Bis-chalcone derivatives derived from natural products as near-UV/visible light sensitive photoinitiators for 3D/4D printing

Four series of bis-chalcone compounds based on benzylpiperidinone, tetrahydrothiopyranone, pyridine or biphenyl central parts are designed and synthesized, enabling the development of ten bis-chalcones varying both by the central cores and by the substitution patterns (ortho, meta, para-positions) and the choice of the different groups attached to the peripheral substituents (alkoxy or allyloxy-substituted aromatic rings, thiophene, or ferrocene). In this series of ten bis-chalcones, eight of them were never synthesized before (i.e. only bis-chalcones 8 and 10 were already reported albeit never used as photoinitiators). These different dyes are proposed as new near-UV/visible light sensitive photoinitiators, in combination with an amine and an iodonium salt, to initiate the free radical photopolymerization (FRP) of PEG-diacrylate and the cationic photopolymerization (CP) of EPOX under LED@405 nm and LED@375 nm irradiation conditions. For the photopolymerization of acrylates carried out between thin films in laminate, all the bis-chalcones proposed in this work show higher photoinitiation abilities upon irradiation with a LED at 375 nm than at 405 nm, which is mainly due to their excellent light absorption properties in the near-UV region. Markedly, in contrast with the other two series of bis-chalcone compounds, pyridine-based bis-chalcones prove to be the most efficient photoinitiators, especially the bis-chalcones 5 and 9. Furthermore, all of them can also promote the cationic polymerization of epoxides upon LED irradiation at 375 nm, in the presence of an iodonium salt and an amine. More interestingly, some 3D patterns fabricated through the free radical polymerization of PEG-diacrylate demonstrate reversible swelling properties and shape-memory for access to 4D printing.