For each compound in this study, the 3D structure was generated from its SMILES 20 code using Open Babel and the MMFF94 forcefield (steepest descent, 1000 steps, 1x10 -4 kcal/mol convergence criteria). Next, a weighted-rotor search was performed with Open Babel to obtain a low energy conformer (MMFF94, 250 conformers, 25 geometry optimization steps). The structure was further optimized with conjugate gradients (MMFF94, 500 steps, 1x10 -6 kcal/mol). These pre-optimized structures were converted to Gaussian09 input files, and their structures were optimized in the gas phase using DFT with the B3LYP functional at the 6-31G* level . The HOMO and LUMO eigenvalues derived from density functional theory have no physical meaning and cannot be directly taken as ionization potentials or electron affinities respectively. However, previous studies have shown that eigenvalues calculated with the B3LYP hybrid functional have a favorable correlation with experimental electron affinities , ionization potentials , and band gaps .