Molecular Engineering of Triazine-Based Cleavage Photoinitiators: Rational Design, Synthesis, and Tailored Photopolymerization Performance

Abstract

Photopolymerization has emerged as a powerful and versatile technique for light-driven material fabrication, offering rapid reaction rates, spatiotemporal precision, and energy efficiency. Cleavage-type photoinitiators (PIs), as the core of this technology, have evolved from traditional UV-responsive systems to advanced visible- and near-infrared-sensitive structures, driven by the increasing use of LED light sources and the growing demand for environmentally friendly and biocompatible materials. This thesis focuses on the rational molecular design and performance evaluation of triazine-based visible-light photoinitiators, aiming to achieve high initiation efficiency, low migration, and sustainable functionality. The work is organized into five chapters, beginning with a comprehensive literature review and followed by four research chapters focusing on the development of novel triazine derivatives and their practical applications.

Chapter 1 provides an overview of recent progress in Type I photoinitiators, emphasizing molecular design strategies that extend absorption from the UV to visible and near-infrared regions. Systems based on phosphine oxide, carbon-group elements, oxime esters, and water-soluble or two-photon-compatible architectures are discussed in relation to their structural features, photophysical behavior, and radical generation mechanisms. The triazine family is introduced as a highly promising platform, with analysis of their advantages and current limitations.

Chapter 2 describes the synthesis of a polymerizable triazine photoinitiator (CT) and its polymeric counterpart (pCT) designed to minimize cytotoxicity and migration. Both compounds exhibit efficient initiation under violet light (LED at 410 nm) and remarkable migration stability, up to 14-fold improvement over benchmark triazines, demonstrating potential for safe use in biomedical and food-packaging applications.

Chapter 3 expands the structural diversity of triazine derivatives through an alternative synthetic route, achieving visible-light absorption up to 500 nm and improved initiation under 410-465 nm irradiation. Methacrylate-functionalized triazines show enhanced migration resistance and potential for two-photon polymerization, marking a step toward multifunctional and high-performance initiator systems.

Chapter 4 integrates carbon dots with triazine frameworks to yield hybrid nanophotoinitiators that combine strong visible absorption, fast steady-state photolysis, and superior photoinitiation ability. Beyond their high 3D printing fidelity, these hybrids act as nanofillers, reinforcing mechanical properties, improving network uniformity, and introducing light-to-heat conversion for responsive material systems.

Chapter 5 concludes that triazine-based photoinitiators, through rational structural design, can overcome the long-standing challenges of UV dependency, toxicity, and limited durability. The developed systems exhibit strong visible-light sensitivity, low migration, and multifunctional performance such as light-responsive behaviour, two-photon absorption, and enhanced mechanical properties, providing a foundation for next-generation photopolymerization. Future work should focus on developing water-soluble and biocompatible triazine derivatives to enable efficient curing in aqueous environments, as well as engineering high molar absorptivity and deep-curing capabilities for thicker and more complex 3D structures.

Collectively, this thesis establishes triazine derivatives as a versatile and sustainable platform for visible-light photopolymerization, paving the way toward environmentally benign, high-precision, and multifunctional light-driven manufacturing technologies. Show more