While some aspects of the luminescence of TPA and IPA have been explored both experimentally and computationally, the precise mechanisms of excited state relaxation in solution and the crystalline phase have yet to be fully understood. There are still many open questions about the competition between different nonradiative and radiative decay pathways and the origin of DF. Our study aims to fill this gap by systematically investigating the molecule-centred excited state relaxation pathways using high-level computational methods. In addition to these pathways, we also analyse the dimer-centred mechanisms and exciton transport mechanisms in both crystal environments. Our calculations provide critical insights into the excited state relaxation mechanisms of TPA and IPA, enhancing the current understanding of their behaviour in solution and crystalline phases.