Twisted but Conjugated: Building Blocks for Low Bandgap Polymers

Of Twists and Curves: Electronics, Photophysics, and Upcoming Applications of Non-Planar Conjugated Organic Molecules

Non-planar conjugated organic molecules (NPCOMs) contain π-conjugation across their length and also exhibit asymmetry in their conformation. In other words, certain molecular fragments in NPCOMs are either twisted or curved out of planarity. This conformational asymmetry in NPCOMs leads to non-uniform charge-distribution across the molecule, with important photophysical and electronic consequences such as altered thermodynamic stability, chemical reactivity, as well as materials properties. Majorly, NPCOMs can be classified as having either Fused or Rotatable architectures. NPCOMs have been the focus of significant scientific attention in the recent past due to their exciting photophysical behavior that includes intramolecular charge-transfer (ICT), thermally activated delayed fluorescence (TADF) and long-lived charge-separated states. In addition, they also have many useful materials characteristics such as biradical character, semi-conductivity, dynamic conformations, and mechanochromism. As a result, rational design of NPCOMs and mapping their structure-property correlations has become imperative. Researchers have executed conformational changes in NPCOMs through a variety of external stimuli such as pH, temperature, anions-cations, solvent, electric potential, and mechanical force in order to tailor their photophysical, optoelectronic and magnetic properties. Converging to these points, this review highlights the lucrative electronic features, photophysical traits and upcoming applications of NPCOMs by a selective survey of the recent scientific literature.

Cobalt-Nitrogen-Doped Helical Carbonaceous Nanotubes as a Class of Efficient Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is of significant importance in the development of fuel cells. Now, cobalt-nitrogen-doped chiral carbonaceous nanotubes (l/d-CCNTs-Co) are presented as efficient electrocatalysts for ORR. The chiral template, N-stearyl-l/d-glutamic acid, induces the self-assembly of well-arranged polypyrrole and the formation of ordered graphene carbon with helical structures at the molecular level after the pyrolysis process. Co was subsequently introduced through the post-synthesis method. The obtained l/d-CCNTs-Co exhibits superior ORR performance, including long-term stability and better methanol tolerance compared to achiral Co-doped carbon materials and commercial Pt/C. DFT calculations demonstrate that the charges on the twisted surface of l/d-CCNTs are widely separated; as a result the Co atoms are more exposed on the chiral CCNTs. This work gives us a new understanding of the effects of helical structures in electrocatalysis.