Long-Range Energy Transport via Plasmonic Propagation in a Supramolecular Organic Waveguide

Azatriseptanes: Strained Framework Analogs of [7,7,7]Circulenes

The synthesis and characterization of heptagon-embedded polycyclic aromatic compounds are essential for understanding the effect of negative curvature on carbon allotropes such as fullerenes and graphenes that have applications in functional organic materials. However, owing to the synthetic difficulties in functionalizing and embedding seven-membered rings, these strain-challenged structures are relatively unexplored. We report here the synthesis, characterization, and properties of a triarylamine core bridged with ethano chains at the 2,2'-positions. In doing so, we provide access to the first heterocycle containing three fused heptagon rings with a nitrogen at its core (BATA-NHAc). X-ray crystallographic analysis and DFT calculations revealed a remarkably strained structure wherein two of the bridged aryl units approach coplanarity, while the third ring is twisted out of plane at 70°. UV-vis and emission spectroscopies identify red-shifted absorption and concentration-dependent emission profiles, respectively, as a result of the unique conformation and self-assembly properties of BATA-NHAc. Furthermore, cyclic voltammetry shows a decrease in the oxidation potential for BATA-NHAc in comparison to the non-bridged analog. This study opens new avenues in understanding the structure-property relationships of curved π-aromatics and the construction of π-frameworks of increasing complexity.

Interplay Between Hydrogen Bonding and Electron Transfer in Mixed Valence Assemblies of Triarylamine Trisamides

Hydrogen-bonding interactions are assumed to play a critical role in the long-range transport of light or charge recently observed in supramolecular assemblies of C₃ -symmetrical discotic molecules. Herein, the structure of mixed valence assemblies formed by irradiating triarylamine trisamide (TATA) molecules was determined by multifarious techniques under various conditions with the aim of probing the interplay between the hydrogen bonding network and the rate of electron transport in different states (solution, gel, film). Irradiation was performed under initial states that vary by the degree of association of TATA monomers through hydrogen bonds. Firstly, a significant shift of the N-H and C=O stretching frequencies was observed by FTIR upon irradiation thus revealing an overlooked signature of TATA⋅+ species and interacting mixed valence aggregates. Secondly, gels and films both mostly consist of hydrogen-bonded TATA polymers but their EPR spectra recorded at 293 K reveal very different behaviors: localized electrons in the gels versus fully delocalized electrons in the films. Hydrogen bonding thus appears as a necessary but not sufficient condition to get fast electron transfer rates and a packing of the TATA monomers particularly suitable for charge transport is assumed to exist in the solid state. Finally, defects in the hydrogen bonding network are detected upon increasing the number of radical species in the mixed valence assemblies present in the film state without impeding the delocalization of the unpaired electrons. A delicate balance between hydrogen bonds and packing is thus necessary to get supramolecular polarons in mixed valence TATA assemblies.

Structure-property investigations in urea tethered iodinated triphenylamines

Herein, we report structural, computational, and conductivity studies on urea-directed self-assembled iodinated triphenylamine (TPA) derivatives. Despite numerous reports of conductive TPAs, the challenges of correlating their solid-state assembly with charge transport properties hinder the efficient design of new materials. In this work, we compare the assembled structures of a methylene urea bridged dimer of di-iodo TPA (1) and the corresponding methylene urea di-iodo TPA monomer (2) with a di-iodo mono aldehyde (3) control. These modifications lead to needle shaped crystals for 1 and 2 that are organized by urea hydrogen bonding, π⋯π stacking, I⋯I, and I⋯π interactions as determined by SC-XRD, Hirshfeld surface analysis, and X-ray photoelectron spectroscopy (XPS). The long needle shaped crystals were robust enough to measure the conductivity by two contact probe methods with 2 exhibiting higher conductivity values (∼6 × 10^-7 S cm^-1) compared to 1 (1.6 × 10^-8 S cm^-1). Upon UV-irradiation, 1 formed low quantities of persistent radicals with the simple methylurea 2 displaying less radical formation. The electronic properties of 1 were further investigated using valence band XPS, which revealed a significant shift in the valence band upon UV irradiation (0.5-1.9 eV), indicating the potential of these materials as dopant free p-type hole transporters. The electronic structure calculations suggest that the close packing of TPA promotes their electronic coupling and allows effective charge carrier transport. Our results show that ionic additives significantly improve the conductivity up to ∼2.0 × 10^-6 S cm^-1 in thin films, enabling their implementation in functional devices such as perovskite or solid-state dye sensitized solar cells.

Diversifying Nanoparticle Superstructures and Functions Enabled by Translative Templating from Supramolecular Polymerization

Biology exploits a transcription-translation approach to deliver structural information from DNA to the protein-building machines with high precision. Here, we show how the structural information of small synthetic molecules could be used to guide the assembly of inorganic nanoparticles into diversified yet long-range ordered superstructures, enabling the information transfer across four or five orders of magnitude in length scale. We designed three perylene diimide (PDI) based isomers differing by their site-specific substitutions of the methyl group, which were able to supramolecularly polymerize into diverse structures. Importantly, coassembly of these PDI isomers with nanoparticles (NPs) could produce diverse long-range ordered nanoparticle superstructures, including one-dimensional NPs chains, double helical NPs assemblies and two-dimensional NPs superlattices. Equally important, we demonstrate that the information originated from small molecules could diversify the functions of the self-assembled nanocomposites.

Supramolecular Polymerization of Triarylamine-Based Macrocycles into Electroactive Nanotubes

A S₆-symmetric triarylamine-based macrocycle (i.e., hexaaza[1₆]paracyclophane), decorated with six lateral amide functions, is synthesized by a convergent and modular strategy. This macrocycle is shown to undergo supramolecular polymerization in o-dichlorobenzene, and its nanotubular structure is elucidated by a combination of spectroscopy and microscopy techniques, together with X-ray scattering and molecular modeling. Upon sequential oxidation, a spectroelectrochemical analysis of the supramolecular polymer suggests an extended electronic delocalization of charge carriers both within the macrocycles (through bond) and between the macrocycles along the stacking direction (through space).

Anisotropic Assembly of Nanocrystal/Molecular Hierarchical Superlattices Decoding from Tris-Amide Triarylamines Supramolecular Networks

Directed assembly of nanocrystals from conventional templates suffers from poor control over the periodicity of the nanocrystal assembly, which is largely due to the fact that the template exists prior to the assembly and is not generally adaptive. Herein, small organic molecules (tris-amide triarylamines, TATA) are demonstrated as conceptual templates from self-assembly through noncovalent interactions. The as-formed supramolecular structures with terminated alkyl chains, resembling the structure of as-synthesized nanocrystals capped with alkyl chains, are able to interact with nanocrystals through van der Waals attractive forces, thereby enabling directed assembly of nanocrystals into ordered superlattices. Specifically, it is found that, as determined by the substituted alkyl chains of TATA, either H or J-aggregates of TATA can be achieved, which eventually produce several distinct supramolecular structures, from rods to spindles, to rings, and to spheres, serving as on-pathway intermediate that directs the assembly of nanocrystals into diverse nanocrystal superlattices. The approach described can be applicable to produce ordered nanocrystal assemblies of a wide range of nanocrystals, independent of size and shape and without ligand exchange process. Strikingly, a helical TATA stacking can direct assembly of binary nanocrystal mixtures into NaZn₁₃ binary superhelix.

Homodyne dynamic light scattering in supramolecular polymer solutions: anomalous oscillations in intensity correlation function

Dilute solutions of electronically active molecules capable of irradiation-driven supramolecular self-assembly are studied by dynamic light scattering. We detect unusual well-defined oscillations in the long time range of the homodyne intensity correlation function for all solutions that were irradiated with white light prior to the measurements. The oscillation effect is attributed to the local laser-induced heating of the samples due to strongly enhanced absorption manifested by the supramolecular filaments. It is found that the oscillation frequency depends on the irradiation time, solution concentration, and the incident laser power, but is independent of the scattering angle. These observations are explained with a semi-quantitative theory relating the oscillation effect to thermo-gravitational convection flows generated by laser beam. The results suggest that the presence of such homodyne oscillations could be a sensitive probe for aggregation in many complex systems.

Covalently Trapped Triarylamine-Based Supramolecular Polymers

C₃ -Symmetric triarylamine trisamides (TATAs), decorated with three norbornene end groups, undergo supramolecular polymerization and further gelation by π-π stacking and hydrogen bonding of their TATA cores. By using subsequent ring-opening metathesis polymerization, these physical gels are permanently crosslinked into chemical gels. Detailed comparisons of the supramolecular stacks in solution, in the physical gel, and in the chemical gel states, are performed by optical spectroscopies, electronic spectroscopies, atomic force microscopy, electronic paramagnetic resonance spectroscopy, X-ray scattering, electronic transport measurements, and rheology. The results presented here clearly evidence that the core structure of the functional supramolecular polymers can be precisely retained during the covalent capture whereas the mechanical properties of the gels are concomitantly improved, with an increase of their storage modulus by two orders of magnitude.

Triarylamine-Based Supramolecular Polymers: Structures, Dynamics, and Functions

Triarylamine molecules and triarylamine-based covalent polymers have been extensively investigated for more than 60 years in academics and industry because of their intriguing electronic and optical characteristics. However, despite the profusion of studies made on these derivatives, only very recently have the first examples of supramolecular polymers based on the triarylamine motif been described in the literature. Specifically, our research group has shown that, by adding supplementary hydrogen bonding moieties such as amide functions in their periphery, it becomes possible to tightly pack triarylamine molecules in columnar supramolecular stacks presenting a collinear arrangement of their central nitrogen atoms. These supramolecular polymers can self-assemble into various soft hierarchical structures such as helical fibers, nanorods, nanospheres, and nanoribbons in the sol and in the gel states, into liquid-crystalline mesophases, and into highly organized supramolecular frameworks and single crystals thereof. Interestingly, the associated supramolecular polymerization mechanism involves a nucleation step of high activation energy, which requires the flattening of the triarylamine core. Because of this singularity and although dependent on the precise chemical nature of the building blocks, it has been demonstrated that their supramolecular polymerization can be triggered by original tools, such as light irradiation or electrochemistry, and that it can display autocatalytic growth behaviors, remarkably strong amplifications of chirality, and complex and competing thermodynamic and kinetic self-assembly pathways. Further, from a functional point of view, it has been highlighted that a partial oxidation of the triarylamine molecules results in an enhanced through-space delocalization of the charge carriers along the π-π stacked supramolecular polymers, a feature that confers to these nanowires exceptional transport properties. Upon increasing the charge carrier concentration, the electronic nature of these soft materials can be switched from semiconducting to metallic behavior, and the presence of highly delocalized unpaired electrons in supramolecular polaronic band structures has been further exploited to implement plasmonic properties within subwavelength organic interconnects and microscopic optical waveguides. Finally, by making use of the unusual dynamics and functions of triarylamine-based nanostructures, it becomes possible to precisely address their self-construction within confined environments or within nano- and micrometer scale devices. This has been demonstrated for instance between nanoparticles and between electrodes, inside inorganic nanopores, and inside phospholipid bilayers, as well as at the liquid-liquid interface. Such a meeting point between bottom-up and top-down technologies is of high interest to envision further developments and applications for this entirely new class of supramolecular polymers, which combine a unique relationship between their structures, their dynamics, and their subsequent emerging functional properties.

3D supramolecular self-assembly of [60]fullerene hexaadducts decorated with triarylamine molecules

A clickable fullerene hexa-adduct scaffold has been functionalized with twelve triarylamine subunits. The light-triggered self-assembly of this molecular unit leads to 3D honeycomb-like structures with inner pores of around 10 nm diameter. Multiple grafting of triarylamine subunits onto a hard-core C₆₀ unit increases the dimensionality of the self-assembly process by reticulating the 1D nanowires typically obtained from the supramolecular polymerization of triarylamine monomers.

Anisotropic Self-Assembly of Supramolecular Polymers and Plasmonic Nanoparticles at the Liquid-Liquid Interface

The study of supramolecular polymers in the bulk, in diluted solution, and at the solid-liquid interface has recently become a major topic of interest, going from fundamental aspects to applications in materials science. However, examples of supramolecular polymers at the liquid-liquid interface are mostly unexplored. Here, we describe the supramolecular polymerization of triarylamine molecules and their light-triggered organization at a chloroform-water interface. The resulting interfacial nematic layer of these 1D supramolecular polymers is further used as a template for the precise alignment of spherical gold nanoparticles coming from the water phase. These hybrid thin films are spontaneously formed in a single process, without chemical prefunctionalization of the metallic nanoparticles, and their ordering is improved by centrifugation. The resulting polymer chains and strings of nanoparticles can be co-aligned with high anisotropy over very large distances. By using a combination of experimental and theoretical investigations, we decipher the full sequence of this oriented self-assembly process. In such a highly anisotropic configuration, electron energy loss spectroscopy reveals that the self-assembled nanoparticles behave as plasmonic waveguides.

A novel self-healing electrochromic film based on a triphenylamine cross-linked polymer

A novel electrochromic material with self-healing properties, which may hold great potential to overcome the scar generation in ECDs, has been synthesized and studied.

Dynamic propeller conformation for the unprecedentedly high degree of chiral amplification of supramolecular helices

An unprecedentedly high degree of chiral amplification of supramolecular helices in a sergeants and soldiers system was realized using a propeller-shaped molecule, triphenylamine (TPA), as the monomer. One sergeant controlled the handedness of 500 soldiers in supramolecular helices. We further demonstrated that a TPA derivative could switch its role from sergeant to soldier and vice versa depending on its partners. These achievements could be realized using the dynamic propeller conformation of TPA and provide new insights into supramolecular assemblies and the supramolecular chiral amplification of helices.