Exploiting Metalloporphyrins for Selective Living Radical Polymerization Tunable over Visible Wavelengths

Abstract

The use of metalloporphyrins has been gaining popularity particularly in the area of medicine concerning sensitizers for the treatment of cancer and dermatological diseases through photodynamic therapy (PDT), and advanced materials for engineering molecular antenna for harvesting solar energy. In line with the myriad functions of metalloporphyrins, we investigated their capability for photoinduced living polymerization under visible light irradiation over a broad range of wavelengths. We discovered that zinc porphyrins (i.e., zinc tetraphenylporphine (ZnTPP)) were able to selectively activate photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of trithiocarbonate compounds for the polymerization of styrene, (meth)acrylates and (meth)acrylamides under a broad range of wavelengths (from 435 to 655 nm). Interestingly, other thiocarbonylthio compounds (dithiobenzoate, dithiocarbamate and xanthate) were not effectively activated in the presence of ZnTPP. This selectivity was likely attributed to a specific interaction between ZnTPP and trithiocarbonates, suggesting novel recognition at the molecular level. This interaction between the photoredox catalyst and trithiocarbonate group confers specific properties to this polymerization, such as oxygen tolerance, enabling living radical polymerization in the presence of air and also ability to manipulate the polymerization rates (kp(app) from 1.2-2.6 × 10(-2) min(-1)) by varying the visible wavelengths.

Engineering of relevant photodynamic processes through structural modifications of metallotetrapyrrolic photosensitizers

“…The most remarkable example is protoporphyrin IX and its iron complex that constitutes the heme prosthetic group and is crucial in oxygen transport. Metalloporphyrins are widely used in medicine, bio-sensing, catalysis and photocatalysis, optoelectronics and other fields [75][76][77].…”

Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization

“…In a manner remarkably similar to the original investigations by Otsu, direct photoactivation of compounds containing a TCT moiety has been shown to produce polymers of low dispersity and high end‐group fidelity (i.e., high “livingness”), provided that the combination of monomer, TCT compound, and light source (wavelength and intensity) is appropriately selected 8. Alternatively, the use of a photoredox catalyst can effectively facilitate electron transfer to a TCT species, with the resulting electronic instability leading to fragmentation, radical generation, and polymerization 9. The versatility of these compounds is demonstrated further by the use of TCTs in cationic polymerizations, where reversible activation is achieved by the coordination of a Lewis acid 10.…”

Unraveling Photocatalytic Mechanism and Selectivity in PET‐RAFT Polymerization

“…[4][5][6][7][8][9][10][11] As the name suggests, these photoredox catalysts harnesses the energy of visible light to accelerate a chemical reaction through electron transfer processes. [5,[14][15][16][17][18][19][20][21][22][23] Inspired by this, Boyer and co-workers have recently utilized photoredox catalysts, [4,8,17,18] such as pheophorbide a (PheoA) and zinc tetraphenylporphine (ZnTPP), to mediate photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization (Scheme 1). [12] The property of compatibility has led to some recent developments in the field of visible-light photocatalysis, where different catalysts are utilized to perform complex organic reactions in a single pot.…”