Chem. J. Chinese Universities ›› 2022, Vol. 43 ›› Issue (4): 20210857.doi: 10.7503/cjcu20210857

• Polymer Chemistry • Previous Articles     Next Articles

Synthesis and Characterization of Phenothiazine-based Schiff Bases as Visible Light Photoinitiators

XU Dandan, ZOU Xiucheng, LUO Jing, LIU Ren()   

  1. International Joint Research Center for Photo?responsive Molecules and Materials,School of Chemical and Material Engineering,Jiangnan University,Wuxi 214122,China
  • Received:2021-12-24 Online:2022-04-10 Published:2022-02-12
  • Contact: LIU Ren E-mail:liuren@jiangnan.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(51673086)

Abstract:

In order to construct photoinitiators with strong molar extinction coefficient in the visible light region, four novel D-π-A type phenothiazine-based derivatives have been designed and synthesized. The structures were cha-racterized by nuclear magnetic resonance and high-resolution mass spectrum. These phenothiazine derivatives, as a strong electron-donating group, can easily undergo photo-induced electron transfer with iodonium salt(Iod), thereby initiating the radical and cationic photopolymerization. Interestingly, the prepared photoinitiators exhibit the characteristics of charge transfer in the ground and excited states and have the strong molar extinction coefficient of 104 L·mol-1·cm-1 in the spectral range of 350—450 nm, and have the red shifts about 50 nm compared with the commercial photoinitiator 2-isopropylthioxanthone(ITX), well matching the emitting spectra of the popularly used 405 nm LED light source. Theoretical calculations of molecular orbitals also explain the excellent optical properties of photoinitiators. The two-component initiating system has faster initiation efficiency and higher conversion rate than that of commercial photoinitiator ITX/Iod for free radical as well as cation photopolymerizations by changing different conditions of the formulas. The formula with PI(0.2%, molar fraction) and Iod(2%, molar fraction) exhibit the best curing effect. An photoinduced electron transfer(PET) mechanism was established based on steady-state photolysis experiments, and electron spin resonance spectroscopy experiment which captured the benzene radicals. The free energy changes(ΔGet) were measured by cyclic voltammetry(CV) experiments which proved the possibility of PET mechanism thermodynamically. Under irradiation, APN/Iod undergo the electronic transfer and the formed benzene radicals initiate polymerization of acrylates, and the active species is produced to initiate cationic polymerization of epoxy at the same time. In addition, the printing of fluorescent light-emitting devices was successfully carried out through the technology of Digital Light Processing(DLP) 3D printing.

Key words: Phenothiazine, Schiff base, Photoinitiator, Electron transfer

CLC Number: 

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