Anisometric Cyclometalated Palladium(II) and Platinum(II) Complexes. Structural and Photophysical Studies

The potentially tridentate ligand 4‘-[4-(dodecyloxy)phenyl]-6‘-phenyl-2,2‘-bipyridine (HL 1 ) easily undergoes metalation at the ortho-C atom, yielding the rodlike complexes [Pd(L 1 )Cl] ( 1 ) and [Pt(L 1 )Cl] ( 2 ). The solid state features and the photophysical properties of the complexes have been studied. Crystal data for 2: PtC 34 H 39 ClN 2 O, triclinic, P 1̄, a = 9.043(2) Å, b = 10.874(2) Å, c = 15.710(4) Å, α = 96.95(2)°, β = 92.51(2)°, γ = 102.32(2)°, V = 1494.3(6) Å 3, Z = 2, and final R = 0.0387 ( R w = 0.0335) for 4333 independent reflections. The electronic spectra of complexes 1 and 2 show intense absorption bands in the UV region due to metal-perturbed ligand-centered (LC) transitions. In addition, complex 2 shows a moderately intense metal-to-ligand charge-transfer (MLCT) band in the visible region. Both complexes 1 and 2 show luminescence, although under different conditions. Strong emission has been observed for a 77 K glassy solution (highest energy feature 495 nm; τ = 74 μs) or room-temperature crystal (λ max = 490 nm) of 1 . In both cases, the emission was assigned to a triplet LC excited state. Complex 2 exhibits emission from a 3 MLCT level both in solution at room temperature (λ max = 590 nm; τ = 700 ns; Φ = 0.037) and in glass at 77 K (λ max = 545 nm; τ = 18 μs). The room-temperature emission of crystalline 2 (highest energy feature 590 nm) is also similar in energy to that observed in fluid solution and exhibits the typical MLCT vibrational progression, thus ruling out a contribution from either metal−metal or strong π−π interactions.