Singlet-diradical character in large PAHs triggers spontaneous-ignition of coal

Chemical phenomena dictating the spontaneous-ignition of coal remain highly speculative with some of the most intriguing questions appearing unaddressed. In this communication, we deploy a synergistic experimental-theoretical approach to elucidate the definite role of singlet-biradical PAHs in driving the low-temperature oxidation of coal. We establish that, five linearly-fused benzene rings (i.e., pentacene, as a model compound for the PAH content in coal, and an example of short-chain graphene nanoribbons) ignites 200 degrees C lower than the corresponding temperature for naphthalene. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.