5-Trimethylsilylethynyl-2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene is synthesized by the Sonogashira coupling reaction of trimethylsilylacetylene and the bromo-derivative of 2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene, which is also prepared from the Suzuki cross-coupling reaction of 2.5 equivalents of 2-methyl-3-benzo[3,2-b]thienylboronic acid and 2,3-dibromothiophene in the presence of the palladium catalyst, Pd(PPh3)4, and sodium carbonate in a heterogeneous mixture of water and THF according to the procedure similar to that of (L1). Subsequent deprotection of the trimethylsilyl group using potassium carbonate in dichloromethane solution gives the target ligand ethynyl-2,3-bis-(2-methyl-3-benzo[3,2-b]thienyl)thiophene (L5). The synthetic route is shown in FIG. 12. Excitation of the ligand with λ≦352 nm light resulted in the formation of the close form, corresponding to the photocyclization product.
