AbstractBACKGROUNDEvaluation of 4‐phenylphenalenones and structural analogues against the fungal pathogen Mycosphaerella fijiensis (causal agent of black sigatoka disease in bananas) under light‐controlled conditions uncovered some key structural features for the design of photodynamic compounds.RESULTSStructure–activity relationship analysis revealed the importance of a chromophoric aryl‐ketone and a steroidomimetic structural motif in the activity of the assayed compounds. The results pointed to 1,2‐dihydro‐3H‐naphtho[2′,1′:3,4]cyclohepta[1,2‐b]furan‐3‐one, which displayed an activity in the range of propiconazole but with photodynamic behaviour.CONCLUSIONThe present work demonstrates that 1,2‐dihydro‐3H‐naphtho[2′,1′:3,4]cyclohepta[1,2‐b]heterocyclic‐3‐one derivatives can be used as potential lead compounds for the development of fungicides, relying on a dual mode of action. © 2015 Society of Chemical Industry