Electronic structure of the two dehydro-meta-xylylene triradicals and their derivatives

The ground and low-lying excited states of the 5-dehydro-meta-xylylene and 2-dehydro-meta-xylylene triradicals, as well as their derivatives are characterized by the equation-of-motion spin-flip coupled-cluster method with single and double substitutions. The effect of substituents in the C2, C4, and C6 positions on electronic states ordering is investigated. In the 5-dehydro-meta-xylylene triradical, which has the 12B2 ground state, charged substituents at C2 stabilize the closed-shell 12A1 state, whereas the NO substituent lowers the 12A2 and 12B1 states. In the 2-dehydro-meta-xylylene triradical with the 14B2 ground state charged substituents also significantly stabilize the 12A1 state and 12B1 state. The observed effects are explained by the nodal structure of the π orbitals and charge localization in the σ radical center.