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 π-bonded catecholate (cat) [(bpy)­Pt­(LM)]­[BF4]n (2–5) (LM = 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 π-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 π–π 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 π-bonded catecholate
system.