Unusual Oxidative Dealkylation Strategy toward Functionalized Phenalenones as Singlet Oxygen Photosensitizers and Photophysical Studies

Abstract

A series of functionalized 6-alkoxy phenalenones was prepared through an unprecedented oxidative dealkylation of readily available phenalene precursors. The starting phenalenes were efficiently synthesized via an aminocatalyzed annulation/O-alkylation strategy starting from simple substrates. The spectroscopic properties of some phenalenones were investigated in different solvents. Introducing an alkoxy substituent at the 6-position onto the phenalenone framework results in a redshift of the absorption. The synthesized phenalenones exhibit low fluorescence quantum yields and the fluorescence decay was studied in different solvents highlighting the presence of several lifetimes. The singlet oxygen ( 1 O 2 ) photosensitizing propensity of some phenalenones was investigated and the results showed the striking importance of the phenalenone molecular structure in generating singlet oxygen with high yields. The ability of phenalenones to generate singlet oxygen was then harnessed in three photooxygenation  AUTHOR INFORMATION

Magnetic Nanoparticle–Polymer Composites Loaded with Hydrophobic Sensitizers for Photodegradation of Azoic Dyes

“…As a proof of concept, we loaded the hybrid MNS–PMAO with PN, an aromatic ketone that has proven to be soluble and photostable in different solvents. PN is a type II PS with an efficient intersystem crossing and is considered a universal reference in singlet oxygen production because of its quantum yield close to unity in a variety of solvents. − , However, its low solubility in aqueous phases has largely limited its applications and has also motivated the synthesis of compounds derived from its structure that include more hydrophilic functional groups to increase the solubility …”

“…The hydrophobic nanodomains in the MNP–PMAO assemblies could therefore be exploited to load different molecules of interest, especially compounds that are scarcely soluble in aqueous media, like many fluorophores and PSs. This is the case of phenalenone (PN), a type II PS with a high quantum yield of singlet oxygen production, − whose low solubility in aqueous phases has greatly limited its practical applications. , …”

Photoinduced Storage and Thermal Release of Singlet Oxygen from 1,2‐Dihydropyridine Endoperoxides

“…Recent works from our group demonstrated that phenalenone 13 was an efficient photosensitizer for the generation of singlet oxygen [26] . To connect this photosensitizer to the singlet oxygen trap, the synthetic route started by the reduction of 13 into the alcohol 14 in 90 % yield.…”

“…The chemicals and solvents were purchased from commercial suppliers without further purification. The 2‐(cyanomethyl)‐1‐methylpyridin‐1‐ium iodide, [27] 1‐methyl‐2‐(2‐oxo‐2‐phenylethyl)pyridin‐1‐ium iodide, [28] diiodo‐BODIPY photosensitizer, [29] and phenalenone 13 [26] were prepared according to literature procedures.…”

Does the chemistry of fungal pigments demand the existence of photoactivated defense strategies in basidiomycetes?

“…For example, funalenone 48 was obtained from Aspergillus niger [90], and new derivatives are frequently isolated from marine sponges [91,92]. Mono-hydroxylated phenalenones-as for example the 3-hydroxy phenalenone 49-differ in their photochemical properties as compared to 47, however, they continue to be interesting PSs [93,94]. Next to the known phototoxic phenyl-phenalenones (50), Flors and Nonell [5] reviewed related photoactive alkaloids from plants, namely oxoaporphines, oxoisoaporphines, and azaporohines.…”