When dissolving open 1 in MeOH, a broad UV absorption band is visible with a maximum at 288 nm leading to a colorless solution. Its absorption I redshifted by 43 nm compared to the our first aza-diarylethene. Irradiation with light of 300 nm results in a 6π-aza-electrocyclization reaction including the fully reversible formation of a C=N bond under breakage of the C-S bond of the former thiophene moiety. As a consequence a charged zwitterion is obtained with an aromatic pyrido[1,2-a]pyrimidin-5-ium moiety and a negatively charged thiolate. The formed zwitterionic species is showing a broad absorption band between 380 nm and 550 nm, which is typical for the closed Z-1 isomer of zwitterionic aza-diarylethene. Compared to the earlier reported system the absorption is redshifted by 36 nm as a result of the extension of the conjugated system in 1. Especially the line broadening of closed Z-1 into the red region of the spectrum leads to an intensive orange coloration (Figure ), as opposed to the yellow color of the first generation derivative (Figure ). Storing closed Z-1 isomer in the dark at 23 °C leads to a fast and quantitative recovery of open 1 within 10 min. The cycle of photoisomerization and thermal back reaction can be repeated multiple times, showing the robustness of this T-type photoswitching mode (Figure ). We additionally performed variable 1 H NMR experiments showing the selective quantitative enrichment of closed Z-1 to 100% by external irradiation with 300 nm light at -78 °C, followed by quantitative thermal recovery within 58 min at -5 °C (Figure ). At this point it needs to be emphasized, that full thermal recovery of open 1 after light irradiation is only possible by using 300 nm light, both at UV/vis or NMR concentrations.