Photoisomerization behavior was scrutinized next in more detail showing very good performance of all derivatives 1-3 in line with the initially reported PAT photoswitch (Figure ). Quantitative enrichment of the blue colored Z isomer is achieved upon 780 nm NIR irradiation of the E isomer and up to 99% of the Z isomer can be recovered upon irradiation with orange light. To test how far in the NIR region the incident light is still effective for proper E to Z photoisomerization we tested also longer wavelength LEDs. With 830 nm direct excitation is still possible and viable photoswitching was observed with again quantitative accumulation of the Z isomer. However, 970 nm irradiation as well as 1020 nm irradiation did not lead to photoisomerization anymore. With these results we could establish that the PAT chromophores can be effectively addressed with light up to 830 nm wavelengths by direct excitation. The quantum yields for both photoisomerization reactions were measured for PAT 1 in three different solvents using 617 nm light (see Supporting Information for details). In benzene solution the highest quantum yields were obtained reaching 20% for E to Z and 34% for Z to E photoisomerization, respectively. In THF the quantum yields are already somewhat diminished and in CH2Cl2 solution noticeably smaller values of 5% for E to Z and 14% for Z to E photoisomerization were measured. This decline of quantum yield with increasing polarity of the solvent can be explained by a competing intramolecular charge transfer (ICT) process, which would be facilitated by the strong electron donating ability of the aniline substituent, similar to the behavior of other donor-substituted indigoid photoswitches. Scrutiny of the thermal Z to E isomerization in the dark revealed good stabilities of the metastable states, which reached several hours to days at ambient temperatures in the three solvents (see Supporting Information for more details).