Recently, we have reported compound 9 undergoing a reversible electrocyclic ring closure mechanism with concomitant C-S bond cleavage leading to a charged zwitterionic species by UV light irradiation (Figure ). In this work we turned our attention to aza-diarylethene 9 and its photoresponse in a polymer context. First, 9 was embedded into polystyrene (PS) and also in this case reversible photoresponse with light of 365 nm is observed allowing to localize photoswitching and inscribe information into the material (Figure , Figure ). Moderate color contrasts are observed as a result of the photoswitching from open 9 to closed Z-9, which allows to distinguish the inscription with the naked eye. Upon diluting the inscribed polymer with benzene at ambient temperature, the inscription can be erased and a transparent colorless material is received again upon drying. Another round of photoinscription directly showed reversible photoswitching of 9 in polystyrene (Figure ). From the corresponding UV/Vis spectroscopic analysis of 9 photoswitching in PS (Figure ) we observed that enrichment of closed Z-9 as well as the charge separation of the zwitterionic state are less pronounced compared to MeOH solution, which explains the smaller color contrast in the polymer. In MeOH solution, closed Z-9 can further undergo light-induced Z/E photoisomerization upon longer light irradiation durations with light of 365 nm to an extent of up to 3%, which leads to a diminishing of the yellow color and corresponding lower intensity of the visible absorption band in the UV/vis spectrum. Further accumulation of the closed E-9 isomer is possible through several irradiation cycles at ambient temperature. Given the only pale-yellow color observed upon photoswitching of 9 in PS and the incomplete recovery of the colorless open 9 form after dilution, we assign the resulting photoproducts in PS to contain a noticeable contribution of the thermally more stable ring closed E-9 isomer.