Metalated porphyrins as versatile visible light and NIR photoinitiators of polymerization

Abstract

A series of metalated porphyrins has been prepared and used as visible light photoinitiators of polymerization activable under low light intensity. Among the six metalated porphyrins examined in this work, five of them have never been reported in the literature and specifically designed to exhibit a good solubility in monomers. Three of the proposed structures were efficient @405nm but remarkably, despites their weak absorptions at 785 nm, efficient Near Infrared (NIR) polymerization profiles could also be obtained during the free radical polymerization of a methacrylate resin. To support the experimental observation of a polymerization process, a mechanism has been proposed based on combined photochemical and photothermal pathways.

Bio-based porphyrins pyropheophorbide a and its Zn-complex as visible-light photosensitizers for free-radical photopolymerization

“…To our knowledge, this is the first use of a porphyrinoid-based three-component system for red-light FRP initiation without adding a thermal initiator. 23,38 While chlorophyll b and chlorophyllin have been reported as slow initiating photoinitiators under red light, 14 Pyro and Zn-Pyro allow conversions of up to 60% to be reached under LED@625 nm in this study. Surprisingly, although Pyro/MDEA was the only two-component systems able to initiate polymerization under air according to the formation of aminoalkyl radicals (see EPR results), Pyro/Iod/MDEA could not.…”

“…Some examples of FRP under NIR were reported with porphyrin initiators, but using four-component systems to combine photothermal and photochemical initiation. 23,38 Although synthetic products can show impressive photochemical properties, porphyrin derivatives also exist in nature, and take part in vital biological processes: chlorophyll a, which is the mainstay of photosynthesis; haemoglobin, which is the oxygen carrier in the blood; or the corrin structure at the base of vitamin B12. 39 Several natural dyes have already been studied and found to promote photopolymerization under visible light, [40][41][42][43] but they generally do not absorb in the red light range, contrary to free base porphyrins that possess absorption bands, namely Q bands, up to 650 nm.…”

Recent advances on perylene-based photoinitiators of polymerization

“…[26] Considering that the development of visible light photoinitiating systems activable under low light intensity and in the visible range is extremely recent, this research is still in a prospective phase, at the search of innovative structures that could act as visible light photoinitiators of polymerization. In the course of the different investigations, a wide range of structures have been examined and naphthalimides, [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] porphyrins, [42,43] chromones and flavones, [44][45][46][47][48] acridones, [49,50] carbazoles, [51][52][53][54][55][56][57][58] benzophenones, [59][60][61][62][63][64] pyrenes, [65][66][67][68][69][70] diketopyrrolopyrroles, [71]...…”

RAFT Polymerization of Semifluorinated Monomers Mediated by a NIR Fluorinated Photocatalyst

“…With long wavelengths and good tissue penetration, the near‐infrared (NIR) light has been utilized to stimulate controlled/living polymerization, either by incorporating upconversion nanoparticles (UCNPs) [ 27–33 ] or using photocatalysts with NIR light presence. [ 34–39 ] The use of UCNPs in photopolymerization is creative, but it also inevitably increases the complexity of the system. Boyer et al.…”

“…With long wavelengths and good tissue penetration, the near-infrared (NIR) light has been utilized to stimulate controlled/living polymerization, either by incorporating upconversion nanoparticles (UCNPs) [27][28][29][30][31][32][33] or using photocatalysts with NIR light presence. [34][35][36][37][38][39] The use of UCNPs in photopolymerization is creative, but it also inevitably increases the complexity of the system. Boyer et al reported the use of phthalocyanine compounds, [40,41] and bacteriochlorophyll 𝛼 [42] as a photoinitiation system for RAFT polymerization under NIR wavelengths.…”