Junjian Xie,Xiangwen Zhang,Chengxiang Shi,Lun Pan,Fang Hou,Genkuo Nie,Jiawei Xie,Qing Liu,Ji-Jun Zou
Hydrocarbons with a highly strained four-membered ring are synthesized via self-photosensitized [2 + 2] cycloaddition and hydrodeoxygenation using cyclohexene and isophorone as feedstocks, which show high density and high heat values. Photoreaction can take place selectively with isophorone as a self-sensitizer and a reactant. Isophorone/cyclohexene co-cycloaddition has a much faster reaction rate than self-cycloaddition of isophorone, and both DFT calculations and photochemical kinetics show that the energy barrier for the former is much lower than that for the latter. Under optimal conditions, the selectivity of co-cycloaddition and self-cycloaddition can reach 93.3% and 94.9%, with isophorone conversion of 95.4% and 68.8%, respectively. In addition, a series of olefins can undergo self-photosensitized [2 + 2] cycloaddition with isophorone smoothly in high selectivity. After hydrodeoxygenation, hydrocarbons derived from isophorone/cyclohexene mixture and pure isophorone (with an overall yield of 82.1% and 61.3%) have high densities of 0.903 g mL−1 and 0.892 g mL−1, respectively, along with good cryogenic properties. Especially, the hydrocarbons synthesized through photosensitized cycloaddition show considerably higher density and heat values compared with those derived from a common C–C coupling route, which is attributed to the constructed strained cyclic structures. This work provides a new way for photosynthesis of high-energy-density hydrocarbons.
Yifu Fu,Yiqi Yan,Zongsu Wei,Richard Spinney,Dionysios D. Dionysiou,Davide Vione,Min Liu,Ruiyang Xiao
Photochemical transformation is an important process that involves trace organic contaminants (TrOCs) in sunlit surface waters. However, the environmental implications of their self-photosensitization pathway have been largely overlooked. Here, we selected 1-nitronaphthalene (1NN), a representative nitrated polycyclic aromatic hydrocarbon, to study the self-photosensitization process. We investigated the excited-state properties and relaxation kinetics of 1NN after sunlight absorption. The intrinsic decay rate constants of triplet (31NN*) and singlet (11NN*) excited states were estimated to be 1.5 × 106 and 2.5 × 108 s–1, respectively. Our results provided quantitative evidence for the environmental relevance of 31NN* in waters. Possible reactions of 31NN* with various water components were evaluated. With the reduction and oxidation potentials of −0.37 and 1.95 V, 31NN* can be either oxidized or reduced by dissolved organic matter isolates and surrogates. We also showed that hydroxyl (•OH) and sulfate (SO4•–) radicals can be generated via the 31NN*-induced oxidation of inorganic ions (OH– and SO42–, respectively). We further investigated the reaction kinetics of 31NN* and OH– forming •OH, an important photoinduced reactive intermediate, through complementary experimental and theoretical approaches. The rate constants for the reactions of 31NN* with OH– and 1NN with •OH were determined to be 4.22 × 107 and 3.95 ± 0.01 × 109 M–1 s–1, respectively. These findings yield new insights into self-photosensitization as a pathway for TrOC attenuation and provide more mechanistic details into their environmental fate.
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