Cinnamoylformate derivatives photoinitiators with excellent photobleaching ability and cytocompatibility for visible LED photopolymerization

In this work, four ethyl cinnamoylformate derivatives photoinitiators (ECFs), which have good photobleaching ability and excellent cytocompatibility in LED-triggered photopolymerization, were designed and synthesized by a simple two-step reaction. The potential initiating and photobleaching mechanisms of ECFs under visible LED were researched by ultraviolet−visible absorption spectroscopy, nuclear magnetic resonance, high−resolution mass spectroscopy and electron spin resonance. The as-prepared photoinitiators ethyl p-methoxycinnamoyl formate (O-ECF) and ethyl p -methylmercaptocinnamoyl formate (S-ECF) exhibited much higher initiating rate under 405 nm and 455 nm LED compared to the commercial photoinitiator 2-isopropylthioxanthone (ITX). More significantly, carbon‑carbon double bonds of ECFs can polymerize in the presence of tertiary amine under the irradiation of 455 nm or 405 nm LED, which endows ECFs with good photobleaching performance and excellent migration stability and cytocompatibility. Furthermore, ECFs are able to greatly initiate deep-layer photopolymerization under 455 nm LED and the photopolymerization depth reached 7.0 cm after the irradiation for 20 min. This work also affords a new perspective for designing photoinitiators with good photobleaching performance.