Exploiting
Metalloporphyrins for Selective Living
Radical Polymerization Tunable over Visible Wavelengths
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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 (<i>k</i><sub>p</sub><sup>app</sup> from 1.2–2.6 × 10<sup>–2</sup> min<sup>–1</sup>) by varying the visible wavelengths