Bottom-up synthesis of carbon materials with remarkably high proportions of pentagons and heptagons using brominated precursors

Abstract

In recent years, the introduction of defect structures, such as 5- and 7-membered rings, edges, and functional groups in carbon materials has received considerable attention because of its potential for improving their performance in various applications. In particular, 5- and 7-membered rings are among the most stable defects because they exist in the basal plane. However, the catalyst-free synthesis of carbon materials with high proportions of both 5- and 7-membered rings out of 5-, 6-, and 7-membered rings is yet to be reported. This study reports the catalyst-free synthesis of carbon materials containing a high percentage of 5- and 7-membered rings by the simple bromination and heating of azulene (Azu) comprised of only 5- and 7-membered rings. Only 31% of edges in Azu reacted after nonbrominated Azu was carbonized at 873 K, whereas a significantly higher percentage of edges in Azu (92%) reacted after brominated Azu was carbonized at the same temperature. Thus, the bromination of Azu significantly improved its reactivity, leading to a relatively low electrical resistivity. Detailed analyses of brominated and carbonized Azu using Raman spectroscopy, infrared spectroscopy, and the full width at half maximum of C1s X-ray photoelectron spectra suggested that the synthesized carbon materials consisted of graphene-like planes in which 90% of the rings were 5- and 7-membered and only 10% were 6-membered.