SPIN-DENSITY DISTRIBUTION AND ELECTRONIC-STRUCTURE OF RADICAL-ANIONS OF LADDER-TYPE OLIGORYLENES

The radical anions of ladder-type oligorylenes have been obtained from a homologous series of soluble oligoperinaphthylenes and characterize d by EPR and ENDOR spectroscopy. By these methods in combination with HMO/McLachlan and PPP calculations and isotopic labeling, all H-1 hype rfine coupling constants have been assigned to the individual position s in the molecules. Considerable spin density prevails at both ends of the oligoperinaphthylenes, making them ideally suited as building blo cks in molecular electronics. In higher oligomers, a redistribution of the position of highest spin density to more inner naphthalene units is predicted theoretically. The experimental and theoretical results p oint to a close relationship to even polyenes, but with the more rigid polyperinaphthylenes possessing a much lower band gap. The spin densi ty distribution within the oligomers is in contrast to that of linear conjugated pi-systems with phenyl end groups like oligo(p-phenylenevin ylenes) and diphenylpolyenes, where the positions of highest spin dens ity occur in the central parts of the molecules already for small olig omers. The chain length dependence of the spin density distribution an d the largest H-1 hyperfine coupling constants are compared to data fr om optical absorption measurements of the neutral and monocharged spec ies. While the former reflects the spin density at certain positions o f the pi-system, the latter characterize the whole conjugated chromoph ore.