Molecular conformation and structural changes in crystalline photochromism of 3-furylfulgide

The conformational changes of the photochromic 3-furylfulgide molecule have been studied in relation to its crystal structure. Intense two-photon irradiation of an initial pale yellow single crystal led to a red material that is no longer crystalline but still photochromic. Conversely, starting from a colored single crystal grown from an irradiated solution, X-ray diffraction gave the first determination of the molecular conformation and crystal structure of the colored form and showed that after visible irradiation the bleached material also lost its crystalline structure. The photoinduced molecular displacements responsible for this behavior are pointed out.