Pressure effect on the lifetime of singlet oxygen in solutions

Abstract

electric response can be probed for a single magnitude of solvation. Similar models have been proposed by others. Marcus and co-workers1 discuss a similar two-dimensional potential, but the reactive motion is modeled via transition-state theory and although useful for electron-transfer reactions, does not seem appropriate for isomerization reactions that couple to the solvent mechanical friction. Agmon et al.37 consider a two-dimensional model where diffusion is considered in both dimensions. However, their model is for two internal coordinates, and the potential with which they numerically solve the diffusion equation may not be appropriate in describing the polarization coordinate. ConclusionsThis work demonstrates the dramatic importance of both static and dynamical dielectric effects on the photoisomerization of stilbenes. In particular, polar solvents are observed to lower the barrier to isomerization over the nonpolar solvent case, hence increasing the rate dramatically. For the case of «-alkanenitriles, which are unassociated solvents, the dielectric response is rapid enough that the more polar members of the homologous series better solvate the transition state. For the case of «-alkyl alcohols, which are associated solvents, the dielectric response lags the reactive motion and the aviscous activation barrier is higher for the more polar members of the homologous series. These observations are consistent with a two-dimensional view of the reaction, consisting of the twisting coordinate and a solvent polarization coordinate. These observations hold for 4,4'-dihydroxystilbene, 4,4'-dimethoxystilbene, and f/ww-stilbene. Although the above behavior is observed for symmetrically substituted stilbenes, it seems likely that they would be enhanced for asymmetrically substituted stilbenes or any reactive system with an initial dipole moment. Studies of the isomerization of 4-(dialkylamino)-4'-azastilbene and 4-(dialkylamino)-4'-nitrostilbene show clearly that increasing solvent polarity leads to a decrease in isomerization yield,43•44 consistent with the results reported here.

Singlet oxygen-mediated selective C–H bond hydroperoxidation of ethereal hydrocarbons

“…Such a chemical deactivation channel was not considered or recognized in the past 35 years to account for short lifetimes of singlet oxygen in various solvents. The observation of the chemical reaction between singlet O 2 and α-ethereal C–H bonds of THF is consistent with some previously observed clues that the inverse singlet O 2 lifetime (1/ τ ) is linearly proportional to molar concentrations of solvent C–H bonds 5 , 6 , and negative activation volume observed in high pressure lifetime measurements 22 .…”

Bis‐Anthracene Fused Porphyrin as an Efficient Photocatalyst: Facile Synthesis and Visible‐Light‐Driven Oxidative Coupling of Amines

“…Compared with commercial photocatalysts for the synthesis of imines, such as tetraphenyl porphyrin (Table 1, entry 6), methylene blue (Table 1, entry 7), and Ru(bpy) 3 Cl 2 ⋅ 6 H 2 O (Table 1, entry 8), which resulted in the yields of 57 %, 40 %, and 72 %, respectively, AFP showed much better catalytic activity with an apparent higher conversion yield. Furthermore, we found that the nature of solvent plays a critical role in the present reaction (Table 1, entries 9–13); the best result was obtained in THF (95 %, Table 1, entry 11), which can be ascribed to the better solubility of both the catalyst and the substrate in THF as well as the effect of the solvent polarity on the life of 1 O 2 [20] . To further study the catalytic performance of AFP , we changed the reaction conditions, by replacing the pure oxygen atmosphere with an air atmosphere and using 9 W LED irradiation, or employing a smaller dosage of AFP .…”

“…Furthermore, we found that the nature of solvent plays ac ritical role in the present reaction( Ta ble 1, entries 9-13);t he best result was obtained in THF (95 %, Ta ble 1, entry 11), which can be ascribed to the better solubility of both the catalyst and the substrate in THF as well as the effect of the solventpolarity on the life of 1 O 2 . [20] To furthers tudy the catalytic performance of AFP,w ec hanged the reactionc onditions, by replacing the pure oxygen atmosphere with an air atmosphere and using 9WLED irradiation, or employing as mallerd osage of AFP.W e found that the yield did not change significantly,d emonstrating that AFP is ah ighly effective photocatalyst fort he present synthesis of imines under oxygen and air atmospheres.…”

Selective photocatalytic epoxidation of cyclooctene by molecular oxygen in the presence of porphyrin sensitizers

“…In an aprotic solvent, the singlet oxygen has a higher lifetime and we got a higher yield in acetonitrile. Methanol is known as a singlet oxygen quencher due to; (i) hydrogen bonding [24], (ii) smaller life time of singlet oxygen in methanol (6.2 ls) relative to acetonitrile (53 ls), [25] therefore the epoxide yield is considerably diminished in methanol (Table 3).…”