In the present work, we apply a quantum mechanical bespoke force field to the modelling of a molecular emitter of importance to OLED design. QUBE force field parameters are obtained for the S 0 and S QUBEKit lacks key parameters for phosphorus (in particular, the free atom radius used to derive Lennard-Jones parameters ). However, it will be possible to extend the number of elements included in QUBEKit in future. Finally, it should be emphasised that alternative approaches for atomistic modelling based on machine learning of the quantum potential energy surface are approaching the speeds required for these simulations, and could readily be extended to electronic excited states. However, extension of these potentials to the