Naphthyl-Naphthalimides as High-Performance Visible Light Photoinitiators for 3D Printing and Photocomposites Synthesis

Abstract

In this article, five new organic dyes based on the naphthalimide scaffold (Napht-1–Napht-5) were synthesized and tested as high-performance photoinitiators for both the Free Radical Photopolymerization (FRP) of acrylates and the Cationic Polymerization (CP) of epoxides using blue Light-Emitting Diodes (LEDs) as a safe irradiation source (LED @405 nm and 455). In fact, very good photopolymerization profiles (high final conversions and high polymerization rates) were obtained once these photoinitiators were combined with an Iodonium salt (Iod) or Iod/amine NPG and NVK). Remarkably, these dyes were able to generate interpenetrating polymer networks (IPN) by polymerization of a blend of monomers. These experiments were carried out to improve the polymerization profiles as well as the mechanical properties of the obtained materials. Due to their high photoinitiation abilities, these compounds were used in some applications such as photocomposite synthesis, direct laser write, and 3D printing experiments. To determine the chemical mechanisms, the photochemical/photophysical properties of these compounds were studied using different characterization techniques such as UV–visible absorption spectroscopy, steady-state photolysis, Fluorescence quenching, time-resolved fluorescence spectroscopy, FTIR spectroscopy, and cyclic voltammetry

Photoinitiation Mechanism and Ability of Thioxanthone‐Based Versatile Visible Photoinitiators

“…E red (A ._ /A)—the electrochemically determined reduction potential of the electron acceptor, for the diaryliodonium salt: E red Iod = −0.68 V versus SCE. [ 26 − 28 ]…”

Recent advances on photobleachable visible light photoinitiators of polymerization

“…[238] Indeed, phenothiazine is a wellknown electron donor that was used for the design of numerous photoinitiators due to the easiness of chemical modifications. [238][239][240][241][242][243][244][245][246][247][248] A similar easiness of chemical modifications can also be mentioned for carbazole [152,206,207,[249][250][251][252][253][254][255][256][257][258][259] and triphenylamine [260,261], but also for other popular scaffolds for the design of photoinitiators such as naphthalimide, [97,227,228,[262][263][264][265][266][267][268][269][270][271][272][273][274][275][276]…”

Recent advances on anthracene-based photoinitiators of polymerization

“…[261][262][263][264] Due to the easiness of synthesis, 1,8-naphthalimides were also used as photoinitiators of polymerization. [46,[80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95] In 2014, the first anthracene-substituted 1,8-naphthalimide CPD-29 was proposed by Lalevée and coworkers (See Figure 15). Unfortunately, due to the lack of substitution on the naphthalimide core, absorption of CPD-29 remained located in the UV range so that this dye was unsuitable for visible light experiments.…”