Electronic and Photophysical Properties of Platinum(II) Biphenyl Complexes Containing 2,2′-Bipyridine and 1,10-Phenanthroline Ligands

Pt­(bph)­(bpy) and Pt­(bph)­(phen), where bph is the 2,2′-biphenyl
dianion, bpy is 2,2′-bipyridine, and phen is 1,10-phenanthroline,
crystallize in the space groups I41/a and P21/c, respectively, in two different configurations as X-shaped and bowed
(B). The distance between Pt centers is 3.5 Å indicative of π–π
stacking. The complexes are optically active, absorb light at 440
nm, and emit in the solid state at room temperature and in the solid
glass phase at 77 K. The emission maxima for both in the glass occur
near 581 nm but are red-shifted to ∼700 nm in the solid state.
Both complexes exhibit solvatochromism in nitrile-based solvents with
the Pt­(bph)­(phen) complex showing greater excited state dipole character
compared to the Pt­(bph)­(bpy) derivative. Frontier orbitals for the
HOMO determined by DFT calculations contain electronic contributions
from the biphenyl ligand and the platinum center. The LUMO orbitals
primarily reside on the diimine ligands. TDDFT calculations indicate
the low-energy transitions occur from the metal/bph combination to
the diimine ligand.