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

Two new dimesitylboron (BMes(2))-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 pi-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 N-2 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 (LLCT)-L-3 and (ILCT)-I-3/(MLCT)-M-3 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 BMes(2)-functionalized (NC)-C-boolean AND-chelate Pt(II) compounds, which are attributed to the introduction of the low-lying pi* orbital by the picolinate ancillary ligand in the Pt(II) compounds.