The Blue‐LED‐Sensitive Naphthoquinone‐Imidazolyl Derivatives as Type II Photoinitiators of Free Radical Photopolymerization

Abstract

In this work, new naphthoquinone‐based photoinitiators are synthesized and applied for the first time in free radical photopolymerization. In the presence of acrylate monomers, these PIs display excellent photoinitiation capabilities under blue‐light LED@405 nm irradiation in a two‐component photoinitiating system in which the additive is a common iodonium salt (bis‐(4‐tert‐butylphenyl)iodonium hexafluorophosphate ‐ Iod) or a tertiary amine (ethyl 4‐dimethylaminobenzoate ‐ EDB). In controlled tests, the polymerization performance of dye4/Iod is equal to or better than that of common commercial Type II photoinitiators (2‐isopropylthioxanthone and benzophenone). Meanwhile, only a trace amount of photoinitiator is required (as low as 0.05%) to initiate the photopolymerization. It is worth noting that some of these compounds can also be used in one‐component photoinitiating system (monocomponent Type II behavior) and exhibit high photoinitiation ability. A series of complementary characterization analyses of two new naphthoquinone dyes (i.e. dye 1 and dye 4) with very similar chemical structures are carried out to investigate the relevant photochemical mechanism. Finally, 3D printing experiments are carried out by a simple and convenient Direct Laser Write (DLW) technique.

Photoinitiators from bio-sourced naphthoquinone – the application of naphthoquinone-based vitamins K1 and K3 in free radical photopolymerization

“…The acrylate group conversion was continuously monitored through real-time Fourier-transform infrared spectroscopy (RT-FTIR, JASCO FTIR 4100) at approximately 6120 cm −1 for the acrylate functionalities in trimethylolpropane triacrylate (TMPTA) and poly(ethylene glycol) diacrylate (PEGDA). 29 The irradiation process commenced at t = 10 s. The fluorescence experiments were performed using a JASCO FP-6200 spectrometer. The Gaussian 16 suite of programs was used to perform computational chemistry calculations at the UB3LYP/6-31G* level.…”

“…28 Therefore, it is expected that natural naphthoquinone derivatives can be effectively utilized in various photochemical fields such as photopolymerization. 29 However, there have been limited reports 24,30 on the application of natural naphthoquinone derivatives in photopolymerization.…”

Naphthoquinone-Based Oxime Esters for Free Radical Photopolymerization under Sunlight or a Blue Light-Emitting Diode

“…In this system, the presence of a chromophore capable of interacting with light is the key component governing the reactivity of the photoinitiating systems and, thus, the efficiency of the radical generation. Depending on the photoinitiating mechanism, photoinitiators can be divided into two main categories, namely, the photocleavable photoinitiators (type I) − and those behaving as hydrogen abstraction photoinitiators (type II). − In the case of a type I initiator, reactive radicals are formed via the homolytic cleavage of a selected chemical bond without any additives. , Conversely, in the case of type II or multicomponent systems, initiators can only produce initiating species in the presence of additives via redox reactions or a hydrogen abstraction mechanism. , Up to now, most of the commercial photoinitiators exhibit light absorption properties centered in the near-UV region (350–400 nm), resulting from the domination of the UV light sources during decades in photopolymerization. However, UV light is harmful to operators, which is responsible for skin cancer and eye damages.…”

“…Naphthoquinones have been extensively studied as anticancer agents but also for their anti-inflammatory or antinociceptive activities. , Naphthoquinones can be easily found in nature, and this scaffold can notably be found in vitamin K, chlorophyll quinone, carob quinone, and so on . Due to the presence of the strong electron-accepting quinone and the concomitant presence of the electron-rich aromatic ring, efficient electronic delocalization can be observed within this structure and naphthoquinones exhibit broad absorption extending over the visible range .…”

Efficient Near-Infrared Photopolymerizations Using azaBODIPYs with Electron-Donating Groups and Intramolecular Charge Transfer

“…This results in longer times to solidification, precluding the use of visible-to-NIR light in the aforementioned applications that often require curing in under ∼60 s or a polymerization rate on the order of ∼0.1 M/s at modest light intensities (≲50 mW/cm 2 ) to be practical. Although recent progress has been made in improving the efficiency (e.g., speed and sensitivity) of visible-to-NIR photocuring, − including for use in 3D printing, − novel photocatalyst systems and greater fundamental insights into their design principles are required to consider implementation in commercially relevant photocuring technologies.…”