10-methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonate

Chemiluminescent System Based on 10-Methyl-9-(Phenoxycarbonyl)Acridinium Trifluoromethanesulfonates

Zadykowicz, Beata, et al. Organic & Biomolecular Chemistry, 2016, 14(2), 652-668.

In this work, a series of 10-methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates (XAEs) with various characteristic substituents on the side phenyl ring (such as halogen, CF3, NO2 and OCH3 located at the ortho, para or meta position of the phenyl ring) were synthesized. Some possible steps for the transformation of XAE in alkaline aqueous environment, in which OH- and OOH- ions are involved, are proposed as follows:
· Pathway one (indicated by blue arrows) represents the "light way" of XAE oxidation, accounting for 1.7-2.4% of the reaction energy released during the transformation, as indicated by experimentally determined quantum yields (QY). The chemiluminescence (CL) of the acridinium cations begins when OOH- attacks the electron-deficient C(9) position. Notably, the resulting acridane-type adduct can undergo further changes through two slightly distinct channels, which highlight the thermodynamic characteristics of the studied systems and the pz LUMO orbital values at the acridinium C(9) atom, illustrating the susceptibility of XAEs to nucleophilic attack.
· The remaining two pathways are classified as "dark," presenting alternative reaction channels to the aforementioned "light way." The second pathway, termed the "pseudobase way" (pathway two, red arrows), culminates in the formation of NMAON in the electronic ground state, while the third pathway, known as the "hydrolytic way" (pathway three, green arrows), concludes with the production of 10-methylacridine-9-carboxylic acid (NMACA) in the ground electronic state.