No abstract

The nomenclature introduced by Platt [1] for the assignment of electronically excited states of cata‐condensed benzenoid hydrocarbons is reinvestigated and extended to higher excited states. The extension to higher excited states was prompted by the increasing amount of knowledge on such states that result from new experimental techniques. The reinvestigation includes a careful consideration of pairing symmetries which were not a part of Platt's original concept. Further, it is shown that the subindices a and b cannot be used for higher excited states. These subindices have been introduced by Platt to distinguish between states that are degenerate in an ideal annulene. To combine the simplicity and generality of Platt's nomenclature with the higher quantitaty predicting ability of more sophisticated methods a formalism is provided that allows the analysis of the results of more advanced calculations in terms of certain “zero order perimeter states”. The analysis allows us to determine if a perimeter based assignment is possible, and if it is it tells us how to assign specific bands.