10-Methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulfonates bearing alkyl substituents at the benzene ring were synthesized, purified, and identified. In the reaction with OOH(-) in basic aqueous media, the cations of the compounds investigated were converted to electronically excited 10-methyl-9-acridinone, whose relaxation was accompanied by chemiluminescence (CL). The kinetic constants of CL decay, relative efficiencies of light emission, chemiluminescence quantum yields, and resistance toward alkaline hydrolysis were determined experimentally under various conditions. The mechanism of CL generation is considered on the basis of thermodynamic and kinetic parameters of the reaction steps predicted at the DFT level of theory. The chemiluminescence efficiency is the result of competition of the electrophilic center at C(9) between nucleophilic substitution by OOH(-) or OH(-) and the ability of the intermediates thus formed to decompose to electronically excited 10-methyl-9-acridinone. Identification of stable and intermediate reaction products corroborated the suggested reaction scheme. The results obtained, particularly the dependency of the "usefulness" parameter, which takes into account the CL quantum yield and the susceptibility to hydrolysis, on the cavity volume of the entity removed during oxidation, form a convenient framework within which to rationally design chemiluminescent 10-methyl-9-(phenoxycarbonyl)acridinium cations.

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Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.002 Å; R factor = 0.047; wR factor = 0.102; data-to-parameter ratio = 21.6.The crystal structure of the title compound, C 25 H 24 NO 2 + Á-CF 3 SO 3 À , is stabilized by C-HÁ Á ÁO, C-HÁ Á ÁF and C-HÁ Á Á hydrogen bonds, and by OÁ Á ÁF [2.94 (1) Å ] and OÁ Á ÁN [2.87 (1) Å ] interactions. In the packing of the molecules, acridine groups are either parallel or inclined at an angle of 5.4 (1) . Similarly, the benzene rings are either parallel or lie at an angle of 72.4 (1) . Experimental Crystal data C 25 H 24 NO 2 + ÁCF 3 SO 3 À M r = 519.52 Monoclinic, P2 1 =c a = 15.307 (4) Å b = 13.480 (3) Å c = 12.263 (3) Å = 102.56 (3) V = 2469.8 (10) Å 3 Z = 4Mo K radiation = 0.19 mm À1 T = 100 (2) K 0.50 Â 0.40 Â 0.07 mm Data collectionKuma KM4 CCD -geometry diffractometer Absorption correction: none 29629 measured reflections 7120 independent reflections 4774 reflections with I > 2(I) R int = 0.056

In the crystal structure of the title compound, C23H20NO2 +·CF3SO3 −, the cations form inversion dimers through π–π inter­actions between the acridine ring systems. These dimers are further linked by C—H⋯π inter­actions. The cations and anions are connected by C—H⋯O and C—F⋯π inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 20.8 (1)°. The carboxyl group is twisted at an angle of 66.2 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel in the lattice.