COUPLING OF CHROMOPHORES - CAROTENOIDS AND PHOTOACTIVE DIARYLETHENES - PHOTOREACTIVITY VERSUS RADIATIONLESS DEACTIVATION

New photochromic carotenoid-like chromophores containing the dithienyl perfluorocyclopentene fragment have been synthesized and characterized by UV/Vis spectroscopy. The quantum yields of the photochromic forwar d and back reactions of these compounds have been determined and are f ound to decrease sharply with increasing chain length of the substitue nt. This decrease in quantum yield can be rationalized in terms of a d ecrease of the excitation density at the central photoreactive unit an d of the excited state lifetime, which is known to shorten in caroteno ids with increasing chain length.