Oxidative cyclodehydrogenation reaction for the design of extended 2D and 3D carbon nanostructures:: A theoretical study

We present a theoretical study on the main mechanistic features of the oxidative cyclodehydrogenation reaction of oligophenylene precursors affording the planar corresponding fully benzenoid, planar polycyclic aromatic hydrocarbons (BPAHs), molecular nanostructures of emerging interest in the field of nanotechnology. We firstly consider the transformation of o-terphenyl molecules, C18H14, into triphenylene, C18H12. Then, our calculations are extended to the primary ring-closure processes promoted in hexaphenylbenzene molecules, C42H30, via the same reactive approach which is experimentally known to yield hexa-peri-hexabenzocoronene, C42H18, as final product. To predict reliable reaction mechanisms, the critical points on the potential energy surfaces of interest are studied by using density functional theory with the hybrid functional B3LYP and the 3-21G basis set. Particular attention is paid to the role that radical cation intermediates may play in this reaction. The study suggests a step by step mechanism in which the new C-C bonds are formed and dehydrogenated one at a time until the final fully benzenoid product is obtained. The conclusions drawn from these preliminary investigations form the basis for a more thorough understanding of the synthetic strategy leading to much larger and complex conjugated carbon nanostructures. (c) 2005 Elsevier B.V. All rights reserved.