Chung Kun-You, Page Zachariah A
Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States.
J Am Chem Soc. 2023 Aug 16;145(32):17912-17918. doi: 10.1021/jacs.3c05373. Epub 2023 Aug 4.
Unimolecular (Type I) radical photoinitiators (PIs) have transformed the chemical manufacturing industry by enabling (stereo)lithography for microelectronics and emergent 3D printing technologies. However, the reliance on high energy UV-violet light (≤420 nm) restricts the end-use applications. Herein, boron-methylated dipyrromethene (methylated-BODIPY) is shown to act as a highly efficient Type I radical PI upon irradiation with low energy green light. Using a low intensity (∼4 mW/cm) light emitting diode centered at 530 nm and a low PI concentration (0.3 mol %), acrylic-based resins were polymerized to maximum conversion in ∼10 s. Under equivalent conditions (wavelength, intensity, and PI concentration), state-of-the-art visible light PIs Ivocerin and Irgacure 784 show no appreciable polymerization. Spectroscopic characterization suggests that homolytic β-scission at the boron-carbon bond results in radical formation, which is further facilitated by accessing long-lived triplet excited states through installment of bromine. Alkylated-BODIPYs represent a new modular visible light PI platform with exciting potential to enable next generation manufacturing and biomedical applications where a spectrally discrete, low energy, and thus benign light source is required.
单分子（I型）自由基光引发剂（PIs）通过实现用于微电子和新兴3D打印技术的（立体）光刻，改变了化学制造业。然而，对高能紫外-紫光（≤420 nm）的依赖限制了其最终应用。在此，硼甲基化二吡咯亚甲基（甲基化-BODIPY）在低能绿光照射下表现为高效的I型自由基光引发剂。使用以530 nm为中心的低强度（约4 mW/cm）发光二极管和低PI浓度（0.3 mol%），丙烯酸基树脂在约10 s内聚合至最大转化率。在等效条件（波长、强度和PI浓度）下，最先进的可见光PIs Ivocerin和Irgacure 784没有明显的聚合反应。光谱表征表明，硼-碳键处的均裂β-断裂导致自由基形成，通过引入溴进入长寿命三重态激发态进一步促进了这一过程。烷基化-BODIPYs代表了一个新的模块化可见光PI平台，具有令人兴奋的潜力，可实现下一代制造和生物医学应用，这些应用需要光谱离散、低能且因此良性的光源。
