Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

Abstract

SummaryIn the present paper, the photoredox catalysis is presented as a unique approach in the field of photoinitiators of polymerization. The principal photocatalysts already reported as well as the typical oxidation and reduction agents used in both reductive or oxidative cycles are gathered. The chemical mechanisms associated with various systems are also given. As compared to classical iridium-based photocatalysts which are mainly active upon blue light irradiation, a new photocatalyst Ir(piq)2(tmd) (also known as bis(1-phenylisoquinolinato-N,C 2’)iridium(2,2,6,6-tetramethyl-3,5-heptanedionate) is also proposed as an example of green light photocatalyst (toward the long wavelength irradiation). The chemical mechanisms associated with Ir(piq)2(tmd) are investigated by ESR spin-trapping, laser flash photolysis, steady state photolysis, cyclic voltammetry and luminescence experiments.

Photocatalysts in Polymerization Reactions

“…Photoredox catalysts are now widely used in organic chemistry under very soft irradiation conditions . The mechanisms involved in PC systems basically rely on oxidation and reduction cycles with PC*/PC −I (reductive pathway) or PC*/PC +I (oxidative pathway) couples (Scheme ) …”

Copper and iron complexes as visible‐light‐sensitive photoinitiators of polymerization

“…Many metal‐free compounds that have been proposed so far exhibit a high efficiency as PIs of polymerization under visible lights (see refs. , , and ). Moreover, a first metal‐free system (based on the use of 10‐phenylphenothiazine in the photomediated process) has been successfully developed for photo‐ATRP .…”

Visible light sensitive photoinitiating systems: Recent progress in cationic and radical photopolymerization reactions under soft conditions

“…[17])). Some PIs having reversible redox potentials are regenerated through either reductive or oxidative cycles in the PISs and avoid any loss of photoreactivity upon light irradiation (as in the well-known photoredox catalysis) [19]. In controlled polymerization reactions, particular PIs can also play the role of control agents [20][21][22][23][24].…”

“…As some reviews regarding PISs have been published [1][2][3]5,7,8,18,25,[95][96][97][98][99][100], this review mainly describes the development of new PISs applicable to visible lights in the period of 2011 to early 2014 and is also an opportunity to gather the relative performance of the PISs we have recently designed, in order to propose a "one pot" comparison to the readers. Photoinitiator catalysts [19] and photosensitive systems in controlled polymerization reactions [20][21][22][23][24] have been reviewed recently and will be considered in Section 6.…”