Precise molecular shape control of linear and branched strips with chirality-assisted synthesis

One-Handed Covalent Helical Ladder Polymers: The Dawn of a Tailorable Class of Chiral Functional Materials

In the last decades, chemists have developed methods to synthesize helical molecular architectures using a combination of covalent and non-covalent interactions. Very recently, the new class of completely covalent, one-handed helical ladder polymers has vigorously emerged. Such polymers can be rationally and programmably obtained through an approach guided by the principles of chirality-assisted-synthesis (CAS) and making use synergically of two disciplines that have so far rarely interacted: non-planar chiral π-conjugated synthons and ladder polymer chemistry. The precise programmability of the 3D structure and new mechanical and chiroptical properties will lead to potential applications in areas such as enantiorecognition, catalysis, spintronics and chiral-related optoelectronics. This minireview examines the emerging field of one-handed helical ladder polymers, analyzing their synthesis, applications, and limitations.

Through-Space, Lone-Pair Promoted Aromatic Substitution: A Relay Mechanism Can Beat Out Direct Activation

We report a detailed experimental and theoretical analysis of through-space arene activation with halogens, tetrazoles and achiral esters and amides. Contrary to previously assumed direct activation through σ-complex stabilization, our results suggest that these reactions proceed by a relay mechanism wherein the lone pair-containing activators form exothermic π-complexes with electrophilic nitronium ion before transferring it to the probe ring through low barrier transition states. Noncovalent interactions (NCI) plots and Quantum Theory of Atoms in Molecules (QTAIM) analyses depict favorable interactions between the Lewis base (LB) and the nitronium ion in the precomplexes and the transition states, suggesting directing group participation throughout the mechanism. The regioselectivity of substitution also comports with a relay mechanism. In all, these data pave the way for an alternate platform of electrophilic aromatic substitution (EAS) reactions.

Activation of Solid-State Emission and Photostability through Molecular Confinement: The Case of Triptycene-Fused Quinacridone Dyes

We report the facile, metal-free convergent synthesis and the characterization of novel quinacridone dyes in which two triptycene units end-cap and sterically confine the quinacridone chromophore. A precise comparison of the confined dyes with their known homologues reveals that the reduction of π-π interactions in triptycene-fused quinacridone dyes compared to classical quinacridone results not only in an increase of solubility and processability but also in an enhancement of fluorescence quantum yield and photostability in the solid state.