Catalytic amounts of a weak base are sufficient to induce the decomposition of anthracene endoperoxides to anthraquinone. The mechanism has been elucidated by isolation of intermediates in combination with DFT calculations. The whole process is suitable for the convenient generation of hydrogen peroxide under very mild conditions.

Singlet oxygen donors are of current interest for medical applications, but suffer from a short half-life leading to low singlet oxygen yields and problems with storage. We have synthesized more than 25 new singlet oxygen donors based on differently substituted naphthalenes in only a few steps. The influence of functional groups on the reaction rate of the photooxygenations, thermolysis, half-life, and singlet oxygen yield has been thoroughly studied. We determined various thermodynamic data and compared them with density functional calculations. Interestingly, remarkable stabilities of functional groups during the photooxygenations and stabilizing effects for some endoperoxides during the thermolysis have been found. Furthermore, we give evidence for a partly concerted and partly stepwise thermolysis mechanism leading to singlet and triplet oxygen, respectively. Our results might be interesting for "dark oxygenations" and future applications in medicine.

The intramolecular transfer of energy (FRET) and electrons (Dexter) are of great interest for the scientific community and are well-understood. In contrast, the intramolecular transfer of singlet oxygen ((1)O2), a reactive and short-lived oxygen species, has until now been unknown. This process would be very interesting because (1)O2 plays an important role in photodynamic therapy (PDT). Herein, we present the first successful intramolecular transfer of (1)O2 from a donor to acceptor. Also, we found a dependence of conformation and temperature comparable with those of FRET. We provide several pieces of evidence for the intramolecular character of this transfer, including competition experiments. Our studies should be interesting not only from the theoretical and mechanistic point of view but also for the design of new (1)O2 donors and applications in PDT.

Herein, we present a model system that allows the investigation of a directed intramolecular singlet oxygen ((1)O2) transfer. Furthermore, we show the influence of singlet oxygen lifetime and diffusion coefficient (D) on the preference of the intramolecular reaction over the intermolecular one in competition experiments. Finally, we demonstrate the distance dependence in quenching experiments, which enables us to draw conclusions about the role of singlet oxygen and (1)O2 carriers in photodynamic therapy.

Oxygen sticks in between acenes: The rate of the photooxygenation of bis(anthryl)alkanes with singlet oxygen shows a maximum for a defined chain length (n=4). In combination with calculations, a bathochromic shift of the UV/Vis absorption for only one endoperoxide and a CT absorption band, this gives considerable evidence for an oxygen anthracene sandwich complex.

The decomposition of anthracene endoperoxides has been investigated under various conditions. Thermolyses proceed via radical intermediates and afford anthracenes and rearrangement products, depending on the substitution pattern. Interestingly, not only the O–O but also the C–O bond can be cleaved homolytically. Under basic conditions fragmentations take place, affording anthraquinone, and reactive oxygen species. This mechanism explains the often observed decomposition of endoperoxides during work‐up. Finally, an acid‐catalyzed cleavage has been observed under release of hydrogen peroxide. The results should be interesting for the mechanistic understanding of peroxide decomposition and the endoperoxides might serve as mild sources of reactive oxygen species for future applications. Copyright © 2016 John Wiley & Sons, Ltd.

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