Properties of Bisdiazo Compounds and Their Derived Carbenes via Density Functional Theory

To better understand the properties of carbene and biscarbene species derived from bisdiazo compounds with varied terminal groups, a density functional theory (DFT) study was conducted on bisdiazo compounds with four terminal groups (bisdiazo-X, where X=H, Me, NO₂ and NH₂) and their mono- and dicarbene derivatives. The studies included computation of their frontier molecular orbitals (FMOs), electronic structures, electrostatic potential (ESP) and polarity, as well as their IR and UV-vis spectra and their color in THF solutions. For bisdiazo compounds at both ground and excited states, the computational results matched well with published experimental data. The formation of carbene species from bisdiazo compounds was confirmed via a generalized IRC path calculation and IGMH analysis. The reaction sites and the lone pair electron locations were predicted using minimum ESP (i.e., ESPmin) and orbital-weighted Fukui dual descriptor for the possible intermediates in the transition state, along with spin density analysis through EPR/ESR predictions. Additionally, physisorption of bisdiazo and carbene species onto single-layer graphene was evaluated through geometry optimization, in which π-π stacking among the aromatic-ring likely determines surface packing via the simulated scanning tunnelling microscope (STM) images. The carbene species permit controlled growth of the patterned functional organic surfaces.