Synthesis, characterization, and DFT study of polycyclic aromatic hydrocarbon precursors, 1,4-diiodo-2,3,5,6-tetraarylbenzene and 1,4-bis(4-bromophenyl)-2,3,5,6-tetraarylbenzene

The molecular structure and spectroscopic properties of 1,4-diiodo-2,3,5,6-tetraarylbenzene and 1,4-bis(4-bromophenyl)-2,3,5,6-tetraarylbenzene have been investigated by density functional theory (DFT), 1H NMR, 13C NMR, IR spectroscopy, and elemental analysis. These compounds are the precursors for the synthesis of large polycyclic aromatic hydrocarbons (PAHs). Because of the flexibility of aliphatic chains, DFT calculations of 13C NMR chemical shifts were only calculated in the aromatic region by introducing H atoms replacing the aliphatic chains and 1H NMR chemical shifts were neglected. A drawback of excluding aliphatic chains in the IR calculation was the loss of vibrational modes for C–H stretching and bending. Due to this significant loss of information, the aliphatic chains were included in the IR calculations. The comparison of the calculated 13C NMR and IR parameters with the experimental spectroscopic data reveals good agreement and thus confirmed the suggested molecular structures. In addition, the electronic structure of these compounds was discussed based on HOMO–LUMO analyses.

► We report the synthesis and characterization of two halogenated precursors used for the bottom-up synthesis of graphenes.
► We evaluate the efficacy of density functional techniques to determine structural information for these compounds.
► The calculated NMR and IR shifts agree well with experimental values.