Excitonic Approach\nfor Nonadiabatic Dynamics: Extending\nBeyond the Frenkel Exciton Model

We report the formulation and implementation of an extended\nFrenkel\nexciton model (EFEM) designed for simulating the dynamics of multichromophoric\nsystems, taking into account the possible presence of interchromophore\ncharge transfer states, as well as other states in which two chromophores\nare simultaneously excited. Our approach involves constructing a Hamiltonian\nbased on calculations performed on monomers and selected dimers within\nthe multichromophoric aggregate. Nonadiabatic molecular dynamics is\naddressed using a surface hopping approach, while the electronic wave\nfunctions and energies required for constructing the EFEM are computed\nutilizing the semiempirical floating occupation molecular orbitals-configuration\ninteraction (FOMO-CI) electronic structure method. To validate our\napproach, we simulate the singlet fission process in a trimer of 2,5-bis(fluorene-9-ylidene)-2,5-dihydrothiophene\n(ThBF) molecules, embedded in their crystal environment, comparing\nthe results of the EFEM to the standard “supermolecule”\napproach.