Self-repairing complex helical columns generated via kinetically controlled self-assembly of dendronized perylene bisimides

Article abstract of DOI:10.1021/ja208501d

The dendronized perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI), (3,4,5)12G1-3-PBI, was recently reported to self-assemble in complex helical columns containing tetramers of PBI as basic repeat unit. These tetramers contain a pair of two molecules a

Full text of DOI:10.1021/ja208501d

ARTICLE
pubs.acs.org/JACS
Self-Repairing Complex Helical Columns Generated via Kinetically
Controlled Self-Assembly of Dendronized Perylene Bisimides
Virgil Percec,*,† Steven D. Hudson,^ Mihai Peterca,†,‡ Pawaret Leowanawat,† Emad Aqad,† Robert Graf,§
Hans W. Spiess,§ Xiangbing Zeng,|| Goran Ungar,||,# and Paul A. Heiney‡
†Roy & Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323,
United States
‡Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396, United States
§Max-Planck Institute for Polymer Research, 55128 Mainz, Germany
||Department of Materials Engineering and Science, University of Sheffield, Sheffield S1 3JD, United Kingdom
^National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8544, United States
#WCU C2E2, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea
S Supporting Information
b
ABSTRACT: The dendronized perylene 3,4:9,10-tetracar-
boxylic acid bisimide (PBI), (3,4,5)12G1-3-PBI, was recently
reported to self-assemble in complex helical columns containing
tetramers of PBI as basic repeat unit. These tetramers contain a
pair of two molecules arranged side-by-side and another pair in
the next stratum of the column turned upside-down and rotated
around the column axis. Intra- and intertetramer rotation angles
and stacking distances are different. At high temperature,
(3,4,5)12G1-3-PBI self-assembles via a thermodynamically
controlled process in a 2D hexagonal columnar phase while at
low temperature in a 3D orthorhombic columnar array via a kinetically controlled process. Here, we report the synthesis and
structural analysis, by a combination of differential scanning calorimetry, X-ray and electron diffraction, and solid-state NMR
performed at different temperatures, on the supramolecular structures generated by a library of (3,4,5)nG1-3-PBI with n = 14À4.
For n = 11À8, the kinetically controlled self-assembly from low temperature changes in a thermodynamically controlled process,
while the orthorhombic columnar array for n = 9 and 8 transforms from the thermodynamic product into the kinetic product. The
new thermodynamic product at low temperature for n = 9, 8 is a self-repaired helical column with an intra- and intertetramer distance
of 3.5 Å forming a 3D monoclinic periodic array via a kinetically controlled self-assembly process. The complex dynamic process
leading to this reorganization was elucidated by solid-state NMR and X-ray diffraction. This discovery is important for the field of
self-assembly and for the molecular design of supramolecular electronics and solar cell.
’ INTRODUCTION
A previous publication from our laboratory10 reported the
discovery of two novel classes of complex helical columns
assembled from PBIs dendronized with first generation self-
assembling dendrons containing 0À4 methylenic units (m)
between the imide group of the dendron, and 12 methylenic
units in their alkyl groups, n = 12, (3,4,5)nG1-m-PBI. The first
example of complex helical column is assembled from tetramers
containing a pair of two dendronized PBIs arranged side-by-side
and another pair in the next stratum of the column, turned
upside-down and rotated around the column axis at different
angles for different m. This angle is different from the angle
between the two pairs forming the tetramer. In this column, the
distance between the pairs within a tetramer is different from the
distance between tetramers. The second example of complex
Self-assembling building blocks constructed from perylene
3,4:9,10-tetracarboxylic acid bisimides (PBIs) have emerged in a
diversity of supramolecular,1 macromolecular,2 and other com-
plex systems3 that have impacted numerous fields such as
industrial dyes and pigments,4 xerographic receptors,5 organic
semiconductors, transistors, light emitting diodes and solar
cells,1,2 artificial photosynthesis,3aÀc life science, and biology.6
PBIs dendronized at the bay7 and respectively at the imide8
groups, or at both, provide self-assembling building blocks that
are of interest for all of these areas. The functions9 of all of these
molecular and supramolecular assemblies are determined by
their two- and three-dimensional (2D and 3D) architectures.
Therefore, elucidating the 2D and 3D structure of these func-
tional assemblies and their mechanism7,8 of formation is crucial
for progress in this field.
Received: September 8, 2011
Published: October 03, 2011
r
2011 American Chemical Society
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helical column is assembled from dimers consisting of pairs of
dendronized PBI arranged on top of each other at a certain angle.
The dimers rotate between themselves with a different angle than
the angle between the molecules forming the dimer. In this
column, the distance between the pair forming the dimer and
between the dimers forming the column is equal. Both the
complex helical columns assembled from dimers and from
tetramers self-organized into 2D-hexagonal columnar phases
with intracolumnar order (Φhio) at high temperature. At low
temperature, the columns generated from tetramers self-organize
into a 3D simple orthorhombic lattice (m = 0, 2, 3, 4) (Φs‑ok),
while those from dimers organize into a 3D monoclinic (m = 1)
(Φmk) periodic array. During the self-assembly in bulk, at high
temperature the Φhio represents the thermodynamic product. At
Scheme 1. Structure and Schematic of the Self-Assembly
Process of Dendronized PBI (3,4,5)nG1-m-PBI
k
k
low temperature, the Φs‑o and Φm are the thermodynamic
products. However, the formation of the Φs‑ok and Φmk phases is
so slow that even with rates of cooling of 1 ꢀC/min, sometimes
io
only the Φh phase, which is the kinetic product at low tem-
perature, can be detected. As a consequence, most of the time
these 3D complex helical columnar structures could not be
detected by a combination of differential scanning calorimetry
(DSC) and X-ray diffraction experiments (XRD).8f,9c,10 There-
fore, dendronized PBIs provide extremely interesting examples
to investigate the kinetically and thermodynamically controlled
self-assembly processes,11 which, upon elucidation, may have
immediate applications in the design of supramolecular electro-
nics and solar cells. For example, an unknown structure obtained
by the self-assembly of (3,4,5)12G1-1-PBI displays higher charge
carrier mobility than amorphous silicon.9c This mobility could
have immediate technological applications.
Our laboratory is involved in the investigation of libraries of
self-assembling dendrons and dendrimers to discover new su-
pramolecular architectures12aÀl,13 and, subsequently, to predict12mÀo
the primary structure that will generate a particular 3D architecture.
The goal of this Article is to apply for the first time the library
approach elaborated previously12 to self-assembling dendronized
PBIs. The first question to address is the following. Is any simple
chemical manipulation of the primary structure of a dendronized
PBI able to transform the extremely slow rate of assembly of a 3D
complex helical column into a fast rate? Or, in other words, is it
possible to transform the kinetically controlled self-assembly of
the 3D structure from low temperature into a thermodynamically
controlled or at least into something close to thermodynamically
controlled self-assembly? For the purpose of these experiments,
we have selected (3,4,5)12G1-3-PBI as the standard dendronized
PBI. The reason for this selection is that the dendronized PBI
with n = 12 and m = 3 already displays a sufficiently high rate of
io
of dendronized PBIs: while annealing in the Φh phase of
(3,4,5)9G1-3-PBI, its helical column generated from tetramers
of dendronized PBI arranged at an intratetramer distance of 4.1 Å
and an intertetramer distance of 3.5 Å10 self-repairs by a complex
dynamic process, elucidated by a combination of XRD and solid-
state NMR, and generates a helical column with the intra- and
intertetramer stacking of 3.5 Å. This new complex helical column
discovered here self-organizes into a new 3D monoclinic (Φm,1
periodic array that differs from that reported previously for
helical columns assembled from dimers of dendronized PBI.10
This self-repaired helical column also form in the case of
(3,4,5)8G1-3-PBI. The self-repaired column and its correspond-
ing Φm,1k phase form only upon annealing in the Φhio phase and
subsequent cooling from the same phase. The other dendronized
PBI with m = 3 and n = 7, 6, 5, and 4 also self-organize into 3D
monoclinic (Φm,2k) phases. However, the structural analysis by
XRD suggests that the Φm,2k phases are generated by columns
containing tilted dendronized PBIs that are not yet elucidated.
k
)
formation of its 3D Φs‑o phase.10 For example, while with
k
heating and cooling rates of 20 and 10 ꢀC/min the Φs‑ok phase
does not form, this structure starts to become detectable by a
combination of DSC and XRD experiments performed with
5 ꢀC/min. This first library approach to dendronized PBIs
consists of the synthesis and structural analysis of 11 dendronized
PBI with m = 3 and n varying from 14 to 4. The results of this
investigation were rewarding. The dendronized PBIs with n = 11,
10, 9, and 8 start to transform the kinetically controlled self-
’ RESULTS AND DISCUSSION
k
assembly of the Φs‑o phase from low temperature into a
Complex Helical Columns Self-Assembled from Dendro-
nized PBI. Scheme 1 describes in a simplified way the structure of
the complex helical columns assembled from dimers of dendro-
nized PBI (m=1;n= 12) (left side) and from tetramers (m =2, 3, 4;
n = 12) (middle).10 In the case of the helical column generated
from dimers, the interdimer and intradimer stacking distances are
thermodynamically controlled process. For these dendronized
PBIs, the assembly of their complex helical columns generated
k
from tetramers is almost as fast in the Φhio phase as in the Φs‑o
phase. However, the central result of these investigations was the
most important generated by the structural analysis of this library
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Scheme 2. Synthesis of Dendronized PBIs (3,4,5)nG1-m-PBI with m = 3 and n = 4À14
identical and equal to 3.5 Å. In the columns generated from
tetramers, the intertetramer stacking is 3.5 Å, while the intrate-
tramer stacking is 4.1 Å. Both the left side and the middle column
Reduction of the azides 5aÀ5k with LiAlH4 in THF at 25 ꢀC for
3 h generated the amines 6aÀ6k in 88À94% yield. The dendonized
PBIs were synthesized in 59À98% yield by a Zn(OAc)2-
mediated imidization of perylene 3,4:9,10-tetracarboxylic acid
dianhydride in quinoline at 180 ꢀC with 2 equiv of the dendritic
amines 6aÀ6k. The dendronized PBIs 7aÀ7k were isolated as
detailed in the Supporting Information and were purified by
column chromatography (silica gel) using CH2Cl2/MeOH
(100/1) as element followed by precipitation into methanol
from CH2Cl2 solution. This sequence was repeated until a
combination of 1H NMR, 13C NMR, TLC, HPLC, and MALDI-
TOF analysis demonstrated >99% purity.
Analysis of Complex Helical Columns and of Their Peri-
odic Arrays via a Combination of DSC and XRD with Different
Heating and Cooling Rates. This discussion requires a com-
parative investigation of Figures 1 and 2. Figure 1 shows first
heating DSC scans (left), first cooling scans (middle), and
second heating scans (right) recorded with 10 ꢀC/min for all
dendronized PBIs synthesized as shown in Scheme 2. Figure 2
illustrates the same DSC traces recorded with 1 ꢀC/min. The
identification of all phases was performed by XRD experiments
to be discussed in the following sections.
io
from Scheme 1 self-organize into 2D Φh phases and into 3D
Φmk and Φs‑ok phases. In bulk state, regardless of the heating and
cooling rate, at high temperature the Φhio phase is the thermo-
dynamic product. At low temperature, the 3D Φmk and Φs‑ok are
the thermodynamic products. However, these 3D structures
form with very slow rate, usually 1 ꢀC/min, and, therefore, most
of the time only the kinetic product, Φhio, is observed.10 The
first goal of this research was to search via libraries of
dendronized PBIs if the thermodynamically stable structure
from low temperature can be generated with high rates of
heating and cooling. Ultimately, it will be demonstrated that
this is indeed possible. In addition, the same experiments will
demonstrate that a self-repairing of the helical column gener-
ated from tetramers is also accessible. The self-repaired
column will have identical intertetramer and intratetramer
stacking distances of 3.5 Å. This is illustrated on the right side
column of Scheme 1.
Synthesis of Dendronized PBI. Scheme 2 outlines the
synthesis of 11 twin-dendronized14 PBIs with identical dendrons
that differ in the number of methylenic units from the alkyl
groups on their periphery from 14 to 4 (n = 14À4). All dendrons
are attached to the imide groups of the PBI via three methylenic
units (m = 3). Therefore, the short name for this library is
(3,4,5)nG1-3-PBI. 3-(3,4,5-Trihydroxyphenyl) propionic acid
methyl ester, 1, was synthesized as reported previously12c and
was alkylated with n-alkyl bromides in DMF at 95 ꢀC in the
presence of K2CO3 to produce 2aÀ2k, (3,4,5)nG1-3-CO2CH3
with n = 4À14 in 88À99% yield. Esters 2aÀ2k were reduced
with LiAlH4 in THF at 0 ꢀC for 30 min to produce the dendritic
alcohols 3aÀ3k in 91À95% yield. Bromination of the alcohols
3aÀ3k with CBr4/PPh312c in CH2Cl2 at 0 ꢀC for 2 h led to the
corresponding bromides 4aÀ4k (in 91À98% yield), which upon
nucleophilic displacement with NaN3 in DMF at 25 ꢀC for 18 h
produced the corresponding azides 5aÀ5k in 88À94% yield.
To set the stage for this discussion, we will first recapitulate the
phase analysis of (3,4,5)12G1-3-PBI that was reported previously
from several laboratories and was analyzed quantitatively for the
first time in a recent publication.10 Let us discuss first the analysis
with 10 ꢀC/min (Figure 1). During the first heating scan, the self-
organization of this dendronized PBI displays an unknown
columnar crystal phase, Φxk, followed by a 2D Φhio liquid crystal
phase generated from helical columns assembled from tetramers
(Scheme 1, middle column). On cooling from the isotropic melt,
io
(i) the Φhio phase is observed up to À23 ꢀC when the 2D Φh
k
phase transforms into a 3D columnar hexagonal crystal (Φh ).
k
io
On second heating scan, the Φh melts back into the 2D Φh
phase, which on further heating transforms into a 3D Φs‑ok phase
near an almost undetectable (by DSC) transition to the same
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Figure 1. DSC traces of (3,4,5)nG1-3-PBI with n = 14À4 recorded with heating and cooling rates of 10 ꢀC/min. Phases, transition temperatures, and
associated enthalpy changes (in brackets in kcal/mol) are indicated. The green circles mark the transitions dependent on rate.
io
k
Φh phase at 84 ꢀC (Figure 1). The 3D Φs‑o phase can be
detected only by XRD experiments.
phase (Figure 2). The conclusion of this analysis is the following.
At high temperature, the thermodynamic product of this assem-
bly is the 2D Φhio phase. At low temperature, the thermodynamic
The analysis by DSC recorded with 1 ꢀC/min clarifies the
behavior of (3,4,5)12G1-3-PBI (Figure 2). The first heating scan
with 1 ꢀC/min (Figure 2) is almost identical to the first heating
scan with 10 ꢀC/min (Figure 1). However, the first cooling scan
with 1 ꢀC/min differs from the same scan recorded with 10 ꢀC/min.
On cooling from the isotropic melt, the Φhio phase forms both
with 1 ꢀC/min and with 10 ꢀC/min. However, with 1 ꢀC/min at
67 ꢀC, a clearer first-order transition from the 2D Φhio phase to
the 3D Φs‑ok phase is detected (Figure 2). This transition is not
observed on cooling with 10 ꢀC/min (Figure 1). At À22 ꢀC, an
k
product is the 3D Φs‑o phase. However, this product can be
obtained only with cooling of 1 ꢀC/min. With 10 ꢀC/min at low
temperature we can detect only the 2D Φhio phase, which is the
kinetic product of this assembly. The research hypothesis set at
the start of this work asked the following question. Can small
chemical modifications of the dendronized PBI transform its
DSC scans recorded with 10 ꢀC/min to look like the DSC scan of
this sample recorded with 1 ꢀC/min? Or, in other words, can we
increase, by simple chemical modification, the rate of formation
of the 3D Φs‑ok thermodynamic product from low temperature
sufficiently to be detected by DSC scans recorded with 10 ꢀC/
min?
k
additional transition from the 3D Φs‑o phase to a second 3D
Φs‑o,1k phase is observed on cooling with 1 ꢀC/min (Figure 2),
io
while on cooling with 10 ꢀC/min at À23 ꢀC the 2D Φh
transforms into the 3D Φhk (Figure 1). On second heating scan
To answer this question, we will first discuss the DSC traces
k
with 1 ꢀC/min, the 3D Φs‑o,1 phase transforms into the 3D
recorded with 1 ꢀC/min for all dendronized PBIs with n = 14À4
io
Φs‑ok phase at À20 ꢀC, while at 85 ꢀC a more distinct first-order
from Figure 1. The Φh Ài transition temperature from the first
phase transition transforms the 3D Φs‑ok phase into the 2D Φh
and second heating scans and the iÀΦhio from the first cooling
io
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Figure 2. DSC traces of (3,4,5)nG1-3-PBI with n = 14À4 recorded with heating and cooling rates of 1 ꢀC/min. Phases, transition temperatures, and
associated enthalpy changes (in brackets in kcal/mol) are indicated. The green circles mark the transitions dependent on rate.
scan for compounds with n = 14À8 demonstrate that the Φhio is
thermodynamically stable and that this phase transition is
thermodynamically controlled. This is demonstrated by the very
small difference between this transition temperature and its enthalpy
change observed on heating and cooling scans (Figures 1 and 2).
At the same time, this transition temperature and its enthalphy
change increase from n = 8 to n = 13, and subsequently both
supercooling of this temperature transition demonstrates that,
although the Φs‑ok phase is the thermodynamic product at low
temperature, its formation is kinetically controlled. As a conse-
quence, even with cooling rates of 1 ꢀC/min for n = 13 and 14,
the thermodynamic product from low temperature does not
form. During the first cooling and second heating scans, an
additional crystal phase is formed between À37 and 9 ꢀC on
cooling, and À36 and 13 ꢀC on heating for n = 11À14. This
crystal phase maintains the symmetry of the next higher tem-
perature phase and is most probably mediated by the crystal-
lization tendency of the alkyl groups of the dendron. During the
first heating scans, n = 10À14 exhibit at low temperature an
unidentified crystal phase that, with the exception of n = 10 and
io
decrease at n = 14. The Φh ÀΦs‑ok transition temperature from
the second heating scan decreases from 105 ꢀC for n = 8 to 75 ꢀC
for n = 14. At the same time, the corresponding enthalphy change
increases from 0.32 kcal/mol at n = 8 to 1.26 kcal/mol at n = 11
and subsequently decreases to 0.56 kcal/mol at n = 14. On the
io
k
first cooling scan, the degree of supercooling of the Φh ÀΦs‑o
k
io
transition decreases from 5 ꢀC for n = 8 to 18 ꢀC for n = 12. No
transition temperature change is observed for n = 13 and 14. The
enthalphy change of this transition decreases continuously from
0.94 kcal/mol at n = 8 to 0.26 kcal/mol at n = 12. It is expected
that subsequent decrease of this temperature for n = 13 and 14
brings it in the range of values overlapping the glass transition
temperature, and, therefore, this phase transition becomes
kinetically prohibited at n = 13 and 14. As a consequence, the
11, overlaps the Φs‑o to Φh transition. The expected trend
generated by the increase of the rate of heating and cooling from
1 ꢀC/min to 10 ꢀC/min is a decrease of all temperature
transitions and of their enthalphy change and an enhancement
of the degree of supercooling that is more substantial for
kinetically controlled phase transitions. As a consequence, the
io
k
Φh to Φs‑o phase transition is not observed with rates of
10 ꢀC/min for any of the dendronized PBIs with n = 12À14 and
on heating only for n = 11À8. However, for n = 8, 9, 10, and 11,
k
Φs‑o phase does not form for n = 13 and 14. The degree of
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Figure 3. DSC traces collected with heating and cooling rates of 1 ꢀC/min from (3,4,5)9G1-3-PBI. Second heating and cooling traces (a); first cooling
to 96 ꢀC, followed by 10 h annealing at 96 ꢀC in the Φhio phase, and the subsequent first and second heating and cooling traces (b); first cooling to 96 ꢀC,
followed by 1, 3, and 6 h annealing at 96 ꢀC in the Φhio phase, and the subsequent second heating (c). The data from (b) and (c) illustrate the complete
and, respectively, partial transformation of the Φhio phase into Φmk crystal after annealing.
the formation of the Φs‑ok is observed with rates of both 1 and
10 ꢀC/min. This is a very rewarding result because for n values
second heating displays a mixture of Φs‑ok, Φm,1k transforming into
k
a mixture of Φhio and Φm,1k that at 116 ꢀC generates only the Φm,1
io
from 11 to 8, the Φh ÀΦs‑ok phase transition starts to transform
phase, which undergoes melting to an isotropic liquid at 118 ꢀC.
At this point, we can reinvestigate the DSC traces of (3,4,5)-
8G1-3-PBI recorded with 1 ꢀC/min from Figure 2. The
second heating scan of (3,4,5)8G1-3-PBI from Figure 2 resem-
bles the sequence of phases displayed by the second heating of
(3,4,5)9G1-3-PBI after annealing for 6 h at 96 ꢀC (Figure 3c). It
displays the sequence Φs‑ok, which transforms at 100 ꢀC into
from a kinetically controlled to a thermodynamically controlled.
However, this remarkable change facilitates an even more
important discovery that will be discussed with the help of the
DSC experiments from Figure 3.
Figure 3a shows the second heating and cooling DSC scans of
(3,4,5)9G1-3-PBI recorded with 1 ꢀC/min. These scans are quite
similar to the second heating and first cooling recorded with
1 ꢀC/min (Figure 2) and 10 ꢀC/min (Figure 1). Figure 3b shows
io
Φh that undergoes isotropization at 105 ꢀC and immediate
crystallization through an exothermic peak that overlaps with the
io
k
k
the first cooling after annealing for 10 h at 96 ꢀC in the Φh
formation of the Φm,1 phase. The Φm,1 phase melts into an
k
phase. Surprisingly, no Φs‑o phase is observed upon cooling
isotropic liquid at 123 ꢀC. During the first heating scans, both
k
after this annealing process. Instead, a new monoclinic columnar
crystal phase is observed (Φm,1k). In this new crystal phase, the
self-repairing13f of the middle column from Scheme 1 takes place
to generate the new column from the right side of the same
scheme. This process will be discussed in more detail in a later
subsection. The second heating scan after cooling shows only the
Φm,1k phase that undergoes melting directly to an isotropic phase
at 118 ꢀC. Cooling from the isotropic melt regenerates a second
cooling DSC scan that is identical to the first cooling scan from
Figure 2. This result also demonstrates that this compound does
not undergo thermal decomposition during 10 h annealing at
high temperature followed by slow cooling and reheating cycles.
Figure 3c investigates the role of the annealing time at 96 ꢀC on the
n = 8 and 9 display only the Φm,1 phase that exhibits a much
lower degree of perfection than the one obtained after annealing
in the Φhio phase. The main message of these experiments is that
the thermodynamic product for n = 8 and 9 is not the Φs‑ok but
the newly discovered and more ordered Φm,1k phase. However, the
formation of the Φm,1k phase is kinetically controlled and forms
very slowly only upon proper annealing in the Φhio phase.
Regardless of the heating and cooling rates, the dendronized
PBIs with n = 7À4 display only an additional monoclinic crystal
(Φm,2k) that was not yet elucidated (Figures 1 and 2). The results
of the DSC analysis combined with the phase assignments
established by XRD are summarized in Table 1. The detailed
analysis of these supramolecular assemblies by a combination of
small-angle (SAXS) and wide-angle (WAXS) XRD experiments
will be presented in the following sections.
k
formation of the new Φm,1 phase. Cooling scans followed by
second heating scans after annealing for 1 and 3 h at 96 ꢀC are not
k
sufficient to generate the Φm,1 phase. After 6 h of annealing at
Structural Analysis of the Library of Dendronized PBIs by
SAXS and WAXS. The phases reported in Tables 1 and 2 and in
96 ꢀC, a mixture of Φs‑ok and Φm,1k phases is formed, which upon
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Table 1. Transition Temperatures and Associated Enthalpy Changes of (3,4,5)nG1-3-PBI with n = 4À14 As Determined by DSC
and XRD
thermal transitions (ꢀC) and corresponding enthalpy changes (kcal/mol)
n
rate (ꢀC/min)
heatinga
cooling
k
k
k
k
k
k
4
10
k1 133 (0.64) k2 141 (4.13) k3 180 (4.84) i
i 143 (3.74) Φm,2
i 163 (4.32) Φm,2
i 142 (3.89) Φm,2
i 153 (3.76) Φm,2
i 114 (1.17) Φm,2
i 124 (3.90) Φm,2
k
Φm,2 179 (4.95) i
1
10
1
k1 140 (1.81) k2 167 (4.16) k3 179 (4.33) i
k
Φm,2 180 (4.80) i
k
5
6
7
8
9
Φm,2 167 (3.78) i
k
Φm,2 167 (4.36) i
k
k
Φm,2 139 (0.38) Φm,2 168 (3.71) i
k
Φm,2 168 (3.83) i
k
10
1
Φm,2 147 (4.03) i
k
k
Φm,2 86 (0.6) Φm,2 147 (3.88) i
k
Φm,2 147 (4.21) i
k
Φm,2 147 (4.59) i
k
b
k
10
1
Φm,2 126 (10.76) i
i À Φm,2
k
k
Φm,2 77 (0.71) Φm,2 110 (1.34) i
k
k
k
Φm,2 125 (8.82) Φm,2 154 (10.03) i
i 71 (0.45) Φm,2
k
k
Φm,2 110 (1.72) Φm,2 154 (10.32) i
k
io
k
k
10
1
Φm,1 121 (2.59) i
i 85 (0.62) Φh 80 (0.40) Φs‑o
k
c
c
Φs‑o 91 (0.33) À 98 (0.26) À 104 (0.30) i
k
k
io
Φm,1 78 (0.67) Φm,1 122 (2.95) i
i 99 (0.39) Φh 89 (0.94) Φs‑o
k
io
k
Φs‑o 100 (1.59) Φh 105 (0.32) Φm,1 123 (1.41) i
k
io
k
k
10
1
Φm,1 116 (2.51) i
i 108 (0.41) Φh 83 (0.58) Φs‑o
k
k
io
Φs‑o 85 (0.12) Φs‑o 96 (1.14) Φh 116 (0.44) i
k
k
io
Φm,1 90 (0.27) Φm,1 117 (2.32) i
i 113 (0.36) Φh 87 (0.76) Φs‑o
k
io
Φs‑o 100 (1.10) Φh 116 (0.35) i
Φm,1 118 (2.73) i d
k
k
io
io
k
k
k
k
10
11
12
13
14
10
1
Φxk 81 (14.18) Φs‑o 96 (0.73) Φh 122 (0.50) i
i 118 (0.45) Φh 80 (0.49) Φs‑o
k
io
Φs‑o 97 (1.05) Φh 123 (0.51) i
Φxk 76 (12.86) Φs‑o 97 (1.01) Φh 122 (0.45) i
i 120 (0.45) Φh 84 (0.76) Φs‑o
k
io
io
k
io
Φs‑o 97 (1.20) Φh 122 (0.43) i
k
io
io
10
1
Φxk 76 (18.08) Φs‑o 90 (0.48) Φh 124 (0.50) i
i 120 (0.50) Φh 70 (0.27) Φs‑o
k
io
Φs‑o 91 (1.03) Φh 124 (0.54) i
Φxk 73 (16.78) Φs‑o 91 (0.97) Φh 124 (0.55) i
i 123 (0.48) Φh 77 (0.68) Φs‑o À37 (1.80) Φs‑o,1
k
io
io
k
k
k
k
io
Φs‑o,1 À36 (5.35) Φs‑o 92 (1.26) Φh 125 (0.54) i
io
io
k
10
1
Φxk 80 (28.91) Φh 125 (0.55) i
i 121 (0.62) Φh À23 (3.96) Φh
k
io
k
io
Φh À17 (4.44) Φh 73 (À0.25) Φs‑o 84 (0.86) Φh 125 (0.59) i
k
k
io
io
k
Φx 72 (26.75) Φs‑o 84 (0.73) Φh 125 (0.54) i
i 123 (0.55) Φh 67 (0.20) Φs‑o À22 (4.76) Φs‑o,1
k
k
io
Φs‑o,1 À20 (4.63) Φs‑o 85 (0.97) Φh 125 (0.55) i
k
io
io
k
10
1
Φx 69 (29.9) Φh 126 (0.68) i
i 123 (0.69) Φh À5 (10.32) Φh
k
io
Φh 0 (10.44) Φh 126 (0.69) i
k
io
io
k
Φx 65 (25.83) Φh 126 (0.62) i
i 125 (0.59) Φh À6 (7.13) Φh
k
io
k
io
Φh À1 (8.12) Φh 69 (À0.06) Φs‑o 78 (0.79) Φh 126 (0.56) i
k
io
io
k
10
1
Φx 75 (16.07) Φh 121 (0.73) i
i 117 (0.55) Φh 8 (12.21) Φh
k
io
Φh 15 (11.59) Φh 121 (0.43) i
Φxk 69 (22.93) Φh 123 (0.40) i
i 122 (0.45) Φh 9 (8.97) Φh
io
io
k
k
io
k
io
Φh 13 (9.32) Φh 56 (À0.27) Φh 75 (0.55) Φh 123 (0.41) i
a First heating data on the first line and second heating data on the second line. b Transition observed by XRD. c Phases could be resolved only in the XRD
experiments performed with 1 ꢀC/min. d Second heating DSC data collected after annealing for 10 h at 96 ꢀC followed by cooling to À40 ꢀC with a rate
of 1 ꢀC/min. Note: Quantitative uncertainties are (1 ꢀC for thermal transition temperatures and ∼2% for the associated enthalpy changes reported
in kcal/mol.
Figures 1, 2, and 3 were assigned by the analysis of SAXS and
WAXS powder and oriented fiber XRD data recorded as a
function of temperature. To match the experimental conditions
used in the DSC experiments, these XRD experiments were
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Table 2. Structural Analysis of (3,4,5)nG1-3-PBI with n = 4À14 by XRD
n
T (ꢀC)
phasea
a, b, c (Å)b
α, β, γ (deg)b
μc
experimental d-spacings (Å)
kp
14
35
120
30
Φx
103.0, 65.0
41.7
À, 55.1, 25.7, 21.2, 18.3, 17.2, 16.3d
Φh
2
2
2
36.1, 20.8, 18.0f
io
Φh
46.8, À, 60.5
45.7, À, 60.1
105.9, 40.6
76.8, 45.0, 58.2
40.5, 23.4, 20.3, À, 33.7e
k
k
À40
50
Φh
39.7, 22.9, 19.8, À, 33.1e
13
12
Φx
53.1, 37.9, À, À, À, 17.7, 16.1d
kp
k
75
Φs‑o
2
À, 38.8, 38.4, 35.6, 32.3, 32.1, 29.1, 29.2, 26.1, 23.3g
22.5, 20.6, 21.6, 20.8, 17.8, 19.2, 17.4, 17.3, 18.2, 17.3, 16.2h
35.5, 20.5, 17.7f
io
110
À25
20
Φh
40.9
2
2
Φh
43.7
37.9, 21.9, 18.9f
52.6, 33.9, 23.9, 20.9, 20.5, 17.0i
60.6, 37.4, 37.2, 35.2, 31.8, 31.7, 30.3, 28.2, 25.6, 23.5g
21.6, 20.6, 20.7, À, 18.3, 18.6, 17.8, 17.7, À, À, 16.4h
34.7, 20.0, 17.3f
60.6, 36.3, 35.8, 34.6, 31.2, 30.8, 30.3, 27.3, 24.9, 23.3g
21.1, 20.3, 20.2, 19.6, 18.2, 17.9, 17.7, 17.6, 17.1, 16.8, 16.2h
k
kp
Φx
76.9, 71.8
74.4, 43.2, 60.6
k
80
Φs‑o
2
io
110
90
Φh
40.0
2
2
k
11
10
9
Φs‑o
71.5, 42.2, 60.6
io
f
110
80
Φh
39.2
2
2
33.9, À, À
Φs‑o
69.0, 40.7, 60.4
À, 35.1, 34.5, 33.8, 30.3, 29.9, 30.2, 26.3, 24.1, 22.9g
k
20.4, 19.8, 19.5, 19.0, 18.1, 17.3, 17.5, 17.4, 16.6, 16.4, 16.0h
io
f
105
25
Φh
38.0
2
2
32.9, À, À
k
j
Φm,1
76.0, 76.8, 28.8
90, 102.0, 90
74.3, 37.2, 33.5, À, 26.7, 26.5, 24.7, 23.9, 23.5, 19.8, 19.0, À
À, 18.9, 18.4, 17.9, À, 17.3, 16.8, À, 16.5, 16.2, 16.0, 14.4, À
À, 34.1, 33.7, 33.2, 29.8, 29.5, 30.4, 25.6, 23.6, 22.7g
k
k
90
Φs‑o
67.3, 39.6, 60.8
2
19.8, 19.6, 19.0, 18.6, 18.1, 16.8, 17.4, 17.3, 16.2, 16.1, 15.9h
io
f
110
80
Φh
37.5
2
2
32.5, À, À
8
Φs‑o
65.0, 38.2, 60.5
À, 32.9, 32.5, 32.3, 28.9, 28.6, 30.3, 24.8, 22.9, 22.3g
k
19.1, 19.2, 18.3, 18.0, 17.8, 16.3, 17.2, 17.1, 15.7, 15.6, 15.6h
io
f
100
120
Φh
36.7
2
2
31.9, À, À
k
Φm,1
72.5, 79.9, 29.7
90, 101.4, 90
À, 35.5, À, 27.3, 26.5, 27.4, À, 23.9, 24.1, 19.9, À, 23.5j
20.6, À, 18.2, À, 17.8, 16.7, À, 13.8, À, À, À, 14.9, 13.5k
28.6, 15.4, 11.6, 10.2, 9.5, 8.5, 8.4l
k
7
6
5
4
25
25
25
25
Φm,2
29.4, 18.3, 15.4
38.5, 44.2, 34.0
71.7, 33.6, 45.1
34.8, 27.8, 28.4
90, 90, 103.5
90, 90, 95.6
90, 90, 109.0
90, 90, 94.8
Φm,2
38.3, 25.4, 22.0, 19.9, 13.5, 12.8, 11.5, 10.9, 8.5, 8.4, 8.1, 7.1m
35.9, 24.9, 22.6, 21.3, 19.3, 18.7n
34.8, 28.4, 27.8, 22.1, 20.9, 19.5, 16.7, 13.9, 12.3, 10.5, 10.0, 9.2, 8.7, 8.3o
k
k
Φm,2
k
Φm,2
a Φh : Columnar hexagonal crystalline phase. Φmk: Monoclinic columnar crystalline phase. Φxk: Unidentified columnar crystalline phase. Φh
:
k
io
Columnar hexagonal phase with intracolumnar order. Φs‑ok: Simple orthorhombic columnar crystalline phase. b Lattice parameters (with uncertainty of
∼1%) calculated using: dhkl = [4(h2 + k2 + hk)/(3a2) + (l/c)2]À1/2 for hexagonal, dhk = [(h/a)2 + (k/b)2]À1/2 for the indexing of the equatorial peaks of
Φxk, dhkl = [(h/a)2 + (k/b)2 + (l/c)2]À1/2 for orthorhombic lattices, and dhkl = [(h/a sin γ)2 + (k/b sin γ)2 + (l/c)2 À(2hk cos γ/ab sin2 γ)]À1/2 or dhkl
=
[(h/a sin β)2 + (k/b)2 + (l/c sin β)2 À (2hl cos β/ac sin2 β)]À1/2 for monoclinic phases. c Average number of dendrimers forming the supramolecular
column stratum with thickness t = 3.7 Å, calculated using: μ = NAabtF/(2Mwt). NA = 6.022 Â 1023 molÀ1 = Avogadro’s number. F = 1.05 g/cm3 and Mwt
are the density and molecular weight. d d20, d11, d40, d13, d33, d60, d04. e d100, d110, d200, d210, d101. f d10, d11, d20. g d001, d110, d200, d011, d111, d201, d002, d210
,
,
,
d
211, d112. h d020, d212, d120, d311, d013, d400, d113, d203, d401, d122, d213. i d11, d21, d03, d32, d42, d51. j d100, d200, d210, d111, d220, d011, d101, d211, d111, d211, d131
d121. k d201, d031, d321, d231, d400, d401, d411, d411, d311, d331, d231, d102, d112. l d100, d001, d011, d111, d300, d220, d211 m d100, d101, d020, d120, d031, d300, d320, d321
.
d
051, d341, d251, d530. n d200, d211, d002, d301, d211, d012. o d100, d001, d010, d101, d110, d011, d111, d020, d021, d220, d311, d030, d320, d321. p Phase observed only in
the first heating of the as-prepared compound.
performed with heating and cooling rates ranging from 1 to
10 ꢀC/min.
into a variety of monoclinic crystalline (Φm,2k) phases character-
ized by a c-axis ranging from 15.4 Å for n = 7 to 45.1 Å for n = 5.
The WAXS fiber patterns of the Φm,2 phases observed in
n = 4À7 (Figure 4) exhibit sharpoff-meridional wide-angle features
in the range of 3.5À4.1 Å. These features, in combination with
the absence of meridian diffraction peaks in the range expected
for the πÀπ stacking corresponding to a distance of ∼3.5 Å,
suggest that, most probably, the dendronized PBIs are tilted with
respect to the long axis of the supramolecular column. A tilted
organization of the dendronized PBIs can also explain the
k
The structural analysis of the periodic arrays self-organized by
the library (3,4,5)nG1-3-PBI will be discussed starting from n = 4
to n = 14 (Figure 4). The diversity of lattices observed for the
dendronized PBIs indicates the significant contribution of n on
their self-assembly (Table 1, Figure 4). For the current discus-
sion, the library of dendronized PBIs was organized into the
following four sublibraries: n = 4, 5, 6, 7; n = 8, 9; n = 10, 11, 12;
and n = 13, 14. The dendronized PBIs with n = 4À7 self-organize
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Figure 4. The wide-angle X-ray patterns collected from the oriented samples of (3,4,5)nG1-3-PBI, with n = 4À14, and the corresponding
meridional plots.
significant variation of the lattice parameters of the Φm,2k phases
upon the increase of n from 4 to 7 (Table 2).
observed in all compounds with n < 8. The WAXS fiber patterns
collected in the low temperature range of Φs‑ok and in the high
temperature of Φhio phases (Figure 4) exhibit equatorial features
at ∼7.6 Å. These equatorial reflections are due to the thickness of
the supramolecular tetramers of 7.6 Å generated by a pair of side-
by-side dendronized PBIs arranged on top of a second pair of
side-by-side dendronized PBI and rotated at a certain angle
(Scheme 1). This arrangement is similar to that observed in the
The second sublibrary of dendronized PBIs, n = 8, 9, exhibits
the 3D Φs‑ok, the 3D Φm,1k, and the 2D Φhio phases. This latter
result demonstrates that the increase of the conformational
freedom of the dendronized PBI induced by the transition of n
io
from 7 to 8 and to 9 is responsible for the creation of the Φh
phase in addition to the low-temperature crystalline phases
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Figure 5. The SAXS fiber pattern collected at 85 ꢀC from the oriented fiber of (3,4,5)9G1-3-PBI (a), and the corresponding plot (b). Fiber axis,
diffraction peaks, indexing, and lattice parameters of the simple crystalline orthorhombic phase, Φs‑ok, are indicated.
k
Figure 6. Comparison of the experimental and simulated fiber patterns of (3,4,5)9G1-3-PBI collected at 90 ꢀC in the Φs‑o phase (a) and the
corresponding molecular model used in the simulation (b).
compound with n = 12 that was reported previously.10 The SAXS
fiber pattern collected from the oriented sample with n = 9 and its
indexing to the Φs‑ok phase with P21212 symmetry are shown in
Figure 5. The SAXS fiber data collected in the Φs‑ok phases with
P21212 symmetry observed in the dendronized PBIs with
n = 8À13 and their indexing are summarized in the Supporting
Information. The simulation of the XRD fiber data collected in
Φs‑ok phase of the dendronized PBI with n = 9 and the molecular
model used in the simulation are outlined in Figure 6. As it was
shown previously for the case of n = 12,10 the analysis of the XRD
data collected in the Φs‑ok and Φhio phases and the simulation of
the XRD fiber patterns (Figure 6) demonstrated that the
columns forming these phases are generated via a helical
arrangement of the supramolecular tetramers (Scheme 1). It is
assembled from the dendronized PBIs with n = 8À14, the
aromatic core of the supramolecular columns is generated by
pairs of PBIs that are arranged side-by-side and another pair in
the next stratum of the column turned upside-down and rotated
at a certain angle. The intratetramer stacking distance in the
helical columns is 4.1 Å, while the intertetramer stacking distance
is 3.5 Å (Scheme 1).
The Φm,1k phases observed in the first heating of the n = 8 and
9 were also detected in the second heating with slow heating rate
for n = 8 (Figure 2) or after annealing in the Φhio phase for n = 9
(Figures 3 and 7). The XRD and electron diffraction (ED) data
collected in the Φm,1k phase of n = 9 (Table 1 and Figures 1, 2, 3,
and 7) will be discussed in the following subsection.
The third sublibrary of dendronized PBIs, n = 10, 11, 12,
k
io
important to note that both in Φs‑o and in Φh phases,
exhibits at low temperatures the Φs‑ok phase with P21212symmetry10
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Figure 8. The SAXS powder data collected from (3,4,5)9G1-3-PBI at
the indicated temperatures.
The transition from Φhio to Φm,1k was also monitored in the
second heating scan of the oriented fibers of this compound
(Figure 9). The experiments performed on oriented fibers are
complementary to the powder XRD data and facilitated a
separation of the diffraction features (hk0) and (hkl) from the
Figure 7. The WAXS fiber pattern collected from (3,4,5)9G1-3-PBI in
the Φm,1k phase obtained after annealing at 110 ꢀC in the Φhio phase for
10 h (see also Figure 3c) (a) and the corresponding qy plot (b).
io
SAXS region. This separation demonstrated that the Φh to
Φm,1k transition begins after ∼30 min of annealing (Figure 9).
On the other hand, the DSC experiments could detect significant
enthalphy changes only following annealing for longer than 180
min (Figure 3). These results indicate that only a relative small
fraction of the compound is transformed after 30 min of
annealing. Considering that in the case of the n = 8 the structure
of the Φm,1k phase was observed to form in the second heating
performed with rates of 1 ꢀC/min, it is not surprising that for
n = 9 the transformation Φhio to Φm,1k starts after ∼30 min of
annealing (Figures 2 and 9). However, this transformation was
complete only after annealing for 600 min (Figures 3 and 9).
A similar annealing experiment was performed on a thin film
prepared by casting a solution from n = 9 dissolved in THF, which
was analyzed by electron diffraction. Figure 10 shows a series of
electron diffraction patterns collected after annealing the thin
film at 96 ꢀC following slow cooling from the isotropic phase. The
electron diffraction data showed that the a and b axes of the lattice
are perpendicular to each other and that the c-axis is inclined by
β = 102ꢀ with respect to the a,b plane. Therefore, the electron
diffraction results are consistent with the Φm,1k unit cell. The lattice
parameters provided by the analysis of the electron diffraction
data are in excellent agreement with those obtained from the
XRD analysis. Furthermore, the same number of layers identified
in the electron diffraction pattern shown in Figure 10c was also
and at high temperatures the Φhio phase (Figure 4). This sequence
is similar to that of the phases observed for the second sublibrary
n = 8, 9. In contrast to the structures with n e 9, the third
sublibrary of dendronized PBIs does not exhibit the Φm,1k phase.
For example, in the case of n = 10, the XRD fiber pattern was
io
unchanged even after annealing in the Φh phase at 115 ꢀC
(Figures 1 and 2) for more than 12 h. However, in the case of
k
n = 9, some of the diffraction features corresponding to the Φm,1
phase were observed after only 30 min of annealing at 110 ꢀC. It
is important to note that only in the narrow range for the
structural parameter n of 8 and 9 does the self-organization
process induce the highly ordered columns to self-repair and
k
assemble into the Φm,1 phase characterized by all side-by-side
dendronized PBIs pairs stacked only at 3.5 Å (Figure 7). The
fourth sublibrary of dendronized PBIs with n = 13 and 14 exhibits
io
at low temperature a Φhk phase and at high temperature the Φh
(Figures 1, 2, and 4). The Φs‑ok phase with P21212 symmetry was
observed only for n = 13 at intermediate temperatures after
second heating scans performed with rates of 1 ꢀC/min or
k
k
slower. In the case of n = 14, a Φh phase replaces the Φs‑o
phase observed for n = 13.
observed in the wide-angle XRD fiber pattern from Figure 10b.
Structural Analysis of (3,4,5)9G1-3-PBI in the Φm,1k Phase
by a Combination of Electron Diffraction (ED) and XRD
Experiments. Figure 8 shows the SAXS powder data collected
for the dendronized PBI with n = 9 from the first heating of the
as-prepared compound as well as from subsequent cooling and
heating scans performed with 1 ꢀC/min. After 10 h of annealing
in the high temperature Φhio phase, the Φm,1k phase identified in
the first heating scan of the as-prepared compound is recovered
(Figures 8 and 9).
io
Figure 11 compares the lattice parameters of the Φs‑ok, Φh
,
and Φm,1k phases observed in the dendronized PBI with n = 9.
The experimental density (Table 2) in combination with the
k
lattice parameters demonstrated that the unit cell of the Φm,1
phase contains four columns with an estimated diameter of ∼38 Å.
This value is close to the diameter of 38.9 and 37.5 Å of the
k
io
supramolecular columns forming the Φs‑o and Φh phases
(Figure 11). This analysis shows that the column stratum with a
thickness of 3.5 Å is generated by two side by side dendronized
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k
PBIs. Although the assessment of the space group of the Φm,1
ingly, the scattering intensity of the fourth line is significantly
larger than the intensity of the eighth line, as indicated in the
WAXS fiber pattern presented in Figure 7. This suggests that the
packing of dendronized perylenes into supramolecular tetramers
phase is not yet definitive, one possible mechanism to generate
this unusual four column unit cell is illustrated in Figure 11.
Inspired by the observation that the packing of the low tempera-
k
k
io
ture Φs‑o phases consists of adjacent rows of columns with a
established for the Φs‑o and Φh phases is most probably
io k
relative registry shift (Figure 11b), most probable is that a similar
registry shift can induce a doubling of the unit cell and generate
the four columns repeat unit illustrated in Figure 11c. Interest-
preserved upon the slow transition from Φh to Φm,1 phase.
Considering that these equatorial diffractions can be generated
by intra- and intercolumnar correlations, it is difficult to separate
their individual contributions. Therefore, the proposed preserva-
tion of the tetramer packing is just one possible solution.
Scheme 3a details the change of the supramolecular arrange-
ment within the complex helical columns generated by dimers
io
k
of (3,4,5)12G1-1-PBI via the Φh to Φm,1 transition.
This transition is accompanied by the formation of long-range
intercolumnar order via coupling of the supramolecular columns.
During this transition, the intra- and interdimer 3.5 Å πÀπ
stacking distance is preserved (Scheme 3a). Consequently,
although the dendritic periphery of the supramolecular helical
column undergoes significant packing changes to accommodate
strong 3D coupling between the columns via the change from
io
alternating upÀdown arrangement of dendronized PBIs in Φh
k
phase to all up or all down in the Φm,1 phase, their PBI
fragments undergo rotational changes but no translational
changes. At the same time, the helical columns assembled from
tetramers of n = 8, 9, m = 3, and the PBI cores undergo both
rotational and translational changes at the transition from Φhio to
k
Φm,1 (Scheme 3b). Most probably, the self-repairing process
form alternating πÀπ stacking of 3.5 and 4.1 Å in the Φhio phase
to 3.5 Å πÀπ stacking in the Φm,1k phase of n = 8, 9, m = 3 was
facilitated by the strong 3D coupling of the helical columns
(Scheme 3b). A close-packed 3.5 Å πÀπ stacking of the PBIs and
stronger 3D coupling of the supramolecular columns in the
Figure 9. The small-angle XRD fiber patterns collected in the second
heating scans of (3,4,5)9G1-3-PBI following the indicated thermal cycle
illustrating the transformation of the Φhio into Φm,1k upon annealing.
Figure 10. Electron diffraction (a,c) and XRD patterns (b) collected in the Φm,1k self-organized from (3,4,5)9G1-3-PBI.
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Figure 11. Assembly of the helical complex columns from tetramers of (3,4,5)9G1-3-PBI, forming the Φs‑ok and Φhio phases (a), and details of the
Φs‑ok (b), Φhio (c), and Φm,1k (d) lattices. The possible registry shift of the supramolecular columns that can explain the unusual four column unit cell of
the Φm,1k phase is shown in (d).
Scheme 3. Self-Repairing Complex Helical Columns Generated from Dimers (a) and Tetramers (b) of Dendronized PBIs
k
k
Φm,1 phase at the transition from the Φs‑o phase is also
demonstrated by the significant increase of the enthalpy change
Analysis of the Φhio to Φm,1k Slow Phase Transition and
the Self-Repairing Process of (3,4,5)9G1-3-PBI by Variable-
1
1
k
Temperature Solid-State H NMR. Variable-temperature H
NMR analysis15 carried out on oriented samples of (3,4,5)9G1-
3-PBI is shown in Figure 12. In the first heating of the fiber
extruded in the Φs‑ok phase, the 1H NMR exhibits broad spectra
in the aromatic region, identical to those of the (3,4,5)12G1-3-
PBI reported previously.10 In the temperature range from 50 to
100 ꢀC, the 1H NMR spectra in the aromatic region exhibit a low
but detectable mobility. After heating above 100 ꢀC, into the
Φhio phase, the 1H NMR spectra exhibit the same line narrowing
observed previously in the n = 12, m = 3,10 which was explained
with the help of computer simulation15 via a mechanism where
associated with the transition from the Φm,1 phase to the
isotropic phase (Figure 3b,c). The ΔH = 2.73 kcal/mol asso-
k
ciated with the Φm,1 Ài transition is 87% larger than the ΔH =
1.1 + 0.36 = 1.46 kcal/mol associated with the combined Φs‑ok to
Φhio to i transitions (Figure 3b).
The self-repairing process of the helical columns generated
from dimers and from tetramers of dendronized PBIs takes place
only upon annealing in their 2D Φh liquid crystalline phase.
Variable-temperature solid-state H NMR technique provided
additional insight into this self-repairing process, as detailed in
the next subsection.
io
1
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Figure 12. Variable-temperature 1H MAS spectra of (3,4,5)9G1-3-PBI recorded at 25 kHz MAS and 700 MHz 1H Larmor frequency in the heating (a)
and cooling (b) experiments performed with a rate of 1 ꢀC/min. The data from (b) were collected after 10 h of annealing at 110 ꢀC in the Φhio phase. The
aliphatic signals of the two phases are reduced by a factor 1/25 in intensity for better comparison.
the Φm,1k phase (Figure 12b). This result can be explained by a
slight temperature gradient throughout the sample, which can
transform parts of the sample into an isotropic melt. Note that in
another variable-temperature experiment (data not shown) the
1
overall H NMR spectra were similar to the data reported in
Figure 12, but the very narrow signal indicated by the red circle in
Figure 12b was not observed. Therefore, the variable-tempera-
ture solid-state 1H NMR data demonstrate that the formation of
k
io
the highly ordered Φm,1 phase after annealing into the Φh
phase is accompanied by a reduction of the molecular dynamics
of the outer alkyl chains and better πÀπ stacking. This complex
dynamics, in which dendronized PBI can leave the column,
rotate, and enter the same or another column,10 provides a route
io
k
to the Φh ÀΦm,1 slow transition and for the self-repairing
Figure 13. Schematic of the mechanism10 that mediates the slow
process.
io
k
Φh ÀΦm,1 transition and the self-repairing process established for
(3,4,5)9G1-3-PBI.
’ CONCLUSIONS
the molecules leave the supramolecular column, flip over, and re-
enter a column at a later time (Figure 13). The line narrowing of
A previous publication from our laboratory10 reported the dis-
covery of a dendronized PBI (3,4,5)12G1-3-PBI that self-assembles
into a complex helical column generated from tetramers containing a
pair of two molecules arranged side-by-side and another pair
in the next stratum of the column, turned upside-down, and
rotated around the column axis at an intratetramer angle that
is different from that of the intertetramer angle. In addition,
the intratetramer stacking distance in this column is 4.1 Å,
while the intertetramer distance is 3.5 Å. At high temperature,
io
the core proton around 7À8 ppm is particularly clear in the Φh
phase (Figure 12a). Therefore, the increased mobility, demon-
k
strated by the line narrowing of the 1H NMR spectra at the Φs‑o
to Φhio transition (Figure 12a), is characteristic both for the PBI
core and for the side groups.
After annealing the oriented sample of (3,4,5)9G1-3-PBI for
10 h at 110 ꢀC in the Φhio phase, the 1H NMR spectra collected
upon cooling in the Φm,1k phase (Figure 12b) do not exhibit the
temperature-dependent line narrowing observed in the first
heating (Figure 12a). In addition, the signals of the core protons
are shifted slightly toward low ppm values by ∼0.2À0.3 ppm.
This result indicate a better πÀπ stacking in the Φm,1k phase, in
excellent agreement with the changes of the stacking distances of
the dendronized PBIs established by XRD from alternating 3.5
and 4.1 Å distances in the Φs‑ok and Φhio phases to only a single
io
this helical column self-organizes in a 2D Φh phase that
represents the thermodynamic product, which is assembled by
a thermodynamically controlled process. At low temperature,
k
the same column self-organizes in a 3D Φs‑o phase via a
kinetically controlled process, although this phase represents
the thermodynamic product. The architecture of this complex
helical column, the structure of its 3D periodic array, and its
kinetically controlled self-organization are not ideal for the
design of supramolecular structures with high charge carrier
mobility, and, as expected, the mobility of electrons in this sample
is moderate.9g Therefore, a library of 11 (3,4,5)nG1-3PBIs with
n = 14À4 was synthesized and the supramolecular assemblies
k
3.5 Å distance in the 3D Φm,1 phase (Scheme 3b). The very
1
narrow signals observed around 1 ppm in the H NMR spectra
collected in the Φhio phase (marked by the red circle in Figure 12a)
were also observed after annealing on top of the broad signals of
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generated were analyzed in an attempt to discover the n value
that will transform the kinetically controlled self-assembly of the
Φs‑ok phase into a thermodynamically controlled process. These
experiments demonstrated that for n = 11, 10, 9, and 8, indeed
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io
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’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures with
b
complete spectral and structural analysis, and complete refs 10
and 12l. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
percec@sas.upenn.edu
’ ACKNOWLEDGMENT
Financial support by the National Science Foundation (DMR-
0548559, DMR-0520020, DMR-1066116, and DMS-0935165),
the Humboldt Foundation, and the P. Roy Vagelos Chair at Penn
is gratefully acknowledged. This work was also financially supported
by the German Research Foundation (DFG) through grant SFB
625, by the European FP7 Project NANOGOLD (grant 228455),
and by the WCU Program funded by the Ministry of Education,
Science, and Technology of Korea (R31-10013).
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