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Visible-Light-Initiated Free-Radical Polymerization by Homomolecular Triplet-Triplet Annihilation
Chem ( IF 23.5 ) Pub Date : 2020-09-16 , DOI: 10.1016/j.chempr.2020.08.019
Nancy Awwad , Anh Thy Bui , Evgeny O. Danilov , Felix N. Castellano

Polymerization reactions initiated by ultraviolet light are ubiquitous in scores of industrial applications but would markedly benefit from visible-light activation to overcome stability, energy consumption, light penetration, and sample geometry limitations. The current work leverages visible-light-driven homomolecular triplet-triplet annihilation (TTA) in zinc(II) meso-tetraphenylporphyrin (ZnTPP) to initiate facile free-radical polymerization in trimethylolpropane triacrylate (TMPTA) and methyl acrylate (MA) monomers through ultrafast electron transfer quenching. Selective Q-band (S1) excitation of ZnTPP in the green or yellow sensitizes TTA occurring between two 3ZnTPP∗ energized chromophores, ultimately generating the highly reducing S2 excited state on one ZnTPP molecule (Ered = −2.13 V versus saturated calomel electrode, SCE). Subsequently, this S2 state engages in electron transfer with TMPTA or MA, thereby initiating the radical polymerization process. Bimolecular electron transfer was confirmed through optically gated fluorescence upconversion. FT-IR and EPR spin-trapping experiments verified visible-light-initiated polymerization leading to the formation of well-defined macro- and microscopic objects.



中文翻译:

可见光引发的自由基聚合,通过分子三重态-三重An灭

紫外光引发的聚合反应在许多工业应用中无处不在,但显着受益于可见光活化以克服稳定性,能耗,光穿透和样品几何形状的局限性。当前的工作是利用可见光驱动的锌(II)内四苯基卟啉(ZnTPP)中的同质三重态三重态三重态an灭(TTA),通过超快引发三羟甲基丙烷三丙烯酸酯(TMPTA)和丙烯酸甲酯(MA)单体中的自由基聚合电子转移猝灭。绿色或黄色的ZnTPP的选择性Q波段(S 1)激发使两个3 ZnTPP *激发的发色团之间发生的TTA敏感,最终生成高度还原的S 2一个ZnTPP分子的激发态(E red  = -2.13 V,相对于饱和甘汞电极,SCE)。随后,该S 2状态与TMPTA或MA进行电子转移,从而引发自由基聚合过程。通过光学选通的荧光上转换证实了双分子电子转移。FT-IR和EPR自旋阱实验验证了可见光引发的聚合反应,导致形成了明确定义的宏观和微观物体。

更新日期:2020-11-06
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