Extending pi-conjugation of triarylborons with a 2,2-bpy core: impact of donor-acceptor geometry on luminescence, anion sensing, and metal ion binding.

Four new 2,2'-bipyridine-based molecules functionalized by either BMes(2)-phenyl (Mes = mesityl) or NPh(2)-phenyl--5,5'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (5,5'-BP2bpy, 1), 4,4'-(p-BMes(2)-phenyl)(2)-2,2'-bpy (4,4'-BP2bpy, 2), 4-(p-BMes(2)-phenyl)-4'-(p-NPh(2)-phenyl)-2,2'-bipy (4,4'-BPNPbpy, 4), and 4,4'-(p-NPh(2)-phenyl)(2)-2,2'-bpy (4,4'-NP2bpy, 5)--have been synthesized. Their complexes with PtPh(2) have been synthesized and fully characterized. The electronic and photophysical properties of the new molecules have been examined by electrochemical, absorption, and luminescence spectroscopic analysis and DFT calculations, which show significant differences from those of the related but smaller 2,2'-bpy derivatives functionalized directly by either BMes(2) or NPh(2) groups that we reported previously. Molecules 1, 2, and 4 and their Pt(II) complexes respond to fluoride ions in both absorption and emission modes. The donor-acceptor molecule 4 and its Pt(II) complex have a distinct fluorescence/phosphorescence turn-on response toward fluoride or cyanide ions. Molecules 1, 2, 4, and 5 also respond to Zn(II) ions in both absorption and emission modes. The diboryl molecules 1 and 2 have a distinct and contrasting fluorescence response toward Zn(II) ion--turn-off for 1 and turn-on for 2--demonstrating the significant impact of molecular geometry on metal ion binding and fluorescence.