Controlled Synthesis of a Helical Conjugated Polythiophene

Two new polymer systems, poly­(3-phenylenevinylene)­thiophene (P3PVT) and poly­(3-phenyl)­thiophene (P3PT), were designed with the aim of obtaining a helical conjugated polymer via a living polymerization. The polymerization proceeded without transfer and termination reactions via the Kumada catalyst transfer condensative polymerization (KCTCP) mechanism, confirming the living nature of the polymerization. Solvatochroism and circular dichroism (CD) experiments showed the helical nature of P3PVT and the stacking behavior of P3PT in poor solvent conditions. Block copolymers of 3-alkyl-substituted polythiophenes and helical P3PVT were prepared to determine the aggregation behavior of such systems. Solvatochroism, CD, and AFM measurements showed that the blocks influence each other’s behavior. If the P3AT block stacks before the helical P3PVT block organizes, one-handed helix formation is hindered. If helix formation occurs first, the stacking behavior is not influenced

Nanoscale Control over the Mixing Behavior of Surface-Confined Bicomponent Supramolecular Networks Using an Oriented External Electric Field

Strong electric fields are known to influence the properties of molecules as well as materials. Here we show that by changing the orientation of an externally applied electric field, one can locally control the mixing behavior of two molecules physisorbed on a solid surface. Whether the starting two-component network evolves into an ordered two-dimensional (2D) cocrystal, yields an amorphous network where the two components phase separate, or shows preferential adsorption of only one component depends on the solution stoichiometry. The experiments are carried out by changing the orientation of the strong electric field that exists between the tip of a scanning tunneling microscope and a solid substrate. The structure of the two-component network typically changes from open porous at negative substrate bias to relatively compact when the polarity of the applied bias is reversed. The electric-field-induced mixing behavior is reversible, and the supramolecular system exhibits excellent stability and good response efficiency. When molecular guests are adsorbed in the porous networks, the field-induced switching behavior was found to be completely different. Plausible reasons behind the field-induced mixing behavior are discussed

Supramolecular Loop Stitches of Discrete Block Molecules on Graphite: Tunable Hydrophobicity by Naphthalenediimide End-Capped Oligodimethylsiloxane

The noncovalent functionalization of surfaces has gained widespread interest in the scientific community, and it is progressively becoming an extremely productive research field offering brand new directions for both supramolecular and materials chemistry. As the end-groups often play a dominant role in the surface properties obtained, creating loops with end-groups only at the surface will lead to unexpected architectures and hence properties. Here we report the self-assembly of discrete block moleculesstructures in-between block copolymers and liquid crystalsfeaturing oligodimethylsiloxanes (ODMS) end-capped with naphthalenediimides (NDIs) at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. These structures produce unprecedented vertically nanophase-separated monolayers featuring NDI moieties that regularly arrange on the HOPG surface, while the highly dynamic ODMS segments form loops above them. Such arrangement is preserved upon drying and generates hydrophobic HOPG substrates in which the ODMS block length tunes the hydrophobicity. Thus, the exact structural fidelity of the discrete macromolecules allows for the correlation of nanoscopic organization with macroscopic properties of the self-assembled materials. We present a general strategy for tunable hydrophobic coatings on graphite based on molecularly combining crystalline aromatic moieties and immiscible oligodimethylsiloxanes

A Shape-Persistent Polyphenylene Spoked Wheel

A shape-persistent polyphenylene with a “spoked wheel” structure was synthesized as a subunit of an unprecedented two-dimensional polyphenylene that we name graphenylene. The synthesis was carried out through a sixfold intramolecular Yamamoto coupling of a dodecabromo-substituted dendritic polyphenylene precursor, which had a central hexaphenylbenzene unit as a template. Characterizations by NMR spectroscopy and matrix-assisted laser ionization time-of-flight mass spectrometry provided an unambiguous structural proof for the wheel-like molecule with a molar mass of 3815.4 g/mol. Remarkably, scanning tunneling microscopy visualization clearly revealed the defined spoked wheel structure of the molecule with six internal pores

Lateral Fusion of Chemical Vapor Deposited <i>N</i> = 5 Armchair Graphene Nanoribbons

Bottom-up synthesis of low-bandgap graphene nanoribbons with various widths is of great importance for their applications in electronic and optoelectronic devices. Here we demonstrate a synthesis of <i>N</i> = 5 armchair graphene nanoribbons (5-AGNRs) and their lateral fusion into wider AGNRs, by a chemical vapor deposition method. The efficient formation of 10- and 15-AGNRs is revealed by a combination of different spectroscopic methods, including Raman and UV–vis-near-infrared spectroscopy as well as by scanning tunneling microscopy. The degree of fusion and thus the optical and electronic properties of the resulting GNRs can be controlled by the annealing temperature, providing GNR films with optical absorptions up to ∼2250 nm

Chemical Vapor Deposition Synthesis and Terahertz Photoconductivity of Low-Band-Gap <i>N</i> = 9 Armchair Graphene Nanoribbons

Recent advances in bottom-up synthesis of atomically defined graphene nanoribbons (GNRs) with various microstructures and properties have demonstrated their promise in electronic and optoelectronic devices. Here we synthesized <i>N</i> = 9 armchair graphene nanoribbons (9-AGNRs) with a low optical band gap of ∼1.0 eV and extended absorption into the infrared range by an efficient chemical vapor deposition process. Time-resolved terahertz spectroscopy was employed to characterize the photoconductivity in 9-AGNRs and revealed their high intrinsic charge-carrier mobility of approximately 350 cm²·V^–1·s^–1