7‐Azaindolyl‐ and 2,2′‐Dipyridylamino‐Functionalized Molecular Stars with Sixfold Symmetry: Self‐Assembly, Luminescence, and Coordination Compounds

Abstract

Two novel star molecules functionalized with 7‐azaindolyl and 2,2′‐dipyridylamino groups have been synthesized. Both molecules possess a sixfold rotation symmetry. Molecule L 1 is based on the hexaphenylbenzene core with the formula of hexa[p‐(7‐azaindolyl)phenyl]benzene, while molecule L 2 is based on the hexakis(biphenyl)benzene core with the formula of hexa[p‐(2,2′‐dipyridylamino)biphenyl]benzene. Both compounds have been characterized by single‐crystal X‐ray diffraction analyses. Molecule L 1 forms extended two‐dimensional layered structure, while L 2 forms interpenetrating columnar stacks in the solid state, as revealed by X‐ray diffraction analyses. Nanowire structures based on columnar stacks through self‐assembly of L 2 on a graphite surface were revealed by an STM study. Molecules L 1 and L 2 are capable of binding to metal ions, resulting in unusual structural motifs. Two Ag^I complexes with the formulae of [(AgNO₃)₂(L 1)] (1) and [(AgNO₃)₃(L 1)] (2) were isolated from the reactions of AgNO₃ with L 1. Compound 1 displays extended intermolecular π–π stacking interactions that are responsible for its extended two‐dimensional structure in the crystal lattice. Complex 2 has a “bowl” shape and forms polar stacks in the crystal lattice. A Cu^II complex with the formula of [{Cu(NO₃)₂}₆(L 2)] (3) was isolated from the reaction of Cu(NO₃)₂ with compound L 2. The six Cu^II ions in 3 are chelated by the 2,2′‐dipyridylamino groups of the star ligand L 2. Intermolecular CuO (nitrate) bonds lead to the formation of an extended two‐dimensional coordination network of 3. Both L 1 and L 2 are blue luminescent. Their interactions with Ag^I or Cu^II cause drastic quenching of emission. In addition, the luminescence of L 1 and L 2 is sensitive to the presence of protons, which cause a reduction of emission intensity and a red shift of the emission energy.