This study reports for the first time the use of β-carotene as a natural photosensitizer for both the cationic photopolymerization and thiol-ene click reactions under visible-light irradiation. In an all-green synthesis approach, this performing dye-based system leads to the cationic and thiol-ene polymerization of bio-based monomers, mono- and di-epoxy limonene, with very high final conversions, and appears as efficient as the common visible-light photosensitizers used in free-radical or cationic photopolymerization, that is, thioxanthone derivatives or camphorquinone. Effective antibacterial and tack-free coatings have been synthesized through the incorporation of a natural antibacterial agent (eugenol) in the limonene-derived polymer network. The antibacterial assays have demonstrated a tremendous effect of the eugenol-containing coatings against the adhesion of Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive).

This contribution reports on the synthesis and the photochemical behavior of two new sulfonium-based photoacid generators (PAGs). We demonstrate that a para-to-meta substitution of a methyl (p-cyanobenzyl) sulfonium group in a 4-alkoxystilbene core strongly influences the photodissociation efficiency of the PAGs and leads to an increase of the quantum yield for acid generation by a factor 2.4. This substantial effect, which was also corroborated by a reactivity enhancement in cationic photopolymerization, is assigned to the modulation of the electronic interaction between two low lying excited states whose energy gap is strongly influenced by this substitution effect. Moreover, it was found that the position of the sulfonium moiety hardly affects the two-photon absorption properties of these push−pull chromophores. By the two-photon fabrication of microstructures, we finally show the potential use of the meta derivative as cationic two-photon initiator.

The photophysical properties of a series of 1,8-naphthalimide photoacid generators were studied by steady state fluorescence and phosphorescence spectroscopy. Emission and excitation anisotropies, triplet quantum yields in polar and nonpolar solvent and photoacid generation were evaluated. The singlet excited state exhibits a low polarity and is strongly deactivated by an efficient intersystem crossing process. In protic solvent, a homolytic singlet cleavage of the N-O bond occurs and leads to the acid production. The existence of a triplet state close to the singlet state was clearly evidenced. The presence of close singlet excited states is supported by fluorescence anisotropy and picosecond laser spectroscopy experiments. Results of DFT calculations well confirm the experimental contentions and yield important information about the cleavage process involved in such compounds.

Electronic Supplementary Information (ESI) available: Evolution of the absorbance of 1,3-diphenylisobenzofuran (DBF) and curcumin alone at 480 nm in acetonitrile under visible light illumination and emission spectrum of the 4 lamps used during the different incubation times. SeeThe development of new antibacterial coating (against Escherichia coli and Staphylococcus aureus) with the use of a natural dye (curcumin) and epoxidized soybean oil, according to a photochemistry process has been investigated.Curcumin has been used both as a photosensitizer and an antibacterial agent under visible light illumination. The photoinduced coatings show good adherence properties on inox substrate and a high thermal stability by 375°C. Under visible light activation, singlet oxygen ( 1 O2) could be generated from the curcumin derivative-coatings, thus inhibiting by 99% and 95% the growth of Staphylococcus aureus and Escherichia coli, respectively, even after 48h of incubation.

A photochromic dithienylethene, bearing a phenyl azacrown as an ionophore and a formyl group as an electron-accepting substituent, changes its binding ability for Ca2+ by a factor higher than 103 by photoirradiation. This new photoionochromic displays a wavelength-dependent competition between fluorescence and photocyclization assigned to a red-shifted absorption of the fluorescing conformer compared to the absorption of the photoreactive conformer.

New quantum dots (QDs) were fabricated with a core/shell/shell structure consisting of CdTe core/CdS shell/ZnO shell. Despite the high lattice mismatch between CdS and ZnO, a ZnO shell was successfully introduced by basic hydrolysis of Zn(OAc)2 at the surface of core/shell CdTe/CdS QDs stabilized by 3-mercaptopropionic acid (MPA). The core/shell/shell CdTe/CdS/ZnO@MPA QDs exhibited a significant redshift of emission peaks (up to 50 nm for green-emitting CdTe/CdS QDs) when the shell grew. By changing the size of the core or the thickness of the ZnO shell, the emission colors of the obtained nanocrystals can be tuned between the green and red regions of the spectrum following an identical procedure. The influence of ZnO shell growth on photoluminescence (PL) quantum yields was found to be more pronounced for CdTe/CdS samples with green or yellow emission for which quantum yields increased up to three times. The epitaxial growth of the ZnO shell was confirmed by X-ray photoelectron spectroscopy and luminescence decay experiments. Because of the passivation of surface defects, a PL lifetime of 33.6 ns was measured for core/shell/shell CdTe/CdS/ZnO QDs prepared with a Zn/Cd ratio of 0.8, while it was only 17.7 ns for core/shell CdTe/CdS QDs.

A performing photoinitiating system based on paprika spice was developed (i) to efficiently initiate, according to a green photoinduced process, the cationic polymerization of a biosourced and renewable monomer, e.g., gallic acid, and (ii) to synthesize environmentally friendly antibacterial coatings in a reduced time. A decrease of 100% of the adhered bacteria was demonstrated upon visible light illumination without any remaining live bacteria.

We report the use of efficient visible-light sensitive allyl (QA) and epoxidized (QE) quinizarin derivatives as photoinitiating systems when combined with an appropriate electron donor (methyldiethanol amine, MDEA), an electron acceptor (iodonium salt, Iod), or a H donor (thiol derivative), for free-radical photopolymerization (FRP), cationic photopolymerization (CP), and a thiol–ene process. These systems have demonstrated excellent initiating properties under air or in laminated conditions under visible-light irradiation (LEDs@405, 455, and 470 nm or Xe lamp) for FRP, CP, or the thiol–ene process and appear more efficient than the well-known camphorquinone-based photoinitiating systems. As highlighted by electron paramagnetic resonance (EPR) and laser flash photolysis experiments, QA (or QE) acts either as an electron donor via a photoinduced electron transfer pathway with Iod or as a proton/proton-coupled electron transfer promoter with MDEA or a thiol derivative. Two types of interpenetrated polymer networks have been synthesized either by CP and the thiol–ene process with di­(ethylene glycol) divinyl ether/trithiol or by a concomitant free-radical and cationic photopolymerization with an epoxide/acrylate blend mixture upon LED@455 or 470 nm exposure. Interestingly, the resulting quinizarin-derived materials showed antiadherence properties under visible-light exposure even after two cycles of antibacterial experiments. Quinizarin derivatives can not only initiate photopolymerization but also generate singlet oxygen on the surface of the materials for preventing the adhesion and proliferation of bacteria under visible-light activation.