Singlet oxygen generation in aqueous suspensions was studied using the sodium salt of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) as a water-soluble probe. The attenuation of the ABDA absorption upon irradiation with green LED light (~7 W, 528 nm) in the presence of BDP-TFP-COF confirms the formation of singlet oxygen. Again, a control experiment with a pristine ABDA solution under otherwise identical conditions showed no changes in absorbance (Figure ). Therefore, we introduce BDP-TFP-COF as a heavy atom-free and metal-free porous photosensitizer that broadly absorbs in the visible region and efficiently generates singlet oxygen without common disadvantages such as high toxicity or poor chemical stability. As a potential application, we investigated the detoxification of mustard gas with BDP-TFP-COF. Due to the extreme hazard of mustard gas and its obvious commercial unavailability, these experiments were instead performed for the mustard gas simulant 2chloroethyl ethyl sulfide (CEES). A CEES solution (0.1 M in MeOH) in the presence of BDP-TFP-COF (1.0 mol%) was irradiated with white light and small probes for 1 H NMR spectroscopy were extracted at varying times. As shown in Figure , proton signals corresponding to the oxidized sulfoxide CEESO arose while the CEES signals attenuated and almost completely vanished after seven hours (Figure ). Apparently, the phototransformation to the non-toxic CEESO was fully completed and also no signals of the again toxic overoxidized sulfone CEESO2 were observed, thus confirming the successful detoxification (detailed monitoring of the complete process is shown in Figure ). Interestingly, efficient photodetoxification is achieved in the absence of any metals or heavy atoms, thus avoiding additional toxicity or poor photo-and chemical stability. Remarkably, the β-ketoenamine linkages provide enhanced robustness and durability, since the PXRD pattern for the recovered BDP-TFP-COF in Figure shows that the polymer retained its crystallinity after the experiments, thus indicating the pronounced stability and potential reusability of this heterogeneous photocatalyst.