Structural Effects in the Iridium Complex Series: Photoredox Catalysis and Photoinitiation of Polymerization Reactions under Visible Lights

Abstract

A series of 18 iridium complexes (Ir) have been prepared and studied. Their abilities to initiate both a ring‐opening cationic polymerization (CP) using an Ir/iodonium salt couple and a free radical polymerization (FRP) in the presence of an Ir/amine/alkyl halide system under very soft irradiation (i.e., halogen lamp) or upon exposure to laser diodes @457 nm and @532 nm are investigated. Interestingly, these photoinitiating systems operate through an oxidative or a reductive photoredox catalytic cycle, respectively. Excellent polymerization profiles are obtained (reactive function conversions >70% for the CP of an epoxide and >60% for the FRP of low viscosity triacrylate). The photochemical mechanisms are studied by fluorescence, steady state photolysis, cyclic voltammetry, and electron spin resonance spin trapping experiments.

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

“…Complexes could also be isolated by precipitation, facilitating the purification process. The way how to recover these complexes is totally different to that used for the previously mentioned iridium complexes that could only be synthesized in low yields, but also required an extensive purification process to be obtained in pure form [37][38][39][40][41][42]. As an interesting feature, the three complexes displayed a strong absorption in the near-visible range, with absorption maxima at 380 nm for Cu-1 and Cu-2, and 383 nm for Cu-3 (See Figure 3).…”

“…As a result of this, the photoinitiator content can be drastically reduced, addressing the toxicity issue. However, organic dyes are not the only ones capable to exhibit high molar extinction coefficients, and, in the literature, highly efficient photoinitiators of polymerization based on iridium complexes have notably been reported, outperforming benchmark photoinitiators such as phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (BAPO) or camphorquinone (CQ) [37][38][39][40][41][42]. Their remarkable efficiencies were notably related to their long-living excited states, enabling the photosensitizers to react efficiently with the different additives introduced into the photocurable resins.…”

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

“…Iridium complexes have been the focus of numerous researches due to the facile tunability of their optical properties as well as their electrochemical properties [39][40][41][42][43][44][45][46]. Indeed, polypyridyl ligands can be easily modified by chemical engineering, so that the absorption of complexes can be shifted from the blue to the red region by replacing the well-known cyclometalated (2,4-difluorophenyl) pyridine (dfppy) ligand [47] with the 1-phenylisoquinoline (piq) ligand [48].…”

Novel Copper Photoredox Catalysts for Polymerization: An In Situ Synthesis of Metal Nanoparticles

“…Among these constituents, the photoinitiator plays an important role in the final properties of the cured coating, as well as in those of reactive oligomers and diluents. Metal complexes (zinc, ruthenium, iridium, and copper) have been used as photoinitiators for radical and cationic polymerization [ 25 , 26 , 27 , 28 , 29 , 30 ].…”