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Pentagons in carbon materials have attracted attentions because of the potential high chemical reactivity, band gap control, and electrochemical activity. However, it is challenging to prepare a carbon film with high pentagon density because of the curvature and the high reactivity caused by the presence of pentagons, and it is also challenging to estimate the percentage of pentagons in carbon materials because of the limitation of current analytical techniques. In this work, the percentage of pentagons in carbon materials was experimentally estimated for the first time using experimental and calculated C1s X-ray photoelectron spectroscopy and elemental analysis. Carbon films with 7% of pentagons (40% of pentagons compared to the raw material) with electrical resistivity of 1.1 × 104 Ω meter were prepared by heat treatment of corannulene at 873 K. On the other hand, fluoranthene and fullerene remained as non-film solid and powder without forming films at 873 K. Experimental and calculated Raman and IR spectra revealed the peaks of different types of pentagons. Decrement of pentagons in corannulene and fluoranthene heated at high temperatures can be explained mainly by the scission of C=C bond in pentagons, as suggested by the results of reactive molecular dynamics simulation (ReaxFF).

Selective doping of nitrogen into carbon materials in the absence of catalysts is a key for various applications of carbon materials. It is well known that most nitrogen-containing raw materials generate unnecessary functional groups during carbonization. Many researchers have noticed the significance of the selective nitrogen doping, whereas only a few works have reported the selective doping. In addition, those few works used catalysts to synthesize nitrogen-doped carbon materials, but the presence of catalysts limits the applications of nitrogen-doped carbon materials. This study found an unusual aromatic compound, imidazo[1,2-a]pyridine (IP), which maintained 88 % of the functional groups of as-received IP even after carbonization at 673 K in the absence of catalysts, and the functional groups were further maintained up to 773 K. The percentage of remaining functional groups was revealed using our state-of-the-art techniques of simulated X-ray photoelectron spectroscopy and Raman spectroscopy combined with transition state calculation using density functional theory. The low carbonization temperature as well as selective doping of nitrogen was achieved because of the low activation energy of dehydrogenation reaction among IP molecules compared to the high activation energy of radical formation for scission of C–N bonding.