Toward a Comparable Reactivity Framework for Type I Photoinitiators in Photocleavage, Photopolymerization and Light-Driven Additive Manufacturing

Type I photoinitiators undergo cleavage upon exposure to light, generating reactive species capable of rapidly converting monomer to polymer, underpinning applications from coatings to patterning microelectronics and─with growing interest─additive manufacturing (i.e., light-driven 3D printing). However, progress in photocleavage, photopolymerization and 3D printing is complicated by diverse and dynamic environments, among other variables, that influence product yields and reactivity, challenging reproducibility across individual studies. The current lack of standardized protocols critically limits the direct comparison of Type I photoinitiators across photopolymerization and 3D printing systems. Herein, we discuss the state-of-the-art in photoinitiator performance assessment and propose a unified experimental framework with the aim of obtaining comparable product yields and reactivity data across three hierarchical levels: photolytic cleavage, photopolymerization kinetics and light-driven 3D-printing performance. Our framework is centered on precise, wavelength-dependent absolute yields via photochemical action plots with a unified set of experimental conditions to assess initiator photolysis, photopolymerization efficiency, and additive manufacturing performance. Comparable data sets will likely reveal structure-reactivity relationships and provide quantitative metrics that enable data-driven analysis, ranging from regression-based models to more advanced machine learning approaches to accelerate the discovery of next-generation Type I photoinitiators.