As already mentioned in the previous section, compound 1 exhibits quite clear symptoms of the photochromic behavior -cold white light illumination leads to a distinct color change of the yellow crystals to blue (green at first) and dark blue typical for this class of compounds (Figure ). Compound 2, on the other hand, does not show any color changes under similar conditions. Since the photochromic behavior is expected in both cases, both compounds were investigated using UV-vis and IR spectroscopy before and after UV light irradiation (365 nm; 1UV) and then, if the change is observed, after visible light irradiation (638 nm; 1vis) to confirm the reversibility of the process. Compound 2 does not show any appreciable changes in the UV-vis and IR spectra after UV photoexcitation while compound 1 exhibits clear changes which are discussed in the following two subsections. Attempts to determine the crystal structure of the compound after UV light irradiation (1UV) using XRD techniques were unsuccessful -the compound loses long-range structural order -in other words it does not show X-ray diffraction after photocyclization. Please note, that the crystals before irradiation are yellow with a bluish tinge, due to the cold LED light of the microscope causing the photoisomerization.