Stille Expands The Family: Access To 5,6-Bis-2-Thienyl-Substituted Phenanthroline Under Mild Conditions For Luminescent Ruthenium Complexes

The Stille coupling method was used to functionalize the 5- and 6-positions of 1,10-phenanthroline with thiophene substituents. Photophysical investigations of 5,6-bis(5-methylthien-2-yl)-1,10-phenanthroline showed a marked influence of the substituents on the absorption properties, as a bathochromic shift of 50 nm regarding the -* transitions was observed. The contribution of the substituents in the corresponding Ru complex, in turn, was negligible on the absorption properties of the compound, while the extinction coefficient for the complex dropped by a factor of 0.5 compared to reference complexes. Structural investigation of the ligand and the complex revealed a perpendicular orientation of the thiophene groups with respect to the phenanthroline plane, while no preferred conformation of sulfur atoms (parallel or antiparallel) could be observed. The newly synthesized complex exhibits a superior photostability relative to [Ru(bpy)(3)](2+), which is promising for future applications.