Chemically Triggered Release of Singlet Oxygen from Bisphenalenyl Endoperoxides with a Brønsted Acid.

Aromatic endoperoxides have emerged as intriguing stimulus-responsive materials for molecular oxygen (O 2 ) storage and delivery but are currently limited in their application because they require heat to trigger O 2 release. Here we present the first example of acid-triggered singlet oxygen ( 1 O 2 ) release that does not require external heating by treating bisphenalenyl endoperoxides (EPOs) with trifluoroacetic acid. Mechanistic studies reveal that diprotonation of EPOs leads to a >10-fold increase in cycloreversion rates by lowering the energy of activation (Δ E a ) by as much as 71.1 kJ mol -1 . Remarkably, acid-catalyzed 1 O 2 release is even demonstrated at room temperature. Chemical trapping experiments indicate that reactive 1 O 2 is present during acid-triggered release, which is promising for the development of these molecular materials for metal-free, on-demand 1 O 2 delivery.