Cycloparaazine, a full-azine carbon nanoring
Till Drennhaus, Daiki Imoto, Elena S. Horst, Lena Lezius, Hiroki Shudo, Tomoki Kato, Klaus Bergander, Constantin G. Daniliuc, Dirk Leifert, Akiko Yagi, Armido Studer, Kenichiro Itami
Abstract
Cycloparaphenylenes (CPPs) and related carbon nanorings (CNRs) represent iconic molecular entities in molecular nanocarbon science. While theoretical studies predict that the introduction of nitrogen atoms (N-doping) onto CPP frameworks would add a number of fascinating properties, only a handful of partially N-doped carbon nanorings have been synthesized. We herein report the synthesis of a long-awaited cycloparaazine (CPA), where every para-connected aromatic moiety consists of a N-heterocycle, and two other highly N-doped CNRs. The evaluation of optoelectronic and structural properties coupled with theoretical studies uncovered the impact of both the amount and positioning of N-doping onto the nanorings properties; far less ring strain, red-shifted UV–vis absorption and fluorescence, smaller HOMO–LUMO gaps and both higher reduction and oxidation potentials than pristine CPPs. Ultimately, new potential applications of highly N-doped nanorings were examined in non-covalent supramolecular property engineering with Lewis acids and as energy storage materials. Theoretical studies predict that the introduction of nitrogen atoms onto cycloparaphenylene frameworks would add fascinating properties but few partially N-doped carbon nanorings have been synthesized. Here, the authors report the synthesis of a cycloparaazine, where every para-connected aromatic moiety consists of a N-heterocycle, and two other highly N-doped carbon nanorings.