A bisphotochromic system featuring two modes of photoisomerization controlled by solvent polarity

Combining two or more photoswitchable units in one molecule results in multiphotochromic hybrids with attractive sophisticated performance. On-demand switching of light-induced isomerization pathways for such systems by change of solvent polarity is a virtually unexplored phenomenon. Using NMR spectroscopy, we have demonstrated that the competition between 6 & pi;-electrocyclization and E-/Z-isomerization of 2,3-bis(2,5-dime-thylthiophen-3-yl)-5-(4-dialkylaminobenzylidene)cyclopent-2-en-1-ones depends on the solvent's nature. Cycli-zation of diarylethene predominates in less polar solvents, whereas isomerization of the arylidene moiety prevails in polar media. This result could be the starting point for the development of multiphotochromic hybrids with efficient solvent-controllable selectivity of photoreactions.