Development of new high‐performance visible light photoinitiators based on carbazole scaffold and their applications in 3d printing and photocomposite synthesis

Abstract

In this article, new compounds based on the carbazole scaffold (DMs = DM1 and DM2, constituted by a carbazole unit connected on positions 3 and 6 to a two 4,4 0dimethoxydiphenylamine groups and differing by the substituent present on the nitrogen heteroatom of the carbazole core) were synthesized and proposed as high-performance visible light photoinitiators/photosensitizers for both the free-radical polymerization of methacrylates and the cationic polymerization of epoxides upon visible light exposure using LED@405 nm. Remarkably, DM2 leads to higher final conversions than DM1. In order to study the photophysical and photochemical properties of the carbazole derivatives, different parameters were taken into account such as the light absorption, the steady-state photolysis, and the fluorescence spectroscopy. Using different techniques such as fluorescence quenching, redox behavior, and cyclic voltammetry, we are able to discuss the photosensitization/photoinitiation reactions providing a full coherent picture of the involved chemical mechanisms. The photosensitization of the carbazole derivatives occurred predominantly via singlet excited states at the rate of the diffusion limit. Upon exposure to laser diode at 405 nm, DMs show high performance in initiating systems for 3D resins. Remarkably, DM2 can also be used in photocomposite synthesis using light-emitting diode conveyor. 1 H NMR 250 MHz (DMSO-d 6 ) δ 3.72 (s, 12H), 5.25 (d, 1H, J trans = 12.6 Hz), 5.08 (d, 1H, J cis = 20.4 Hz), 6.71 (dd, 1H, J cis = 22.0 Hz, J trans = 13.5 Hz), 6.82-6.91 (m, 16H), 7.12 (dd, 2H, J o = 10.3 Hz, J m = 2.9 Hz), 7.25 (d, 2H, J o = 9.6 Hz), 7.44 (d, 2H, J o = 9.9 Hz), 7.58 (d, 2H, J o = 10.5 Hz), 7.73 (d, 2H, J m = 2.1 Hz).

Coumarins as Powerful Photosensitizers for the Cationic Polymerization of Epoxy-Silicones under Near-UV and Visible Light and Applications for 3D Printing Technology

“…Actually, the investigated coumarins can efficiently absorb a blue light as aforementioned, then the corresponding generated excited states of such coumarins are expected to interact with IOD as a photoinitiator in order to generate reactive species (Coumarin ●+ ; see reactions r1 and r2 in Scheme 3 ), which are able to initiate the CP of thin (25 μm) epoxy-silicone films (using EPOX-Si200 as the benchmarked monomer) upon exposure to the LED at 405 nm as shown in the Figure 3 . The proposed photochemical mechanism for the coumarin/IOD interaction which occurs through the classical reduction of iodonium salt [ 28 ] is given in Scheme 3 , and a full description of the mechanism has been already described by us in detail in [ 13 , 15 ]. The two-component coumarin/IOD (0.05%/1% w / w ) photoinitiating systems are very efficient to initiate the CP under air where very high final functional conversions (FCs) and also high rates of polymerization (Rp) were achieved i.e., FC = 55% for coumarin 3 /IOD (0.05%/1% w / w ) (curve 3 in Figure 3 A; see also in Table 2 for the other coumarins).…”

“…It results from the fact that the propagated cations do not react with oxygen. The cationic polymerization of several monomers such as vinyl ethers, epoxides, and so on, has been largely reported in the literature [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

Recent advances on carbazole-based photoinitiators of polymerization

“…In this case, a small electronic delocalization exists between the nitrogen and the aldehyde function, inducing a small push-pull effect and thus enhancing the absorption. To extend the π-conjugation, another strategy consisted in introducing electron donating groups such as triphenylamine as peripheral groups of carbazole [115]. In this case, the adjunction of electron-donating groups to an electron donor cannot induce a push-pull effect within the molecules, no electronic interaction being possible between electron donors.…”

Recent advances on push–pull organic dyes as visible light photoinitiators of polymerization

“…Concomitant to the development of visible light photoinitiating systems, cheap, compact and lightweight irradiation setups have been developed such as the Light-emitting Diodes (LEDs) or the Laser diodes making the traditional irradiation systems obsolete. Over the years and in order their absorption spectra to perfectly fit with the emission spectra of the different visible light sources, a wide range of structures have been examined as visible light photoinitiators such as acridones 1, [18,19] acridine-1,8-dione 2, [20,21] benzophenones 3, [22][23][24][25] camphorquinones 4, [26,27] carbazoles 5, [28][29][30][31][32][33] chalcones 6, [34,35] chromones 7, [36][37][38] coumarins 8, [39][40][41][42][43] copper complexes 9, [44][45][46][47][48][49][50][51][52][53][54] cyclohexanones 10, [55][56][57] dihydroanthraquinone 11, [58] 2,3-diphenylquinoxaline derivatives 12, [59] diketopyrrolopyrrole 13, [60]…”