The substituents in HEPTA-INVEST15 span a wide range of electronic properties. While Hammett parameters (σ p = σ I + σ R ) are commonly used to quantify substituent effects, they alone may not explain impacts on excited states. Our work aims to quantify how substituents differentially affect excited state energies and the inverted singlet-triplet gap. Additionally, excited-state aromaticity (ESA) and Baird's rule may influence energy levels, particularly as triplet state (anti-)aromaticity can be significantly affected by substitution even though singlet aromaticity remains relatively insensitive .