Blue Luminescent Rigid Molecular Rods Bearing N-7-Azaindolyl and 2,2-Dipyridylamino and Their Zn(ll) and Ag(l) Complexes

To investigate the luminescent and thermal properties of organic compounds with rigid entities, a series of new blue/purple luminescent bridging ligands, 4,4ʹ-(N-7-azaindolyl)diphenylacetylene (5), 4-(N-7-azaindolyl)-4ʹ-(2,2ʹdipyridylamino)diphenylacetylene (6), 4,4ʹ-(2,2ʹ-dipyridylamino)diphenylacetylene (7), and 4,4ʹ-(dipyridytamino)diphenylbutadiyne (8) have been synthesized through Pd-mediated Sonogashira coupling. The structures of compounds 6 and 8 were determined by single-crystal X-ray diffraction analyses. Compounds 5-8 are luminescent in solution at room temperature, with emission /lmax = 361,382,386, and 405 nm, respectively. At 77 K, compounds 5-8 exhibit both fluorescent and phosphorescent emission. The 2,2ʹ-dipyridylamino symmetrically substituted ligand 7 forms a linear dinuclear complex 9 with zinc(ll) ions, in which the two pyridyl rings of the dipyridylamino portion are chelated to the metal center. However, with Ag(l) ions, ligand 7 forms a dinuclear complex (10), which displays a macrocyclic structure with only one of the two pyridyl rings from each dipyridylamino portion being coordinated to the silver atom. Both 9 and 10 exhibit luminescence in the near-UV region in CH2C12 at room temperature with delta(max) = 385 and 384 nm, respectively. The fluorescence of 7 can be partially quenched by either Zn^2+ or H^+. The behavior of ligands 8 toward Ag(l) and Zn(ll) ions is similar to that of 7.