Vladimir Stepanenko

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 pi-pi 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 pi stacks and red gels, whereas by introducing branched alkyl chains the formation of J-type pi stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2-ethylhexyl group completely suppressed the pi stacking. Coaggregation studies with H- and J-aggregating chromophores revealed the formation of solely H-type pi 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.

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 nucleation-growth 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 nucleation-growth supramolecular polymerization accompanied by thermal hysteresis can be controlled in a living manner.

Functional organogels from highly efficient organogelator based on perylene bisimide semiconductor

A new n-type semiconducting perylene bisimide dye has been synthesized that gelates a broad variety of organic solvents to afford well-defined nano- and mesoscopic helical fibers and bundles.

Cooperative supramolecular polymerization driven by metallophilic Pd···Pd interactions.

A new oligophenyleneethynylene (OPE)-based Pd(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 UV-vis studies in methylcyclohexane supported by DFT calculations demonstrate for the first time that cooperative supramolecular polymerization processes can be driven by metallophilic interactions.

Supramolecular block copolymers by kinetically controlled co-self-assembly of planar and core-twisted perylene bisimides

New synthetic methodologies for the formation of block copolymers have revolutionized polymer science within the last two decades. However, the formation of supramolecular block copolymers composed of alternating sequences of larger block segments has not been realized yet. Here we show by transmission electron microscopy (TEM), 2D NMR and optical spectroscopy that two different perylene bisimide dyes bearing either a flat (A) or a twisted (B) core self-assemble in water into supramolecular block copolymers with an alternating sequence of (AmBB)n. The highly defined ultralong nanowire structure of these supramolecular copolymers is entirely different from those formed upon self-assembly of the individual counterparts, that is, stiff nanorods (A) and irregular nanoworms (B), respectively. Our studies further reveal that the as-formed supramolecular block copolymer constitutes a kinetic self-assembly product that transforms into thermodynamically more stable self-sorted homopolymers upon heating.

Self-Assembly and (Hydro)gelation Triggered by Cooperative π–π and Unconventional CH⋅⋅⋅X Hydrogen Bonding Interactions†

Weak C-H···X hydrogen bonds are important stabilizing forces in crystal engineering and anion recognition in solution. In contrast, their quantitative influence on the stabilization of supramolecular polymers or gels has thus far remained unexplored. Herein, we report an oligophenyleneethynylene (OPE)-based amphiphilic Pt(II) complex that forms supramolecular polymeric structures in aqueous and polar media driven by π-π and different weak C-H···X (X=Cl, O) interactions involving chlorine atoms attached to the Pt(II) centers as well as oxygen atoms and polarized methylene groups belonging to the peripheral glycol chains. A collection of experimental techniques (UV/Vis, 1D and 2D NMR, DLS, AFM, SEM, and X-Ray diffraction) demonstrate that the interplay between different weak noncovalent interactions leads to the cooperative formation of self-assembled structures of high aspect ratio and gels in which the molecular arrangement is maintained in the crystalline state.

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, PBI-1-C2 to PBI-1-C5) 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 π-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.

Biosupramolecular Nanowires from Chlorophyll Dyes with Exceptional Charge‐Transport Properties

Conductive tubes: Self-assembled nanotubes of a bacteriochlorophyll derivative are reminiscent of natural chlorosomal light-harvesting assemblies. After deposition on a substrate that consists of a non-conductive silicon oxide surface (see picture, brown) and contacting the chlorin nanowires to a conductive polymer (yellow), they show exceptional charge-transport properties.

Spermine‐Functionalized Perylene Bisimide Dyes—Highly Fluorescent Bola‐Amphiphiles in Water

A series of four spermine-functionalized perylene bisimide dyes without linkers (1) and with linkers (2-4) between the chromophore and the polyamine was synthesized. Protonation of the spermine moieties resulted in the formation of highly water-soluble dyes with up to six positively charged ammonium ions. The aggregation behavior of these strongly fluorescent bola-amphiphiles was studied in pure water as solvent by UV/Vis and fluorescence spectroscopy, and an astonishingly high fluorescence quantum yield of up to Phi(fl)=0.90 was observed for PBI 1. Atomic force microscopy and transmission electron microscopy were applied for the visualization of the aggregates on surfaces. Molecular modeling studies were performed by force-field calculations to explore the aggregate morphologies, which also provided valuable information on the influence of the additional alkylcarbonyl linkers. Our detailed spectroscopic and microscopic investigations revealed that the excellent optical properties of perylene bisimide chromophores can be used even in pure deionized water if their aggregation is efficiently suppressed.

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 J-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 UV-vis, AFM, and XRD experiments. Selenium-containing donor-acceptor (D-A) dimethine dye 4 showed the highest hole mobility of 0.08 cm(2) V(-1) s(-1). BHJ solar cells based on dye 4 were optimized by taking advantage of the high crystallinity of the donor material and afforded a PCE of up to 6.2%.