Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible‐Light Applications

Abstract

Various photosensitizers were grafted by conventional peptide coupling methods to functionalized silica with several macroscopic shapes (powders, films) or embedded in highly transparent and microporous silica xerogel monoliths. Owing to the transparency and free-standing shape of the monoliths, the transient species arising from irradiation of the PSs could be analyzed and were not strikingly different from those observed in solutions. The observed reactivity for either liquid-solid (α-terpinene oxygenation vs dehydrogenation) or gas-solid (dimethylsulfide, DMS, solvent-free oxidation) reactions was consistent with the properties of the excited states of the PSs under consideration. Immobilized anthraquinone-derived materials preferentially react in both cases by electron transfer from the substrate to the triplet state of the sensitizer, in spite of an efficient singlet oxygen production. The recently developed 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, DBTP-COOH, efficiently reacts via energy transfer to yield singlet oxygen from its triplet state. It was shown to perform better than 9,10-dicyanoanthracene and rose bengal for DMS oxidation and α-terpinene photooxygenation to ascaridole, respectively. Thus, by a proper choice of the organic immobilized photocatalyst, it is possible to develop efficient and reusable materials, activated under visible light, for various applications and to tune the reaction pathway, opening the way to green oxidation processes.

Photostability of plasma polymerized γ-terpinene thin films for encapsulation of OPV

“…While undesired for polymers, these reactions are useful in organic synthesis with sunlight3839. Photostable polymers are also often used as solid supports for photooxygenation reactions40.…”

Gas‐Phase Photooxidation: Reactors and Materials

“… (a) Single‐pass photoreactor containing (b) silica xerogels embedding various photosensitizers (DBTP: 9,14‐dicyanobenzo[ b ]triphenylene, MV: methylene violet, PN: phenalenone, RB: Rose bengale, NMB + : new methylene blue, DCA: 9,10‐dicyano‐anthracene, OC: trimethoxy(octyl)‐silane containing silica xerogel; SG0: the silica‐xerogel is only embedding the sensitizer, SG2: the sensitizer is covalently grafted to the silica xerogel. (c) Dimethylsulfide concentration at the outlet of the reactor as a function of the sensitizing material used; reproduced from 58 with permission from ACS and from 80 with permission from Wiley. …”

“…Silica monoliths containing embedded or grafted photosensitizers were highly efficient for solvent‐free oxygenation of volatile sulfides in the gas phase (Fig. 10) 58–60, 80. These silica monoliths obtained by a sol‐gel process present several advantages: (i) they are optically transparent ensuring a good penetration of light, (ii) depending on the xerogel synthesis they have a high micro or micro/meso porosity with high specific surface area in the 500–700 m 2 g −1 range, (iii) they are mechanically stable, (iv) their shape may be tuned according to the chosen mould, (v) the silica support is chemically inert contrary to polymer matrices, (vi) the light absorption range may be tuned by proper choice of the photosensitizer.…”

Efficient Photooxygenation Process of Biosourced α-Terpinene by Combining Controlled LED-Driven Flow Photochemistry and Rose Bengal-Anchored Polymer Colloids

“…[31][32][33][34][35][36] In parallel, the concept of solid-supported sensitizers offers many advantages as it makes it easier to separate the organic sensitizer from the other reactants and products, avoiding expensive downstream separation. [37][38][39][40][41][42][43][44][45][46] It is also a strategy for transposing poorly soluble photosensitizers into green solvents, while simultaneously enhancing their photostability and reusability. Solid-supported sensitizers in continuous-flow microstructured reactors were first implemented in the form of polymer/silica films cast onto the walls of the reactor.…”