Towards safe phosphine oxides photoinitiators with good cytocompatibility for 3D printing of thermoplastics

3D printing is the technology of choice for the rapid production of objects with complex morphologies and controlled physical and chemical properties. 3D printing by photopolymerization is of great interest because of its ability to access very small scales and its high resolution. In the case of recent 3D printers, the preferred wavelength for light irradiation is 405 nm since it is a safe and energy-economical irradiation. For 3D printing to be effective, it is therefore necessary to develop easily accessible, stable and highly efficient photoinitiating systems at the 405 nm wavelength. Beside, with the increasing use of photoinitiators, it is essential to develop structures with low cytotoxicity. Hence, the development of new photoinitiators is currently of major interest. To this end, the photochemical properties (triplet energy, bond dissociation energy, cleavage reaction enthalpy, and absorption properties) of several molecules have been calculated by molecular modeling and the most promising compounds have been synthesized. In this paper, four phosphine oxides photoinitiators (ADPO-1, CPO-2, CPO-3, and FPO-1) are synthesized and characterized. Subsequently, their absorption properties are measured and their efficiencies in photopolymerization under LED irradiation at 405 nm are evaluated. It is important to note that these structures have never been reported in 3D printing. Markedly, among the obtained photoinitiators, two of them show better efficiency than the commercially available and widely used phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) in photopolymerization (i.e., (Rp/[M-0]) x100 values are 6.94, 12.95, and 4.93 s(-1) for CPO-2, ADPO-1, and BAPO; with [M-0] the initial acrylate function concentration). Furthermore, one of the synthesized photoinitiators is successfully used in 3D printing of thermoplastics for potential recycling ability. Finally, one of the obtained structures shows a lower cytotoxicity than the benchmark structure diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO).