Deuterium effect on the quenching of aromatic hydrocarbon triplet excited states by oxygen

Abstract

By using ultraviolet light flash excitation, the triplet (phosphorescence) decay time τ of a series of protonated (p) and deuterated (d) aromatic hydrocarbons dissolved in a fluffy freeze-dried polystyrene matrix was studied as a function of oxygen pressure [O2] at 298°K. The quenching constants γ were calculated from linear plots of τ−1 as a function of [O2] and the ratios of γ(p)/γ(d) are 1.2±0.1 for anthracene and 1,2-benzanthracene, 1.9±0.2 for pyrene, 1.4±0.2 for chrysene, and 2.5±0.4 for naphthalene. These results are interpreted in terms of Franck-Condon factors and the energy transfer quenching model proposed by Kawaoka, Khan, and Kearns in which the 1Δg and Σg+1 excited states of oxygen are generated, and in which the remaining energy is dissipated by the vibrational modes of the quenched aromatic molecules. In pyrene and in naphtalene, the 1Δg pathway appears to be more important than in chrysene and dominates over the Σg+1 mechanism. No conclusions can be reached about the preferred mode of energy transfer to oxygen in anthracene and 1,2-benzanthracene.

Kinetics of Quenching of Ketone Phosphorescence by Oxygen in a Glassy Matrix

“…The errors in these data represent 1 standard deviation on the average value for measurements on three films of different thickness for each polymer. For comparison, values available in the literature range from 1.2 × 10 -8 to 3.6 × 10 -8 cm 2 s -1 for PVC, − 1.2 × 10 -8 to 3.7 × 10 -8 cm 2 s -1 for PMMA, ,− and 1 × 10 -8 to 1.2 × 10 -6 cm 2 s -1 for PS. ,− We can also compare our results with those derived for the quenching of singlet oxygen by several quenchers dissolved in PS and PMMA, as reported by Ogilby et al The systems studied by these workers are such that quenching occurs at the diffusion controlled limit, i.e., k q = k d , particularly if nickel(II) bis[diisopropyl dithiophosphate] ( N ) is used. The values of k q presented by Ogilby et al .…”

Deoxygenation of solutions and its analytical applications

“…Molecular oxygen quenches the excited species considerably in fluorescence analysis (3, 7, 9-28) and completely in phosphorescence analysis (33)(34)(35)(36)(37)(38)(39)(40) unless preventative measures are taken. In fluorescence analysis, the excited singlet state is dynamically quenched by molecular oxygen.…”

“…Fluorescence quenching by oxygen is not as severe as is phosphorescence quenching because of the relatively short lifetime of the excited singlet state (approximately 1 X l(Ta s) (9)(10)(11)(12)(13)39). Conversely, because of the long triplet-state lifetime (1 X 10"3-10 s) and the fact that excited molecules tend to return to the ground state via the pathway that most greatly minimizes the lifetime of the excited state, oxygen completely quenches phosphorescence in solution (33)(34)(35)(36)(37)(38)(39)(40).…”

“…For example, the sensitivity of luminescence analysis can be considerably improved with the removal of oxygen, because many fluorescent and phosphorescent compounds are highly susceptible to quenching by molecular oxygen (3,. Sample deoxygenation is a necessity for analysis by room-temperature phosphorescence (RTF) because the long-lived excited triplet state that produces phosphorescence emission is totally quenched by molecular oxygen in liquid solution (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40).…”

“…Sample deoxygenatin is a necessity for analysis by room temperature phosphorescence (RTP) because the long-lived excited triplet state that produces emission is totally quenched by molecular oxygen in liquid solution (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40).…”