RESUMEN
A new approach to fused helicenes is reported, where varied substituents are readily incorporated in the extended aromatic frame. From the alkynyl precursor, the final helical compounds are obtained under mild conditions in a two-step process, in which the final C-C bond is formed via a photochemical cyclization/ dehydroiodination sequence. The distortion of the π-system from planarity leads to unusual packing in the solid state. Computational analysis reveals that substituent incorporation perturbs geometries and electronic structures of these nonplanar aromatics.
RESUMEN
We describe here the metal-templated transformation of carbon nitride (C3N4) into nitrogen-containing carbons as anodes for Li-ion batteries (LIBs). Changing the template from the carbon- and nitrogen-immiscible Cu powder to the carbon- and nitrogen-miscible Fe powder yields different carbons; while Fe templating produces graphitized carbons of low (<10%) nitrogen content and moderate pore volume, Cu templating yields high defect-density carbons of high (32-24%) nitrogen content and larger pore volume. The Li+ storage capacity of the high nitrogen content and larger pore volume Cu-templated carbons exceeds that of the more graphitic Fe-templated carbons due to added contribution from Li+ insertion/extraction from pores and defects and to reversible faradaic Li+ reaction with nitrogen atoms. The Cu-templated carbon annealed at 750 °C delivers the highest specific capacity of 900 mAh g-1 at 0.1 A g-1 and 275 mAh g-1 at 20 A g-1, while also achieving a 96% capacity retention after 2000 cycles at 2 A g-1. The fabrication of higher mass loading electrodes (4.5 mg cm-2) provided a maximum areal capacity of 2.6 mAh cm-2 at 0.45 mA cm-2 (0.1 A g-1), comparable to the capacities of commercial LIB cells and favorable compared to other reported carbon materials.