69 (t, 6H), 3.52 (t, 6H), 3.81 (t, 6H), 6.51 (d, 6H), 7.13
(t, 3H), 7.58 ppm (d, 6H); 13C NMR (CDCl3, TMS): d=14.51, 23.10,
26.52, 29.72, 29.78, 29.95, 30.08, 30.13, 32.34, 38.10, 53.92, 68.45, 114.20,
126.28, 129.34, 161.89, 168.14 ppm; MALDI-TOF MS: m/z: 1049.29
[M+K+], 1033.30 [M+Na+], 1011.87 [M+].
¯
ship between the Fh and Pm3n lattices.We have postulated
a mechanism by which a transition between the two meso-
phases can occur.Appending nonmesogenic dedrimers with
self-assembling dendrons provides supramolecular structural
diversity previously unavailable from low-generation den-
drimers[4,8] functionalized at their periphery with mesogens
and heralds further opportunities when this approach is ex-
tended to higher generation self-assembling dendrons and
other nonmesogenic dendrimer cores.
Tris(2-CAHTRE{UGN 3,4-bis[(4’-dodecan-1-yloxy)benzyloxy]benzamido}ethyl)amine
(3b): A procedure analogous to that described above was employed.
After several recrystallizations from acetone, 3b (94% yield) was ob-
tained as a colorless solid: 1H NMR (CDCl3, TMS): d=0.88 (t, 18H),
1.26 (m, 96H), 1.43 (m, 12H), 1.74 (m, 12H), 2.72 (m, 6H), 3.56 (m,
6H), 3.87–3.81 (overlapped m, 12H), 4.69 (s, 6H), 4.87 (s, 6H), 6.28 (d,
3H), 6.65 (dd, 12H), 7.02 (d, 12H), 7.16 (d, 6H), 7.53 ppm (d, 3H);
13C NMR (CDCl3, TMS): d=14.51, 23.10, 26.52, 26.58, 29.78, 29.87, 29.99,
30.05, 30.09, 30.11, 30.14, 32.35, 38.15, 53.86, 68.38, 70.90, 71.67, 113.08,
114.54, 114.68, 115.21, 120.95, 126.89, 128.72, 129.20, 129.70, 148.84,
152.40, 159.25, 168.13 ppm; MALDI-TOF MS: m/z: 2237.33 [M+K+],
2221.18 [M+Na+], 2199.87 [M+].
Experimental Section
Materials: 1,1’-Carbonyldiimidazole (CDI; Acros, 97%) was used as re-
ceived.Its purity was assessed by melting-point measurement and
1H NMR spectroscopy.Tris(2-aminoethyl)amine (TREN; Acros, 96%)
was used as received.THF was refluxed over sodium ketyl until the solu-
tion turned purple and was then distilled before use.CH 2Cl2 was freshly
distilled from CaH2.Synthesis of imidazolides 2a–c has been reported
previously.[13]
Tris(2-{3,4,5-tris[(4’-dodecan-1-yloxy)benzyloxy]benzamido}ethyl)amine
(3c): A procedure analogous to that described above was employed.The
product was purified by column chromatography on silica, with first a
CH2Cl2/ethyl acetate mixture and then a chloroform/methanol mixture as
the eluting solvent, with subsequent evaporation of the solvent.Pure
product was isolated as waxy colorless solid in 79% yield: 1H NMR
(CDCl3, TMS): d=0.88 (t, 27H), 1.26 (m, 144H), 1.41 (m, 18H), 1.74 (m,
18H), 2.72 (m, 6H), 3.52 (m, 6H), 3.87–3.81 (overlapped m, 18H), 4.76
(s, 12H), 4.78 (s, 6H), 6.65 (d, 6H), 6.73 (d, 12H), 7.17–7.09 (overlapped
m, 24H), 7.25 ppm (m, 3H); 13C NMR (CDCl3, TMS): d=14.51, 23.10,
26.58, 26.53, 29.79, 29.95, 30.09, 30.13, 32.34, 39.75, 56.82, 68.37, 71.37,
75.09, 107.23, 114.40, 114.67, 129.05, 129.53, 129.73, 130.17, 130.41, 141.80,
153.22, 159.21, 168.18 ppm; MALDI-TOF MS: m/z: 3107.97 [M+K+],
3092.04 [M+Na+], 3071.48 [M+].
Techniques: All H (500 MHz) and 13C NMR (125 MHz) spectra were re-
1
corded on a Bruker DRX-500 instrument at 208C with CDCl3 as the sol-
vent (tetramethylsilane (TMS) as an internal standard).DSC was per-
formed on a Differential Scanning Calorimeter 2920 instrument (TA In-
struments) at a rate of 58CminÀ1.A polarized optical microscope (Olym-
pus BX-60) equipped with a Mettler FP 82 hot stage was used to investi-
gate the bulk properties of the compounds synthesized.All MALDI-
TOF spectra were recorded on a Voyager-DE apparatus (Perceptive Bio-
systems) with dihydroxybenzoic acid (Aldrich, 97%; recrystallized from
water before use) as a matrix.The purity of the products was determined
by
a combination of techniques, including TLC on silica-gel plates
2-[N,N-Bis(2-ACHTER{UNG 3,4-bis[(4’-dodecan-1-yloxy)benzyl]benzamido}ethyl)ami-
(Kodak) with fluorescent indicator, HPLC with a Perkin–Elmer Series 10
high-pressure liquid chromatograph equipped with an LC-100 column
oven, Nelson Analytical 900 Series integrator data station, and two
Perkin–Elmer PL gel columns.Melting points were measured by using a
Unimelt capillary melting point apparatus (Arthur H.Thomas Company,
no]ethylamine (4b): This compound was isolated by column chromatog-
raphy as a byproduct from the incomplete acylation of TREN by 2b.
When the chromatographic separation and purification method described
above was applied to the mixture of products, 4b was isolated as a yel-
lowish solid: 1H NMR (CDCl3, TMS): d=0.87 (t, 12H), 1.26 (m, 64H),
1.41 (m, 8H), 1.76 (m, 10H), 2.57 (t, 2H), 2.72 (t, 4H), 2.74 (t, 2H), 3.50
(q, 4H), 3.90 (t, 8H), 4.90 (s, 4H), 4.96 (s, 4H), 6.37 (d, 2H), 6.82 (over-
lapped m, 8H), 7.24 (dd, 10H), 7.32 (t, 2H), 7.51 ppm (d, 2H); 13C NMR
(CDCl3, TMS): d=14.52, 23.10, 26.50, 29.77, 29.88, 30.06, 30.10, 32.34,
38.52, 40.02, 68.43, 71.16, 71.47, 113.84, 114.73, 114.79, 120.63, 127.71,
128.89, 129.22, 129.44, 129.59, 149.07, 152.14, 159.33, 167.72 ppm;
Philadelphia, USA).XRD measurements were performed by using Cu
Ka1
radiation (l=1.54178 Š) from a Bruker-Nonius FR-591 rotating anode
X-ray source equipped with a 0.2”0.2 mm2 filament operated at 3.4 kW.
The Cu radiation beam was collimated and focused by a single bent
mirror and sagittally focused through an SiACHTREU(NG 111) monochromator, thereby
generating a 0.3”0.4 mm2 spot on a Bruker-AXS Hi-Star multiwire area
detector.To minimize attenuation and background scattering, an integral
3360
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Chem. Eur. J. 2008, 14, 3355 – 3362

Hybrid Dendrimers and Twin Dendrons
FULL PAPER
MALDI-TOF MS: m/z: 1054.79 [M+K+], 1539.30 [M+Na+], 1516.87
[M+].
Schlueter, J.C.Ronda, G.Johansson, G.Ungar, J.P.Zhou,
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2-[N,N-Bis(2-{3,4,5-tris[(4’-dodecan-1-yloxy)benzyloxy]benzamido}ethyl)-
amino]ethylamine (4c): This compound was isolated by column chroma-
tography as a byproduct from the incomplete acylation of TREN by 2c.
When the chromatography separation and purification method described
above was applied to the mixture of products, 4c was isolated as a yel-
lowish solid: 1H NMR (CDCl3, TMS): d=0.87 (t, 18H), 1.26 (m, 96H),
1.43 (m, 16H), 1.76 (m, 18H), 2.59 (m, 2H), 2.71 (m, 6H), 3.52 (m, 4H),
3.89 (m, 12H), 4.84 (s, 4H), 4.85 (s, 8H), 6.66 (d, 4H), 6.80 (d, 8H),
7.25–7.13 ppm (m, 18H); 13C NMR (CDCl3, TMS): d=14.50, 23.09, 26.52,
29.77, 29.90, 30.06, 30.10, 32.33, 39.09, 40.13, 54.39, 56.37, 68.38, 68.47,
71.41, 107.39, 114.43, 114.76, 114.79, 129.24, 129.62, 129.94, 130.18, 130.46,
141.69, 153.13, 159.33, 168.08 ppm; MALDI-TOF MS: m/z: 2135.10
[M+K+], 2118.53 [M+Na+], 2096.33 [M+].
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