We evaluated the photochemical stability of our best-performing SBP system, TT-TAB, in longterm hydrogen evolution experiments. Initially, TT-TAB was irradiated for four cycles each of 5 h length with hourly gas chromatography measurements. After each cycle, the initial amount of sacrificial agent was replenished by addition of solid ascorbic acid, the solvent was exchanged, and the reaction mixture was degassed thoroughly before further irradiation. Over the course of this experiment, the catalytic activity of TT-TAB remained effectively constant (Error! Reference source not found.F). We verified the chemical integrity of the TT-TAB polymer before and after 15 h of continuous photocatalysis using FTIR, solid-state NMR, and UV/Vis spectroscopy, and we observed no significant changes (Figure ). NOTE: without the suggested solvent exchange, we observe an accumulation of side-product from the oxidation of L-ascorbic acid in the reaction vessel which has a detrimental effect on HER activity over time (Figure ). SBPs with L-ascorbic acid as sacrificial agent; E) comparison of sacrificial agents using TT-TAB as catalyst; C) influence of platinum as co-catalyst; F) long-term hydrogen evolution using TT-TAB and L-ascorbic acid as sacrificial agent without added platinum. Dashed lines denote exchange of solvent and addition of fresh sacrificial agent. General conditions for HER experiments using L-ascorbic acid: 1 mg of catalyst, 8 mL acetonitrile, 8 mL L-ascorbic acid (0.1 M), platinum (3 wt%) unless marked platinum-free. Further conditions can be found in the SI.