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A dimethyldihydropyrene (DHP) photochromic unit has been functionalized by donor (triphenylamine group) and acceptor (methylpyridinium) substituents. This compound was characterized by NMR, absorption and emission spectroscopies as well as cyclic voltammetry, and its properties were rationalized by theoretical calculations. The incorporation of both electron‐donor and ‐withdrawing groups at the photochromic center allows i) an efficient photo‐isomerization of the system when illuminated at low energy (quantum yield: Φc‐o=13.3 % at λex=660 nm), ii) the reversible and quantitative formation of two endoperoxyde isomers when illuminated under aerobic conditions at room temperature, and iii) the storage and production of singlet oxygen. The photo‐isomerization mechanism was also investigated by spin‐flip TD‐DFT (SF‐TD‐DFT) calculations. [ABSTRACT FROM AUTHOR]

The self-sensitized photo-oxygenation and singlet oxygen thermal release mechanisms in a pyridinium-substituted dimethyldihydropyrene (DHP) derivative have been investigated using quantum chemical calculations. First, the main photophysical pathway for intersystem crossing was identified, allowing the production of a DHP triplet state. Second, the energy transfer pathway between this triplet state and the oxygen triplet ground state was computed revealing a very efficient route for the photosensitized generation of singlet oxygen. Finally, the thermal pathway for the formation of a metacyclophanediene endoperoxide and the singlet oxygen release was characterized. A concerted and a stepwise mechanism were identified, the first one being lower in energy. All these results are consistent with recent experimental results and confirm that this type of system could be attractive oxygen carriers and singlet oxygen delivery agents. [ABSTRACT FROM AUTHOR]

Photochromism, dimethyldihydropyrene, singlet oxygen, endoperoxide, spin-flip time-dependent density functional theory Keywords: photochromism; dimethyldihydropyrene; singlet oxygen; endoperoxide; spin-flip time-dependent density functional theory EN photochromism dimethyldihydropyrene singlet oxygen endoperoxide spin-flip time-dependent density functional theory 16527 16527 1 12/06/21 20211201 NES 211201 B A dimethyldihydropyrene photochromic system b substituted by donor and acceptor units (left) is presented by M. Boggio-Pasqua, G. Royal, and co-workers in their Full Paper (DOI: 10.1002/chem.202103003). This photochrome can also play the role of oxygen photosensitizer and is able to reversibly trap singlet oxygen in the form of endoperoxide derivatives (right) when illuminated at room temperature under aerobic conditions. [Extracted from the article]