Electronic structure of the 1,3,5-tridehydrobenzene triradical in its ground and excited states

The ground and low-lying electronic states of the 1,3,5-tridehydrobenzene triradical are characterized by electronic structure calculations. It is found that the ground state is the A1 doublet of C2v symmetry. Another doublet state lies 0.1–0.2 eV higher in energy, and the lowest quartet state of D3h symmetry is 1.2–1.4 eV higher in energy. Both doublets are degenerate at D3h geometries and undergo different Jahn–Teller distortions. Structurally, the triradical is tighter than the parent neutral molecule ~benzene!, because the interaction among the unpaired electrons results in additional bonding even in the high-spin state ~quartet!. The adiabatic doublet–quartet energy gap and the excitation energies calculated at the equilibrium geometries of the 3,5-dehydrophenyl anion are provided to aid in the design and interpretation of photoelectron experiments. © 2003 American Institute of Physics. @DOI: 10.1063/1.1569845#