Photo-induced Proton-Coupled Electron Transfer Reactions of Acridine Orange: Comprehensive Spectral and Kinetics Analysis
2014
Eisenhart, Thomas T. | Dempsey, Jillian L.
The triplet excited state of acridine orange (³*AO) undergoes a proton-coupled electron transfer (PCET) reaction with tri-tert-butylphenol (ᵗᵗᵇPhOH) in acetonitrile. Each of the reaction components possesses a spectroscopic signature, providing a rare opportunity to monitor the individual proton transfer, electron transfer, and H•-transfer components in parallel via transient absorption spectroscopy. This enhanced optical tracking, along with excited-state thermochemical analysis, facilitates assignment of the mechanism of excited-state PCET reactivity. ³*AO is quenched via concerted proton–electron transfer (CPET) from ᵗᵗᵇPhOH to form acridine radical (AOH•) and ᵗᵗᵇPhO• (kCPET = 3.7 × 10⁸ M–¹ s–¹, KIE = 1.3). Subsequently, AOH• reduces the phenoxyl radical (kET = 5.5 × 10⁹ M–¹ s–¹), forming AOH⁺ and ᵗᵗᵇPhO–, followed by proton transfer (kPT = 1.0 × 10⁹ M–¹ s–¹) to regenerate the starting reactants.
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