Photochromic Polymers Based on Fluorophenyl Oxime Ester Photoinitiators as Photoswitchable Molecules
Yuyang Ding, Shengling Jiang, Yanjing Gao, Jun Nie, Hongguang Du, Fang Sun
Abstract
We designed and synthesized two novel fluorophenyl oxime ester photoinitiators (E-FBOXEs) with the ability to prepare photochromic polymers, and then photochromic polymers based on E-FBOXEs were prepared by fast photopolymerization. E-FBOXEs can initiate photopolymerization of tripropylene glycol diacrylate under UV LED irradiation at 395 nm, and the final double bond conversion is achieved up to 81%. Meanwhile, the photocured film (PTPGDA) initiated or doped with E-FBOXE-Me displays thermally reversible photochromism at a moderate temperature (50 °C), switching from brown to colorless, because the photochromism of E-FBOXE-Me depends on the cleavage of the N–O bond, resulting in the generation of acetoxy radicals and colored iminyl radicals in the planar conformation under irradiation at 395 nm, and the recombination of the radicals to form colorless E-FBOXE-Me molecules in the nonplanar conformation under heating. Importantly, the PTPGDA film exhibits good fatigue resistance. The E-FBOXEs have great potential for application in the preparation of photochromic polymeric materials.