Spin-orbit coupling effects on the zero field splitting of (π, π*) triplet states of conjugated enones

The optically detected paramagnetic resonance transitions of five cyclic conjugated enones have been observed in zero field. The |E|/h c parameters are small and nearly invariant for series, but the |D|/ h c parameters range from 0.22 to 0.30 cm−1. Simple theory suggests that both spin-spin dipolar interactions and spin-orbit interactions make significant contributions to the ZFS. The large variation in the ZFS of these enones is primarily due to the dependence of the spin-orbit interaction on the energy gaps between the 3(π, π*) state and the 1(n, π*) and 3(n, π*) states.