Visible-Light Organic Photocatalysis for Latent Radical-Initiated Polymerization via 2e鈥?/sup>/1H+ Transfers: Initiation with Parallels to Photosynthesis
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- 作者：Alan Aguirre-Soto ; Chern-Hooi Lim ; Albert T. Hwang ; Charles B. Musgrave ; Jeffrey W. Stansbury
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：May 21, 2014
- 年：2014
- 卷：136
- 期：20
- 页码：7418-7427
- 全文大小：577K
- 年卷期：v.136,no.20(May 21, 2014)
- ISSN：1520-5126
文摘
We report the latent production of free radicals from energy stored in a redox potential through a 2e鈥?/sup>/1H+ transfer process, analogous to energy harvesting in photosynthesis, using visible-light organic photoredox catalysis (photocatalysis) of methylene blue chromophore with a sacrificial sterically hindered amine reductant and an onium salt oxidant. This enables light-initiated free-radical polymerization to continue over extended time intervals (hours) in the dark after brief (seconds) low-intensity illumination and beyond the spatial reach of light by diffusion of the metastable leuco-methylene blue photoproduct. The present organic photoredox catalysis system functions via a 2e鈥?/sup>/1H+ shuttle mechanism, as opposed to the 1e鈥?/sup> transfer process typical of organometallic-based and conventional organic multicomponent photoinitiator formulations. This prevents immediate formation of open-shell (radical) intermediates from the amine upon light absorption and enables the 鈥渟torage鈥?of light-energy without spontaneous initiation of the polymerization. Latent energy release and radical production are then controlled by the subsequent light-independent reaction (analogous to the Calvin cycle) between leuco-methylene blue and the onium salt oxidant that is responsible for regeneration of the organic methylene blue photocatalyst. This robust approach for photocatalysis-based energy harvesting and extended release in the dark enables temporally controlled redox initiation of polymer syntheses under low-intensity short exposure conditions and permits visible-light-mediated synthesis of polymers at least 1 order of magnitude thicker than achievable with conventional photoinitiated formulations and irradiation regimes.