Coupling of Chromophores: Carotenoids and Photoactive Diarylethenes – Photoreactivity versus Radiationless Deactivation

New photochromic carotenoid-like chromophores containing the dithienylperfluorocyclopentene fragment have been synthesized and characterized by UV/Vis spectroscopy. The quantum yields of the photochromic forward and back reactions of these compounds have been determined and are found to decrease sharply with increasing chain length of the substituent. This decrease in quantum yield can be rationalized in terms of a decrease of the excitation density at the central photoreactive unit and of the excited state lifetime, which is known to shorten in carotenoids with increasing chain length.