Novel D–π-A and A–π-D–π-A three-component photoinitiating systems based on carbazole/triphenylamino based chalcones and application in 3D and 4D printing†
A series of carbazole or triphenylamine based mono-chalcones, displaying either D–π-A or A–π-D–π-A architecture, have been designed and synthesized for intense absorption bands at around 405 nm with high molar extinction coefficients around 105 M−1 cm−1 corresponding to π–π* electronic transitions. Photosensitivity of the new photoinitiating systems composed of a chalcone and an iodonium salt (Iod) was investigated by UV-visible absorption and fluorescence spectroscopies, and their photoinitiation abilities were examined during the free radical polymerization of acrylates, whose polymerization kinetics were monitored by real-time Fourier Transform Infrared (RT-FTIR) spectroscopy upon irradiation with a LED@405 nm. In this work, a series of ten chalcones comprising a carbazole unit or a triphenylamine (TPA) group used as the electron donor for chalcones were specifically designed. Remarkably, nine of the proposed chalcones were never reported in the literature (never synthesized before). Only chalcone 7 was reported but only as a precursor for the design of pyrazolines for optical materials. As a result of this strategy, highly conjugated high-molecular-weight photoinitiators were obtained, displaying improved light absorption properties due to their extended polyaromaticity. These new photoinitiators offer new prospects for the design of novel and efficient photoinitiators. To evidence the interest of these new chalcones, 3D and 4D printing experiments were carried out with a polyethylene glycol (PEG)-diacrylate photosensitive resin comprising the best photoinitiating systems investigated. The shapes of 3D patterns can be reversibly modified by means of a thermal or hydrophilic response of PEG for a 4D activation.