N-[2-(Dimethylamino)ethyl]-1,8-naphthalimide derivatives as photoinitiators under LEDs

Four N-[2-(dimethylamino)ethyl]-1,8-naphthalimide derivatives (ANNs) with different substituents (bromo group, primary amine, secondary amine, and tertiary amine) in the naphthalimide skeleton have been synthesized and can be used as one-component free radical photoinitiators or incorporated into multi-component photoinitiating systems for free radical or cationic photopolymerization under the irradiation of various LEDs. ANN2 (with secondary amine substituent) or ANN3 (with tertiary amine substituent) alone is capable of initiating the free radical polymerization of acrylates under a LED at 405 nm while ANN0 (with bromo substituent) or ANN1 (with primary amine substituent) does not work. When combined with various additives (e.g. iodonium salt, N-vinylcarbazole, chloro triazine, or tertiary amine), most of the ANN1–3 based multi-component photoinitiating systems are efficient in free radical photopolymerization at 385 nm, 405 nm, 455 nm, 470 nm and even under a low-intensity polychromatic visible light (from a halogen lamp) with the final conversions being higher than 60% (even more efficient than commercial photoinitiators bisacylphosphine oxide and camphorquinone). In addition, ANN1–3 based photoinitiating systems also exhibit a high efficiency for cationic photopolymerization of epoxides upon diverse LEDs. The ANN2 based photoinitiating system can also be used for the synthesis of interpenetrated polymer networks and adapted for 3D printing. The photochemical mechanisms of the ANN based systems have been comprehensively investigated and discussed in detail.