To obtain an estimate of the energy of the doubly excited state, the S 0 , S 1 and S 2 states were computed using the state-averaged complete active space self-consistent field (SA-CASSCF) method, with active spaces of (4,3), (6,5) and (8,7) for Systems 1, 2 and 3, respectively. The active spaces were chosen to include the frontier n-and π-type orbitals involved in the S 0 → S 1 and S 1 →S 2 transitions. The state-averaging was carried out by assigning equal weights to the S 0 , S 1 and S 2 states.