Blue luminescent rigid molecular rods bearing N-7-azaindolyl and 2,2′-dipyridylamino and their Zn(II) and Ag(I) omplexes

To investigate the luminescent and thermal properties of organic compounds with rigid entities, a series of new blue/purple luminescent bridging ligands, 4,4'-(N-7-azaindolyl)diphenylaceiylene (5), 4-(N-7-azaindolyl)-4'-(2,2'-dipyridylamino)diphenylacetylene (6), 4,4'-(2,2'-dipyridylamino)diphenylacetylene (7), and 4,4'-(dipyridylamino)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 lambda(max) = 361, 382, 386, and 405 nm, respectively. At 77 K, compounds 5-8 exhibit both fluorescent and phosphorescent emission. The 2,2'-dipyridyl amino symmetrically substituted ligand 7 forms a linear dinuclear complex 9 with zinc(I) ions, in which the two pyridyl rings of the dipyridylamino portion are chelated to the metal center. However, with Ag(I) 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 regicn in CH2Cl2 at room temperature with lambda(max) = 385 and 384 nm, respectively. The fluorescence of 7 can be partially quenched by either Zn2+ or H+. The behavior of ligands 8 toward Ag(I) and Zn(II) ions is similar to that of 7.