Impact of a Picolinate Ancillary Ligand on Phosphorescence and Fluoride Sensing Properties of BMes2-Functionalized Platinum(II) Compounds

Abstract

Two new dimesitylboron (BMes2)-functionalized 2-phenylpyridine cyclometalated Pt(II) complexes (2 and 3) with a picolinate or a methyl-picolinate as the ancillary ligand have been synthesized via a one-pot procedure at ambient conditions with high yields (>70%). The crystal structures of these Pt(II) complexes were determined by single-crystal X-ray diffraction analysis, which revealed the presence of extended π-stacking interactions in the crystal lattice of 2 and discrete dimer formation in the lattice of 3. Both complexes exhibit dual phosphorescence emission in solution at room temperature under N2 atmosphere. These unusual photophysical properties have been systematically investigated by spectroscopic and computational studies, which established that the phosphorescent dual emission originates from admixture of 3LLCT and 3ILCT/3MLCT transitions. Fluoride titration experiments were conducted to further confirm the origin of phosphorescence in these compounds. The phosphorescent properties and the phosphorescent response toward fluoride ions by compounds 2 and 3 are distinctly different from the previously known BMes2-functionalized N∧C-chelate Pt(II) compounds, which are attributed to the introduction of the low-lying π* orbital by the picolinate ancillary ligand in the Pt(II) compounds.