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

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.