Photochem, Volume 3, Issue 3 (September 2023) – 5 articles

The introduction and cleavage of protecting groups and the subsequent release of protected molecules is an important tool in synthetic organic chemistry. When polyfunctionalized substrates are involved, the reactivity of similar functional groups must be differentiated and selectively switched on and off. A very useful switching agent is visible or UV-light in photoremovable protecting groups (PRPG), allowing the PG release upon interaction with electromagnetic radiation. The reverse principle is the release of a protected molecule, which is accompanied by emission of light, i.e., chemiluminescent protecting groups (CLPG). This principle is proposed and investigated for phenylalanine (using ureido carboxylic acid 2 and its methyl ester derivative 3) and the carbamate derivatives of paracetamol 4 and L-menthol 7, protected as the corresponding urea-/carbamate-coumaranones 5A, 5E, 6 and 8, respectively. While the carbamate derivative 6 released the protected substrate with a short and strong emission of blue light when treated with a base under atmospheric oxygen, 8 had to be treated additionally with potassium hydroxide in boiling ethanol to completely cleave the PG. Both urea-coumaranone derivatives 5A/5E had a flash-like CL without release of the protected amino acid and, thus, were converted into a fluorescent protecting group (FPG). Full article

Due to its favorable excited-state physicochemical properties, indium oxide (In₂O₃) has widely captured attention as a potentially great photocatalyst. However, an inferior charge separation efficiency limits its application. Recently, an increasing amount of evidence has demonstrated that the construction of surface defects is an effective strategy to boost photocatalytic performances. In this work, a ruthenium (Ru) species was successfully introduced into the lattice of In₂O₃ nanoparticles through co-precipitation and thermal treatment. It was found that the content of surface oxygen vacancies was directly related to the amount of Ru³⁺ doping, which further determines the separation efficiency of photogenerated carriers. As a result, the 0.5% Ru-In₂O₃ samples enriched with oxygen vacancies exhibit dramatically enhanced photocatalytic dehalogenation performances of decabromodiphenyl ether and hexabromobenzene, about four times higher than that of the pure In₂O₃ nanoparticles. This study emphasized the significance of the surface defects of the photocatalyst and may provide a valuable strategy to prepare highly active photocatalysts for photocatalytic dehalogenation reactions. Full article

In the continuation of our sustained interest in porphyrin-based dendrimers and their use as luminescent photosensitizers for two-photon photodynamic therapy (2P-PDT), we wondered about the effect of changing the connectors in our macromolecular structures. We also wanted to initiate preliminary studies on meso-tetraarylporphyrins decorated with more electron-releasing arms. Thus, various meso-tetrafluorenylporphyrin-cored star-shaped and dendrimeric derivatives have been synthesized and characterized, as well as their zinc(II) complexes. In the new dendrimeric derivatives, the peripheral fluorenyl units of the dendrons are linked to the inner core either by N-phenylcarbazole (C_Cbz) or triphenylamine (C_Tpa) connectors instead of the more classic 1,3,5-phenylene (C_Ph) linkers previously used by us. Selected linear and non-linear optical (LO and NLO) properties were then determined for these compounds via absorption or emission studies and by two-photon excited fluorescence (TPEF) measurements. It was found that the C_Cbz-containing dendrimer, which has the most rigid structure, exhibits a significantly lower two-photon absorption (2PA) cross-section than its C_Tpa analog, presenting a more flexible structure while rather similar luminescence and singlet oxygen activation quantum yields are found for both. The origin of this unexpected discrepancy is briefly discussed based on our photophysical data. It is then demonstrated that the latter dendrimer also outperforms several closely related dendrimers in terms of 2PA action cross-section and 2PA-oxygen sensitization, making its molecular architecture quite appealing for developing new 2PA photosensitizers suited to theranostic uses. Full article

When volatile alkenes are emitted into the atmosphere, they are rapidly removed by oxidizing agents such as hydroxyl radicals and ozone. The latter reaction is termed ozonolysis and is an important source of Criegee intermediates (CIs), i.e., carbonyl oxides, that are implicated in enhancing the oxidizing capacity of the troposphere. These CIs aid in the formation of lower volatility compounds that typically condense to form secondary organic aerosols. CIs have attracted vast attention over the past two decades. Despite this, the effect of their substitution on the ground and excited state chemistries of CIs is not well studied. Here, we extend our knowledge obtained from prior studies on CIs by CF₃ substitution. The resulting CF₃CHOO molecule is a CI that can be formed from the ozonolysis of hydrofluoroolefins (HFOs). Our results show that the ground state unimolecular decay should be less reactive and thus more persistent in the atmosphere than the non-fluorinated analog. The excited state dynamics, however, are predicted to occur on an ultrafast timescale. The results are discussed in the context of the ways in which our study could advance synthetic chemistry, as well as processes relevant to the atmosphere. Full article

A Sn(IV) meso-tetra(4-methylthiolphenyl) N-confused porphyrin (4-Sn) complex was prepared to facilitate a comparison of the photophysicochemical and singlet oxygen photosensitiser properties of a series of Sn(IV) complexes of meso-4-methylthiolphenyl-substituted porphyrin, corrole, chlorin, and N-confused porphyrin. 4-Sn has an unusually high singlet oxygen quantum (Φ_Δ) yield of 0.88, markedly higher than the Φ_Δ values of the other complexes in this series. A Thorlabs M660L4 LED (280 mW · cm⁻²) was used to study the photodynamic activity of Sn-4 against the MCF-7 cancer cell line through irradiation at 660 nm for 30 min. The IC₅₀ value was calculated to be 1.4 (± 0.8) µM, markedly lower than the previously reported values for the rest of the series. Photodynamic antimicrobial activity was also determined against Staphylococcus aureus and Escherichia coli, and 4-Sn was found to deactivate both Gram-(+) and Gram-(−) bacteria despite the absence of cationic charges on the ligand structure. Full article