Coumarin-Based Oxime Esters: Photobleachable and Versatile Unimolecular Initiators for Acrylate and Thiol-Based Click Photopolymerization under Visible Light-Emitting Diode Light Irradiation

Abstract

Developing efficient unimolecular visible light-emitting diode (LED) light photoinitiators (PIs) with photobleaching capability, which are essential for various biomedical applications and photopolymerization of thick materials, remains a great challenge. Herein, we demonstrate the synthesis of a series of novel PIs, containing coumarin moieties as chromophores and oxime ester groups as initiation functionalities and explore their structure-activity relationship. The investigated oxime esters can effectively induce acrylates and thiol-based click photopolymerization under 450 nm visible LED light irradiation. The initiator O-3 exhibited excellent photobleaching capability and enabled photopolymerization of thick materials (∼4.8 mm). The efficient unimolecular photobleachable initiators show great potential in dental materials and 3D printings.

Disubstituted Aminoanthraquinone-Based Multicolor Photoinitiators: Photoinitiation Mechanism and Ability of Cationic Polymerization under Blue, Green, Yellow, and Red LEDs

“…Photopolymerization technology 1-10 is a promising approach in various applications such as 3D printing, [11][12][13][14][15][16][17][18][19][20][21] (bio)medicine, optics technologies, microelectronics, and materials science. 16,[22][23][24][25][26][27][28][29][30][31][32] In photopolymerizable formulations, the photoinitiator (PI) plays the significant role of absorbing the light and then triggering the transformation of liquid monomers and resins into solids for the fabrication of various materials. 1,5,33,34 A challenge is to design and develop multicolor PIs of polymerization that can work under the whole visible light range (i.e.…”

Conjugated Bifunctional Carbazole‐Based Oxime Esters: Efficient and Versatile Photoinitiators for 3D Printing under One‐ and Two‐Photon Excitation

“…Oxime‐ester derivatives has been proven to undergo photoinduced decarboxylation and then generate free radicals at high quantum yields . The released CO 2 can be confirmed via color disappearance of the solution containing pH indicator phenolphthalein, when the PI solutions were irradiated . ESR spectroscopy was employed to further characterize the radicals generated after photodecarboxylation.…”

“…[21] The released CO 2 can be confirmed via color disappearance of the solution containing pH indicator phenolphthalein, when the PI solutions were irradiated. [25] ESR spectroscopy was employed to further characterize the radicals generated after photodecarboxylation. As shown in Figure 5, after photolysis of 4 d, the generated free radicals trapped by PBN provide only one radical adduct with hyperfine coupling constants of a N = 14.60 G, a H = 3.0 G).…”

“…[22] Wang et al, reported a series of phenothiazine-substituted oxime esters as photocleavable PIs sensitive to 405 nm laser diodes. [23,24] Our recent work has proven that when integrating the oxime-ester moiety into a visible light sensitive coumarin skeleton, the NÀ O bond can be cleaved under 450 nm LED light irradiation [25,26] or even under 980 nm near infrared laser excitation with assistance of upconversion nanoparticles. [27] It should be noted that these asymmetric oxime-esters can produce only one active initiation species after photolysis because the initiation ability of the generated primary iminyl radicals is limited.…”

“…[27] It should be noted that these asymmetric oxime-esters can produce only one active initiation species after photolysis because the initiation ability of the generated primary iminyl radicals is limited. Therefore, under 405 nm LED irradiation, the initiation performance of the monofunctional oxime-esters exhibit inferior initiation performance to commercial PI phosphine oxide TPO, [25] which can produce a benzoyl radical and a phosphinyl radical after the photo fragmentation and both radicals are very reactive. [28] Therefore, a proper molecular design is highly desired to fabricate more efficient oxime-esters PIs.…”