As a preliminary screening, potential substructures were defined via Morgan-fingerprints 55 of different bondradii (see Fig. ). As illustrated in Fig. , this revealed a number of highly enriched substructures, which confirmed the initial impression that acetylene-bridged and cyclopentadiene containing structures are highly favourable. However, the substructures obtained in this fashion are often redundant and chemically unintuitive (i.e. by only containing parts of aromatic rings). We therefore manually derived a number of reasonable substructures from this analysis, in order to elucidate a robust and general design rule for low-λ molecules (see Fig. ). Here, we focused on acetylene-bridged benzene rings, as cyclopenatdiene is prone to dimerize in Diels-Alder reactions, pointing to potential stability issues with these molecules.