On the mechanism of peripentacene formation from pentacene: computational studies of a prototype for graphene formation from smaller acenes

The formation of peripentacene during the high-temperature vacuum sublimation of pentacene (P) in the presence of trace amounts of 6,13-dihydropentacene (DHP) has been studied computationally with density functional theory. Computational and kinetic analyses indicate that competing mechanisms involving a series of H atom transfers initiated by hydrogen transfer from DHP to P can account for the formation of peripentacene. The overall reaction is predicted to proceed with a free energy barrier of 36.1 kcal/mol and to be autocatalytic. Kinetic modeling supports the proposed mechanism.