Phenothiazine Photosensitizers for Onium Salt Photoinitiated Cationic Polymerization

Abstract

The syntheses of several different substituted phenothiazines are described and the ability of these compounds to photosensitize the photolysis of different onium salt cationic photoinitiators is described. These photosensitizers (PS) are generally operative in the mid-and long-range regions of the UV spectrum. The efficiencies of photosensitization of the cationic photopolymerizations of several typical epoxide and vinyl ether monomers by different substituted phenothiazine compounds were evaluated and compared. In addition, a phenothiazine-containing monomer and polymer were prepared and were shown to be effective photosensitizers.Currently, the most commonly used photoinitiators employed for photoinduced cationic polymerizations are diaryliodonium, I, and triarylsulfonium salts, Π, with the general structures shown below in which MtX n " represents a weakly nucleophilic counterion. Another promising class of photoinitiators is dialkylphenacylsulfonium salts, HI.

In-Silico Design of a Donor–Antenna–Acceptor Supramolecular Complex for Photoinduced Charge Separation

“…To verify the presence of a potential gradient between the donor, the antenna, and the acceptor suitable to induce charge separation, we compute the ground- and excited-state redox potentials of each subunit following the procedure described in section . As shown in Table , the redox values calculated at the B3LYP/DCM (COSMO) level compare well with the experimental cyclic voltammetry onset values. ,, These results overall confirm the validity of the applied method and computational setup. Considering also the positive results obtained with TD-DFT, the choice of the hybrid B3LYP functional appears to be appropriate for studying the electronic and optical properties of molecular complexes employing these functional subunits.…”

“…As shown in Table 1, the redox values calculated at the B3LYP/DCM (COSMO) level compare well with the experimental cyclic voltammetry onset values. 19,20,23 These results overall confirm the validity of the applied method and computational setup. Considering also the positive results obtained with TD-DFT, the choice of the hybrid B3LYP functional appears to be appropriate for studying the electronic and optical properties of molecular complexes employing these functional subunits.…”

“…Finally, phenothiazine is a strong reducing agent photoactive only in the UV region that is already widely employed as pesticide and in pharmaceutical or optical applications. ,, Thanks to the strong interaction between the 2p z electrons of the nitrogen atom of the central heterocyclic ring with the peripheral benzenes, PTZ can easily form cation-radical species and stabilize them through resonance delocalization of the positive charge into those electron-rich moieties . PTZ is therefore an optimal electron donor able to quench the hole created in the antenna upon photoexcitation.…”

Review on UV-Induced Cationic Frontal Polymerization of Epoxy Monomers

“…These hydroxyl groups enhance solubility of the photosensitizer in the epoxy monomer and also reduce toxicity of the photosensitizer by forming covalent bonds with terminating ether groups in the polymer chain [ 68 ]. Gomurashvili and Crivello [ 69 ] reported dual property of phenothiazines as photosensitizers as well as co-monomers in the cationic ring opening polymerization of various epoxide monomers. These polymerizable photosensitizers also possessed an absorption maximum between 254–333 nm and were able to speed up the cationic ring opening polymerization of various epoxides [ 70 ].…”

UV-Light Effects on Cytochrome C Modulated by the Aggregation State of Phenothiazines

“…As previously mentioned, the UV light irradiation of cytochrome c with low concentrations of phenothiazines at pH 8.0 led to protection of the protein against photo-damage and increased the turbidity of the samples. Literature data [29,37] and our laboratory results (unpublished) have demonstrated that phenothiazinescation radicals can oligomerize and form nanostructures in the presence and in the absence of polymers such polyethylene glycol. Consistently, in the conditions in which a reduced form of cytochrome c was detected by UV-visible spectroscopy, a significant increase of baseline was also present (Figures 2C, 2F, 3B and 3E, dotted lines).…”