N-Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J- and H-Aggregates

The unique self-assembling features of N-annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1 , in which no H-bonding interactions are operative, corroborates the significance of long-range van der Waals and dipole–dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N-annulated PBI in 2 stimulates pathway differentiation to achieve up to three J-type aggregates and a fourth H-type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self-assembly and the rich differentiation that N-annulated PBIs exhibit, opening the door to new, complex, functional supramolecular materials.     

Pathway Complexity Versus Hierarchical Self‐Assembly in N‐Annulated Perylenes: Structural Effects in Seeded Supramolecular Polymerization

Studies were carried out on the hierarchical self‐assembly versus pathway complexity of N‐annulated perylenes 1 – 3 , which differ only in the nature of the linking groups connecting the perylene core and the side alkoxy chains. Despite the structural similarity, compounds 1 and 2 exhibit noticeable differences in their self‐assembly. Whereas 1 forms an off‐pathway aggregate I that converts over time (or by addition of seeds) into the thermodynamic, on‐pathway product, 2 undergoes a hierarchical process in which the kinetically trapped monomer species does not lead to a kinetically controlled supramolecular growth. Finally, compound 3 , which lacks the amide groups, is unable to self‐assemble under identical experimental conditions and highlights the key relevance of the amide groups and their position to govern the self‐assembly pathways.     

Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J‐Aggregates

The self‐assembly of a new perylene bisimide (PBI) organogelator with 1,7‐dimethoxy substituents in the bay position affords non‐fluorescent H‐aggregates at high cooling rates and fluorescent J‐aggregates at low cooling rates. Under properly adjusted conditions, the kinetically trapped “off‐pathway” H‐aggregates are transformed into the thermodynamically favored J‐aggregates, a process that can be accelerated by the addition of J‐aggregate seeds. Spectroscopic studies revealed a subtle interplay of π–π interactions and intra‐ and intermolecular hydrogen bonding for monomeric, H‐, and J‐aggregated PBIs. Multiple polymerization cycles initiated from the seed termini demonstrate the living character of this chain‐growth supramolecular polymerization process.     

Chiral J‐Aggregates of Atropo‐Enantiomeric Perylene Bisimides and Their Self‐Sorting Behavior

Herein we report on structural, morphological, and optical properties of homochiral and heterochiral J‐aggregates that were created by nucleation–elongation assembly of atropo‐enantiomerically pure and racemic perylene bisimides (PBIs), respectively. Our detailed studies with conformationally stable biphenoxy‐bridged chiral PBIs by UV/Vis absorption, circular dichroism (CD) spectroscopy, and atomic force microscopy (AFM) revealed structurally as well as spectroscopically quite different kinds of J‐aggregates for enantiomerically pure and racemic PBIs. AFM investigations showed that enantiopure PBIs form helical nanowires of unique diameter and large length‐to‐width ratio by self‐recognition, while racemic PBIs provide irregular‐sized particles by self‐discrimination of the enantiomers at the stage of nucleation. Steady‐state fluorescence spectroscopy studies revealed that the photoluminescence efficiency of homochiral J‐aggregated nanowires (47±3 %) is significantly higher than that of heterochiral J‐aggregated particle‐like aggregates (12±3 %), which is explained in terms of highly ordered molecular stacking in one‐dimensional nanowires of homochiral J‐aggregates. Our present results demonstrate the high impact of homochirality on the construction of well‐defined nanostructures with unique optical properties.     

Self‐Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra‐Bay‐Acyloxy Perylene Bisimide

A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self‐assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen‐bond‐directed self‐assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid‐crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo‐ or heterochiral self‐assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self‐sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self‐assemblies proceeds by dissociation via the monomeric state.     

Kinetic Control of the Supramolecular Chirality of Porphyrin J‐Aggregates

The aggregation of achiral sulfonatophenyl‐ and phenyl‐meso‐substituted diprotonated porphyrins to chiral J‐aggregates is a hierarchical noncovalent polymerization process preceded by a critical nucleation stage. This allows significant enantiomeric excesses by the formation of a few primary nuclei and the control of their growth by the effect that flows (imperfect mixing) have on the secondary nucleation of the J‐aggregate particles. In addition, the results strongly suggest that when only one species of aggregate predominates, the CD signals of the three excitonic bands in the visible region (around 420, 490, and 700 nm) show the same sign. Thus, differences on their relative sign would be due to the presence of different species.     

Effect of an Aromatic Solvent on Hydrogen-Bond-Directed Supramolecular Polymerization Leading to Distinct Topologies

Beyond phenomenon, self-assembly of synthetic molecules, is now becoming an essential tool to design supramolecular materials not only in the thermodynamically stable state but also in kinetically trapped states. However, an approach to design complex self-assembly processes comprising different types of self-assembled states remains elusive. Herein, an example of such systems is demonstrated based on a unique supramolecular polymer mediated by supermacrocyclization of hydrogen-bonding π-conjugated molecules. By adding an aromatic solvent into nonpolar solutions of the monomer, spontaneous nucleation triggered by supermacrocyclization was suppressed so that isothermal supramolecular polymerization could be achieved from kinetically formed topological variants and amorphous agglomerates to afford helicoidal structures hitherto obtainable only with very slow cooling of a hot solution. By increasing the proportion of aromatic solvent further, another self-assembly path was found, based on competing extended hydrogen-bonded motifs affording crystalline nanowires.     

Living Supramolecular Polymerization of an Aza‐BODIPY Dye Controlled by a Hydrogen‐Bond‐Accepting Triazole Unit Introduced by Click Chemistry

An aza‐BODIPY dye 1 bearing two hydrophobic fan‐shaped tridodecyloxybenzamide pendants through 1,2,3‐triazole linkages was synthesized by a click reaction and characterized. ¹H NMR studies indicated that dye 1 exhibited variable conformations through intramolecular H‐bonding interaction, which is beneficial for the polymorphism of aggregation. The thermodynamic, structural, and kinetic aspect of the supramolecular polymerization of dye 1 was investigated by UV/Vis absorption spectroscopy, IR spectroscopy, AFM, TEM, and SEM. Biphasic aggregation pathways of dye 1 , leads to the formation of off‐pathway, metastable Agg. I and thermodynamically stable Agg. II with distinct H‐aggregation spectra and nanoscale morphology. The living manner of the supramolecular polymerization of dye 1 was demonstrated in seeded polymerization experiments with temperature‐modulated successive cooling–heating cycles.     

Supramolecular Copolymerization as a Strategy to Control the Stability of Self‐Assembled Nanofibers

A major challenge in supramolecular polymerization is controlling the stability of the polymers formed, that is, controlling the rate of monomer exchange in the equilibrium between monomer and polymer. The exchange dynamics of supramolecular polymers based on benzene‐1,3,5‐tricarboxamide (BTA) can be regulated by copolymerizing molecules with dendronized (dBTA) and linear (nBTA) ethylene glycol‐based water‐soluble side chains. Whereas nBTAs form long nanofibers in water, dBTAs do not polymerize, forming instead small spherical aggregates. The copolymerization of the two BTAs results in long nanofibers. The exchange dynamics of both the BTA monomers in the copolymer are significantly slowed down in the mixed systems, leading to a more stable copolymer, while the morphology and spectroscopic signature of the copolymers are identical to that of nBTA homopolymer. This copolymerization is the supramolecular counterpart of styrene/ maleic anhydride copolymerization.     

Cation‐Tuned Stimuli‐Responsive and Optical Properties of Supramolecular Hydrogels

Hierarchical self‐assembly of an amphiphilic tris‐urea in aqueous media is shown. A mixture of the amphiphilic tris‐urea and an alkaline solution gave a viscous solution composed of fibrous aggregates. This viscous solution transformed into supramolecular hydrogels, which are capable of hierarchically organizing into higher‐order aggregates in response to several cationic triggers. The resulting supramolecular hydrogels were relatively stiff and their storage moduli attained over 10³ Pa. The stimuli‐responsive and optical properties of the resulting hydrogels were influenced by the cationic trigger. Proton and calcium ion triggers gave pH‐ and chemical stimuli‐responsive hydrogels, respectively. A terbium ion trigger also provided a highly luminescent hydrogel through energy transfer from the tris‐urea to terbium.     

Peculiar Triarylamine‐Based Co‐assembled Supramolecular Polymers That Exhibit Two Transition Temperatures in the Formation of a Coiled Helical Bundle

This paper describes the peculiar co‐assembly supramolecular polymerization behavior of triphenylamine trisamide derivatives with d ‐alanine ( T‐ala ) or glycine ( T‐gly ) moieties. Concentration and temperature‐dependent circular dichroism (CD) spectroscopy revealed that the heating curves of co‐assemblies obtained at various molar ratios of T‐ala to T‐gly exhibited two distinct transition temperatures. The first transition was due to the transformation from coiled helical bundles to single helical fibers without handedness. The second was due to a change from typical elongation to nucleation. These phenomena were confirmed by solvent‐dependent decoiling of coiled helical structures and concentration‐dependent morphological analysis. The two transitioning temperatures were dependent on the concentration of T‐ala in the co‐assemblies, suggesting that T‐ala concentration plays an important role in the formation of coiled helical bundles. Our study demonstrated the first observation of two distinct transition temperatures in supramolecular polymers.     

Control of H‐ and J‐Type π Stacking by Peripheral Alkyl Chains and Self‐Sorting Phenomena in Perylene Bisimide Homo‐ and Heteroaggregates

The synthesis, self‐assembly, and gelation ability of a series of organogelators based on perylene bisimide (PBI) dyes containing amide groups at imide positions are reported. The synergetic effect of intermolecular hydrogen bonding among the amide functionalities and π–π stacking between the PBI units directs the formation of the self‐assembled structure in solution, which beyond a certain concentration results in gelation. Effects of different peripheral alkyl substituents on the self‐assembly were studied by solvent‐ and temperature‐dependent UV‐visible and circular dichroism (CD) spectroscopy. PBI derivatives containing linear alkyl side chains in the periphery formed H‐type π stacks and red gels, whereas by introducing branched alkyl chains the formation of J‐type π stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2‐ethylhexyl group completely suppressed the π stacking. Coaggregation studies with H‐ and J‐aggregating chromophores revealed the formation of solely H‐type π stacks containing both precursor molecules at a lower mole fraction of J‐aggregating chromophore. Beyond a critical composition of the two chromophores, mixed H‐aggregate and J‐aggregate were formed simultaneously, which points to a self‐sorting process. The versatility of the gelators is strongly dependent on the length and nature of the peripheral alkyl substituents. CD spectroscopic studies revealed a preferential helicity of the aggregates of PBI building blocks bearing chiral side chains. Even for achiral PBI derivatives, the utilization of chiral solvents such as (R)‐ or (S)‐limonene was effective in preferential population of one‐handed helical fibers. AFM studies revealed the formation of helical fibers from all the present PBI gelators, irrespective of the presence of chiral or achiral side chains. Furthermore, vortex flow was found to be effective in macroscopic orientation of the aggregates as evidenced from the origin of CD signals from aggregates of achiral PBI molecules.     

Interplay Between J‐ and H‐Type Coupling in Aggregates of π‐Conjugated Polymers: A Single‐Molecule Perspective

Strong dipole–dipole coupling within and between π‐conjugated segments shifts electronic transitions, and modifies vibronic coupling and excited‐state lifetimes. Since J‐type coupling between monomers along the conjugated‐polymer (CP) chain and H‐type coupling of chromophores between chains of a CP compete, a superposition of the spectral modifications arising from each type of coupling emerges, making the two couplings hard to discern in the ensemble. We introduce a single‐molecule H‐type aggregate of fixed spacing and variable length of up to 10 nm. HJ‐type aggregate formation is visualized intuitively in the scatter of single‐molecule spectra.     

Supramolecular assembly of H‐bonded side‐chain polymers containing conjugated pyridyl H‐acceptor pendants and various low‐band‐gap H‐donor dyes bearing cyanoacrylic acid groups for organic solar cell applications

Novel supramolecular side‐chain polymers were constructed by complexation of proton acceptor (H‐acceptor) polymers, i.e., side‐chain conjugated polymers P1–P2 containing pyridyl pendants, with low‐band‐gap proton donor (H‐donor) dyes S1–S4 (bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique mesomorphic properties confirmed by DSC and XRD results, the H‐bonds of supramolecular side‐chain structures formed by pyridyl H‐acceptors and cyanoacrylic acid H‐donors were also confirmed by FTIR measurements. H‐donor dyes S1–S4 in solid films exhibited broad absorption peaks located in the range of 471–490 nm with optical band‐gaps of 1.99–2.14 eV. Furthermore, H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 exhibited broad absorption peaks in the range of 440–462 nm with optical band‐gaps of 2.11–2.25 eV. Under 100 mW/cm² of AM 1.5 white‐light illumination, the bulk heterojunction polymer solar cell (PSC) devices containing an active layer of H‐bonded polymer complexes P1/S1–P1/S4 and P2/S1–P2/S4 (as electron donors) mixed with [6,6]‐phenyl C₆₁ butyric acid methyl ester (i.e., PCBM, as an electron acceptor) in the weight ratio of 1:1 were investigated. The PSC device containing H‐bonded polymer complex P1/S3 mixed with PCBM (1:1 w/w) gave the best preliminary result with an overall power conversion efficiency (PCE) of 0.50%, a short‐circuit current of 3.17 mA/cm², an open‐circuit voltage of 0.47 V, and a fill factor of 34%. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5998–6013, 2009     

A Molecular Strategy to Lock‐in the Conformation of a Perylene Bisimide‐Derived Supramolecular Polymer

Locking‐in the conformation of supramolecular assemblies provides a new avenue to regulate the (opto)electronic properties of robust nanoscale objects. In the present contribution, we show that the covalent tethering of a perylene bisimide (PBI)‐derived supramolecular polymer with a molecular locker enables the formation of a locked superstructure equipped with emergent structure–function relationships. Experiments that exploit variable‐temperature ground‐state electronic absorption spectroscopy unambiguously demonstrate that the excitonic coupling between nearest neighboring units in the tethered superstructure is preserved at a temperature (371 K) where the pristine, non‐covalent assembly exists exclusively in a molecularly dissolved state. A close examination of the solid‐state morphologies reveals that the locked superstructure engenders the formation of hierarchical 1D materials which are not achievable by unlocked assemblies. To complement these structural attributes, we further demonstrate that covalently tethering a supramolecular polymer built from PBI subunits enables the emergence of electronic properties not evidenced in non‐covalent assemblies. Using cyclic voltammetry experiments, the elucidation of the potentiometric properties of the locked superstructure reveals a 100‐mV stabilization of the conduction band energy when compared to that recorded for the non‐covalent assembly.     

Design of Heterocomplementary H‐Bonding RAFT Agents – Towards the Generation of Supramolecular Star Polymers

Supramolecular poly(vinyl acetate) PVAc 3‐arms stars were successfully generated by Reversible Addition–Fragmentation chain Transfer (RAFT)‐polymerized chains bearing hydrogen‐bonding heterocomplementary associating units. Chain Transfer Agents (CTA) bearing thymine‐ and diaminopyridine‐based units were first synthesized and proved to mediate efficiently the polymerization of VAc. The binding ability of the chains in solution was then demonstrated by ¹H NMR and GPC measurements, proving the formation of the supramolecular stars.