Although we have only examined a subset of substituted derivatives in this work due to the computational cost of the EOM-CCSD method, it is clear that there are some exceptions where the Heilbronner strategy does not appear to have the desired effect (Table ). There appears to be a price for reducing symmetry that we see in several of the substituted azaphenalenes, as also recently described in detail by Ricci et al. While the substituent strategy described here seems to be generally applicable, there will be many cases where other effects are more pronounced. Deviations should not be surprising considering how we are fine-tuning energies in very small ranges and any structural distortions, however small, may have a large effect, which may change the sign of the singlet-triplet gap. The Heilbronner substituent strategy thus does not eliminate the need to assess potential molecules on an individual basis.