In heptazine-based INVEST systems, S 1 and T 1 transitions display intramolecular CT characteristics with minimal HOMO-LUMO spatial overlap due to alternating localization sites . Unlike intermolecular CT in donor-acceptor complexes , partitioning for intramolecular CT is slightly more challenging. Using 1-TDM and NTO analysis, we quantify CT from HONTO to LUNTO, leveraging their natural separation in these systems (Figure ). We compute the degree of intramolecular CT in the S 1 and T 1 states of HEPTA-INVEST15 molecules to assess how their difference correlates with ∆E ST . Figure shows a strong linear correlation (R 2 = 0.94) between ∆CT ST and ∆E ST for monosubstituted systems. This supports previous design principles focused on spatial HOMO-LUMO separation to minimize exchange integral K , as spatial overlap of wavefunctions is a common, albeit imperfect, metric for assessing degree of charge transfer. 87-89