In contrast, gaining precise and reversible control of the cAMPrelated signaling pathway would provide new experimental options for studying the behavior of cells in more detail and offer the opportunity for other research areas to precisely trigger these signaling cascades in living cells for various purposes. Therefore, by chemically attaching reversible photoswitches to cAMP in appropriate positions, one could repeatedly switch its bioactivity on and off with high spatiotemporal accuracy simply upon irradiation with light of a suitable wavelength. Photoswitching controls the geometry of the photochromic unit and thus, the bioactivity of cAMP and its downstream signaling cascade. Using visible light for photoswitching is especially appealing for controlling biochemical processes in living organisms since it is precisely tunable in time and space and can penetrate living systems to a certain extent without harming them as long as the light intensity is carefully adjusted. We synthesized an azobenzene-functionalized derivative of cAMP (8-azo-cAMP) and characterized its photophysical properties by UV/Vis spectroscopy to control the cAMP-related signal pathway in mammalian cells with visible light. It was our aim to monitor the cellular response to changes in cAMP activity in real-time while the photochromic molecule is switched back and forth. Therefore, it was mandatory to avoid any interference of cell observation with the optical switching. Thus, non-optical readouts are favorable, and we made use of electrochemical impedance measurements to monitor the cell response. We have reported previously on the use of electric cell-substrate impedance sensing (ECIS) to analyze the bioactivity of photochromic molecules in the example of GPCR agonists. In ECIS experiments, the cells are grown on thin gold film electrodes, and the impedance of the cell-covered electrode is recorded continuously using small, non-invasive AC currents. Since cells behave like insulating dielectric bodies, when the AC frequency is properly adjusted, the current is forced to flow around the cells, and the impedance monitors any change in cell morphology with nanometer resolution. ECIS assays have been used frequently to study cytotoxicity, the impact of xenobiotics of any kind, and in particular, signal transduction. Since impedance measurements integrate over the entire cell body without molecular specificity, we conducted control experiments with well-known and approved pharmacological modulators of the signaling cascade under study to support and validate our interpretation of the time-resolved ECIS readings reporting on the photoswitchable cAMP activity in real-time.