A Chirally Locked Bis-perylene Diimide Macrocycle: Consequences for Chiral Self-Assembly and Circularly Polarized Luminescence.

Macrocycles containing chiral organic dyes are highly valuable for the development of supramolecular circularly polarized luminescent (CPL) materials, where a preorganized chiral framework is conducive to directing π-π self-assembly and delivering a strong and persistent CPL signal. Here, perylene diimides (PDIs) are an excellent choice for the organic dye component because, alongside their tunable photophysical and self-assembly properties, functionalization of the PDI's core yields a twisted, chiral π-system, capable of CPL. However, configurationally stable PDI-based macrocycles are rare, and those that are also capable of π-π self-assembly beyond dimers are unprecedented, both of which are advantageous for robust self-assembled chiroptical materials. In this work, we report the first bay-connected bis-PDI macrocycle that is configurationally stable (ΔG⧧ > 155 kJ mol-1). We use this chirally locked macrocycle to uncover new knowledge of chiral PDI self-assembly and to perform new quantitative CPL imaging of the resulting single-crystal materials. As such, we discover that the chirality of a 1,7-disubstituted PDI provides a rational route to designing H-, J- and concomitant H- and J-type self-assembled materials, important arrangements for optimizing (chir)optical and charge/energy transport properties. Indeed, we reveal that CPL is amplified in the single crystals of our chiral macrocycle by quantifying the degree of emitted light circular polarization from such materials for the first time using CPL-Laser Scanning Confocal Microscopy.

The Pink Box: Exclusive Homochiral Aromatic Stacking in a Bis-perylene Diimide Macrocycle.

This work showcases chiral complementarity in aromatic stacking interactions as an effective tool to optimize the chiroptical and electrochemical properties of perylene diimides (PDIs). PDIs are a notable class of robust dye molecules and their rich photo- and electrochemistry and potential chirality make them ideal organic building blocks for chiral optoelectronic materials. By exploiting the new bay connectivity of twisted PDIs, a dynamic bis-PDI macrocycle (the "Pink Box") is realized in which homochiral PDI-PDI π-π stacking interactions are switched on exclusively. Using a range of experimental and computational techniques, we uncover three important implications of the macrocycle's chiral complementarity for PDI optoelectronics. First, the homochiral intramolecular π-π interactions anchor the twisted PDI units, yielding enantiomers with half-lives extended over 400-fold, from minutes to days (in solution) or years (in the solid state). Second, homochiral H-type aggregation affords the macrocycle red-shifted circularly polarized luminescence and one of the highest dissymmetry factors of any small organic molecule in solution (glum = 10-2 at 675 nm). Finally, excellent through-space PDI-PDI π-orbital overlap stabilizes PDI reduced states, akin to covalent functionalization with electron-withdrawing groups.

The Green Box: An Electronically Versatile Perylene Diimide Macrocyclic Host for Fullerenes.

The powerful electron accepting ability of fullerenes makes them ubiquitous components in biomimetic donor-acceptor systems that model the intermolecular electron transfer processes of Nature's photosynthetic center. Exploiting perylene diimides (PDIs) as components in cyclic host systems for the noncovalent recognition of fullerenes is unprecedented, in part because archetypal PDIs are also electron deficient, making dyad assembly formation electronically unfavorable. To address this, we report the strategic design and synthesis of a novel large, macrocyclic receptor composed of two covalently strapped electron-rich bis-pyrrolidine PDI panels, nicknamed the "Green Box" due to its color. Through the principle of electronic complementarity, the Green Box exhibits strong recognition of pristine fullerenes (C60/70), with the noncovalent ground and excited state interactions that occur upon fullerene guest encapsulation characterized by a range of techniques including electronic absorption, fluorescence emission, NMR and time-resolved EPR spectroscopies, cyclic voltammetry, mass spectrometry, and DFT calculations. While relatively low polarity solvents result in partial charge transfer in the host donor-guest acceptor complex, increasing the polarity of the solvent medium facilitates rare, thermally allowed full electron transfer from the Green Box to fullerene in the ground state. The ensuing charge separated radical ion paired complex is spectroscopically characterized, with thermodynamic reversibility and kinetic stability also demonstrated. Importantly, the Green Box represents a seminal type of C60/70 host where electron-rich PDI motifs are utilized as recognition motifs for fullerenes, facilitating novel intermolecular, solvent tunable ground state electronic communication with these guests. The ability to switch between extremes of the charge transfer energy continuum is without precedent in synthetic fullerene-based dyads.

Supramolecular Assemblies for Electronic Materials.

This work presents a synergy between organic electronics and supramolecular chemistry, in which a host-guest complex is designed to function as an efficacious electronic material. Specifically, the noncovalent recognition of a fullerene, phenyl-C61 -butyric acid methyl ester (PC61 BM), by an alternating perylene diimide (P)-bithiophene (B) conjugated macrocycle (PBPB) results in a greater than five-fold enhancement in electron mobility, relative to the macrocycle alone. Characterization and quantification of the binding of fullerenes by host PBPB is provided alongside evidence for intermolecular electronic communication within the host-guest complexes.

Anion-Mediated Photophysical Behavior in a C60 Fullerene [3]Rotaxane Shuttle.

By addressing the challenge of controlling molecular motion, mechanically interlocked molecular machines are primed for a variety of applications in the field of nanotechnology. Specifically, the designed manipulation of communication pathways between electron donor and acceptor moieties that are strategically integrated into dynamic photoactive rotaxanes and catenanes may lead to efficient artificial photosynthetic devices. In this pursuit, a novel [3]rotaxane molecular shuttle consisting of a four-station bis-naphthalene diimide (NDI) and central C60 fullerene bis-triazolium axle component and two mechanically bonded ferrocenyl-functionalized isophthalamide anion binding site-containing macrocycles is constructed using an anion template synthetic methodology. Dynamic coconformational anion recognition-mediated shuttling, which alters the relative positions of the electron donor and acceptor motifs of the [3]rotaxane's macrocycle and axle components, is demonstrated initially by 1H NMR spectroscopy. Detailed steady-state and time-resolved UV-vis-IR absorption and emission spectroscopies as well as electrochemical studies are employed to further probe the anion-dependent positional macrocycle-axle station state of the molecular shuttle, revealing a striking on/off switchable emission response induced by anion binding. Specifically, the [3]rotaxane chloride coconformation, where the ferrocenyl-functionalized macrocycles reside at the center of the axle component, precludes electron transfer to NDI, resulting in the switching-on of emission from the NDI fluorophore and concomitant formation of a C60 fullerene-based charge-separated state. By stark contrast, in the absence of chloride as the hexafluorophosphate salt, the ferrocenyl-functionalized macrocycles shuttle to the peripheral NDI axle stations, quenching the NDI emission via formation of a NDI-containing charge-separated state. Such anion-mediated control of the photophysical behavior of a rotaxane through molecular motion is unprecedented.

Anion- and Solvent-Induced Rotary Dynamics and Sensing in a Perylene Diimide [3]Catenane.

A novel dynamic [3]catenane consisting of a large four-station central macrocycle which incorporates a bay tetrachloro-functionalized perylene diimide (PDI) unit and two triazolium anion-binding motifs, mechanically bonded with two smaller isophthalamide-containing macrocycles, is constructed using an anion template synthetic methodology. Proton NMR, electronic absorption, and fluorescence emission spectroscopies together with molecular dynamics simulations are used to investigate the anion recognition- and solvent-dependent dynamic properties of the higher-order mechanically interlocked molecule. Importantly, unprecedented solvent-dependent and anion-binding-induced circumrotatory motion in a hetero[3]catenane system is demonstrated where the exotic dual rotary switching behavior provides a unique and sophisticated mechanism for optical anion sensing in competitive protic organic and aqueous-organic media.

Selective Nitrate Recognition by a Halogen-Bonding Four-Station [3]Rotaxane Molecular Shuttle.

The synthesis of the first halogen bonding [3]rotaxane host system containing a bis-iodo triazolium-bis-naphthalene diimide four station axle component is reported. Proton NMR anion binding titration experiments revealed the halogen bonding rotaxane is selective for nitrate over the more basic acetate, hydrogen carbonate and dihydrogen phosphate oxoanions and chloride, and exhibits enhanced recognition of anions relative to a hydrogen bonding analogue. This elaborate interlocked anion receptor functions via a novel dynamic pincer mechanism where upon nitrate anion binding, both macrocycles shuttle from the naphthalene diimide stations at the periphery of the axle to the central halogen bonding iodo-triazolium station anion recognition sites to form a unique 1:1 stoichiometric nitrate anion-rotaxane sandwich complex. Molecular dynamics simulations carried out on the nitrate and chloride halogen bonding [3]rotaxane complexes corroborate the (1) H NMR anion binding results.

Investigating the diastereoselective synthesis of a macrocycle under Curtin-Hammett control.

This work sheds new light on the stereoselective synthesis of chiral macrocycles containing twisted aromatic units, valuable π-conjugated materials for recognition, sensing, and optoelectronics. For the first time, we use the Curtin-Hammett principle to investigate a chiral macrocyclisation reaction, revealing the potential for supramolecular π-π interactions to direct the outcome of a dynamic kinetic resolution, favouring the opposite macrocyclic product to that expected under reversible, thermodynamically controlled conditions. Specifically, a dynamic, racemic perylene diimide dye (1 : 1 P : M) is strapped with an enantiopure (S)-1,1'-bi-2-naphthol group (P-BINOL) to form two diastereomeric macrocyclic products, the homochiral macrocycle (PP) and the heterochiral species (PM). We find there is notable selectivity for the PM macrocycle (dr = 4 : 1), which is rationalised by kinetic templation from intramolecular aromatic non-covalent interactions between the P-BINOL π-donor and the M-PDI π-acceptor during the macrocyclisation reaction.

Anion sensing by solution- and surface-assembled osmium(II) bipyridyl rotaxanes.

We report the preparation of [2]rotaxanes containing an electrochemically and optically active osmium(II) bipyridyl macrocyclic component mechanically bonded with cationic pyridinium axles. Such interlocked host systems are demonstrated to recognise and sense anionic guest species as shown by (1)H NMR, luminescence and electrochemical studies. The rotaxanes can be surface assembled on to gold electrodes through anion templation under click copper(I)-catalysed Huisgen cycloaddition conditions to form rotaxane molecular films, which, after template removal, respond electrochemically and selectively to chloride.

Superior anion induced shuttling behaviour exhibited by a halogen bonding two station rotaxane.

Two bistable halogen and hydrogen bonding-naphthalene diimide [2]rotaxanes have been prepared and the system incorporating a halogen bond donor anion recognition site is demonstrated to exhibit superior anion induced translational motion of the macrocyclic wheel component relative to the hydrogen bonding analogue. Proton NMR spectroscopy is used to estimate the percentage occupancies of the macrocycle at the respective station and importantly indicates that the halogen bonding rotaxane displays superior positional integrity in competitive protic solvent media as a consequence of strong halogen bond-halide anion binding interactions.