Tobias and Yujin’s paper trying to answer this question for a SAM formed of spiropyrans has been accepted for publication in Journal of Physics: Condensed Matter. In it they show that if you’d like to build an electrochemical sensor using an electrode covered with a photoswitchable SAM (and, well, of course you’d like to) you need to¬†quantitatively account for the influence of the surface potential on the composition of the photostationary states. For those who need more, the abstract:

Surfaces whose macroscopic properties can be switched by light are potentially useful in a wide variety of applications. One such promising application is electrochemical sensors that can be gated by optically switching the electrode on or o ff. One way to make such a switchable electrode is by depositing a self-assembled monolayer of bistable, optically switchable molecules onto an electrode surface. Quantitative application of any such sensor requires understanding how changes in interfacial field aff ect the composition of photostationary states, i.e. how does electrode potential a ect the extent to which the electrode is on or o ff when irradiated, and the structure of the SAM. Here we address these questions for a SAM of a 6-nitro-substituted spiro[2H- 1-benzopyran-2,2′-indoline] covalently attached through a dithiolane linker to an Au electrode immersed in a 0.1 M solution of Tetramethylammonium hexauorophosphate in Acetonitrile using interface-speci c vibrational spectroscopy. We find that in the absence of irradiation, when the SAM is dominated by the closed spiropyran form, variations in potential of 1 V have little eff ect on spiropyran relative stability. In contrast, under UV irradiation small changes in potential can have dramatic e ects: changes in potential of 0.2 V can completely destabilize the open, merocyanine form of the SAM relative to the spiropyran and dramatically change the chromophore orientation. Quantitatively accounting for these e ects is necessary to employ this, or any other optically switchable bistable chromophore, in electrochemical applications.