BA is perfectly planar in the ground singlet and triplet states (S0 and T1) and low-lying singlet excited states (S1 and S2). It has a global T1 minimum with a 3 n* character. With TD-B3LYP, we could neither find a 3 * minimum in T1 nor T2. Nevertheless, a 3 * stationary structure lies 0.09 eV above the 3 n* minimum. We will refer to this structure as 3 * T1 minimum, but remember that it has an imaginary frequency of 171i cm -1 . State energies at the S0 and S1 minima are given in Table . Energies at the T1 and T2 minima are in Table . The electronic excitations and molecular orbitals to identify the state characters are given in the SI-1.