Synthesis And Performance Research Of Chalcone Derivtives As LED Photoinitators

Photopolymerization technology is widely used in coatings,inks,3D printing,microelectronics,biomedical materials and other fields because of its economic and efficient,energy-saving and environmental protection,without VOC emissions,and spatial and temporal controllability.However,the common light source of mercury lamp has the disadvantages of ozone generation,high energy consumption and harm to human body,and its use is restricted as people pay more attention to environmental protection.Compared with mercury lamps,organic lightemitting diode(LED)light source has the advantages of energy saving and environmental protection,long service life,etc.,and gradually become a common light source for light polymerization.But the wavelength of LED light sources commonly used in commercialization is above 365 nm,the absorption of traditional commercial photoinitiators doesn’t match the emission spectrum of LED light sources,causing low initiation efficiency.Therefore,it is important to develop photoinitiators that can efficiently initiate polymerization under common LED light sources.Chalcones are a class of dyes widely found in plants and have a wide range of biological activities.The main structure consists of two aromatic rings connected by α,β-unsaturated carbonyl groups,and the larger conjugated structure facilitates light absorption.These compounds can be prepared in one step by the Claisen-Schmidt reaction,and the raw materials are widely available and inexpensive,while the easy modification of the aromatic rings on both sides gives them strong structural design.In this paper,a series of long-wavelength photoinitiators were designed and synthesized with chalcone as the basic backbone to match the LED light source.The successful synthesis of the target compounds was demonstrated by NMR hydrogen and carbon spectra;the effects of substituent effects on the photoinitiating activity of chalcones were analyzed by UV-Vis absorption spectrum,real-time IR spectroscopy,redox potential and theoretical calculations.The chalcone derivatives with efficient photoinitiating activity under LED light source were obtained.The main research of this paper is as follows.(1)Eight chalcone derivatives monosubstituted on the aldehyde side or ketone side,respectively,were synthesized by the Claisen-Schmidt reaction using chalcone as the basic backbone.The optical absorption properties were characterized by UV-Vis absorption spectrum and DFT theoretical calculations.Their photochemical activities were investigated by RT-FTIR,steady-state photolysis,and cyclic voltammetry.The results showed that the maximum absorption wavelength of the compounds was red-shifted with the enhancement of the electron-donating ability of the substituents,and the absorption red-shift was more obvious with the greater effect of the aldehyde side substitution structure on the conjugation.However,the introduction of electron-donating substituents also reduces the photochemical reaction driving force of the molecule.The photopolymerization kinetics showed that the C4S/TEOA photoinitiated system has excellent photoinitiating activity under 365 nm and 405 nm light sources due to its better light absorption properties and photochemical reaction activity.Moreover,due to its light color and photobleaching properties,the polymer can be cured at 0.0625 wt% with a thickness of 2.4 cm,which is nearly colorless.(2)Six bilaterally para-substituted chalcone derivatives were designed and synthesized.Their optical absorption properties were investigated by UV absorption spectrum and DFT theoretical calculations,and their photochemical activities were studied by RT-FTIR,steady-state photolysis and cyclic voltammetry.The results showed that the bilaterally chalcone derivatives have better light absorption ability and photochemical activity compared to the monosubstituted structures with the same substituents.Among the five structures,C4’CN has excellent photoinitiating activity and photobleaching effect.Polymers with a depth of more than 7 cm could be cured at low concentrations(0.031 wt%)under irradiation with a 405 nm LED light source.