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 (HL1) 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: PtC34H39-ClN2O, triclinic, P (1) over bar, a = 9.043(2) Angstrom, b = 10.874(2) Angstrom, c = 15.710(4) Angstrom, alpha = 96.95(2)degrees, beta = 92.51(2)degrees, degrees = 102.32(2)degrees, V = 1494.3(6) Angstrom(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; tau = 74 mu s) or room-temperature crystal (lambda(max) = 490 nm) of 1. In both cases, the emission was assigned to a triplet LC excited state. Complex 2 exhibits emission from a (MLCT)-M-3 level both in solution at room temperature (lambda(max) = 590 nm; tau = 700 ns; Phi = 0.037) and in glass at 77 K (lambda(max) = 545 nm; tau = 18 mu s). 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 pi-pi interactions.