The triplet excited state reactivity towards phenolic hydrogen of the α-diketones benzil and 2,2′-furil in the ionic liquid 1-
n-butyl-3-methyl imidazolium hexafluorophosphate [bmim.PF
6] was investigated employing the nanosecond laser flash photolysis technique. Irradiation (λ
max = 355 nm) of benzil
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The triplet excited state reactivity towards phenolic hydrogen of the α-diketones benzil and 2,2′-furil in the ionic liquid 1-
n-butyl-3-methyl imidazolium hexafluorophosphate [bmim.PF
6] was investigated employing the nanosecond laser flash photolysis technique. Irradiation (λ
max = 355 nm) of benzil yields its triplet excited state with λ
max at 480 nm and τ
T = 9.6 μs. Under the same conditions, 2,2′-furil shows a triplet-triplet absorption spectrum with bands at 380, 410, 450, and 650 nm and τ
T = 1.4 μs. Quenching rate constants (
kq) of the reaction between benzil triplet and substituted phenols ranged from 1.4 × 10
7 L mol
−1 s
−1 (
para-chlorophenol) to 1.8 × 10
8 L mol
−1 s
−1 (
para-methoxyphenol). A new transient was formed in all cases, assigned to the benzil ketyl. Similar results were obtained for the quenching of 2,2′-furil triplet by phenols, for which
kq ranged from 1.9 × 10
8 L mol
−1 s
−1 (
para-chlorophenol) to 2.2 × 10
8 L mol
−1 s
−1 (
para-methoxyphenol). The 2,2′-furil ketyl radical was also observed in all cases (λ
max = 380 nm). The quenching rate constants are almost independent of the substituent and diffusion-controlled (
kq ~ 10
8 L mol
−1 s
−1). The proposed mechanism for the phenolic hydrogen abstraction by benzil and 2,2′-furil triplet may involve a proton-coupled electron transfer reaction, ultimately leading to the radical pair ketyl/aryloxyl.
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