Reconfiguration of π-conjugated superstructures enabled by redox-assisted assembly

Article abstract of DOI:10.1039/c9cc01939a

We show that n-doping supramolecular assemblies built from perylene diimide units provides a means to modulate the structure-function properties of these materials. In addition to highlighting the design principles, a combination of spectroscopic and micr

Full text of DOI:10.1039/c9cc01939a

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: K. Liu, A.
Mukhopadhyay, A. Ashcraft, C. Liu, A. Levy, P. Blackwelder and J. Olivier, Chem. Commun., 2019, DOI:
10.1039/C9CC01939A.
This is an Accepted Manuscript, which has been through the
Volume 52 Number
1 4 January 2016 Pages 1–216
Royal Society of Chemistry peer review process and has been
accepted for publication.
ChemComm
Accepted Manuscripts are published online shortly after
Chemical Communications
www.rsc.org/chemcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1359-7345
COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
=
3
rsc.li/chemcomm

Please do not adjust margins
Page 1 of 5
ChemComm
View Article Online
DOI: 10.1039/C9CC01939A
Journal Name
COMMUNICATION
Reconfiguration of π-Conjugated Superstructures Enabled by
Redox-Assisted Assembly
Kaixuan Liu,a Arindam Mukhopadhyay,a Adam Ashcraft,a Chuan Liu,a Adam Levy,a Patricia
Received 00th January 20xx,
Accepted 00th January 20xx
Blackwelder,b,c and Jean-Hubert Olivier a*
DOI: 10.1039/x0xx00000x
www.rsc.org/
parameters and electronic properties can be leveraged to modify the
structure-function properties of supramolecular polymers.
We show that n-doping supramolecular assemblies built from
perylene diimide units provides a means to modulate the structure-
function properties of these materials. In addition to highlighting
design principles, a combination of spectroscopic and microscopic
characterization correlates an increase of free-exciton bandwidth
with the formation of mesoscale hierarchical superstructures.
Due to their unique photophysical and electrochemical
properties, perylene-3,4:9,10-bis(dicarboxyimide) (PDI) derivatives
have been extensively exploited as building blocks to investigate
assembly processes.16-18 Diverging from conventional heating-
cooling processes recent studies have demonstrated that redox
treatment of one-dimensional (1D) PDI-based supramolecular
polymers can assist in navigating the assembly free-energy landscape
and form kinetically trapped superstructures characterized by
structure-function relationships not evidenced in initially formed,
equilibrium architectures.19-20 Aiming to further expand the scope of
redox-assisted assembly and investigate the extent to which
structure-function relationships of non-covalent assemblies can be
modulated by design, we have synthesized the two PDI-based
building blocks, PDI-C3Im-C2OH and PDI-TEOAm-C2OH, presented in
Scheme 1A and studied their assembly properties following the flow
chart shown in Scheme 1B. While these two building blocks share
similar structural attributes as both are flanked with cationic
functional groups (imidazolium or ammonium) and terminal hydroxyl
functions, linear linkers that tether redox active, hydrophobic PDI
cores and hydrophilic functionalities have been modified. As
The development of molecular strategies to modulate
structure-function relationships of nanoscale objects opens new
avenues to construct organic semiconducting materials equipped
with emergent (opto)electronic properties.1-3 Contingent on the
solvent dielectric property,4 heating-cooling cycles,5 external forces,6
and the use of chemical fuels,7-8 thermodynamic equilibrium, static
and dissipative out-of-equilibrium states can be formed and dictate
the structure-function properties of non-covalent assemblies.9-10 At
the molecular level, conformations of supramolecular polymers built
from π-conjugated chromophores are regulated by non-covalent
interactions between subunits that consequently regulate the extent
to which frontier molecular orbitals overlap.11 Electrostatic
interaction and local electric field are two parameters that are
recognized to play an important role in defining the orientation of
building blocks.12-13 Pioneering experimental and theoretical studies
have unambiguously demonstrated that minor displacements
between neighboring chromophores can result in a profound
perturbation of the photophysical properties evidenced in
superstructures.14-15 Intricate interplays between structural
a. Department of Chemistry, University of Miami, Cox Science Center, 1301 Memorial
Drive, Coral Gables, FL 33146
jh.olivier@miami.edu
Center for Advanced Microscopy (UMCAM), Department of Chemistry, University of
b
Miami, Coral Gables, FL 33146
Marine Geological Sciences, Rosentsteil School of Marine and Atmospheric Science,
c
University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149
Electronic Supplementary Information (ESI) available: Synthesis, characterization
and aggregation mechanisms of redox-active building blocks. SEM, TEM, absorption
spectra, NMR, IR, MS, See DOI: xxxxxxxxxxxxxxxxxxx
Scheme 1: (A) Molecular Structures of the amphiphilic PDI-based building
blocks utilized to investigate redox-assisted assembly process shown in (B).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 5
COMMUNICATION
Journal Name
View Article Online
DOI: 10.1039/C9CC01939A
Fig. 1: Ground-state electronic absorption spectra recorded in D2O for non-
covalent PDI-C3Im-C2OH (A) and PDI-TEOAm-C2OH (B) assemblies upon the
addition of sodium hydrosulfide (NaSH). Experimental conditions: initial
[PDI]= 200 µM; final [PDI] = 140 µM; T = 20 ˚C; Argon atmosphere, optical
pathlength = 2 mm; initial pH = 7.00; final pH = 10.85; initial ionic strength
= 4.22 x 10-4 M; final ionic strength = 2.53 x 10-4 M.
chronicled in Figure S1-S4 and associated text, temperature-
dependent aggregation experiments performed with PDI-C3Im-C2OH
and PDI-TEOAm-C2OH building blocks in water and under identical
concentration conditions (5 µM) suggest that the combination of
propylene linker and imidazolium cation facilitates a more complete
supramolecular polymerization process compared to that of
ethoxyether tether (TEO) and ammonium cation.
Fig. 2: Deconvolution of the experimental ground state electronic
absorption spectra (red) recorded for PDI-C3Im-C2OH (A-B) and PDI-
TEOAm-C2OH (C-D) before and after redox-assisted assembly respectively.
The deconvoluted purple, orange and green peaks correspond to 0-0, 0-1,
0-2 vibronic transitions. The reconvoluted absorption spectra are shown by
the dotted blue lines.
To glean further insights into the structure-function relationships
of the supramolecular polymers built from PDI-C3Im-C2OH and PDI-
TEOAm-C2OH subunits, reductive titrations have been conducted
and the results are chronicled in Fig. 1. Because electronic properties
of organic superstructures and aggregates are intimately related to
the conformation of building blocks,21 we hypothesized that
spectroscopic signatures of n-doped PDI-assembly (Scheme 1B) can
be exploited as a sensitive diagnostic tool to probe any potential
perturbation of assembly conformation. As evidenced in Fig. 1A,
implementation of a PDI-C3Im-C2OH D2O solution with sodium
hydrosulfide (NaSH) utilized as a chemical reductant is accompanied
with the apparition of absorptive features that span the visible to
near infrared (NIR) detection windows and indicate the formation of
n-doped PDI assembly. For further details on the reductive titration
experiments please refer to Section 4 in the ESI. It is interesting to
underscore that at earlier titration points (0.1 to 0.3 eq.), the
spectroscopic signatures of aggregated PDI-radical anion can be
detected at 988, 816, 731, and 615 nm,22 while further addition of
reductant (0.5 eq. to 1.0 eq.) witnesses the formation of a new
species confirmed by: 1) the formation of broad, asymmetric
absorption bands between 400 and 900 nm, 2) the drastic decrease
of the 988-nm band diagnostic of aggregated PDI-radical anion, and
3) the bathochromic shift by more than 130 nm (60 meV) of the
broad NIR transition initially centered at 1570 nm. Notably,
increasing the concentration of reductant above 1 eq. is not
associated with any relevant spectroscopic change as shown in
Figure S6. Congruent with the fact that previous studies have
attributed the emergence of NIR spectral signatures with the
formation of π-anion stacks,23-26 we posit that electron injection into
PDI-C3Im-C2OH assembly initiates the formation of a n-doped
assembly that does not share the same electronic properties as the
aggregated PDI-radical anion.
In sharp contrast, the PDI-TEOAm-C2OH reductive titration
experiments chronicled in Fig. 1B preserve the spectroscopic
signatures reminiscent to that of aggregated PDI-radical anion.22 This
conclusion is based on the fact that addition of up to 5 eq. of sodium
hydrosulfide is characterized by: 1) the continuous rise of an
absorption band at 608 nm, and 2) the lack of discernible shift of the
1550 nm absorption band as a function of reductant equivalent
(Figure S7). Furthermore, it is important to emphasize the 135 nm
(70 meV) shift when comparing the NIR absorptive features of the
PDI-TEOAm-C2OH (1550 nm) and n-doped PDI-C3Im-C2OH (1700 nm)
assembly. All taken together, these reductive titration experiments
underscore that n-doped PDI-C3Im-C2OH superstructure is
characterized by electronic states that differ with respect to those
evidenced in n-doped PDI-TEOAm-C2OH assembly.
To further investigate if n-doped assemblies can be exploited to
navigate the assembly free-energy landscapes and modify the
structure-function properties of equilibrium assemblies, Fig. 2
compares the ground state electronic absorption spectra (EAS) of
oxygen-neutralized assemblies with those of initially formed
supramolecular polymers (Scheme 1B). Please note that the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 5
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
kinetically trapped assembly was formed by letting the freshly superstructure, an increase of more than 52 meV is evidenced when
View Article Online
DOI: 10.1039/C9CC01939A
oxidized n-doped assemblies age during 18 hours. Deconvolution of comparing the initially formed assembly (ExBW = 308 meV) and redox-
treated assembly (ExBW = 360 meV). In sharp contrast, n-doping the
initially formed PDI-TEOAm-C2OH assembly does not increase the
ExBW as the calculated ExBW before (153 meV) and after redox
treatment PDI-TEOAm-C2OH (156 meV) remains virtually unaltered
(Table 1). Please note that to ensure that the reported change of
electronic properties is not a consequence of ionic strength
perturbation achieved during the reductive titration experiment, the
ExBW for each initially formed assembly has been calculated from the
EAS of a solution that mimics the ionic strength of the solution after
reductive titration (see control samples, Section 4 in the ESI). By
combining reductive titration experiments with the photophysical
properties of PDI-C3Im-C2OH and PDI-TEOAm-C2OH assemblies
before and after redox treatment, the apparent increase of ExBW
evidenced in the redox-treated PDI-C3Im-C2OH superstructure can
be associated with the n-doped intermediate assembly formed
during reductive titration experiments. This correlation is based on
the fact that, when compared to PDI-TEOAm-C2OH, the red-shifted
NIR spectroscopic signatures of the n-doped PDI-C3Im-C2OH
intermediate at 1700 nm may indicate a higher magnitude of π-
orbital interactions.
Because perturbation of the photophysical properties of π-
conjugated superstructures can originate from
a structural
reconfiguration, we have investigated the solid-state morphologies
of PDI-C3Im-C2OH superstructure before and after redox treatment
(Fig. 3 and Fig. S8-S17) and compared it to that evidenced by PDI-
TEOAm-C2OH assembly (Fig. S18-S22). Comparing SEM images
recorded for initially prepared PDI-C3Im-C2OH assembly (Fig. 3E-F)
with that corresponding to redox-treated superstructures (Fig. 3A-B)
reveals a striking contrast. While drop casting the initially prepared
assembly engenders the formation of aggregates that appear
amorphous under SEM, redox-treated superstructures organize into
1D materials spanning the microscale dimension as seen in Fig. 3A. It
is interesting to note that rod-like structures with a width of 140 to
170 nm laterally interact to evolve into compact, micron-sized fiber-
like materials. Noteworthy is the fact that the hierarchical mesoscale
objects presented in Fig. 3A-B are in all likelihood tracing their
genesis from local concentration effects associated with the drop
casting deposition method and suggest non-negligible perturbation
of the solvated PDI-C3Im-C2OH superstructure conformation with
respect to that of the initially prepared, parent assemblies. To gain
further insights into the nanoscale superstructure comprising fiber-
like materials, we monitored redox-treated PDI-C3Im-C2OH
superstructures and precursor assemblies by TEM. As can be seen in
Fig. 3C-D, rod-like structures sharing a 15-40 nm width are easily
detectable and further confirm our initial hypothesis that redox-
assisted assembly enforces formation of mesoscale hierarchical
superstructures. Sharply contrasting this finding, TEM images
recorded for parent PDI-C3Im-C2OH assembly fail to demonstrate any
organized domains as shown in Fig. 3G-H.
Fig. 3: Microscopic characterization of kinetically trapped (A-D) and
equilibrium (E-H) PDI-C3Im-C2OH assemblies from D2O solution.
a
Comparative scanning electron microscopic (SEM) images recorded after (A-
B) and before redox treatment (E-F) highlight the formation of hierarchical
mesoscale materials during redox-assisted assembly process. Transmission
electron microscopic (TEM) images acquired after (C-D) and before redox
treatment (G-H) show a drastic change of superstructure morphology at the
nanoscale.
the EAS of PDI-TEOAm-C2OH and PDI-C3Im-C2OH before and after
titration allows for calculation of the oscillator strength of the 0-0, 0-
1, and 0-2 vibrionic transitions between the PDI relaxed ground-state
S0 and the first singlet excited state S1. Analysis of the deconvoluted
PDI-C3Im-C2OH EAS indicates a non-negligible redistribution of the 0-
0 and 0-1 transition oscillator strengths suggesting that n-doping the
PDI-C3Im-C2OH superstructure perturbs the photophysical
properties of the initially formed assembly. In sharp contrast, no
apparent evolution of the photophysical properties is evidenced
when comparing the oscillator strength of the 0-0 and 0-1 transitions
in PDI-TEOAm-C2OH assemblies before and after the n-doping
process.
Seminal studies have demonstrated that ExBW of π-conjugated
superstructures that feature PDI-based building blocks and other π-
conjugated units is intimately related to frontier molecular orbital
overlaps. Consequently, ExBW can be utilized to glean additional
information on structure-function relationships of non-covalent
assemblies.15, 27-28 Using the model pioneered by Spano et al. (see
Section 5 in ESI), we have calculated the ExBW for PDI-C3Im-C2OH
assemblies before and after the n-doping process and compared it to
that of PDI-TEOAm-C2OH assemblies (Table 1). As suggested by the
change of oscillator strength initially detected in the PDI-C3Im-C2OH
By combining the data presented so far for PDI-C3Im-C2OH-
derived supramolecular architectures, the increase of ExBW can be
associated with the formation of hierarchical materials. This
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 5
COMMUNICATION
Journal Name
assumption is further validated by elucidating the solid-state
morphologies of PDI-TEOAm-C2OH-derived assemblies. As expected
from the lack of ExBW increase reported for redox-treated PDI-
TEOAm-C2OH assembly, no distinguishable organized domains are
observed in the SEM images shown in Fig. S18-S22 where globular,
amorphous aggregates best characterize the solid-state morphology
of this class of assembly.
Conflicts of interest
There are no conflicts to declare.
View Article Online
DOI: 10.1039/C9CC01939A
Notes and references
1.Moulin, E.; Niess, F.; Maaloum, M.; Buhler, E.; Nyrkova, I.;
Giuseppone, N. Angew. Chem. Int. Ed. 2010, 49, 6974-6978.
2.vanꢀderꢀWeegen, R.; Teunissen Abraham, J. P.; Meijer, E. W. Chem.
Eur. J. 2017, 23, 3773-3783.
3.Liu, C.; Liu, K.; Klütke, J.; Ashcraft, A.; Steefel, S.; Olivier, J.-H. J.
Mater. Chem. C 2018, 6, 11980-11991.
4.Mabesoone, M. F. J.; Markvoort, A. J.; Banno, M.; Yamaguchi, T.;
Helmich, F.; Naito, Y.; Yashima, E.; Palmans, A. R. A.; Meijer, E. W. J.
Am. Chem. Soc. 2018, 140, 7810-7819.
5.Fukui, T.; Kawai, S.; Fujinuma, S.; Matsushita, Y.; Yasuda, T.;
Sakurai, T.; Seki, S.; Takeuchi, M.; Sugiyasu, K. Nat. Chem. 2016, 9,
493.
6.Micali, N.; Engelkamp, H.; van Rhee, P. G.; Christianen, P. C. M.;
Scolaro, L. M.; Maan, J. C. Nat. Chem. 2012, 4, 201.
7.Dhiman, S.; Jain, A.; George, S. J. Angew. Chem. Int. Ed. 2017, 56,
1329-1333.
8.Dhiman, S.; Sarkar, A.; George, S. J. RSC Advances 2018, 8, 18913-
18925.
9.De Greef, T. F. A.; Smulders, M. M. J.; Wolffs, M.; Schenning, A. P.
H. J.; Sijbesma, R. P.; Meijer, E. W. Chem. Rev. 2009, 109, 5687-5754.
10.Korevaar, P. A.; de Greef, T. F. A.; Meijer, E. W. Chem. Mater.
2014, 26, 576-586.
11.Ostroverkhova, O. Chem. Rev. 2016, 116, 13279-13412.
12.Martinez, C. R.; Iverson, B. L. Chem. Sci. 2012, 3, 2191-2201.
13.Raju, R. K.; Bloom, J. W. G.; Wheeler, S. E. J. Chem. Theory Comput.
2013, 9, 3479-3490.
Comparing the photophysical properties and solid-state
morphologies presented for PDI-C3Im-C2OH superstructure with
those of PDI-TEOAm-C2OH assembly allows the elucidation of critical
parameters that need to be considered during a redox-assisted
assembly process. As indicated by the temperature-dependent
aggregation and the reductive titration experiments, TEO side chains
flanked on PDI cores confers hydrophilicity to PDI-TEOAm-C2OH
building blocks that prevent access to superstructure conformation,
during the n-doping process, comparable to that of PDI-C3Im-C2OH.
Consequently, while recovery of the neutral ground state of the PDI-
C3Im-C2OH n-doped intermediate is accompanied by an increase of
ExBW, no apparent change of photophysical properties is evidenced
in redox-treated PDI-TEOAm-C2OH assembly. This observation
underscores the pivotal role played by the n-doped intermediates.
We postulate that upon electron injection, electrostatic repulsion
between negatively charged PDI-TEOAm-C2OH hydrophilic building
blocks may compromise the assembly integrity. Furthermore, the
suspected conformational change of the PDI-C3Im-C2OH
superstructure, signaled by the increase of ExBW, is further validated
by the formation of mesoscale 1D hierarchical materials.
In conclusion, we have demonstrated that the initial
photophysical and solid-state properties of PDI-derived
supramolecular polymers can be modified by exploiting redox-
assisted assembly. Analysis of the reductive titration, ExBW, and
morphological attributes of PDI-C3Im-C2OH and PDI-TEOAm-C2OH
assemblies before and after redox treatment has unraveled pivotal
structural and electronic parameters that enable the evolution of
structure-function relationships. Because reductive titrations of
initially prepared PDI-C3Im-C2OH assemblies demonstrate a 70-meV
bathochromic shift of the π-anion stack spectral signature when
compared to that of PDI-TEOAm-C2OH assemblies, the increase of
ExBW, exclusively evidenced in PDI-C3Im-C2OH superstructures, can
be correlated to the electronic properties of the n-doped
intermediates. To complement the change of electronic function,
redox-assisted assembly of the PDI-C3Im-C2OH supramolecular
polymer enforces the formation of highly ordered 1D mesoscale
materials that span the nano-to-microscale dimensions. We
postulate that n-doping the initially prepared PDI-C3Im-C2OH
assembly engenders a superstructure conformational change that
assists the formation of hierarchical supramolecular architectures.
This work provides a new tool to navigate the self-assembly free
energy landscape and create semiconducting superstructures
relevant to optoelectronic applications.
14.Kaufmann, C.; Bialas, D.; Stolte, M.; Würthner, F. J. Am. Chem. Soc.
2018, 140, 9986-9995.
15.Hestand, N. J.; Spano, F. C. Acc. Chem. Res. 2017, 50, 341-350.
16.Görl, D.; Zhang, X.; Würthner, F. Angew. Chem. Int. Ed. 2012, 51,
6328-6348.
17.Sorrenti, A.; Leira-Iglesias, J.; Sato, A.; Hermans, T. M. Nat.
Commun. 2017, 8, 15899.
18.Leira-Iglesias, J.; Tassoni, A.; Adachi, T.; Stich, M.; Hermans, T. M.
Nat. Nanotechnol. 2018, 13, 1021-1027.
19.Liu, K.; Levy, A.; Liu, C.; Olivier, J.-H. Chem. Mater. 2018, 30, 2143-
2150.
20.Leira-Iglesias, J.; Sorrenti, A.; Sato, A.; Dunne, P. A.; Hermans, T.
M. Chem. Commun. 2016, 52, 9009-9012.
21.Vura-Weis, J.; Ratner, M. A.; Wasielewski, M. R. J. Am. Chem. Soc.
2010, 132, 1738-1739.
22.Marcon, R. O.; Brochsztain, S. J. Phys. Chem. A 2009, 113, 1747-
1752.
23.Graf, D. D.; Duan, R. G.; Campbell, J. P.; Miller, L. L.; Mann, K. R. J.
Am. Chem. Soc. 1997, 119, 5888-5899.
24.Miller, L. L.; Mann, K. R. Acc. Chem. Res. 1996, 29, 417-423.
25.Zhong, C. J.; Kwan, W. S. V.; Miller, L. L. Chem. Mater. 1992, 4,
1423-1428.
26.Wu, Y.; Frasconi, M.; Gardner, D. M.; McGonigal, P. R.; Schneebeli,
S. T.; Wasielewski, M. R.; Stoddart, J. F. Angew. Chem. Int. Ed. 2014,
53, 9476-9481.
27.Spano, F. C.; Silva, C. Annu. Rev. Phys. Chem. 2014, 65, 477-500.
28.Clark, J.; Chang, J.-F.; Spano, F. C.; Friend, R. H.; Silva, C. Appl. Phys.
Lett. 2009, 94, 163306.
This work was supported by the University of Miami. Additional
support provided by the Arnold and Mabel Beckman Foundation (BYI
Award 2018) is gratefully acknowledged. We thank Brianna Bernard
and Victor Paulino for their constructive comments.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 5
ChemComm
View Article Online
DOI: 10.1039/C9CC01939A
TOC
Redox-Assisted Assembly enforces reconfiguration of π-conjugated superstructures