Strongly Chemiluminescent Acridinium Esters under Neutral Conditions: Synthesis, Properties, Determination, and Theoretical Study

Various novel acridinium ester derivatives having phenyl and biphenyl moieties were synthesized, and their optimal chemiluminescence conditions were investigated. Several strongly chemiluminescent acridinium esters under neutral conditions were found, and then these derivatives were used to detect hydrogen peroxide and glucose. Acridinium esters having strong electron-withdrawing groups such as cyano, methoxycarbonyl, and nitro at the 4-position of the phenyl moiety in phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt showed strong chemiluminescence intensities. The chemiluminescence intensity of 3,4-dicyanophenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt was approximately 100 times stronger than that of phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt at pH 7. The linear calibration ranges of hydrogen peroxide and glucose were 0.05-10 mM and 10-2000 μM using 3,4-(dimethoxycarbonyl)phenyl 10-methyl-10λ⁴-acridine-9-carboxylate trifluoromethanesulfonate salt at pH 7 and pH 7.5, respectively. The proposed chemiluminescence reaction mechanism of acridinium ester via a dioxetanone structure was evaluated via quantum chemical calculation on density functional theory. The proposed mechanism was composed of the nucleophilic addition reaction of hydroperoxide anion, dioxetanone ring formation, and nonadiabatic transition due to spin-orbit coupling around the transition state (TS) to the triplet state (T₁) following the decomposition pathway. The TS which appeared in the thermal decomposition would be a rate-determining step for all three processes.