Towards mechanochemical generation of singlet oxygen

Singlet oxygen is a short-lived reactive species which is involved a number of biochemical processes and implicated as the primary photo-generated cytotoxic agent in photodynamic therapy (PDT) of cancer. Precise chemical control of singlet oxygen generation and or storage is therefore of immense interest. In this particular study, the possibility of mechanochemical release of singlet oxygen in cross-linked polymers carrying anthracene 9,10-endoperoxides was explored. 9,10-Diphenylanthracenes are stable at room temperature but undergo thermal cycloreversion when heated to produce singlet oxygen. Thus, a cross-linked polyacrylate was synthesized, incorporating anthracene-endoperoxide modules with chain extensions at the 9,10-positions. Previously in our lab, thermal lability of the anthracene endoperoxides were shown when attached to gold nanorods. In this work, it was demonstrated that on mechanical agitation in a cryogenic ball mill, fluorescence emission due to anthracene units in the polymer is enhanced, with a concomitant generation of singlet oxygen as proved by detection with a selective probe, SOSG. Also, a cross-linked polyacrylate and a PDMS elastomer incorporating anthracene-endoperoxide modules with chain extensions at the 9,10-positions were synthesized as the polymeric matrix for a better manifestation of mechanochemical process.