Iridium Photocatalysts in Free Radical Photopolymerization under Visible Lights

Abstract

International audienceA series of iridium(III) complexes was designed and investigated as new potential photocatalysts for radical polymerization reactions. The photocatalytic reduction cycle involves the combination of an iridium complex with an amine (e.g., N-methyldiethanolamine) and an alkyl halide (e.g., phenacylbromide). The different three-component systems herein investigated are very attractive for acrylate polymerization upon visible light irradiation. They are much more reactive than those based on Ru(bpy)3 2+. Free radicals generated during the reaction were investigated by ESR spectroscopy and the chemical mechanisms are discussed. The crucial role played by the photocatalyst (reduction ability and excited state lifetime) is also demonstrated

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

“…Even though the molar extinction coefficients of [(5,5 -dimethyl-2,2 -bipyridine)-bis-(2-phenylpyridine)iridium (III)] hexafluorophosphate (Ir b) in the 400-500 nm range are lower than that of Ir(ppy) 3 , the Ir b/MDEA/R-Br PIS is better than Ir(ppy) 3 /MDEA/R-Br in the FRP of EPT [127]. This indicates that other factors (in addition to the light absorption property) must be taken into account for a discussion on the relative polymerization initiating abilities of various PISs.…”

One‐Pot Synthesis of PTFEMA‐b‐PMMA‐b‐PTFEMA by Controlled Radical Polymerization with a Difunctional Initiator in Conjugation with Photoredox Catalyst of Ir(ppy)3 Under Visible Light

“…[ 18 ] The PDIs of the products were much narrower than that of photoinduced conventional radical polymerization with PABr/IrCs/ MDEA. [ 31 ] In addition, the PDI of the product was comparable to the visible-light-mediated ATRP of MMA with [EBPA]/[CuBr 2 ]/[TPMA] as the initiating system in DMF solvent (PDI = 1.34). [ 21 ] GPC chromatograms of the MMA polymerization with different concentrations of difunctional initiator DMDBHD are presented in Figure 3 .…”

“…[26][27][28][29] This attractive green chemistry was eventually adapted to initiate free radical polymerization under visible-light irradiation. For example, EBiB/Ru(bpy) 3 +/Pr 2 Net [ 30 ] and PABr/IrCs/ MDEA [ 31 ] systems were successfully applied in free radical and ring-opening polymerizations under weak-light irradiation. The recent breakthrough contributed by Fors and Hawker [ 18 ] offered a new pathway to tailor polymers with well-defi ned structures with visible light as the stimulus.…”

Photopolymerization Reactions: On the Way to a Green and Sustainable Chemistry

“…The current efforts result in an amazing series of proposals of new PISs . For example, we have recently introduced PISs ( [99][100][101][102][103][104][105][106][107]) exhibiting really novel absorption properties (red-shift absorptions, multicolor absorptions, enhanced molar extinction coefficients, ε): e.g., colored substituted or functionalized ketones [60], modified organometallic derivatives [70][71][72][108][109][110][111][112][113][114][115][116][117] (ruthenium-, iridium-, platinum-, zirconium-and zinc-based complexes, titanocene derivatives…), various series of dye-based skeletons [61][62][63][65][66][67][68][74][75][76] (e.g., phenylenediamine, polystilbene, polyazine, violanthrone, acridinedione, 2,7-di-tert-butyldimethyldihydropyrene, bodipy, boranyl, thiophene, perylene bis-dicarboximide, hydrocarbons, pyrromethene, pyridinium salt…), di-and tri-functional architectures of photo initiators [64], light harvesting compounds [57,58] (where a strong molecular orbital coupling occurs, leading to ε huge values) and push-pull and multicolor photoinitiators (novel chromophores; donor--acceptor arrangements; unusual broad absorptions from the blue to the red wavelengths…).…”

“…The further introduction of the silyl chemistry into photoredox cycles (as those known in organic synthesis purposes using photocatalysts (PC) [108][109][110][111][112][113][114][115][116][117]) has recently led to interesting possibilities of FRP and FRPCP reactions under soft conditions in aerated media [75,76,[105][106][107]. Novel PIs working as PCs through an oxidation cycle (metal complexes or organic metal-free compounds) in combination with a silane and an iodonium salt have been designed (22)(23)(24)(25); they allow successful excitations of cationic or radical matrices up to 635 nm under air.…”