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Eine Zeitschrift der Gesellschaft Deutscher Chemiker
Akzeptierter Artikel
Titel: Living Supramolecular Polymerization of a Perylene Bisimide Dye
into Fluorescent J-Aggregates
Autoren: Wolfgang Wagner, Marius Wehner, Vladimir Stepanenko,
Soichiro Ogi, and Frank Würthner
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Für die AA-Fassung trägt der Autor die alleinige Verantwortung.
Zitierweise: Angew. Chem. Int. Ed. 10.1002/anie.201709307
Angew. Chem. 10.1002/ange.201709307
Link zur VoR:
Angewandte Chemie
Living Supramolecular Polymerization of a Perylene Bisimide Dye
into Fluorescent J-Aggregates
Abstract: Self-assembly of a new, in bay-position 1,7- dimethoxysubstituted perylene bisimide (PBI) organogelator affords nonfluorescent H-aggregates at fast cooling rates and fluorescent Jaggregates at slow cooling rates. Under properly adjusted conditions
the kinetically trapped “off-pathway” H-aggregates transform into the
thermodynamically favored J-aggregates, a process that can be
accelerated by the addition of J-aggregate seeds. Spectroscopic
studies revealed a subtle interplay of - interactions and intra- and
intermolecular hydrogen bonding for monomeric, H- and Jaggregated PBIs. Multiple polymerization cycles initiated from the
seed termini demonstrate the living character of this chain-growth
supramolecular polymerization process.
Although living covalent polymerization was introduced as
early as in the late 1950s,[1] and since then this research field
has undergone a comprehensive development, [2] its
supramolecular counterpart has emerged only recently.
Spearheaded by research on seeded “living” block copolymer
self-assembly from crystal facets by Manners, [3] Sugiyasu,
Takeuchi and coworkers demonstrated for the first time in 2014
the seed-initiated living supramolecular polymerization of a
single aggregate chain with a porphyrin dye.[4] This step marks
the logical advancement of a research field that has initially been
established based on thermodynamic considerations, i.e.
formation of equilibrium structures,[5] and only later on developed
toward kinetic control[6] leading to “off-pathway” products,[7] i.e.
out-of-equilibrium species.[8] The final step towards living
supramolecular polymerization has been achieved recently by
both the seed-induced[4,9] as well as the initiator moleculeinduced[10] approach, where either added seeds or properly
designed molecules function as initiators for the chain growth of
monomers into one-dimensional non-covalently bound molecular
A crucial requirement for the chain-growth supramolecular
polymerization is the retardation of the competing spontaneous
self-assembly of monomers which can be accomplished by
kinetically trapped “inactive” species.[3, 4, 8-10] We have recently
shown that such kinetically trapped species can be programed
by molecular design.[9a,b] Thus, simple perylene bisimide (PBI)
organogelator molecules bearing terminal amide groups are
kinetically trapped by intramolecular hydrogen bonding under
appropriate conditions either in unimolecular [9a] or “off-pathway”
aggregate[9b] states, and hence inactivated for spontaneous
supramolecular polymerization but active upon addition of seeds.
With a similar design, Miyajima and Aida demonstrated that the
spontaneous polymerization of a bowl-shaped corannulene
bearing multiple amide groups can be retarded by intramolecular
hydrogen bonding and its chain-growth polymerization can be
initiated by addition of a non-hydrogen bonded derivative.[10]
W. Wagner, M. Wehner, Dr. V. Stepanenko, Prof. Dr. F. Würthner
Universität Würzburg, Institut für Organische Chemie,
Am Hubland, 97074 Würzburg (Germany)
Dr. V. Stepanenko, Dr. S. Ogi, Prof. Dr. F. Würthner
Universität Würzburg, Center for Nanosystems Chemistry (CNC)
and Bavarian Polymer Institute (BPI)
Theodor-Boveri-Weg, 97074 Würzburg (Germany)
Supporting information for this article is given via a link at the end of
the document.
Chart 1. Chemical structures of the dimethoxy-substituted MeO-PBI,
[9a, 12]
reference PBI organogelator H-PBI
and benzamide 1.
A unique feature of “living” polymers is their active termini that
enable initiation of repeated growth cycles of monomers until the
“living” ends being terminated.[2] Until to-date, such repeated
cycles have been shown only for very few living supramolecular
polymerization systems,[4,10] that are, however, not yet exciting
from the functional point of view. Here we report the first
example of a PBI dye for which the multicycle living
supramolecular polymerization is successfully demonstrated and
a fluorescent J-aggregate[11] is obtained. Our present studies
revealed that the newly designed core-twisted PBI organogelator
MeO-PBI (Chart 1) self-assembles into kinetically trapped nonfluorescent H-type aggregates, which can be transformed into
thermodynamically favored fluorescent J-aggregates by seedinduced living polymerization. More significantly, the
polymerization cycle could be repeated for several times by
using the “living” polymer of the preceding cycle.
The PBI organogelator MeO-PBI was synthesized by
imidization of 1,7-dimethoxy-perylene-3,4:9,10-tetracarboxylic
acid bisanhydride with N-(2-aminoethyl)-3,4,5-tris(dodecyloxy)benzamide[12] in imidazole using Zn(OAc)2 as a catalyst. The
respective bisanhydride precursor was synthesized by a recently
developed copper-mediated cross-coupling reaction[13] from
tetrabutyl 1,7-dibromoperylene-3,4,9,10-tetracarboxylate. The
detailed synthetic procedure and characterization data are
provided in the Supporting Information.
The optical properties of the monomeric MeO-PBI were
investigated by UV/vis absorption and steady state fluorescence
spectroscopy in 1,1,2,2-tetrachloroethane (TCE). In this solvent
the absorption spectrum of MeO-PBI shows the characteristic
vibronic structure of bay-substituted PBIs with an absorption
λmax = 577 nm
(Figure S5),
which is
bathochromically shifted compared to that of the previously
reported core-unsubstituted H-PBI (λmax = 533 nm).[12] The
methoxy substituents at 1,7 bay-position lead to a twist of the
perylene core of 11° according to DFT calculations (Figure S4).
This distortion of the perylene core evokes a decrease of the
extinction coefficient of MeO-PBI ( = 6.0  104 M-1 cm-1 in TCE)
compared with the core-planar reference H-PBI ( = 8.1  104 M1
cm-1 in TCE).[12] The fluorescence spectrum of MeO-PBI shows
a maximum at 598 nm and resembles a mirror image shape of
the absorption spectrum (Figure S5). Interestingly, MeO-PBI
exhibits a remarkably higher fluorescence quantum yield of
fl = 0.68 than H-PBI (fl = 0.10) in TCE. The appreciably
intense fluorescence of the former might be explained by a less
electron-deficient character of the dimethoxy-substituted PBI
core, which makes the photoinduced electron transfer from the
electron-rich tridodecyloxyphenyl side groups to the core
The supramolecular polymerization of MeO-PBI was studied by
temperature-dependent UV/vis spectroscopy in a 2:1 (v/v)
solvent mixture of methylcyclohexane (MCH) and toluene (Tol)
with varying cooling/heating rates (Figure 1). Upon cooling the
monomer solution of MeO-PBI from 90 to 10 °C with a cooling
rate of 5 °C/min, the absorption maximum is hypsochromically
This article is protected by copyright. All rights reserved.
Accepted Manuscript
Wolfgang Wagner, Marius Wehner, Vladimir Stepanenko, Soichiro Ogi, and Frank Würthner*
Angewandte Chemie
Figure 1. Temperature-dependent absorption spectra of MeO-PBI (cT = 15  10 M) in MCH/Tol (2:1, v/v) upon cooling from 90 to 10 °C with a cooling rate of
5 °C/min (a) and with a slower cooling rate of 1 °C/min (b). The plots of the extinction coefficients (  at 560 nm against temperature for the respective cooling
(black dots) and heating (orange dots) processes are shown in the insets; cooling and heating rates are for (a) 5 °C/min and for (b) 1 °C/min. (c) Timedependent UV/vis absorption (solid lines) and emission spectra (dashed lines, λex = 487 nm) of the spontaneous transformation from the H-aggregate MeOPBIagg I (cT = 15  10-6 M) into the J-aggregate MeO-PBIagg II at 20 °C.
shifted with a loss of vibronic fine structure and concomitant
appearance of a weak transition at higher wavelength (620 nm).
These spectral features are typical for the formation of PBI Haggregates (denoted here as MeO-PBIagg I).[12] The plot of the
apparent extinction coefficients (ε) at the absorption maximum of
the monomer (560 nm) against the temperature reveals a
sigmoidal transition, which is indicative of an isodesmic
aggregation mechanism[5b] (Figure 1, inset). Surprisingly, upon
cooling the same solution from 90 to 10 °C with a slower cooling
rate of 1 °C/min the formation of a J-type aggregate (denoted as
MeO-PBIagg II) with a strongly bathochromically shifted
absorption maximum at 655 nm was observed (Figure 1b). The
plot of the ε values at 560 nm against the temperature for the
aggregation of MeO-PBIagg II shows, in contrast to that of MeOPBIagg I, a pronounced hysteresis of ca. 25 °C between the
thermodynamically controlled heating and the kinetically
controlled cooling process (Figure 1a,b insets).
The thermodynamically controlled non-sigmoidal (Figure 1b
inset) transition upon heating could be fitted by using the
cooperative nucleation-elongation model introduced by
Smulders et al.,[14] giving a critical temperature of Te = 359 K and
elongation enthalpy of ΔHe = -88.6 kJ mol-1 at cT = 15  10-6 M
(Figure S6, Table S1). Upon diluting the total concentration, the
elongation temperature Te decreased with a linear relationship
as the van’t Hoff plot illustrates (Figure S7). From this plot the
standard enthalpy (ΔH0) and entropy (ΔS0) were determined to
be -97.6 kJ mol-1 and -179.7 J mol-1 K-1, respectively; the former
value is in good agreement with ΔHe determined by fitting of the
temperature-dependent data with the cooperative model (Figure
The monitoring of a solution of the kinetically formed Haggregate MeO-PBIagg I (cT = 15  10-6 M) in MCH/Tol (2:1, v/v)
by time-dependent UV/vis spectroscopy at 20 °C revealed an
interesting transformation of the H-aggregate MeO-PBIagg I into
the J-aggregate MeO-PBIagg II (Figure 1c, solid lines). The timedependent absorption data clearly confirm that MeO-PBIagg I is a
kinetically metastable aggregate, which is completely
transformed into the thermodynamically favored MeO-PBIagg II
within a period of about 6 h. Repeating the measurements
revealed a faster transformation of MeO-PBIagg I into MeOPBIagg II with decreasing total concentration from 20  10-6 M to
10  10-6 M (Figure S8). This concentration-dependence
indicates that MeO-PBIagg I is an “off-pathway” (kinetically
trapped) aggregate.[4, 7a] The transformation of H- into Jaggregate caused a drastic change in fluorescence. While the
H-aggregate MeO-PBIagg I is nearly non-fluorescent, MeOPBIagg II is appreciably fluorescent with a quantum yield of
fl = 0.14 (Figure 1c, S12). Time-dependent fluorescence
spectra (Figure 1c, dashed lines) with an excitation at the
isosbestic point of MeO-PBIagg I and MeO-PBIagg II (λex = 487 nm)
reveal a transformation of the non-fluorescent H-aggregate
MeO-PBIagg I into the emissive J-aggregate MeO-PBIagg II with a
strong increase of the fluorescence. Such unique change in
fluorescence properties upon transformation of a kinetically
trapped H-aggregate into the thermodynamically stable Jaggregate has been rarely reported.[15]
The influence of hydrogen bonding for the stabilization of the
different aggregated species was investigated by Fouriertransform infrared (FT-IR) spectroscopy (for details see
Supporting Information and Figures S13, S14). These FT-IR
studies revealed that the aggregates of MeO-PBIagg II are formed
from monomers with extended conformation (denoted as MeOPBIopen) by intermolecular hydrogen bonding between the amide
groups, while MeO-PBIagg I consists of intramolecularly
hydrogen-bonded monomers MeO-PBIclosed that are selfassembled by π-π interactions between the PBI molecules
(Figure 2).
Figure 2. Schematic illustration of the equilibrium between the open
(MeO-PBIopen) and the closed conformation (MeO-PBIclosed) and the
formation of metastable H-aggregate MeO-PBIagg I and the
thermodynamically favored J-aggregate MeO-PBIagg II.
As discussed before, MeO-PBI shows an interesting interplay
between kinetically trapped state and thermodynamically stable
aggregate states. Therefore, we have explored the seedinduced living supramolecular polymerization of this PBI. For this
purpose, seeds of MeO-PBIagg II with different lengths were
produced by treating solutions of MeO-PBIagg II in an ultrasonic
bath for various time intervals. Increasing the sonication time
from 2 to 10 min leads to a decreased length of the seeds of
MeO-PBIagg II from 55-200 nm (2 min) to 45-170 nm (5 min) and
This article is protected by copyright. All rights reserved.
Accepted Manuscript
Angewandte Chemie
20-80 nm (10 min) as revealed by AFM (Supporting Information,
Figure S16). However, the morphology, i.e. the helical structure
of the individual strands of the seeds is similar to that of the
polymer (MeO-PBIagg II) and also the UV/vis spectrum of MeOPBIagg II-seed resembles that of freshly prepared MeO-PBIagg II.
The addition of MeO-PBIagg II-seed (ratio 1:100, sonication time:
10 min) induces the transformation of MeO-PBIagg I into MeOPBIagg II instantaneously (Figure S10), which indicates that
polymers with controlled length and size dispersion can be
obtained. Thus, the seeded polymerization occurs without a lag
time and the transformation rate is remarkably higher compared
with the spontaneous aggregation process. Stirring (400 rpm) of
MeO-PBIagg I solution is another option to accelerate the
transformation of MeO-PBIagg I into MeO-PBIagg II, however, only
after an induction period of ca. 30 min that is obviously needed
to afford the nucleation (Figure S10b).
Final proof for the living growth of the supramolecular polymer
chain of MeO-PBI from the seed termini was derived by UV/vis
absorption spectroscopy in MCH/Tol (2:1, v/v) applying the
experimental protocol schematically illustrated in Figure 3a and
S1. For this purpose, 1 equivalent (equiv.) of a freshly prepared
solution of the kinetically trapped MeO-PBIagg I in this solvent
mixture (cT = 15  10-6 M) was added to 1 equiv. of a solution of
MeO-PBIagg II-seed (sonication time 10 min) at 20 °C. Upon mixing
of these two stock solutions, the supramolecular polymerization
occurred instantaneously and completed after few minutes
because of the high fraction of “active” seeds that function as
initiators. Subsequently, 1 equiv. of the supramolecular polymer
solution obtained after the first cycle was removed to keep the
overall volume of the sample constant. For a second cycle,
another 1 equiv. of MeO-PBIagg I was added to the remaining
polymer solution (1 equiv.), which is now acting as the seed for
the subsequent polymerization cycle. This procedure was
repeated for another three cycles. With this experiment the living
supramolecular polymerization process could be followed very
easily by monitoring the apparent absorbance at 655 nm
(absorption maximum of MeO-PBIagg II) during the whole
experiment and plotting the absorbance data against the time
(Figure 3b). After the first addition of MeO-PBIagg I the apparent
absorbance at 655 nm drops to 0.22 and subsequently a very
fast seeded supramolecular polymerization process occurs,
accompanied by an increase of the absorption nearly reaching
the initial value of 0.33. This observation confirms the
transformation of the kinetically trapped aggregates MeOPBIagg I into a “first generation” thermodynamically stable
polymer MeO-PBIagg II. The obtained polymers after the first
cycle can now act as the nuclei for the second cycle and so on.
Interestingly, the rate of the polymerization into MeO-PBIagg II
gets slower with increasing cycle number because the number
of “active termini” of the seed is reduced by half after each cycle.
The initial slopes of the graphs determined by fitting the
respective first data points with a linear relationship are
supportive of this conclusion. The values of the initial slopes can
be fitted by the exponential equation y = 0.0303 min-1  (1/2)n-1
with the cycle number n (Figure S11), clearly showing that the
values of the initial slopes are reduced by half for each cycle.
Concomitantly, the fiber length should increase which is
confirmed by atomic force microscopy (AFM). Indeed, AFM
images of the samples prepared by spin-coating of the solutions
of the polymers obtained after each cycle (Figure 3c-e, S17)
show a successive increase of polymer length from 35-130 nm
(1st cycle) to 50-300 nm (2nd cycle), 150-600 nm (3rd cycle) and
extended µm long polymer networks (4th and 5th cycles). These
remarkable results clearly prove that the polymers MeO-PBIagg II
can indeed act as seeds for the kinetically trapped MeO-PBIagg I
and that the formed polymers stay unchanged during the time
course of experiments. Our highly interesting results discussed
above clearly revealed the living character by chain-growth
mechanism from the fiber termini for this supramolecular
polymerization of MeO-PBI through a precise kinetic control of
the aggregation process.
In conclusion, we have presented here the first example for a
living supramolecular polymerization leading to a fluorescent Jaggregate. This progress became possible by the molecular
design of a slightly core-twisted PBI that self-assembles
preferentially into metastable “off-pathway” H-aggregates (MeOPBIagg I) that could be transformed into thermodynamically more
stable fluorescent J-aggregates (MeO-PBIagg II) by seed-induced
Figure 3. (a) Schematic illustration of a stepwise living supramolecular polymerization process of MeO-PBI. (b) Time course of the apparent absorbance at
655 nm (λmax of MeO-PBIagg II) during the living polymerization of MeO-PBI. The grey areas indicate the time for opening the sample compartment to add the
respective equivalent of MeO-PBIagg I. AFM height images of the supramolecular polymers (MeO-PBIagg II) obtained after the first (c), second (d) and fourth cycle
(e) prepared by spin-coating of the respective solutions on HOPG. The Z scale is 12 nm (c, d, e).
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Accepted Manuscript
Angewandte Chemie
living supramolecular polymerization. The experimental protocol
developed for the living polymerization has potential for the
construction of interesting functional supramolecular polymers
and even supramolecular block copolymers that may serve as
highly promising architectures for the investigation of exciton
and charge carrier transport phenomena on the nanoscale.
We thank the Bavarian State Ministry of Education, Science and
the Arts for generous support for the newly established Key
Laboratory for Supramolecular Polymers at the Center for
Nanosystems Chemistry.
Keywords: J-aggregates • Living polymerization • Perylene
dyes/pigments • Self-assembly • Supramolecular chemistry
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This article is protected by copyright. All rights reserved.
Accepted Manuscript
Angewandte Chemie
Wolfgang Wagner, Marius Wehner,
Vladimir Stepanenko, Soichiro Ogi and
Frank Würthner*
Page No. – Page No.
Living Supramolecular
Polymerization of a Perylene Bisimide
Dye into Fluorescent J-Aggregates
Accepted Manuscript
Living supramolecular
polymerization. First example of a
perylene bisimide (PBI) based
multicycle living polymerization
system is reported. The baysubstituted PBI organogelator forms
“off-pathway” H-aggregates that are
transformed into thermodynamically
favored fluorescent J-aggregates by a
living seeded polymerization.
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