Sonochemiluminescence of lucigenin using amines as coreactant: Reactivity and mechanism studies

Sonochemiluminescence (SCL) from aqueous solution of lucigenin (Luc²⁺) has been studied using aliphatic amines as coreactant. The SCL intensity are strongly dependent on the dissolved gases such as air, oxygen, nitrogen and argon. The most strong SCL signals are observed from oxygen saturated alkaline solution containing Luc²⁺ when small amount of trialkylamine, such as tripropylamine (TPrA) was added into the solution. In an ultrasonic field, TPrA can adsorb onto the cavitation bubble/solution interface where TPrA is oxidized by OH to form a radical cation TPrA⁺ and subsequently produce a highly reducing TPrA species through a deprotonation reaction of the TPrA⁺. TPrA is suggested to initiate the reduction reactions of Luc²⁺ and molecule oxygen to produce Luc⁺ and superoxide radical anion (O₂⁻), respectively. The radical-radical coupling reaction between Luc⁺ and O₂⁻ is expected to initiate the light emission. The production of O₂⁻ is examined by spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as a fluorescent probe. The results show that the production of O₂⁻ by ultrasound was more efficient in oxygen saturated solution in the presence of coreactants, consistent with the results with SCL measurements.