Efficient photocyclization of dithienylethene dimer, trimer, and tetramer: quantum yield and reaction dynamics.

Multi-dithienylethene arrays, in which two, three, or four 1,2-bis(2,4-dimethylthiophen-3-yl)perfluorocyclopentenes are ethynylene-bridged, were synthesized. Upon irradiation with ultraviolet light the hexane solutions of the arrays turned violet-blue and the color disappeared by irradiation with visible light. The quantum yields of photocyclization reactions successively increased from 0.21 to 0.40 by increasing the number of the dithienylethene moieties in the arrays from one to four. Picosecond laser photolysis as well as the fluorescence depolarization experiment confirmed that efficient excited energy migration in the arrays from the photochemically inactive parallel conformer to the photoactive antiparallel conformer resulted in the high quantum yields.