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

Abstract

The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N=C=N-coordinating ligand cyclometalated at C2 of the benzene ring ([PtL(1)Cl]), have been investigated, together with those of two new 5-substituted analogues [PtL(2)Cl] and [PtL(3)Cl] [HL(2) = methyl-3,5-di(2-pyridyl)benzoate; HL(3) = 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 CH(2)Cl(2)), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 micros). 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 x 10(-)(5) M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL(2)Cl] is also reported.

Cyclometallated platinum(ii) complexes containing NHC ligands: synthesis, characterization, photophysics and their application as emitters in OLEDs

“…Analysis of the data obtained also shows that in degassed solutions the quantum yield of emission as well as the excited state lifetime of the phenylpyridine complexes (1-3, 5, 6) display appreciable correlation with the Pt-C (cyclometallated) bond length (see Table S1 and Fig. S17 †) that is completely in line with the trend observed earlier 31 for the photophysics of the structurally related Pt(II) complexes. The lower values of the Pt-C bond length (a stronger ligand field effect) result in the higher energy of the d-d excited state, thus cutting off nonradiative relaxation through this excited state.…”

Time-resolved and two-photon emission imaging microscopy of live cells with inert platinum complexes

“…1), the Pt(II) complexes of the cyclometalating, terdentate, N^C^N-coordinating ligand 1,3-di(2-pyridyl)benzene and derivatives. These compounds can be readily synthesized in two steps from simple starting materials in high yields (20). The core structure is easily derivatized at the central position of the ligand (R, Fig.…”

Neutral N^C^N terdentate luminescent Pt(ii) complexes: their synthesis, photophysical properties, and bio-imaging applications

“…† Upon increasing the water content, a steady negative solvatochromic shift and decrease of the intensity of the lowestlying band is clearly visible, which is in line with the attribution of the CT character of the electronic excitation in such a class of compounds. 33,37 Also, such a finding implies the sizeable decrease of the excited-state electric dipole moment with respect to that of the ground state. 37 A similar hypsochromic shift upon the increase of the solvent polarity has been observed in the photoluminescence spectra, indicating significant variation, and in particular a decrease, of the excited state dipole moment.…”