EPR Hyperfine Structures of Cation and Anion Radicals of Triafulvalene, Pentafulvalene and Heptafulvalene; A Theoretical Study

In this study, the EPR hyperfine coupling constants and spin densities of cation and anion radicals of triafulvalene, pentafulvalene and heptafulvalene were calculated by using DFT method with B3LYP functional at LanL2DZ level. The hyperfine structures formed EPR spectra of all the cation and anion radicals were determined. It was seen that in the cation cases of triafulvalene and heptafulvalene spin density is delocalized throughout the molecule whereas in their anion cases it is essentially localized on only a single ring. The reason of this distribution of the unpaired spin was investigated by their Natural Bond Orbital (NBO) and Mullikan charge analyses. These analyses showed that in the anion cases of the molecules the interaction energies between the interring C-C bond and the ring C-C bonds are different for both the two rings and one of them is quite higher than the other. The simulated EPR spectra obtained by EPR Simulator software program were harmoniously given with together their experimental spectra.