Improving Continuous Flow Singlet Oxygen Photooxygenations with Functionalized Mesoporous Silica Nanoparticles

Continuous flow photochemistry relying on photosensitizers faces two main challenges: the photodegradation (bleaching) and the downstream removal of the photosensitizer. Rose Bengal (RB) is a common photosensitizer utilized for photooxygenations with singlet oxygen (1O2), but is notoriously sensitive to photobleaching and difficult to remove from reactor effluents. The heterogenization of photosensitizers on mesoporous silica nanoparticles (MSNs) is arguably a viable option for such applications. Herein, we report on the use of RB covalently incorporated into MSNs (RB@MSNs) for photooxygenations under continuous flow conditions. RB@MSNs enable the 1O2 photooxygenation of various organic substrates upon irradiation with 540 nm LEDs. A series of organic substrates were evaluated including methionine, α‐terpinene, 2‐furoic acid, triphenylphosphine, citronellol and cyclopentadiene. These results emphasize an improved resistance to photobleaching, and the possibility to use RB@MSNs as easily recoverable catalyst, which could be removed from the reactor effluent either (a) by centrifugation or (b) in‐line membrane filtration.