We note that this CAE is not identical to the exciton binding energy, which is the energy difference between an exciton and both isolated negative and positive free charges. We use and consequently lowers the CAE. We note that rule (iii) applies only to the lowest excited states, since at higher states the hole wavefunction involves the conjugated backbone of the acceptor units and consequently leads to a similar overlap between electron and hole for larger and smaller acceptor units.