Next, we proceed to the optimised minimum of the S 1 state. The S 1 energy is found at an adiabatic energy of 2.37 and 2.36 eV using LR-PCM and SS-PCM, respectively. The obtained emission energy is 2.19 eV. We find that the S 1 state at the S 1 minimum geometry has significant local BDT character (blue, 56 % at SS-PCM level) and a small exciton size of 6.20 Å, which is slightly reduced when compared to the ground state geometry (6.52 Å). We can understand this in the sense that the planarisation of the Ph-BDT-Ph unit, as represented by the θ 2 /θ 2 values in Table , provides the basis for an extended locally excited state. The state retains the formal gerade symmetry present at the S 0 geometry and, therefore, has vanishing oscillator strength.