An Alternative Route to Highly Luminescent Platinum(II) Complexes: Cyclometalation with N^C^N-Coordinating Dipyridylbenzene Ligands

The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N^C^Ncoordinating ligand cyclometalated at C2 of the benzene ring ([PtL1Cl]), have been investigated, together with those of two new 5substituted analogues [PtL2Cl] and [PtL3Cl] {HL2 = methyl-3,5-di(2-pyridyl)benzoate; HL3 = 3,5-di(2-pyridyl)toluene}. All three complexes are intense emitters in degassed solution at 298 K ((lambda)max 480-580 nm; (phi)lum = 0.60, 0.58, and 0.68 in CH2Cl2), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 (mu)s). On the basis of the very small Stokes shift, the highly structured profiles, and the relatively long lifetimes, the emission is attributed to an excited state of primarily 3(pi)- (pi)* character. At concentrations >1 × 10^-5 M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL2Cl] is also reported.