7 research outputs found
Impact of Alkyl Spacer Length on Aggregation Pathways in Kinetically Controlled Supramolecular Polymerization
We
have investigated the kinetic and thermodynamic supramolecular
polymerizations of a series of amide-functionalized perylene bisimide
(PBI) organogelator molecules bearing alkyl spacers of varied lengths
(ethylene to pentylene chains, <b>PBI-1-C2</b> to <b>PBI-1-C5</b>) between the amide and PBI imide groups. These amide-functionalized
PBIs form one-dimensional fibrous nanostructures as the thermodynamically
favored states in solvents of low polarity. Our in-depth studies revealed,
however, that the kinetic behavior of their supramolecular polymerization
is dependent on the spacer length. Propylene- and pentylene-tethered
PBIs follow a similar polymerization process as previously observed
for the ethylene-tethered PBI. Thus, the monomers of these PBIs are
kinetically trapped in conformationally restricted states through
intramolecular hydrogen bonding between the amide and imide groups.
In contrast, the intramolecularly hydrogen-bonded monomers of butylene-tethered
PBI spontaneously self-assemble into nanoparticles, which constitute
an off-pathway aggregate state with regard to the thermodynamically
stable fibrous supramolecular polymers obtained. Thus, for this class
of Ļ-conjugated system, an unprecedented off-pathway aggregate
with high kinetic stability could be realized for the first time by
introducing an alkyl linker of optimum length (C4 chain) between the
amide and imide groups. Our current system with an energy landscape
of two competing nucleated aggregation pathways is applicable to the
kinetic control over the supramolecular polymerization by the seeding
approach
Mechanism of Self-Assembly Process and Seeded Supramolecular Polymerization of Perylene Bisimide Organogelator
The mechanism of supramolecular polymerization
has been elucidated
for an archetype organogelator molecule composed of a perylene bisimide
aromatic scaffold and two amide substituents. This molecule self-assembles
into elongated one-dimensional nanofibers through a cooperative nucleationāgrowth
process. Thermodynamic and kinetic analyses have been applied to discover
conditions (temperature, solvent, concentration) where the spontaneous
nucleation can be retarded by trapping of the monomers in an inactive
conformation, leading to lag times up to more than 1 h. The unique
kinetics in the nucleation process was confirmed as a thermal hysteresis
in a cycle of assembly and disassembly processes. Under appropriate
conditions within the hysteresis loop, addition of preassembled nanofiber
seeds leads to seeded polymerization from the termini of the seeds
in a living supramolecular polymerization process. These results demonstrate
that seeded polymerizations are not limited to special situations
where off-pathway aggregates sequester the monomeric reactant species
but may be applicable to a large number of known and to be developed
molecules from the large family of molecules that self-assemble into
one-dimensional nanofibrous structures. Generalizing from the mechanistic
insight into our seeded polymerization, we assert that a cooperative
nucleationāgrowth supramolecular polymerization accompanied
by thermal hysteresis can be controlled in a living manner
Cooperative Self-Assembly Transfer from Hierarchical Supramolecular Polymers to Gold Nanoparticles
The transfer of information encoded by molecular subcomponents is a key phenomenon that regulates the biological inheritance in living organisms, yet there is a lack of understanding of related transfer mechanisms at the supramolecular level in artificial multicomponent systems. Our contribution to tackle this challenge has focused on the design of a thiolated Ļ-conjugated linking unit, whose hierarchical, cooperative self-assembly in nonpolar media can be efficiently transferred from the molecular to the nanoscopic level, thereby enabling the reversible self-assembly of gold nanoparticle (AuNP) clusters. The transfer of supramolecular information by the linking Ļ-system can only take place when a specific cooperative nucleation-elongation mechanism is operative, whereas low-ordered noncooperative assemblies formed below a critical concentration do not suffice to extend the order to the AuNP level. To the best of our knowledge, our approach has allowed for the first time a deep analysis of the hierarchy levels and thermodynamics involved in the self-assembly of AuNPs
Cooperative Supramolecular Polymerization Driven by Metallophilic PdĀ·Ā·Ā·Pd Interactions
A new oligophenyleneethynylene (OPE)-based PdĀ(II) pyridyl
complex
has been synthesized, and its self-assembly has been investigated
in solution, in the bulk state, and on surfaces. Detailed analysis
of concentration- and temperature-dependent UVāvis studies
in methylcyclohexane supported by DFT calculations demonstrate for
the first time that cooperative supramolecular polymerization processes
can be driven by metallophilic interactions
A Covalent Organic Framework for Cooperative Water Oxidation
The future of water-derived hydrogen as the āsustainable
energy sourceā straightaway bets on the success of the sluggish
oxygen-generating half-reaction. The endeavor to emulate the natural
photosystem II for efficient water oxidation has been extended across
the spectrum of organic and inorganic combinations. However, the achievement
has so far been restricted to homogeneous catalysts rather than their
pristine heterogeneous forms. The poor structural understanding and
control over the mechanistic pathway often impede the overall development.
Herein, we have synthesized a highly crystalline covalent organic
framework (COF) for chemical and photochemical water oxidation. The
interpenetrated structure assures the catalyst stability, as the catalystās
performance remains unaltered after several cycles. This COF exhibits
the highest ever accomplished catalytic activity for such an organometallic
crystalline solid-state material where the rate of oxygen evolution
is as high as ā¼26,000 Ī¼mol Lā1 sā1 (second-order rate constant k ā
1650 Ī¼mol L sā1 gā2). The
catalyst also proves its exceptional activity (k ā
1600 Ī¼mol L sā1 gā2) during
light-driven water oxidation under very dilute conditions. The cooperative
interaction between metal centers in the crystalline network offers
20ā30-fold superior activity during chemical as well as photocatalytic
water oxidation as compared to its amorphous polymeric counterpart
Exciton Coupling of Merocyanine Dyes from H- to Jātype in the Solid State by Crystal Engineering
A key
issue for the application of Ļ-conjugated organic molecules
as thin film solid-state materials is the packing structure, which
drastically affects optical and electronic properties due to intermolecular
coupling. In this regard, merocyanine dyes usually pack in H-coupled
antiparallel arrangements while structures with more interesting J-type
coupling have been rarely reported. Here we show that for three highly
dipolar merocyanine dyes, which exhibit the same Ļ-scaffold
and accordingly equal properties as monomers in solution, the solid-state
packing can be changed by a simple variation of aliphatic substituents
to afford narrow and intense absorption bands with huge hypsochromic
(H) or bathochromic (J) shifts for their thin films and nanocrystals.
Time-dependent density functional theory calculations show that the
energetic offset of almost 1 eV magnitude results from distinct packing
motifs within the crystal structures that comply with the archetype
H- or J-aggregate structures as described by Kashaās exciton
theory
Influence of Solid-State Packing of Dipolar Merocyanine Dyes on Transistor and Solar Cell Performances
A series of nine dipolar merocyanine
dyes has been studied as organic
semiconductors in transistors and solar cells. These dyes exhibited
single-crystal packing motifs with different dimensional ordering,
which can be correlated to the performance of the studied devices.
Hereby, the long-range ordering of the dyes in staircase-like slipped
stacks with <i>J</i>-type excitonic coupling favors charge
transport and improves solar cell performance. The different morphologies
of transistor thin films and solar cell active layers were investigated
by UVāvis, AFM, and XRD experiments. Selenium-containing donorāacceptor
(DāA) dimethine dye <b>4</b> showed the highest hole
mobility of 0.08 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>. BHJ solar cells based on dye <b>4</b> were optimized by taking
advantage of the high crystallinity of the donor material and afforded
a PCE of up to 6.2%