Measuring the energetic cost for charge-carriers to move between molecular sites, λ provides an important contribution to the charge-carrier mobility in a) Electronic mail: margraf@fhi-berlin.mpg.de crystalline and amorphous organic semiconductors. While computational screening for low-λ molecular structures has successfully guided discovery, its sensitivity to small variations in molecular structure renders a targeted molecular design challenging. Fragment or rule-based design strategies have been proposed to tackle this problem, while virtual screening or dataefficient discovery were used to assess large molecular candidate spaces, albeit without fully capturing the underlying structure-property relationships.