No abstract

Highly versatile BODIPY dyes proved themselves to be very useful as photosensitizers. These dyes can be derivatized to absorb essentially anywhere in the visible the near IR region of the spectrum. As a result of their diverse reactivity, singlet oxygen generation efficiency can be modulated very precisely, leading to a number of selective photosensitizers for photodynamic therapy. Among the biologically relevant modulators, glutathione concentration and pH received particular attention. In this review, we highlight modulatable BODIPY-based photodynamic photosensitizers, and various synthetically useful chemical reactions triggered by singlet oxygen and other reactive oxygen species generated by BODIPY-based photosensitizers.

The photosensitized generation of singlet oxygen within tumor tissues during photodynamic therapy (PDT) is self-limiting, as the already low oxygen concentrations within tumors is further diminished during the process. In certain applications, to minimize photoinduced hypoxia the light is introduced intermittently (fractional PDT) to allow time for the replenishment of cellular oxygen. This condition extends the time required for effective therapy. Herein, we demonstrated that a photosensitizer with an additional 2-pyridone module for trapping singlet oxygen would be useful in fractional PDT. Thus, in the light cycle, the endoperoxide of 2-pyridone is generated along with singlet oxygen. In the dark cycle, the endoperoxide undergoes thermal cycloreversion to produce singlet oxygen, regenerating the 2-pyridone module. As a result, the photodynamic process can continue in the dark as well as in the light cycles. Cell-culture studies validated this working principle in vitro.

The development of methods to detect damage in macromolecular materials is of paramount importance to understand their mechanical failure and the structure–property relationships of polymers. Mechanofluorophores are useful and sensitive molecular motifs for this purpose. However, to date, tailoring of their optical properties remains challenging and correlating emission intensity to force induced material damage and the respective events on the molecular level is complicated by intrinsic limitations of fluorescence and its detection techniques. Now, this is tackled by developing the first stress‐sensing motif that relies on photon upconversion. By combining the Diels–Alder adduct of a π‐extended anthracene with the porphyrin‐based triplet sensitizer PtOEP in polymers, triplet–triplet annihilation photon upconversion of green to blue light is mechanochemically activated in solution as well as in the solid state.