Plasmonic photocatalyst has become a kind of promising photocatalysts. Herein, we report precisely tuning electric field at sub-nanometer scale by using three mercapto-carboxylic acid linker molecules with 16, 11 and 3 alkyl carbons at interface of Au-Cu2O. Characterization results show the existence of the linker molecules at interface. Intrinsic photocatalytic reaction rates increased exponentially with the decrease of linker length, indicating sub-nanometer-dependence of photocatalytic activity on chain lengths, in good agreement with finite-element analysis (FEA) simulations.Graphical AbstractPhotocatalytic activity of plasmonic photocatalyst Au-Cu2O is precisely tuned by electric field at sub-nanometer scale by using three mercapto-carboxylic acid linker molecules with 16, 11 and 3 alkyl carbons at the interface. [GRAPHICS] .