Butadiyne-Bridged (Porphinato)Zinc(II) Chromophores Assemble into Free-Standing Nanosheets

Article abstract of DOI:10.1021/acs.organomet.0c00345

The molecular engineering of chromophores that enables the controlled and reliable formation of hierarchical solid-state architectures is at the forefront of developing hybrid semiconducting materials. While the rules and principles to assemble monomeric porphyrin-derived building blocks are well established, the aggregation of larger π-conjugated cores that feature electronically coupled porphyrin arrays has been vastly underexplored. In the present contribution, we report the synthesis, spectroscopy, assembly, and solid-state properties of a class of butadiyne-bridged (porphinato)zinc(II) dimer chromophores. A spectroscopic investigation unraveled the formation of aggregates in an aqueous medium, leading to the formation of two-dimensional objects that expanded across microscale dimensions. An analysis of the height profile, by atomic force microscopy, indicated that one porphyrin dimer comprises the thickness of the solid-state hierarchical superstructure, which underscores the promise of this approach to engineer solid-state platforms for (opto)electronic devices. Furthermore, the initiation of noncovalent interactions between building blocks by means of a chemical stimulus (pH) revealed that a nucleation-growth process governs the aggregation of the π-conjugated chromophores in an aqueous medium. This work provides tools to modulate the structure-function relationships of supramolecular architectures equipped with enticing optical properties.

Full text of DOI:10.1021/acs.organomet.0c00345

pubs.acs.org/Organometallics
Article
Butadiyne-Bridged (Porphinato)Zinc(II) Chromophores Assemble
into Free-Standing Nanosheets
Chuan Liu, Kaixuan Liu, Arindam Mukhopadhyay, Victor Paulino, Brianna Bernard,
and Jean-Hubert Olivier*
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Supporting Information
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ABSTRACT: The molecular engineering of chromophores that
enables the controlled and reliable formation of hierarchical solid-
state architectures is at the forefront of developing hybrid
semiconducting materials. While the rules and principles to
assemble monomeric porphyrin-derived building blocks are well
established, the aggregation of larger π-conjugated cores that
feature electronically coupled porphyrin arrays has been vastly
underexplored. In the present contribution, we report the
synthesis, spectroscopy, assembly, and solid-state properties of a
class of butadiyne-bridged (porphinato)zinc(II) dimer chromo-
phores. A spectroscopic investigation unraveled the formation of
aggregates in an aqueous medium, leading to the formation of two-
dimensional objects that expanded across microscale dimensions.
An analysis of the height profile, by atomic force microscopy, indicated that one porphyrin dimer comprises the thickness of the
solid-state hierarchical superstructure, which underscores the promise of this approach to engineer solid-state platforms for
(opto)electronic devices. Furthermore, the initiation of noncovalent interactions between building blocks by means of a chemical
stimulus (pH) revealed that a nucleation−growth process governs the aggregation of the π-conjugated chromophores in an aqueous
medium. This work provides tools to modulate the structure−function relationships of supramolecular architectures equipped with
enticing optical properties.
Controlling the assembly of π-conjugated building blocks into
nano- to mesoscale superstructures paves the way for the
development of organic materials required for advances in solar
energy capture, conversion and storage,1−6 nonlinear
optics,7−10 organic electronics,11−16 and, more recently,
spintronics.17−20 In this regard, recent progress in supra-
molecular chemistry has delineated cardinal design principles
to modulate the structure−function relationships of π-
conjugated superstructures.21−23 Because of their strong
absorptivity in the visible spectral windows, combined with
compelling redox properties to engineer (opto)electronic
materials, porphyrin-derived chromophores are a promising
class of π-conjugated building blocks for unearthing supra-
molecular polymerization mechanisms and regulating the
formation of one-dimensional (1D) and two-dimensional
(2D) superstructures.24−29 While the assembly of porphyrin
monomers as building blocks has been widely explored, only a
handful of examples have examined the aggregation mecha-
nism of porphyrin oligomers.
attractive prospect for engineering (opto)electronic materials.
Common strategies to access these oligomers exploit ethyne-
and butadiyne-based linkers to tether porphyrin units in an
effort to enforce strong chromophore−chromophore electronic
interactions, leading to ground and excited states that are
electronically delocalized. In butadiyne-bridged porphyrin
oligomers, the dihedral angle between monomer planes is
recognized as regulating the electronic properties, where an
increase in the dihedral angle translates to a decrease in the π-
electron delocalization. Experimental and theoretical studies
performed on butadiyne-bridged (porphinato)zinc(II) dimers
have unambiguously demonstrated that torsional conformers
sampling all torsion angles (0° to 90°) exist in solution at room
temperature.41,42 The distinct absorptive features that charac-
terize each torsional conformer represent ideal spectroscopic
handles, which were exploited to investigate excited state
Received: May 16, 2020
Bolstered by their tunable optical band gaps that enable the
capture of near-infrared photons,30−33 large two-photon cross
sections and hyperpolarizabilities,34−36 and unique excited
state dynamic properties,37−40 π-conjugated oligomers that
feature electronically coupled (porphinato)metal units are an
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Scheme 1. (A) Chemical Structures of the Butadiyne-
Bridged (Porphinato)zinc(II) Building Block
MPZnE2PznM and the Parent Monomer Derivative
MPZnM and (B) Electrostatic Potential Map Derived from
the DFT Calculation (ωb97xd/cc-pvdz) of a Representative
Noncovalent Dimer That Features Truncated
a
MPZnE2PZnM Cores
Figure 1. Variable temperature (VT) ground state electronic
absorption spectra (EAS) recorded for the MPZnE2PZnM dimer in
(A) a DMF solution and (B) a 1:1 DMF/H2O aqueous mixture. The
optical path length was 2 mm and [MPZnE2PZnM] = 23 μM.
a
See Section 3 of the Supporting Information for more details.
properties42−46 and media viscosity.47,48 While the mecha-
nisms that regulate the aggregation of butadiyne-bridged
(porphinato)zinc(II) building blocks have been elucidated in
organic media,49−51 insights into the assembly properties of
similar building blocks in aqueous media and the structure−
function relationships of the resulting superstructures are
lacking; however, they are critical to advance the molecular
engineering of biocompatible (opto)electronic materials.
Herein, we elucidate the assembly properties of the novel
butadiyne-bridged (porphinato)zinc(II) building block
MPZnE2PZnM (Scheme 1A) in an aqueous medium. Our
design principle relies on terminal ammonium side chains
expected to stabilize nascent aggregates in an aqueous medium.
Scheme 1B illustrates the electrostatic potential map of a
truncated MPZnE2PZnM noncovalent dimer, suggesting that a
slipped geometry may regulate the conformation of the
building blocks in the aggregate. Exploiting ground state
electronic absorption spectroscopy, we show that this class of
building blocks initiates the formation of aggregates that
further evolve into 2D microscale objects in the solid state. To
gain further insights into the mechanism that regulates the
formation of aggregates in solution, we leveraged a pH-
triggered process that capitalizes on protected MPZnE2PZnM
building blocks for which noncovalent interactions are
transiently hampered due to steric hindrance. By exploiting a
two-step aggregation model, we suggest that a nucleation−
growth process regulates the assembly of MPZnE2PZnM
building blocks in an aqueous medium.
ground state electronic absorption spectra (EAS) of the
MPZnE2PZnM building blocks in pure DMF, the π-conjugated
porphyrin array features the hallmarks of a molecularly
dissolved species across the probed temperature range (263−
383 K). Congruent with benchmark studies reported by
Anderson on butadiyne-bridged porphyrin dimers,41,42 it is fair
to assume that the spectroscopic features centered at 750 and
684 nm in DMF at a low temperature (263 K) correspond to
Q-type transitions derived from the two extreme conforma-
tions adopted by the porphyrin cores in the dimeric array. The
two extreme torsional conformations govern the magnitude of
the π-electron delocalization; a perpendicular conformation,
characterized by a dihedral angle of 90° between the PZn units,
hampers the π-delocalization, while a planar conformation
results in the strong coupling of the π-conjugated rings. The
time-dependent density functional theory (TD-DFT) calcu-
lations performed on the MPZnE2PZnM building block as a
function of the dihedral angles between porphyrin cores are
shown in Section 3 of the Supporting Information, further
validating the origin of the 750 and 684 nm absorptive features
that correspond to the planar and perpendicular conformers,
respectively. Interestingly, Figure 1A unravels the non-
negligible and synchronous hypsochromic shift of these two
Q-type transitions as well as a decrease in the oscillator
strength with increasing temperature. These observations may
indicate that a different set of rotational conformers regulates
the spectroscopic properties of the MPZnE2PZnM dimer at
high temperatures in a polar aprotic solvent.
The optical properties of MPZnE2PZnM building blocks
recorded in DMF and 50% DMF in water indicate the non-
negligible aggregation of the building blocks in an aqueous
medium. As suggested by Figure 1A, which chronicles the
As shown in Figure 1B, the ground state electronic
absorption properties of MPZnE2PZnM recorded in 50%
B
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DMF in water as a function of temperature differs marginally
from those evidenced in pure DMF (Figure 1A). While the Q-
type transitions of the planar conformer manifested a modest
bathochromic shift in addition to a slight increase of the
oscillator strength during the descent from 373 to 333 K
(Figure S5), a pronounced decrease of the extinction
coefficient at 750 nm and the emergence of a new
spectroscopic feature centered at 718 nm were unambiguously
detected between 303 and 263 K (Figures 1B and S5B). It is
interesting to note that the optical properties characterizing the
perpendicular conformer appear virtually unchanged in the
373−283 K temperature range. More details are provided in
Section 4 of the Supporting Information. In addition, after
decreasing the temperature to 263 K, an increase in the
temperature to 293 K did not yield the recovery of the
absorptive species detected during the descent from 373 to 263
K. It is also worth noting that the apparition of new
spectroscopic features located on the blue edge of the B-type
transition appeared and were centered at 415 nm (Figures 1B
and S5B). This finding suggests that the MPZnE2PZnM
aggregate formed at a low temperature is nested in a more
stabilized region of the energy potential well. In all likelihood,
the molecular species initially detected at 293 K, during the
descent from 373 K, can be described as metastable and may
initiate the formation of aggregates. Furthermore, monitoring
the ground state spectroscopic properties of the aggregates
after 4 and 24 h (green and dotted green lines in Figure 1B,
respectively) revealed the dynamic nature of the process and
may diagnose the continued growth of the species in the
solution. While a matter of speculation at this time, the
spectroscopic features of the newly formed aggregate species
may signal the formation of an H-like aggregate. This
assumption is based on (1) the DFT model shown in Figure
1B that highlights a slipped geometry and (2) the emergence
of spectroscopic features at higher energy with respect to these
characteristics of the molecularly dissolved planar conformer.
Contrasting the spectroscopic properties elucidated for the
MPZnE2PZnM dimer building block, the VT-EAS recorded for
the parent MPZnM monomer in a similar concentration range
(Figure S6) revealed a modest perturbation of the absorptive
features across the 373−283 K temperature range. This
observation suggests that the structural attributes of the
MPZnM monomer enforce negligible interactions between the
PZn monomer cores in an aqueous medium. It is fair to
assume that the triethylene oxide side chains, combined with
the ammonium terminal groups, offer sufficient hydrophilic
interactions with the solvent medium to minimize nascent
hydrophobic interactions between the π-conjugated cores.
The elucidation of the solid-state morphologies of
MPZnE2PZnM-derived nanoscale objects formed by drop
casting parent DMF and 50% DMF in H2O solutions
underscores the important role played by the solvated
precursors, namely molecularly dissolved MPZnE2PZnM
building blocks (DMF) and the MPZnE2PZnM aggregate
(DMF/H2O). As gleaned in Figure 2B, which displays the
AFM image of an MPZnE2PZnM-dropcast DMF solution, flat
and rod-like nanoscale objects were observed with associated
widths ranging from 200 to 350 nm. Additional AFM images
are shown in Figure S11. The height profile, which ranges from
3 to 4 nm, suggests that the thickness of these probed objects
corresponds to one porphyrin unit. Our hypothesis was
supported by the energy-minimized structure computed at
the DFT level of theory. Please refer to Section 3 and Figure
Figure 2. Topographic intermittent contact mode AFM images of
MPZnE2PZnM building blocks dropcast on a silicon substrate from a
parent (A) 1:1 DMF/H2O solution and (B) DMF solution. (C)
Corresponding height profile along the line numbers shown in panels
A and B. (D) Solid-state EAS recorded on a quartz substrate.
S1 of the Supporting Information, which show that the length
and width of a truncated MPZnE2PZnM building block are 4.5
and 1.6 nm, respectively. While a matter of speculation at this
time, we believe that the ∼3:1 aspect ratio of the
MPZnE2PZnM building block is an important structural
parameter that regulates the formation of uniform and free-
standing nanosheets characterized by a thickness of one
building block.
In contrast to the flat and rod-like objects formed by the
parent DMF solution, the MPZnE2PZnM aggregates dropcast
from an aqueous solution engender the creation of nanosheets
that expand across microscale dimensions. Figure 2A highlights
the formation of continuous domains that feature a height
profile of 2−3 nm. The additional AFM images shown in
Figure S12 confirm this solid-state morphology. The formation
of larger monolayer-like domains when dropcasting an aqueous
solution of MPZnE2PZnM aggregates traces its genesis from
the structural properties of the solvated species. As shown by
the spectroscopic investigation, the MPZnE2PZnM aqueous
solution evidenced the existence, at room temperature, of a
non-negligible population of aggregates whereas the analogous
DMF solution was characterized by a molecularly individu-
C
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alized species. It is important to underscore that during the
drying process a local concentration gradient that accompanies
the coffee ring effect is likely to induce the formation of large
nanosheets that initiate from the solvated MPZnE2PZnM
aggregates.
schematically illustrated in Figure 3A, we envisioned that
triggering the decoordination of the pyridine (Py) ligands
would lead to activated building blocks capable of initiating
noncovalent interactions between the π-conjugated cores.
Figure 3B depicts the evolution of the EAS recorded as a
function of time following the addition of a 0.87 M HCl
solution (1.25 equiv with respect to pyridine) to the protected
building blocks (Py)2MPZnE2PZnM. Please note that under
this experimental condition the final pH of the solution is ∼2,
and demetalation of the Zn centers is unlikely.52−55 Following
the addition, a hypsochromic shift (from 756 to 750 nm) of
the Q-type transitions signals the decoordination of the
pyridine chelates enforced by the protonation of the ligands.
Over the course of 2 h, the intensity of the Q-type transitions
at 750 nm, which characterize the planar conformers,
decreased marginally and were accompanied by the rise of a
new transition centered at 716 nm, which was reminiscent of
Figure 2D presents the solid-state EAS recorded for the
MPZnE2PZnM nanosheets as a function of solvent deposition.
It further underscores the noninnocent role played by solvated
precursors. It is interesting to note that the absorptive
signatures of the perpendicular conformer, centered at 684
and 683 nm (DMF and 1:1 DMF/H2O, respectively), do not
substantially deviate from those recorded in solution and may
suggest that aggregation has minimal effect on the ground state
spectroscopic properties of this conformer. In sharp contrast,
the Q-band absorption maxima of the coplanar conformers in
solution (750 nm for both DMF and DMF/H2O) experience a
non-negligible hypsochromic shift in the solid state. While the
nanoscale objects formed by dropcasting a DMF solution of
molecularly dissolved MPZnE2PZnM building blocks are
characterized by broad and unresolved transitions that span
the 700−800 nm spectral window, nanosheets engendered
from the MPZnE2PZnM aggregate in DMF/H2O are
diagnosed by a resolved transition centered at 728 nm. It
appears that the spectroscopic signatures of the planar
conformer populations are more sensitive to the solvent
system used during dropcasting. Please note that, as recently
reported by Anderson et al., the weak absorption peak
positioned at 589 nm is a signature of the planar conformer
while that centered at 640 nm possesses a contribution from
the perpendicular conformer.41
As elucidated during the spectroscopic investigation of
MPZnE2PZnM building blocks, while butadiyne-bridged
porphyrin dimers remain molecularly dissolved in the DMF
solvent, a mixture of DMF/H2O facilitates the formation of
solvated aggregates. Similarly, we hypothesize that the
evaporation of the DMF/H2O solvent initiates the formation
of larger aggregates that evolve toward the free-standing
monolayers shown in Figures 2A and S12. The spectroscopic
properties of MPZnE2PZnM nanosheets indicate that these
nanoscale materials are composed of a more homogeneous
distribution of aggregates when compared to those recorded
for MPZnE2PZnM dropcast from the DMF solution.
After unraveling the solid-state properties as a function of
solvent composition, the pH-triggered assembly of
MPZnE2PZnM units was exploited to gain further insight
into the assembly properties of these building blocks. As shown
in Figure 1, a temperature treatment did not provide a valid
strategy to probe the degree of aggregation as a function of
temperature due to overlapping absorptive features associated
with the change of the torsional conformer population, which
adds spectral complexity. To glean further insight into the
mechanism that regulates the aggregation of MPZnE2PZnM
building blocks, we hypothesized that initiating the formation
of noncovalent interactions between π-conjugated cores by
means of a chemical trigger, at a fixed temperature, may open a
new pathway in the assembly energy landscape. While the
MPZnE2PZnM building blocks access a metastable state that
evolves toward the formation of aggregates over time in the
DMF/H2O solution at room temperature, coordination of the
zinc(II) centers by the addition of pyridine (0.2% with respect
to solvent volume) enables the π-conjugated cores to exist as
stable individualized building blocks, as shown in Figure S7
and the associated text in the Supporting Information. As
Figure 3. (A) Schematic illustration of a strategy that exploits
protected MPZnE2PZnM building blocks to trigger the formation of
MPZnE2PZnM aggregates under a chemical stimulus (pH). Please
note that the planar conformer is shown as an exemplary building
block. (B) EAS of (Py)2MPZnE2PZnM (pink) as a function of time
after the addition of 1.25 equiv of HCl with respect to pyridine (0.2%
in 1:1 DMF/H2O). The volume was 500 μL, [MPZnE2PZnM] = 23
μM, the temperature was 293 K, and the optical path length was 2
mm. (C and D) Kinetic analysis that chronicles the degree of
aggregation as a function of time at 775 and 415 nm, respectively, and
the HCl equivalency (1.25 and 1.5 equiv with respect to pyridine).
The solid black lines correspond to the curve fit using the two-step
Finke and Watzky (F−W) model.
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that of the aggregated species observed during the heating−
cooling treatment. Concomitantly, transitions at 676 and 659
nm were unveiled and may diagnose the existence of additional
aggregates that originate from interactions of nonplanar
MPZnE2PZnM conformers. Significant changes in the
absorption profile of the B-band region should also be
mentioned. An overall decrease of the oscillator strength
accompanied the rise of a distinct new transition (415 nm in
Figure 3B) on the blue edge of the B-type transition. Please
note that the control sample, which monitors the EAS of
MPZnE2PZnM units in the presence of pyridinium chloride
(Figure S9), rules out the idea that the apparent spectroscopic
changes are induced by the nascent organic salt. Furthermore,
the addition of a HCl solution to dimer building blocks not
coordinated with an axial pyridine ligand does not trigger an
aggregation process over the course of 2 h, as shown in Figure
S10.
Monitoring the degree of aggregation of MPZnE2PZnM
building blocks as a function of time provides important
insights into the possible mechanism that regulates the
assembly of the π-conjugated cores. Panels C and D of Figure
3 narrate the assembly kinetics recorded at 775 and 415 nm,
respectively, as these two wavelengths track the decrease of
activated MPZnE2PZnM building blocks and the growth of the
MPZnE2PZnM aggregate. The successful fitting (R2 > 0.99) of
this data by exploiting the 2-step model introduced by Finke
and Watzky (F−W) indicates that a nucleation−growth
process governs the interactions of butadiyne-bridged
porphyrin building blocks.56−58 Please note that this two-step
nucleation−growth mechanism has been exploited to elucidate
the aggregation of π-conjugated cores.59−61 More details are
provided in Section 6 of the Supporting Information. While the
F−W model comprises two simple pseudoelementary steps,
namely nucleation and growth, it provides insights not only
into the assembly mechanism but also for estimating the
average rate constants k1 and k2 associated with the nucleation
and growth steps, respectively. Notably, similar values of k1 and
k2 were extracted from the kinetic analysis performed at 775
and 415 nm, further indicating that the formation of aggregates
is intimately correlated with the decrease in planar conformers.
It is interesting to note that the k1 and k2 values are in the same
order of magnitude as the nucleation and growth/elongation
rate constants reported for planar π-conjugated molecules and
peptide structures sharing a similar molecular weight range
(1.5−4 kDa).61,62
in Figures 2B and 3B, it is fair to assume that their structural
properties in solution are similar. Consequently, the solid-state
morphologies of the dropcast aggregates are identical
regardless of the strategy exploited to trigger the noncovalent
interaction.
In summary, we have reported the synthesis, character-
ization, electronic spectral properties, solid-state morphologies,
and assembly properties of a novel and water-compatible
butadiyne-bridged (porphinato)zinc(II) building block. While
temperature-dependent spectroscopy indicates formation of H-
like aggregates, probing the mechanism of their formation
appears challenging due to additional overlapping processes,
such as temperature-dependent conformer populations.
Dropcasting H-like MPZnE2PZnM aggregates formed in
solution onto a silicon substrate enables the formation of 2D
nanosheets spanning microscale dimensions. A height profile
of 3 nm indicates that the free-standing monolayers are one
MPZnE2PZnM building block thick. It is important to
underscore that the facile formation of 2D nanomaterials
built from butadiyne-bridged MPZnE2PZnM building blocks
opens new avenues to construct novel organic semiconducting
materials relevant to the engineering of field-effect transistors
and spintronic devices.
We further demonstrated that initiating the noncovalent
assembly of MPZnE2PZnM building blocks by means of a
chemical trigger (pH) allowed for the unravelling of the
mechanism that regulates the formation of MPZnE2PZnM
aggregates. Coordination of the Zn(II) metal center by
pyridine ligands bolsters the solubilization of the π-conjugated
core in the solvent mixture where parent building blocks exist
in an aggregated state. Protonation of the pyridine ligands
enables the formation of activated building blocks that
assemble as a function of time. The investigation of the
assembly kinetics exploiting the Finke-Watzky model indicates
that a nucleation−growth/elongation process regulates the
assembly of MPZnE2PZnM building blocks. We posit that the
development of novel water-soluble chromophores capable of
forming hierarchical superstructures under chemical signaling
paves the way to engineer complex dissipative systems
equipped with unique (opto)electronic properties.
ASSOCIATED CONTENT
■
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* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00345.
An increase in both the nucleation and growth rate constants
was evidenced when a higher equivalency of HCl (1.5 equiv
with respect to pyridine) was used to trigger aggregation. The
EAS as a function of time are shown in Figure S8. This
observation suggests that a larger excess of HCl (1.5 vs 1.25
equiv) promotes the formation of a higher concentration of
“activated” building blocks involved in the nucleation process,
consequently increasing the value of k1. In addition, the fact
that the elongation rate constant k2 increases as a function of
the HCl equivalency may originate from the overall increase of
the solution ionic strength.63,64
Similar to the solid-state morphologies of the aggregates
formed by exploiting a temperature treatment, the pH-
triggered assembly of MPZnE2PZnM building blocks engen-
ders the creation of 2D nanosheets with an associated height
profile of 2−3 nm (Figure S13). Because MPZnE2PZnM
aggregates induced by temperature and chemical (pH)
treatments share similar spectroscopic properties, as observed
Synthesis of MPZnE2PZnM and MPZnM building
blocks, atomic force microcsopy images, 1H NMR
spectra, 13C NMR spectra, and high-resolution mass
spectra (PDF)
Dihedral angle data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
Jean-Hubert Olivier − Department of Chemistry, The
University of Miami, Coral Gables, Florida 33146, United
States; orcid.org/0000-0003-0978-4107; Phone: +1
(305) 284-3279; Email: jh.olivier@miami.edu
Authors
Chuan Liu − Department of Chemistry, The University of
Miami, Coral Gables, Florida 33146, United States
E
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Kaixuan Liu − Department of Chemistry, The University of
Miami, Coral Gables, Florida 33146, United States
Arindam Mukhopadhyay − Department of Chemistry, The
University of Miami, Coral Gables, Florida 33146, United
States; orcid.org/0000-0002-0620-4157
Victor Paulino − Department of Chemistry, The University of
Miami, Coral Gables, Florida 33146, United States
Brianna Bernard − Department of Chemistry, The University of
Miami, Coral Gables, Florida 33146, United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00345
Funding
The work was funded by the Arnold and Mabel Beckman
Foundation through the Beckman Young Investigator award
2018.
(16) Ashcraft, A.; Liu, K.; Mukhopadhyay, A.; Paulino, V.; Liu, C.;
Bernard, B.; Husainy, D.; Phan, T.; Olivier, J.-H. A Molecular Strategy
to Lock-in the Conformation of a Perylene Bisimide-Derived
Supramolecular Polymer. Angew. Chem., Int. Ed. 2020, 59, 7487−
7493.
Notes
The authors declare no competing financial interest.
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■
The authors thank Prof. Orlando Acevedo for his help and
constructive discussion with DFT and TDDFT calculations.
The authors are grateful to BioNIUM and Dr. Kevin Luongo
for his assistance with atomic force microscopy.
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