Symmetric Iodonium Salts Based on Benzylidene as One-Component Photoinitiators for Applications in 3D Printing

Abstract

We present a group of seven new advanced symmetric iodonium salts bearing two benzylidene-based chromophores. This is the first example of the use of a double bond in the structure of a symmetric iodonium salt. Such an improvement ensures excellent absorbing properties in the UV-A and visible range, representing a significant advance over the commonly used diaryliodonium salts. New symmetric iodonium derivatives effectively photoinitiate cationic polymerization using light-emitting diodes (LEDs) with no additives. Thus, they can act as one-component photoinitiators even in visible light, where common diaryliodonium salts remain inactive. They can be used in advanced applications such as three-dimensional (3D) VAT printing using an LCD printer. In addition, it was possible to study in detail substituent effects on the properties of the new iodonium salts due to the easily modifiable structure of the benzylidene chromophore. The research described represents a significant advance in the development of iodonium salts.

Push–pull coumarin-based one-component iodonium photoinitiators for cationic nanocomposite 3D-VAT printing

“…The quantum yield of acid generation was determined according to previous literature. 56,57 As a light source for irradiation, the UV-LED M340L4 (intensity I 0 = 53 mW cm −2 ) powered by a DC2200 regulated power supply (both from Thorlabs Inc.) was used. The irradiated solutions of iodonium salts in acetonitrile were prepared so that their absorbance was 2.5 or more over the entire emission of the LED used for measurements (for absorption of nearly all incident photons).…”

“…However, the situation changed radically with the appearance of new methods for the synthesis of iodonium salts. 53 The last decade has seen the emergence of many new structures of iodonium salts equipped with sophisticated chromophores such as naphthalimide, 54,55 benzylidene derivatives, 56,57 BODIPY 58 or anthraquinone, and flavone. 59 Nevertheless, despite this progress, one of the first salts with a coumarin chromophore remains one of the most active solutions, absorbing to the desired range and undergoing photobleaching.…”

Recent advances on diaryliodonium-based monocomponent photoinitiating systems

“…To address this issue, more reactive photoinitiating systems have thus to be designed. Over the years, various structures have been examined in order to design visible light photoinitiating systems and cyclohexanones, [20][21][22][23] cyanines, [24][25][26][27][28][29][30] iodonium salts, [31][32][33][34][35][36][37][38][39][40][41] naphthoquinones, [42][43][44] naphthalimides, [32,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] benzylidene ketones, [64][65][66][67]…”

Exploiting Visible‐Light Induced Radical to Cation Transformation Pathway for Reactivity Enhanced Electrophilic Aromatic Substitution Polymerization of Heteroaromatics

“…These features are particularly desirable in polymerization applications such as dental fillings, 3D printing, inks, adhesives, coatings, and photoresists. [ 7–17 ] Consequently, photoinduced methods have been extensively explored and adapted for various polymerization types, including free radical, cationic, controlled, and click reactions. [ 18–36 ]…”