Testing new chromophores for singlet fission:A computational protocol applied to 2,3-diamino-1,4-benzoquinone

We present a computational protocol devised to test the suitability of newly proposed chromophores for singlet fission. The protocol includes two main steps: testing the basic energetic requirements by ab initio calculations and simulating the photodynamics to determine singlet fission quantum yields. We applied this protocol to 2,3-diamino-1,4-benzoquinone (DAPBQ), recently proposed as a possible chromophore for singlet fission. We determined the excitation energies of DAPBQ by second order perturbation CASPT2 and NEVPT2 calculations. Then, we optimized a possible crystal structure of DAPBQ, we identified the most favourable pair of molecules within it and we ran a simulation of the excited state dynamics for that dimer embedded in the crystal at a semiempirical QM/MM level. The results indicate that DAPBQ in the crystalline phase does not undergo singlet fission and the initially prepared singlet excited state rapidly decays to the ground state.