We present a combined experimental and theoretical study of the photodissociation of the bisanthenequinone (C28H12O2) cation, Bq(+). The experiments show that, upon photolysis, the Bq(+) cation does not dehydrogenate, but instead fragments through the sequential loss of the two neutral carbonyl groups, causing the formation of five-membered carbon cycles. Quantum chemical calculations confirm this Bq(+) -> [Bq - CO](+) -> [Bq - 2CO](+) sequence as the energetically most favorable reaction pathway. For the first CO loss, a transition state with a barrier of similar to 3.2 eV is found, substantially lower than the lowest calculated H loss dissociation pathway (similar to 4.9 eV). A similar situation applies for the second CO loss channel (similar to 3.8 eV vs. similar to 4.7 eV), but where the first dissociation step does not strongly alter the planar PAH geometry, the second step transforms the molecule into a bowl-shaped one. (C) 2017 Elsevier B.V. All rights reserved.