Recent advances on visible light Coumarin-based oxime esters as initiators of polymerization

Simplification of the photocurable resin is a great challenge that has been the focus of intense research efforts during the last decade. Indeed, if efficient photoinitiating systems have been developed in the past, based on multicomponent systems, the complexity of the formulations has rendered this approach difficult to transpose in industry. With aim at developing photoinitiating systems activable under low light intensity and in the visible range, highly reactive structures have also to be identified. In this field, coumarins have been extensively studied as Type II photoinitiators in combination with various additives. Using these structures, efficient multicompo-nent photoinitiating systems could be prepared. Face to these considerations, coumarins were thus identified as a promising scaffold for the design of Type I photoinitiators and especially of oxime esters. In this review, an overview of the recent development concerning coumarin-based oxime esters is presented. Comparisons with reference compounds will also be presented to evidence the interest of coumarins as light absorbing materials for the design of oxime esters.