A voltage-activated molecular-plasmonics device was created to demonstrate molecular logic based on resonant surface-enhanced Raman scattering (SERS). SERS output was achieved by a combination of chromophore plasmon coupling and surface adsorption at the interface between a solution and a gold nanodisc array. The chromophore was created by the self-assembly of a supramolecular complex with a redox-active guest molecule. The guest was reversibly oxidized at the gold surface to the +1 and +2 oxidation states, revealing spectra that were reproduced by calculations. State-specific SERS features enabled the demonstration of a multigate logic device with electronic input and optical output.