For the case of HOMO-LUMO gap, there is a wellestablished underlying physical principle in determining this property: it is known that the HOMO-LUMO gap of individual functional groups (called chromophores in this context) is transferable, with values documented in standard reference texts . These chromophores also form the foundation for both accurate ML models and earlier empirical rules for the prediction of HOMO-LUMO gaps . The HOMO-LUMO gap of a single functional group can be understood based on the molecular orbital theory, the most common version of which is the Hückel theory for conjugated systems. For instance, the inverse proportionality between the number of monomers and the HOMO-LUMO gap of polyenes is well-explained within this theory . In the case of non-interacting functional groups, their optical spectra are effectively independent and, consequently, the frontier energy gap of a molecule is determined by the lowest value for the constituent functional groups, making it an inherently size-independent (intensive) property.