Control of electrochemical processes by photoisomerizable spiropyran monolayers immobilized onto Au electrodes: amperometric transduction of optical signals

Photoisomerizable self-assembled spiropyran (SP) monolayers on Au electrodes provide a means of transducing optical signals recorded by the monolayers as amperometric responses. An SP-modified monolayer on a Au electrode photostimulated the redox communication of pyrroloquinolinoquinone (PQQ) with the electrode interface. The electrical communication of PQQ with the SP monolayer state generated by visible light irradiation (λ > 475 nm) is inefficient. However, effective electrical communication is attained between PQQ and the protonated merocyanine monolayer electrode ((MRH)⁺ electrode) generated by illumination (360 nm < λ < 400 nm). Reversible photoisomerization of the monolayer between the SP and (MRH)⁺ states is transduced by cyclic amperometric responses. A mixed PQQ + SP monolayer on a Au electrode provides an active electrode for the photostimulated oxidation of NAD(P)H cofactors in the presence of Ca²⁺ ions. While the PQQ + SP monolayer electrode exhibits effective electrocatalytic properties towards the oxidation of NAD(P)H, the PQQ + (MRH)⁺ monolayer electrode state reveals poor electrocatalytic properties towards oxidation of the cofactors. Reversible photoisomerization of the monolayer across the PQQ + SP and PQQ + MRH)⁺ states provides a means of transducing the recorded optical signals by means of the electrocatalyzed oxidation of the cofactors as light-controlled amperometric responses.