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

Toward Two-Dimensional Supramolecular Control of Hydrogen-Bonded Arrays: The Case of Isophthalic Acids

The two-dimensional pattern formation of hydrogen bonding isophthalic acid derivatives at the liquid/solid interface has been investigated using scanning tunneling microscopy. By varying the location and nature of alkyl substituents on the aromatic core in combination with the intrinsic hydrogen bonding properties of the isophthalic acid units, the two-dimensional supramolecular ordering has been controlled, leading to several different motifs

Conjugated Covalent Organic Frameworks via Michael Addition–Elimination

Dynamic covalent chemistry enables self-assembly of reactive building blocks into structurally complex yet robust materials, such as covalent organic frameworks (COFs). However, the synthetic toolbox used to prepare such materials, and thus the spectrum of attainable properties, is very limited. For π-conjugated COFs, the Schiff base condensation of aldehydes and amines is the only general dynamic reaction, but the resulting imine-linked COFs display only a moderate electron delocalization and are susceptible to hydrolysis, particularly in acidic conditions. Here we report a new dynamic polymerization based on Michael addition–elimination reaction of structurally diverse β-ketoenols with amines, and use it to prepare novel two-dimensional (2D) π-conjugated COFs, as crystalline powders and exfoliated micron-size sheets. π-Conjugation is manifested in these COFs in significantly reduced band gap (1.8–2.2 eV), solid state luminescence and reversible electrochemical doping creating midgap (NIR absorbing) polaronic states. The β-ketoenamine moiety enables protonation control of electron delocalization through the 2D COF sheets. It also gives rise to direct sensing of triacetone triperoxide (TATP) explosive through fluorescence quenching

Periodic Functionalization of Surface-Confined Pores in a Two-Dimensional Porous Network Using a Tailored Molecular Building Block

We present here the periodic functionalization of a two-dimensional (2D) porous molecular network using a tailored molecular building block. For this purpose, a dehydrobenzo[12]­annulene (DBA) derivative, <b>1-isoDBA</b>, having an isophthalic acid unit connected by an azobenzene linker to a C₁₂ alkyl chain and five C₁₄ chains, was designed and synthesized. After the optimization of monolayer preparation conditions at the 1,2,4-trichlorobezene (TCB)/graphite interface, scanning tunneling microscopy (STM) observation of the self-assembled monolayer of <b>1-isoDBA</b> revealed the formation of extended domains of a porous honeycomb-type molecular network, which consists of periodically located nanowells each functionalized by a cyclic hexamer of hydrogen-bonded isophthalic acid units and those without functional groups. This result demonstrates that the present strategy based on precise molecular design is a viable route to site-specific functionalization of surface-confined nanowells. The nanowells of different size can be used for guest coadsorption of different guests, coronene <b>COR</b> and hexakis­[4-(phenylethynyl)­phenylethynyl]­benzene <b>HPEPEB</b>, whose size and shape match the respective nanowells. STM observation of a ternary mixture (<b>1-isoDBA</b>/<b>COR</b>/<b>HPEPEB</b>) at the TCB/graphite interface revealed the site-selective immobilization of the two different guest molecules at the respective nanowells, producing a highly ordered three-component 2D structure

Structural Insights into the Mechanism of Chiral Recognition and Chirality Transfer in Host–Guest Assemblies at the Liquid–Solid Interface

Understanding structure–efficiency relationships in chiral recognition and chirality transfer constitutes an important step toward the rational design of improved chiral probes and chirality auxiliaries or inducers. Recently discovered enantioselective host–guest adsorption opened a new pathway toward the enantioselective reconstruction of on-surface monolayers. In this study, we explored the importance of size matching between host cavity and chiral guest for the efficiency of chiral recognition and subsequent chirality induction in the initially racemic host

Aggregation Properties of Soluble Quinacridones in Two and Three Dimensions

The aggregation properties of derivatives of linear trans-quinacridone, an archetypal pigment, have been explored in two and three dimensions. The sparse solubility of the parent quinacridone pigment in common organic solvents can be traced back to the formation of a network of hydrogen bonds. Introducing aliphatic substituents on specific positions of the quinacridone core leads to an increased solubility without hampering the formation of intermolecular hydrogen bonds. With UV−Vis absorption, steady-state fluorescence, and infrared spectroscopy, the aggregation behavior of these substituted quinacridone derivatives is studied. On the basis of these data, models are proposed for the aggregate structure in solution. In addition, the two-dimensional ordering on graphite of these compounds and N,N‘-dialkylated analogues has been investigated with scanning tunneling microscopy. The comparison between the two-dimensional organization and the solution data allows one to identify the extent of intermolecular interactions involved in the aggregation process

Self-Assembly of a Functionalized Alkylated Isophthalic Acid at the Au(111)/Electrolyte Interface: Structure and Dynamics

The self-assembly of 5-(12-cyano-dodecyloxy)-isophthalic acid has been investigated at the Au(111)/aqueous electrolyte interface by means of electrochemical scanning tunneling microscopy (ECSTM). At potentials below the potential of zero charge (pzc), the molecules form a row type pattern, both on the reconstructed Au(111) surface (Au(111)-(22 × √3)) as well as on the unreconstructed Au(111) surface (Au(111)-(1 × 1)). On both surfaces the isophthalic acid groups arrange commensurately along the √3 direction of the surface. The cyano containing alkyl chains are interdigitated leading to the formation of cyano functional rows on the surface. The self-assembled layers show a strong dependency on the electrode potential. The potential induced phase transition of the organic layer, the lifting of the Au(111)-(22 × √3) surface reconstruction in the presence of this molecular layer, as well as the growth of an ordered layer from a disordered phase, have been potentio-dynamically investigated

Self-Assembly of a Functionalized Alkylated Isophthalic Acid at the Au(111)/Electrolyte Interface: Structure and Dynamics

The self-assembly of 5-(12-cyano-dodecyloxy)-isophthalic acid has been investigated at the Au(111)/aqueous electrolyte interface by means of electrochemical scanning tunneling microscopy (ECSTM). At potentials below the potential of zero charge (pzc), the molecules form a row type pattern, both on the reconstructed Au(111) surface (Au(111)-(22 × √3)) as well as on the unreconstructed Au(111) surface (Au(111)-(1 × 1)). On both surfaces the isophthalic acid groups arrange commensurately along the √3 direction of the surface. The cyano containing alkyl chains are interdigitated leading to the formation of cyano functional rows on the surface. The self-assembled layers show a strong dependency on the electrode potential. The potential induced phase transition of the organic layer, the lifting of the Au(111)-(22 × √3) surface reconstruction in the presence of this molecular layer, as well as the growth of an ordered layer from a disordered phase, have been potentio-dynamically investigated

Synthesis and Optical Properties of Polyphenylene Dendrimers Based on Perylenes

A series of polyphenylene-dendronized perylenes have been synthesized, and their physical and mesoscopic properties have been investigated. The attached polyphenylene dendrons have significant effects on the physical properties of the perylenes. They increase the solubility of perylenes in common organic solvents, suppress significantly the aggregation of the perylene core, and lead to red-shifted absorption and emission. The polyphenylene dendrons give rise to a strong absorption band in the UV region and exhibit efficient intramolecular energy transfer to the perylene moiety. The functionalization of perylenes with polyphenylene dendrons allows the preparation of films by spin-coating