Controlling Aggregation in Highly Emissive Pt(II) Complexes Bearing Tridentate Dianionic N^∧N^∧N Ligands. Synthesis, Photophysics, and Electroluminescence

Abstract

Neutral Pt(II) complexes bearing tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine and ancillary alkyl-substituted pyridine ligands have been synthesized and characterized. They show bright green emission, reaching 73% photoluminescence quantum yield in deareated chloroform solution, which can be assigned to a predominantly metal-perturbed ligand-centered phosphorescence. We have followed two strategies to preserve the spectral purity of the monomeric species by varying the substituents on the chromophoric or on the ancillary ligands. However, variations in the substitution patterns only modestly affected the radiative and radiationless deactivation rate constants of the monomers. Photophysical and electrochemical properties have been measured for all the complexes and correlated with calculations using time-dependent density functional theory. The electroluminescence spectra of the brightest, nonaggregating derivative showed a better color purity than that of iridium(III) tris(phenylpyridine), thus proving that aggregation was hindered in a running electroluminescent device.

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

“…In this regard, dianionic tridentate N^N^N ligands bearing pyrazolate [69], triazolate [69–73] or tetrazolate [74] units have been used to successfully prepare highly luminescent neutral platinum(II) complexes in dilute solution and/or as aggregated state. Due to their promising emitting features, these complexes have also been employed as phosphors in optoelectronic devices [71–72]. Neutral platinum(II) complexes with an asymmetrical triazolate- and tetrazolate-containing tridentate ligand, complexes 28 , were also reported [75] (Fig.…”

Recent Advances in Phosphorescent Pt(II) Complexes Featuring Metallophilic Interactions: Properties and Applications

“…58,59 These derivatives contain dianionic N trz^Npy^Ntrz -based ligands as chromophoric moiety, where trz is a 1,2,4-triazolate moiety and py is a pyridyl group, and an ancillary pyridine which can be functionalized to improve solubility and tune self-assembly properties.…”

Unraveling Orbital Hybridization of Triplet Emitters at the Metal-Organic Interface

“…Interactions of an Ir complex with its local environment lack defined directionality and are thus barely controllable, which usually leads to quenching effects and reduced quantum efficiencies when the Ir-complex loading in an OLED is too high [5]. In contrast, recently synthesized platinum(II) complexes not only yield quantum efficiencies of more than 85%, but they also exhibit no quenching effects even when aggregated into fibers or gels [6,7]. The planar geometry enables well-defined interactions with the local environment that should be tunable.…”

“…Hence, we expect that well-defined interaction also occurs in host-guest environments as well as within aggregated structures of Pt(II) complexes. This interaction should even be tunable in a controlled fashion by systematic variation of the ligand side groups (e.g., replacing CF 3 by tert-butyl or adamantyl [7]) or by changing the host or substrate material [10,28].…”

“…The synthesis of pyridine 2,6-bis(3-(trifluoromethyl)-1,2,4-triazolato-5-yl)pyridine platinum(II) (Pt-H) and 4-pentyl-pyridine 2,6-bis(3-(trifluoromethyl)-1,2,4-triazolato-5-yl)pyridine platinum(II) (Pt-amyl) is described elsewhere [7,16]. The Au(111) single crystal was cleaned by standard sputter-annealing procedures, followed by thermal deposition of either Pt-H or Pt-amyl from a Knudsen cell at about 480 K and 420 K, respectively, while keeping the Au substrate at room temperature.…”