Influence of Ester versus Amide Linkers on the Supramolecular Polymerization Mechanisms of Planar BODIPY Dyes

Article abstract of DOI:10.1002/chem.201602592

We report the H-type supramolecular polymerization of two new hydrophobic BODIPY derivatives equipped with ester and amide linkages. Whereas the ester-containing BODIPY derivative undergoes an isodesmic supramolecular polymerization in which the monomers are parallel-oriented, the replacement of the ester by amide groups leads to a highly cooperative self-assembly process into H-type aggregates with a rotational displacement of the dye molecules within the stack. The dye organization imposed by simultaneous π–π and hydrogen bonding interactions is the driving force for the cooperative supramolecular polymerization, whereas the absence of additional hydrogen bonds for the ester-containing moiety does not suffice to induce cooperative phenomena.

Full text of DOI:10.1002/chem.201602592

DOI: 10.1002/chem.201602592
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Supramolecular Chemistry |Hot Paper|
Influence of Ester versus Amide Linkers on the Supramolecular
Polymerization Mechanisms of Planar BODIPY Dyes
Alexander Rçdle,[a, b] Benedikt Ritschel,[b] Christian Mꢀck-Lichtenfeld,[a]
Vladimir Stepanenko,[b] and Gustavo Fernꢁndez*[a, b]
Abstract: We report the H-type supramolecular polymeri-
zation of two new hydrophobic BODIPY derivatives
equipped with ester and amide linkages. Whereas the ester-
containing BODIPY derivative undergoes an isodesmic supra-
molecular polymerization in which the monomers are paral-
lel-oriented, the replacement of the ester by amide groups
leads to a highly cooperative self-assembly process into H-
type aggregates with a rotational displacement of the dye
molecules within the stack. The dye organization imposed
by simultaneous p–p and hydrogen bonding interactions is
the driving force for the cooperative supramolecular poly-
merization, whereas the absence of additional hydrogen
bonds for the ester-containing moiety does not suffice to
induce cooperative phenomena.
tence of a sterically hindered PtII center, a clear transition from
J- to H-type aggregates is observed when replacing the ester
by the amide moiety, thus showing the potential of these
linkers.
Introduction
The phenomenon of self-assembly has been extensively stud-
ied over the last decades with the main goal of providing
access to functional materials.[1] The molecular organization
correlates with the specific intermolecular interactions during
the supramolecular polymerization process and is more ame-
nable to detailed research when using one-dimensional sys-
tems.[2] In this regard, hierarchical supramolecular structures
that follow a cooperative self-assembly mechanism are desira-
ble due to their higher degree of internal order compared to
non-cooperative counterparts.[3] The exploitation of coopera-
tive hydrogen bonds based on functional groups such as
ureas,[4] bisureas,[5] amides,[6] bisamides,[7] melamines[8] and pep-
tides[9] often reinforced by p–p interactions[10] is a well-known
strategy to fine tune the aggregation modes and in turn, the
degree of order in these systems. In sharp contrast, the direct
influence of ester linkages on supramolecular polymerization
mechanisms remain thus far unexplored, despite the fact that
ester functionalities are commonly used, synthetically accessi-
ble building blocks in self-assembled structures[11] and liquid
crystals.[12] Recently, the influence of the linking group (ester
vs. amide) on the self-assembly and gelation of trans-bis(pyri-
dine) dichloroplatinum(II) complexes has been studied.[13] Al-
though the molecular packing is strongly biased by the exis-
We envisaged that a planar p-system without any sterically
demanding groups would represent an ideal building block to
directly analyze the influence of ester versus amide groups on
aggregation mechanisms. To this end, we have selected a 4,4-
difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)[14] core not
only for its small size and planarity but also due to its well-
known ability to self-assemble in an H-[15] or J-type[16] fashion,
which can be readily investigated by common spectroscopic
methods.
For instance, our group has recently described the self-as-
sembly of rod-like hydrophobic[17] and amphiphilic BODIPY
dyes[18] as well as the ability of the latter to encapsulate hydro-
phobic dye molecules in aqueous media.[18] The self-assembly
of these systems is primarily driven by p–p interactions of the
dipyrromethane core, leading in most cases to an isodesmic
(non-cooperative) supramolecular polymerization due to the
absence of supportive noncovalent forces. In this work, we ex-
amine whether the self-assembly mechanism of BODIPY dyes
can be tuned by introducing ester or amide groups that can
eventually reinforce the stacking of the BODIPY units by
additional noncovalent interactions.
[a] A. Rçdle, Dr. C. Mꢀck-Lichtenfeld, Prof. Dr. G. Fernꢁndez
Organisch-Chemisches Institut, Westfꢂlische Wilhelms-Universitꢂt Mꢀnster
Corrensstraße 40, 48149 Mꢀnster (Germany)
Results and Discussion
The target ester- (1; Scheme 1) and amide-containing (2)
BODIPY derivatives are readily obtained in moderate to good
yields by modified literature procedures.[17,19] Previously de-
scribed 4-iodophenyl-3,4,5-tris(dodecyloxy)benzoate[19d] and
3,4,5-tris(dodecyloxy)-N-(4-iodophenyl)benzamide[19c] were used
as starting materials for the synthesis of compounds 5a and
5b through a Sonogashira reaction in the presence of trime-
E-mail: fernandg@uni-muenster.de
[b] A. Rçdle, B. Ritschel, Dr. V. Stepanenko, Prof. Dr. G. Fernꢁndez
Institut fꢀr Organische Chemie and Center for Nanosystems Chemistry
Julius-Maximilians-Universitꢂt Wꢀrzburg
Am Hubland, 97074 Wꢀrzburg (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201602592.
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Scheme 1. Synthesis route towards BODIPY compounds 1 and 2.
thylsilylacetylene (TMS). Further deprotection of the TMS
group was carried out following two different procedures. The
amide derivative was converted to 4b by using K2CO3 in a mix-
ture of THF/MeOH, whereas for the ester compound less nucle-
ophilic conditions were chosen, as a result of the lower stabili-
ty of the ester functionality, using tetra-n-butylammonium fluo-
ride (TBAF) in THF yielding 4a. Finally, a Sonogashira reaction
using CuI, Pd(PPh3)4 in NEt3 with the diiodo BODIPY derivative
3[17] was carried out to synthesize the final compounds 1 and
1
2. Both molecules were fully characterized by H/13C NMR spec-
troscopy, HRMS and elemental analysis.
Initial comparison between the self-assembly behavior of
1 and 2 was provided by complementary UV/Vis and fluores-
cence studies. Nevertheless, due to the differing nature of the
linking groups (ester vs. amide) both molecules (1 and 2) show
differences in their solubility, solvent-dependent UV/Vis and
fluorescence spectra. Figure 1a shows the absorption spectra
of 1 in different solvents (c=1ꢃ10ꢀ4 m) at room temperature
(RT).
Figure 1. Solvent-dependent fluorescence studies of: a) 1 (lex =500 nm,
c=1ꢃ10ꢀ5 m), and c) 2 (lex =440 nm, c=1ꢃ10ꢀ5 m) at RT; and solvent-
dependent UV/Vis spectroscopy of: b) 1 (c=1ꢃ10ꢀ4 m), and d) 2
(c=1ꢃ10ꢀ5 m).
These experiments show minor spectral changes exhibiting
a collective maximum at ꢁ569 nm, which is assigned to the
S0!S1 (p–p*) transition of the BODIPY chromophore, whereas
the S0!S2 transition appears in the region around 400 nm
(Figure S11 in the Supporting Information).[20] By contrast, the
absorption spectra in methylcyclohexane (MCH) (Figure 1a)
and other selected aliphatic solvents, such as cyclohexane and
n-hexane (Figure S11), show a blue-shifted shoulder at 539 nm
that appears in addition to the maximum at 567 nm. These ob-
servations suggest the initial stages of an H-type aggregation
phenomenon that takes place exclusively in aliphatic solvents
(cyclohexane, n-hexane and MCH) from among all investigated
solvents (Figure S11). Due to a comparable self-assembly be-
havior in these media, we have restricted ourselves to MCH for
further studies due to its higher solubility and boiling point
compared to hexane and cyclohexane. In analogy to UV/Vis
spectroscopy, solvent-dependent fluorescence experiments of
1 were carried out at RT (Figure 1b). The curve progression,
relative intensities as well as the position of the maxima
(593 nm) are similar in most investigated solvents. A somewhat
different behavior is observed in a selected nonpolar solvent
(MCH) at a slightly higher concentration (c=10ꢀ4 m) wherein
a red-shift to 614 nm and a decrease in the fluorescence inten-
sity can be noticed (Figure 1b). Slightly different optical prop-
erties are observed for the amide-substituted BODIPY deriva-
tive 2. For instance, the majority of the absorption spectra fea-
ture a common maximum at 573 nm (Figure 1c). In contrast,
a hypsochromic shift (Dl=34 nm) of the absorption spectrum
in MCH and cyclohexane can be noticed (Figure 1c and Fig-
ure S14). This effect is even more pronounced in hexane (Fig-
ure S14), however due to the limited solubility of 2 in this
medium, this solvent was not considered for further investiga-
tions. These findings are in line with solvent-dependent fluo-
rescence studies. The majority of the fluorescence spectra fea-
ture a common maximum at 613 nm. In contrast, a bathochro-
mic shift (Dl=34 nm) of the absorption spectrum in MCH and
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a dramatically reduced emission intensity (ꢁ90%) can be no-
ticed (Figure 1d). The observations extracted from absorption
and emission studies indicate a supramolecular polymerization
with an H-type excitonic coupling of the dye molecules.[21] An
interesting spectral feature that is worth mentioning is the ap-
pearance of a red-shifted shoulder at 620 nm in the aggregate
spectrum of the amide-containing BODIPY dye 2 (Figure 1c)
that is absent in the aggregate spectrum of the ester-contain-
ing system 1 even at millimolar concentration (Figure 2a). This
appreciable difference points to a different dye arrangement in
both systems.
To investigate the process of self-aggregation in detail, tem-
perature- and concentration-dependent spectroscopic meas-
urements are powerful tools. Due to the higher solubility and
reduced aggregation propensity of 1, its supramolecular poly-
merization was analyzed by concentration-dependent UV/Vis
and fluorescence experiments, whereas related temperature-
dependent investigations are necessary for 2 in order to identi-
fy the monomer species. Figure 2a depicts the concentration-
dependent UV/Vis studies of 1 in MCH between 5.09ꢃ10ꢀ3
and 2.20ꢃ10ꢀ6 m at RT. On increasing the concentration, the
previously described monomer band (569 nm) decays in favor
of a transition at 539 nm corresponding to the self-assembled
species. The isosbestic points at 548 and 603 nm indicate an
equilibrium between the monomeric and aggregated species.
In order to inspect the supramolecular polymerization mecha-
nism, the molar absorptivity at 569 nm of this transition pro-
cess was monitored against concentration (Figure 2c). The re-
sulting sigmoidal curve can be suitably fitted to the concentra-
tion-dependent isodesmic aggregation model (Figure 2c),[1i]
obtaining a binding constant K of 6.6ꢃ103 mꢀ1 (Table 1). The
concentration-dependent fluorescence studies of 1 in MCH
(Figure 2b and Figure S13 in the Supporting Information)
show that an increase in concentration (1ꢃ10ꢀ5–1ꢃ10ꢀ3 m) in-
duces a steady red shift and decrease in the emission intensity,
which is in accordance with the results obtained by UV/Vis ex-
periments and demonstrates a face-to-face H-type stacking of
the dyes within the aggregate.
Figure 2. a) Concentration-dependent UV/Vis studies of 1 (5.09ꢃ10ꢀ3 to
2.20ꢃ10ꢀ6 m, MCH), and b) concentration-dependent fluorescence spectros-
copy of 1 (1ꢃ10ꢀ6–1ꢃ10ꢀ3 m, MCH) at RT. c) Fit of the data of the absorption
experiments of 1 to the isodesmic model (aagg vs. log[c], 569 nm). d) Tem-
perature-dependent UV/Vis experiments of 2 (c=1ꢃ10ꢀ5 m, MCH), and
e) temperature-dependent fluorescence spectroscopy of 2 (c=1ꢃ10ꢀ5 m,
MCH) between 365 and 285 K. f) Cooling curves (aagg vs. T) obtained by
monitoring the absorption of 2 at 576 nm versus T at different concen-
trations (5ꢃ10ꢀ6–3ꢃ10ꢀ5 m) and fits to the nucleation–elongation model.
The arrows in (a) and (d) indicate the spectral changes with increasing
concentration and decreasing temperature, respectively.
UV/Vis absorption spectra of 2 in MCH at a concentration of
1ꢃ10ꢀ5 m. On cooling, the depletion of the absorption maxi-
mum at 576 nm is concomitant with the rise of a blue-shifted
aggregate band at 540 nm (Figure 2d). The existence of two
isosbestic points at 548 and 616 nm is indicative of an equilib-
rium between monomeric and H-type species. Temperature-de-
pendent fluorescence spectroscopy of 2 (c=1ꢃ10ꢀ5 m) in MCH
(Figure 2e) shows both a red-shift and quenching of the emis-
On the other hand, the aggregation behavior of 2 is slightly
different. For this dye, temperature-dependent studies ap-
peared to be the most suitable experiments for analyzing in
detail the spectral changes, as dilution experiments are not
sufficient for reaching a fully monomeric state. Figure 2d
shows the impact of a temperature decrease (90–258C) on the
Table 1. Thermodynamic parameters associated to the self-assembly of 1 and 2 in MCH.[a]
Compound
l [nm]
K [mꢀ1
]
ꢀDG298 [kJmolꢀ1
]
1
569
6579.7ꢂ257.7
21.8
C(2) [m]
DH0
DH0
[kJmolꢀ1
DS0
[kJmolꢀ1 Kꢀ1
Te
[K]
Knucl
[mꢀ1
Kel
[mꢀ1
s
nucl
[kJmolꢀ1
]
]
]
]
]
1.0ꢃ10ꢀ5
ꢀ15.0ꢂ0.2
ꢀ85.3ꢂ0.5
ꢀ0.1516ꢂ0.0014
344.8ꢂ0.07
5.3ꢃ102
1.0ꢃ105
5.3ꢃ10ꢀ3
[a] K=equilibrium constant; ꢀDG298 =standard Gibbs free energy; DH0nucl =nucleation enthalpy; DH0 =enthalpy difference; DS0 =entropy difference;
Te =elongation temperature; Knucl =equilibrium constant of the nucleation process; Kel =equilibrium constant of the elongation process; s=degree of co-
operativity (Knucl/Kel).
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sion spectra upon cooling from 908C to RT, which supports
the formation of an H-type supramolecular polymer.
ure S20 in the Supporting Information). By monitoring chemi-
cal shifts of proton HA versus concentration, a sigmoidal aggre-
gation curve was observed and fitted to the isodesmic model
(Figure S21).
In order to understand the specific process in more detail,
cooling curves of 2 (cooling rate=1 Kminꢀ1) extracted from
temperature-dependent UV/Vis studies in MCH at different
concentrations were measured, as shown in Figure 2 f. Each
cooling curve could be perfectly fitted to the cooperative nu-
cleation–elongation model.[22] The thermodynamic parameters
are shown in Table 1 and Table S1 in the Supporting Informa-
tion. The high binding constants of the supramolecular elonga-
tion step (up to 2.0ꢃ105 mꢀ1), which is around three times
higher than the K value of 1, along with the low s values (be-
tween 4.8ꢃ10ꢀ3 and 5.7ꢃ10ꢀ3) correspond to a cooperative
self-aggregation process. By comparing the self-assembly be-
havior as well as the supramolecular polymerization mecha-
nism, one can notice significant differences between 1 and 2.
In order to understand this dissimilarity, the reason for it has to
lie on the molecular level, since the linking group is the only
difference between both molecules. An amide group is, in con-
trast to the ester linker, both a hydrogen bond acceptor and
donor, which provides an additional intermolecular force. The
UV/Vis spectra of 2 are reminiscent of the H-type aggregates
reported by the Wꢀrthner group[23] and us[18] in terms of
a blue-shifted transition as well as a red-shifted shoulder rela-
tive to the monomer spectrum. The blue-shifted peak at
520 nm indicates a face-to-face H-type stacking whereas the
red-shifted shoulder at 620 nm correlates with a rotational dis-
placement of the BODIPY chromophores in the stack.[21] Thus,
to provide intermolecular hydrogen bonds between the amide
groups, the molecules undergo a rotational face-to-face stack-
ing on the account of the grade of the p–p stacking’s overlap.
In sharp contrast ester-containing BODIPY 1 shows also a blue-
shift in the spectra but no red-shifted shoulder, which indicates
that the rotational displacement becomes less prominent for
this system. Ultimately, the additional intermolecular force as-
sisting hydrogen bonding tunes the isodesmic to a cooperative
H-type self-aggregation process.
We next attempted to analyze the influence of temperature
on the chemical shifts of 2 in [D14]MCH, as it was previously
observed that temperature-dependent spectroscopic studies
worked well for this system. However, the stronger tendency
of 2 to self-assemble compared to 1 leads to a severe broaden-
ing of the proton NMR signals even at elevated temperatures.
Thus, the selection of a more appropriate solvent mixture was
required in order to monitor the self-assembly of 2 through
NMR spectroscopy experiments. CD2Cl2 was the first solvent of
choice, however, the good solvation of the units of 2 in this
solvent, results in minor changes in the chemical shifts upon
increasing concentration. In order to find the right conditions
providing the balance between both a strong tendency to ag-
gregate and a sufficient solubility, we selected CCl4 as a “poor
solvent” in combination with CD2Cl2. Previous UV/Vis and fluo-
rescence results (Figure 1c and d) had suggested the initial
stages of a self-assembly process in this solvent. However, this
was not as strong as in hydrocarbon solvents. By mixing
CD2Cl2 and CCl4 in different ratios, we found that the solvent
mixture CCl4/CD2Cl2 (9:1, v/v) was the most appropriate one in
To investigate the participating intermolecular forces during
the aggregation process in more detail, concentration-depen-
1
dent H NMR measurements were recorded. A concentration-
dependent shift of the proton signals in the NMR spectrum in-
dicates participation of the very same during the supramolec-
ular polymerization process, caused by a change of the spatial
environment of the particular protons. For instance, the shield-
ing of the aromatic protons is commonly attributed to the p–p
stacking of the aromatic planes whereas hydrogen-bond inter-
actions usually cause a downfield shift of the involved proton
NMR signals.[24] For the target systems 1 and 2, concentration-
dependent 1H NMR measurements were recorded (Figure 3).
Upon increasing the concentration of 1 ([D14]MCH, Fig-
ure 3a), both proton signals of the aromatic plane (HA, HB and
HC) and those of the methyl groups of the BODIPY core (HD, HE
and HF) undergo upfield shifts, thus supporting p–p stacking
of the molecules (for proton labeling see Scheme 1; capital let-
ters 1, small letters 2). A similar shielding effect upon cooling
a solution of 1 from 343 K to RT was observed by tempera-
1
Figure 3. Concentration-dependent H NMR spectroscopy of: a) 1 (400 MHz,
1
ture-dependent H NMR experiments (17.5 mm, 600 MHz; Fig-
298 K, [D14]MCH), and b) 2 (500 MHz, 298 K, CCl4/CD2Cl2 9:1, v/v).
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terms of both sufficiently sharp NMR signals and significant
chemical shifts upon aggregation (Figure 3b). Similar to 1 in
[D14]MCH, the upfield shifts of the protons of both the aromat-
ic rings (Ha, Hc and Hd) and BODIPY core (He, Hf and Hg) with in-
creasing concentration suggest the presence of strong p–p
stacking interactions of the molecules. In addition, the down-
field shift of the amide proton (Hb) with increasing concentra-
tion is a clear indication of hydrogen bonding during the
supramolecular polymerization. These results are in agreement
with a cooperative self-assembly, as previously shown by
UV/Vis and fluorescence studies.
Quantum chemical calculations (PBEh-3c/HF-3c+COSMO-
RS)[25] were performed to better understand the influence of
the linkers on the molecular organization. For this, monomer,
dimer and tetramer structures for BODIPY derivatives of 1 and
2 with peripheral OC12H25 groups omitted (1’/2’) were opti-
mized. Dimerization of 1’ and 2’ gave free energies of aggrega-
tion lower than experimentally determined (ꢀ0.3 kcalmolꢀ1 for
ester 1’ and ꢀ1.6 kcalmolꢀ1 for amide 2’), indicating that the
omitted alkoxy groups provide additional stabilization of the
stacks of 1 and 2. The formation of tetramers from 1’ is pre-
dicted to be endothermic (+5.5 kcalmolꢀ1), but exothermic
from 2’ (ꢀ2.6 kcalmolꢀ1). Clearly, the amide hydrogen bonds
provide additional (enthalpic) stabilization to the p-stack of 2’
over 1’. The conformations of both tetramers (1’)4 and (2’)4
show a tilting of the peripheral aromatic groups upon oligo-
merization, which is more pronounced for one side of the
stack than for the other one (Figure 4, and Figures S27 and
S28 in the Supporting Information). Interestingly, this rotational
displacement induces a larger helical pitch for the amide (2’)4
than for the ester tetramer (1’)4, most likely to facilitate an op-
timal conformation of the amide groups for hydrogen bond-
ing. On increasing the stack length, subsequent torsions of the
aromatic cores induce a progressive helicity in the stack, which
is in agreement with previous spectroscopic investigations.
The molecular lengths of 1’ and 2’ deduced by the calcula-
tions (3.5 nm) are in very good agreement with the diameter
of the supramolecular polymers observed by AFM (Figure 5).
These studies for aggregate solutions of both 1 (1ꢃ10ꢀ3 m)
and 2 (1ꢃ10ꢀ4 m) in MCH on highly oriented pyrolytic graphite
(HOPG) reveal the formation of fiber-like structures with a regu-
lar diameter of 3.6 nm and lengths of approximately 100 nm.
As the length of the molecular core is only slightly smaller
than the average diameter of the aggregates, a strong inter-
digitation of the dodecyl chains between neighboring fibers
should exist, which is apparent in Figure 5.
Figure 4. Optimized (HF-3c) conformation of: a) (1’)4, and b) (2’)4. Free
energies of aggregation (DG298 in cyclohexane) are +5.5 kcalmolꢀ1 for 1’
and ꢀ2.6 kcalmolꢀ1 for 2’.
Figure 5. AFM images obtained by spin-coating of an aggregated solution
of: a,b) 1, and c,d) 2 on HOPG.
absence of hydrogen bonding in the ester derivative induces
a non-cooperative parallel dye arrangement. Our results show
that the interplay of various types of orthogonal noncovalent
interactions is an efficient method to create ordered supra-
molecular polymers that are stabilized by cooperative effects.
Our current efforts are focused on exploiting cooperative non-
covalent forces in aqueous medium towards fluorescent
BODIPY dye aggregates with potential application as drug
delivery vehicles.
Conclusions
To sum up, by comparing the self-assembly of two new hydro-
phobic BODIPY dyes that only differ in the linking group (ester
vs. amide) we have shed light on the influence of these groups
on the dye arrangement and, in turn, on the supramolecular
polymerization mechanism. Although both dyes self-assemble
in an H-type fashion, the participation of cooperative p–p and
hydrogen bonding interactions impose a rotationally displaced
dye organization for the amide-containing dye, whereas the
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[9] H. Frisch, J. P. Unsleber, D. Lꢀdeker, M. Peterlechner, G. Brunklaus, M.
Waller, P. Besenius, Angew. Chem. Int. Ed. 2013, 52, 10097–10101;
Angew. Chem. 2013, 125, 10282–10287.
[10] C. Rest, R. Kandanelli, G. Fernꢁndez, Chem. Soc. Rev. 2015, 44, 2543–
2572.
Experimental Section
For detailed synthesis and characterization of the new compounds
and target BODIPYs 1 and 2, methods, additional experiments and
images, see the Supporting Information.
[11] a) D. Sivaramakrishna, M. J. Swamy, Langmuir 2015, 31, 9546–9556;
b) M. Dirany, V. Ayzac, B. Isare, M. Raynal, L. Bouteiller, Langmuir 2015,
31, 11443–11451; c) C. Kulkarni, K. K. Bejagam, S. P. Senanayak, K. S. Nar-
ayan, S. Balasubramanian, S. J. George, J. Am. Chem. Soc. 2015, 137,
3924–3932; d) A. Ajayaghosh, V. K. Praveen, S. Srinivasan, R. Varghese,
Adv. Mater. 2007, 19, 411–415.
Acknowledgements
We thank the Alexander von Humboldt Foundation for
[12] T. Kato, N. Mizoshita, K. Kishimoto, Angew. Chem. Int. Ed. 2006, 45, 38–
68; Angew. Chem. 2006, 118, 44–74.
financial support (Sofja Kovalevskaja Award).
[13] M. Chen, C. Wei, X. Wu, M. Khan, N. Huang, G. Zhang, L. Li, Chem. Eur. J.
2015, 21, 4213–4217.
Keywords: BODIPY dyes
·
cooperativity
·
non-covalent
[14] A. Treibs, F.-H- Kreuzer, Liebigs Ann. Chem. 1968, 718, 208–223.
[15] a) L. Yang, G. Fan, X. Ren, L. Zhao, J. Wang, Z. Chen, Phys. Chem. Chem.
Phys. 2015, 17, 9167–9172; b) H. Liu, J. Mack, Q. Guo, H. Lu, N. Kobaya-
shi, Z. Shen, Chem. Commun. 2011, 47, 12092–12094; c) Y. Tokoro, A.
Nagai, Y. Chujo, Tetrahedron Lett. 2010, 51, 3451–3454.
[16] a) S. Choi, J. Bouffard, Y. Kim, Chem. Sci. 2014, 5, 751–755; b) T. T. Vu, M.
Dvorko, E. Y. Schmidt, J.-F. Audibert, P. Retailleau, B. A. Trofimov, R. B.
Pansu, G. Clavier, R. Mꢅallet-Renault, J. Phys. Chem. C 2013, 117, 5373–
5385; c) G. Fan, Y.-X. Lin, L. Yang, F.-P. Gao, Y.-X. Zhao, Z.-Y. Qiao, Q.
Zhao, Y.-S. Fan, Z. Chen, H. Wang, Chem. Commun. 2015, 51, 12447–
12450; d) F. Camerel, L. Bonardi, M. Schmutz, R. Ziessel, J. Am. Chem.
Soc. 2006, 128, 4548–4549.
interactions · self-assembly · supramolecular chemistry
[1] a) A. Das, S. Ghosh, Chem. Commun. 2016, 52, 6860–6872; b) H. Frisch,
P. Besenius, Macromol. Rapid Commun. 2015, 36, 346–363; c) A. S. Tayi,
A. Kaeser, M. Matsumoto, T. Aida, S. I. Stupp, Nat. Chem. 2015, 7, 281–
294; d) S. Yagai, Bull. Chem. Soc. Jpn. 2015, 88, 28–58; e) R. D. Mukho-
padhyay, A. Ajayaghosh, Science 2015, 349, 241–242; f) S. S. Babu, V. K.
Praveen, A. Ajayaghosh, Chem. Rev. 2014, 114, 1973–2129; g) E. Busser-
on, Y. Ruff, E. Moulin, N. Giuseppone, Nanoscale 2013, 5, 7098–7140;
h) C. Kulkarni, S. Balasubramanian, S. J. George, ChemPhysChem 2013,
14, 661–673; i) T. F. A. de Greef, M. M. J. Smulders, M. Wolffs, A. P. H. J.
Schenning, R. P. Sijbesma, E. W. Meijer, Chem. Rev. 2009, 109, 5687–
5754.
[2] a) P. A. Korevaar, S. J. George, A. J. Markvoort, M. M. J. Smulders, P. A. J.
Hilbers, A. P. H. J. Schenning, E. W. Meijer, Nature 2012, 481, 492–496;
b) R. Thirumalai, R. D. Mukhopadhyay, V. K. Praveen, A. Ajayaghosh, Sci.
Rep. 2015, 5, 9842.
[3] T. Aida, E. W. Meijer, S. I. Stupp, Science 2012, 335, 813–817.
[4] H. Kar, S. Ghosh, Chem. Commun. 2014, 50, 1064–1066.
[5] a) B. Isare, M. Linares, L. Zargarian, S. Fermandjian, M. Miura, S. Motoha-
shi, N. Vanthuyne, R. Lazzaroni, L. Bouteiller, Chem. Eur. J. 2010, 16,
173–177; b) M. Roman, C. Cannizo, T. Pinault, B. Isare, B. Andrioletti, P.
van der Schoot, L. Bouteiller, J. Am. Chem. Soc. 2010, 132, 16818–16824.
[6] a) A. Sikder, B. Ghosh, S. Chakraborty, A. Paul, S. Ghosh, Chem. Eur. J.
2016, 22, 1908–1913; b) M. Yamauchi, T. Ohba, T. Karatsu, S. Yagai, Nat.
Commun. 2015, 6, 8936; c) H. Kar, D. W. Gehrig, F. Laquai, S. Ghosh,
Nanoscale 2015, 7, 6729–6736; d) J. S. Valera, J. Calbo, R. Gꢄmez, E.
Orti, L. Sꢁnchez, Chem. Commun. 2015, 51, 10142–10145; e) S. S. Babu,
V. K. Praveen, K. K. Kartha, S. Mahesh, A. Ajayaghosh, Chem. Asian J.
2014, 9, 1830–1840; f) J. M. Malicka, A. Sandeep, F. Monti, E. Bandini, M.
Gazzano, C. Ranjith, V. K. Praveen, A. Ajayaghosh, N. Armaroli, Chem.
Eur. J. 2013, 19, 12991–13001; g) A. Das, M. R. Molla, B. Maity, D. Koley,
S. Ghosh, Chem. Eur. J. 2012, 18, 9849–9859; h) M. R. Molla, A. Das, S.
Ghosh, Chem. Eur. J. 2010, 16, 10084–10093.
[17] A. Florian, M. J. Mayoral, V. Stepanenko, G. Fernꢁndez, Chem. Eur. J.
2012, 18, 14957–14961.
[18] N. K. Allampally, A. Florian, M. J. Mayoral, C. Rest, V. Stepanenko, G.
Fernꢁndez, Chem. Eur. J. 2014, 20, 10669–10678.
[19] a) Y.-Y. Ren, N.-W. Wu, J. Huang, Z. Xu, D.-D. Sun, C.-H. Wang, L. Xu,
Chem. Commun. 2015, 51, 15153–15156; b) D. S. Janni, M. K. Manheri,
Langmuir 2013, 29, 15182–15190; c) F. Wang, M. A. J. Gillissen, P. J. M.
Stals, A. R. A. Palmans, E. W. Meijer, Chem. Eur. J. 2012, 18, 11761–
11770; d) K. C. Majumdar, B. Chattopadhyay, P. K. Shyam, N. Pal, Tetrahe-
dron Lett. 2009, 50, 6901–6905.
[20] W. Qin, V. Leen, T. Rohand, W. Dehaen, P. Dedecker, M. Van der Auwera-
er, K. Robeyns, L. Van Meervelt, D. Beljonne, B. Van Averbeke, J. N. Clif-
ford, K. Driesen, K. Binnemans, N. Boens, J. Phys. Chem. A 2009, 113,
439–447.
[21] a) F. C. Spano, C. Silva, Annu. Rev. Phys. Chem. 2014, 65, 477–500;
b) F. C. Spano, Acc. Chem. Res. 2010, 43, 429–439; c) M. Kasha, H. R.
Rawls, M. A. El-Bayoumi, Pure Appl. Chem. 1965, 11, 371–392.
[22] H. M. M. ten Eikelder, A. J. Markvoort, T. F. A. de Greef, P. A. J. Hilbers, J.
Phys. Chem. B 2012, 116, 5291–5301.
[23] a) X.-Q. Li, V. Stepanenko, Z. Chen, P. Prins, L. D. A. Siebbeles, F. Wꢀrth-
ner, Chem. Commun. 2006, 3871–3873; b) F. Wꢀrthner, B. Hanke, M. Ly-
setska, G. Lambright, G. S. Harms, Org. Lett. 2005, 7, 967–970.
[24] C. Shao, M. Grꢀne, M. Stolte, F. Wꢀrthner, Chem. Eur. J. 2012, 18, 13665–
13677.
[7] a) F. Aparicio, S. Cherumukkil, A. Ajayaghosh, L. Sꢁnchez, Langmuir
2016, 32, 284–289; b) S. S. Babu, S. Prasanthkumar, A. Ajayaghosh,
Angew. Chem. Int. Ed. 2012, 51, 1766–1776; Angew. Chem. 2012, 124,
1800–1810; c) P. Besenius, G. Portale, P. H. H. Bomans, H. M. Janssen,
A. R. A. Palmans, E. W. Meijer, Proc. Natl. Acad. Sci. USA 2010, 107,
17888–17893.
[25] a) S. Grimme, J. G. Brandenburg, C. Bannwarth, A. Hansen, J. Chem.
Phys. 2015, 143, 054107; b) R. Sure, S. Grimme, J. Comput. Chem. 2013,
34, 1672–1685.
[8] a) M. Yamauchi, S. Kubota, T. Karatsu, A. Kitamura, A. Ajayaghosh, S.
Yagai, Chem. Commun. 2013, 49, 4941–4943; b) T. Seki, A. Asano, S.
Seki, Y. Kikkawa, H. Murayama, T. Karatsu, A. Kitamura, S. Yagai, Chem.
Eur. J. 2011, 17, 3598–3608.
Received: May 31, 2016
Published online on && &&, 0000
&
&
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
6
ꢂ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Small strokes make big change: Two
new hydrophobic BODIPY dyes, which
only differ in the linking group (ester vs.
amide; see figure), were synthesized
and fully characterized. Exchanging the
ester linkages with amide groups is
found to influence the mode of self-
aggregation by tuning the isodesmic
supramolecular polymerization to a
cooperative process.
&
Supramolecular Chemistry
A. Rçdle, B. Ritschel, C. Mꢀck-Lichtenfeld,
V. Stepanenko, G. Fernꢁndez*
&& – &&
Influence of Ester versus Amide
Linkers on the Supramolecular
Polymerization Mechanisms of Planar
BODIPY Dyes
Chem. Eur. J. 2016, 22, 1 – 7
www.chemeurj.org
7
ꢂ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ