Recent advances on photobleachable visible light photoinitiators of polymerization

Photopolymerization under visible light has known major breakthroughs in recent years due to the development of new irradiation setups based on Light-Emitting Diodes (LEDs) enabling now to polymerize resins with low light intensities but also by the urgent need to develop efficient photoinitiating systems perfectly fitting the light sources currently under use in 3D printers. If the use of visible light is the key parameter to increase the thickness of the polymerized films, visible light photoinitiators are also strongly colored compounds that can adversely impact the future use of photopolymers for daily applications. Indeed, colorless coatings are highly desired by industry, what can not currently be achieved by use of visible light photoinitiators. To address this issue, the development of photobleachable photoinitiating systems has become an active research field. In this review, an overview of the recent advances on photobleachable photoinitiators is provided. Face to the difficulty to access to these highly desired structures, a wide range of structures have been explored and an overview of the different structures is given.