Selective Bottom-up Synthesis of Carbon Materials with a Reactive C-H Adjacent to Pyridinic Nitrogen from Brominated Two-fused-ring Aromatics

Abstract

Carbon materials containing pyridinic nitrogen have been reported to exhibit high catalytic and electrode performance. Especially, one sp²C-H group adjacent to pyridinic nitrogen on one pyridine ring (denoted as N-SOLO) has been reported to act as an active site for oxygen reduction reactions in fuel cells. However, for the mass production of carbon materials with such structures, precise structural control must be achieved without using metal catalysts because the difficulty in removing metals afterwards increases costs. In this study, brominated compounds with two fused rings were utilized as precursors to increase the percentages of both pyridinic nitrogen and N-SOLO. Heat treatment of 3,7-dibromo-1,5-naphthyridine at 623 K yielded 74% pyridinic nitrogen (N content: 11 at.%) with 74% of N-SOLO/one sp²C-H group on one aromatic ring (SOLO), which is the highest percentage of N-SOLO/SOLO in carbon materials ever obtained without using catalysts. Screening of precursors by density functional theory calculations and molecular dynamics simulations with a reactive force field (ReaxFF) revealed that 3,7-dibromo-1,5-naphthyridine favored the formation of pyridinic nitrogen due to the suppression of tertiary nitrogen formation. Furthermore, N-SOLO exhibited the highest occupied orbital energy among various sp²C-H groups adjacent to pyridinic nitrogen, suggesting that N-SOLO is the most active site.