A phenoxynaphthacenequinone photoisomerizable monolayer was assembled onto an Au electrode. The resulting "trans"-quinone monolayer exhibits poor electrochemical reversibility due to a nondensely-packed configuration. Treatment of the trans-quinone monolayer with 1-tetradecanethiol yields a densely-packed monolayer that exhibits electrochemical reversibility. The electrochemical response of the irans-quinone monolayer electrode is pH-dependent, consistent with a two-electron and two-proton redox process. Photoisomerization of the trans-quinone monolayer (305 nm < lambda < 320 nm) generates the ana-quinone monolayer that lacks electrochemical activity. Upon photoisomerization of the ana-quinone monolayer to the trans-quinone state (lambda > 430 nm), the electroactivity of the monolayer is restored. By cyclic photoisomerization of the electrode between the ana- and trans-quinone states, reversible amperometric transduction of the recorded optical signals was accomplished.