Electron confinement in structurally constrained sigma-bonded pi-systems. An experimental and density functional investigation

We have explored the effect of resonance overlap on electronic communicatio n in sigma-bonded pi-systems through a combined experimental and computatio nal investigation. The system studied consists of a series of diphenyl-subs tituted acenaphthofluoranthenes and fluoranthenes with constrained dihedral angles between polycyclic core and phenyl substituents of 90 degrees, 70 d egrees, and 15 degrees. The spin density distribution within the radical an ions of these conformationally restricted polycyclic aromatic hydrocarbons was assessed via DFT-B3LYP calculations validated through SEEPR-derived Exp erimental hyperfine coupling constants (hfc's). Orthogonal subsystems were essentially insulated, while substantial delocalization of spin density was observed for near-planar subsystems. The insulation of the phenyl substitu ents combined with the possibility of farming ladder-type polymers makes th e orthogonal diphenyl-substituted acenaphthofluoranthenes intriguing buildi ng-blocks for molecular electronics.