The drawback of assessing molecules based on λ -, without considering crystal packing, is clear from the values of µ GM , the calculated electron mobility of the most likely crystal structure of each molecule. These values have a weak relationship with λ -; for example, molecule 7, which has one of the lowest values of λ -, has a very low predicted electron mobility in its global minimum energy predicted crystal structure. In contrast, some of the isomers with high λ -achieve good electron mobilities in their lowest energy crystal structures; for example, molecule 15 has µ GM 5.6 times greater than that of molecule 1, despite a 53 meV higher λ -. Thus, we find that, over this range of reorganization energies, strong electronic coupling due to favourable crystal packing can make up for a moderately high λ -while, conversely, a molecule with a promising, low λ -can lead to poor properties if it adopts an unfavourable crystal packing. As a result of the strong influence of crystal packing, molecule 1 is not in the top 10 molecules when ranked by µ GM , despite having the lowest λ -. Molecule 5 has the highest predicted electron mobility among the global lattice energy minimum crystal structures of all 28 isomers (µ GM = 2.706 cm 2 /Vs), eclipsing the calculated mobility of the observed (and global minimum predicted) crystal structure of 1 (µ e = 0.240 cm 2 /Vs). 5 is the only molecule for which the low energy part of the CSP landscape is dominated by sheet-like crystal packing (Fig. ). The extended hydrogenbonded flat ribbon structure in the predicted global minimum structure for 5 (Fig. ) promotes π-stacking along the out-of-plane direction.