Sustainable carbon dots (CDs) based on furfuraldehyde (F-CD) resulted in a photosensitive material after pursuing the Alder-Longo reaction. The porphyrin moiety formed connects the F-CDs in a covalent organic network. This heterogeneous material (P-CD) was characterized by XPS indicating incorporation of the respective C, N and O moieties. Time resolved fluorescence including global analysis showed contribution of three linked components to the overall dynamics of the excited state. Electrochemical and photonic properties of this heterogeneous material facilitated photopolymerization in a photo-ATRP setup where either CuBr 2 /TPMA, FeBr 3 /Br À or a metal free reaction setup activated controlled polymerization. Chain extension experiments worked in all three cases showing end group fidelity for activation of controlled block copolymerization using MMA and styrene as monomers. Traditional radical polymerization using a diaryl iodonium salt as co-initiator failed.
NIR exposure at 790 nm activated photopolymerization of monomers comprising UV‐absorbing moieties by using [CuII/(TPMA)]Br2 (TPMA=tris(2‐pyridylmethyl)amine) in the ppm range and an alkyl bromide as initiator. Some of them comprised structural elements selected either from those showing proton transfer or photocycloaddition upon UV excitation. Polymers obtained comprise living end groups serving as macroinitiator for controlled synthesis of block copolymers with relatively narrow molecular weight distributions. Chromatographic results indicated formation of block copolymers produced by this synthetic approach. Free‐radical polymerization of monomers pursued for comparison exhibited the expected broader dispersity of molecular weight compared to photo‐ATRP. Polymerization of these monomers by UV photo‐ATRP failed on the contrary to NIR photo‐ATRP demonstrating the UV‐filter function of the monomers. This work conclusively provides a new approach for the polymerization of monomers comprising UV‐absorbing moieties through photo‐ATRP in the NIR region. This occurred in a simple and efficient pathway. However, studies also showed that not all monomers chosen successfully proceeded in the NIR photo‐ATRP protocol.
Cyanines with heptamethine pattern namely 5- (6-(2-(3-ethyl-,3,6-tetrahydropyrimidin-4-olate comprising a barbiturate group facilitate controlled radical polymerization using FeBr 3 in the ppm range applying radiation at 790 nm. Tris(4-methoylphenyl) phosphine, Tris(2-pyridylmethyl)amine or tetrabutylammonium bromide served as ligand. The latter showed the best performance resulting in a system needing no amino nitrogen for photo-ATRP. Ethyl α-bromophenylacetate worked as initiator. The cyanine interacts with FeBr 3 resulting in a new absorption band at 877 nm that also resulted in formation of polymer exhibiting similar molecular weight but higher dispersity compared to that obtained by 790 nm radiation by exposure with a light-emitting diode (LED) emitting at 870 nm. This explains the reactivity of the system while other cyanines such as 2--indolium chloride showed no activity by exposure at 790 nm in combination with FeBr 3 /Br À . Controlled radical polymerization was confirmed by successful chain extension and block copolymerization experiments resulting in polymers, which exhibit a dispersity of about 1.3. Interestingly, the new system comprising the aforementioned barbiturate substituted cyanine, FeBr 3 /Br À and ethyl α-bromophenylacetate showed a certain oxygen tolerance. Polymers obtained exhibited similar dispersity as those made under inert conditions.
A photo‐ATRP protocol uses NIR radiation released by an LED at 790 nm to facilitate synthesis of block copolymers comprising UV‐absorbing moieties enabling the function of an optical filter there. Cyanines with heptamethine pattern and barbiturate group favor to activate copper(II) complexes to initiate the light‐induced synthesis of block copolymers with highly UV‐absorbing components. Comparative experiments with UV LEDs applying a UV‐based ATRP system show no initiation of living photopolymerization. Find out more in the Full Paper by B. Strehmel et al. on page 10444 ff.
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