Tuning Excited States of Bipyridyl Platinum(II) Chromophores with π-Bonded Catecholate Organometallic Ligands: Synthesis, Structures, TD-DFT Calculations, and Photophysical Properties

A series of bipyridyl (bpy) Pt(II) complexes with pi-bonded catecholate (cat) [(bpy)Pt(L-M)][BF4](n) (2-5) (L-M = Cp*Rh(cat), n = 2; Cp*Ir(cat), n = 2; Cp*Ru(cat), n = 1; and (C6H6)Ru(cat), n = 2) were prepared and fully characterized. The molecular structures of the four compounds were determined and showed that the solid-state packing is different and dependent on the pi--bonded catecholate unit. For instance, while the (bpy)Pt(II) complexes 2 and 3 with rhodium and iridium catecholates did not show any Pt Pt interactions those with the ruthenium catecholates 4 and 5 showed the presence of Pt ... Pt and pi-pi interactions among individual units and generated one- and two-dimensional supramolecular chains. The photophysical properties of these compounds 2-5 were investigated and showed that all compounds are luminescent at low temperature, in contrast to the well-known parent compound [(C6H4O2)Pt(bpy)] (1), which is weakly luminescent at 77 K. Time-dependent density functional theory studies are advanced to explain this difference in behavior and to highlight the role of the pi-bonded catecholate system.