Developing efficient and long wavelength sensitive unimolecular photoinitiators(PIs)is still facing a great challenge.In this work,a series of thioxanthone-based N-hydroxyphthalimide esters(TX-NHPIEs)were synthesized by installing NHPIEs along the TX backbone and characterized.The investigated TX-NHPIEs have a 60 nm redshift and demonstrate sterling initiating efficiency for free radical photopolymerization(FRP)under LED@450 nm light irradiation compared with the commercialized isopropylthioxanthone(ITX).Real-time1Hnuclear magnetic resonance(1H NMR),electron spin resonance(ESR),decarboxylation and gas chromatograph-mass spectrometer(GC–MS)experiments and density functional theory(DFT)reveal that TX-NHPIEs can generate one alkyl radical and one N-centered iminyl radical,which can initiate FRP directly and indirectly,respectively.In other words,TX-NHPIEs absorb one photon and can generate two active radicals,which break through the limitations of common PIs.TX-NHPIE-Cpe demonstrates the highest initiating efficiency,and its application in coatings and 3D printing was also studied,indicating TX-NHPIEs have broad potential applications in photopolymerization processes.
Yi ZhuJingyan ZhangYuchao ZhangYing ChenGuanghui AnRen Liu
