Control experiments revealed that photocatalyst, light, and base are essential for this transformation (Table , entries 2-4). Even at elevated temperature (60 °C), the absence of light leads to an insignificant deuterium incorporation, which clearly indicates that the reaction is of photocatalytic rather than thermal nature (Table , entries 5 and 6). Increasing the reaction time to 24 h slightly increases the deuterium incorporation further to 1.85 D/molecule. The complete optimization process, including photocatalyst, base, solvent, and time screening is given in the SI (Table