Characterization and Quantification of Polyradical Character

The decomposition of ⟨<i>Ŝ</i>²⟩ into atomic and diatomic contributions (local spin analysis) is used to detect and quantify the polyradical character of molecular systems. A model triradical system is studied in detail, and the local spin analysis is used to distinguish several patterns of local spin distributions and spin–spin interactions that can be found for different electronic states. How close a real molecular system is to an ideal system of <i>k</i> perfectly localized spin centers is utilized to define a measure of its <i>k</i>-radical character. The spin properties and triradical character of the lowest-lying electronic states of a number of all σ, all π, and σ–π organic triradicals are discussed in detail. The local spin contributions exhibit good correlation with experimental triradical stabilization energies