Electron Spin-Spin Interaction in Excited Triplet States of Aromatic Hydrocarbons with a Trigonal Symmetry Axis

Zero-field splitting (ZFS) parameters of benzene, triphenylene, and coronene molecules in their lowest and second excited triplet states are calculated from the electron spin-spin interaction using semi-empirical self-consistentfield π-electron molecular orbitals. The results show that in obtaining a good agreement of the evaluated ZFS parameters with the experimental values the selection of the basis functions in LCAO-MO’s with zero-differential overlap is actually important. The ZFS parameters in some distorted structures are also calculated.