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Abstract
Various subclasses of fluoranthenoid/fluorenoid hydrocarbons are studied where fluoranthenes is a special subclass. The unique connection between Pauling's first-excited valence-bond resonance structures and fluoranthene bistability is demonstrated. Bistable fluoranthene hydrocarbons have nearly degenerate singlet-triplet electronic states, and candidate bistable fluoranthenes are identified. An algorithm for determining the number of Kekulé resonance structures in fluoranthenoids with centrally located pentagonal rings is given and illustrated. New numerical results are reported for the number of Kekulé resonance structures in fluoranthenoid/fluorenoid hydrocarbons and related circulenes.