What accounts for the color purity of tetradentate Pt complexes? A computational analysis

Abstract

The microscopic mechanism of high color purity was elucidated by computational investigation.

Luminescent Pd(II) Complexes with Tridentate − Aryl‐pyridine‐(benzo)thiazole Ligands

“…The addition of the 4‐phenyl group to the central pyridine (py→ppy) leads to a marginal red‐shift (Figures S25 to S27), while the introduction of tert ‐butyl groups to this phenyl group (ppy→tbppy) has no impact. The two last trends are in line with previous reports [13,26–28,32,45] . Overall, we were able to tune the long‐wavelength absorption cut‐off between 2.71 and 2.40 eV, in quite good agreement with the electrochemical band gaps.…”

“…From the viewpoint of the choice of design cyclometalated tetradentate ligand fit perfectly to the square planar geometry of d 8 ‐configured metal cations and conform with the requested rigidity [2,4,7–9,14,15,21,27,49–53] . Nevertheless, tridentate cyclometalating ligands have been very successfully used in luminescent Pt(II), [2,13,20,26,28–31,45,51–53] Pd(II) [5,12,19,20,24,28,31,43,45] and especially Au(III) complexes, [2,51,54–56] as their synthesis is easier than for the complex scaffolds related to tetradentate ligands, whereas the fourth coordination site allows for fine‐tuning of the electronic properties.…”

“…d 8 ‐configured Pt(II) and Pd(II) complexes containing π‐accepting ligand moieties with low lying π* orbitals have allowed to design and tune long‐lived metal‐to‐ligand charge transfer (MLCT) or mixed MLCT/π–π* (LC) excited states for efficient triplet emission [1–24] . Moreover, rigidity of both the organic ligand and the square planar coordination environment around the metal centre help suppressing competitive radiationless decay paths [6,7,10,11,13,17–20,23–31] . Cyclometalating heteroaromatic ligands have been frequently used for luminescent Pt(II) or Pd(II) complexes as they provide rigidity, a strong ligand field and suitable LC excited states [2,4–25,31] .…”

“…Cyclometalating heteroaromatic ligands have been frequently used for luminescent Pt(II) or Pd(II) complexes as they provide rigidity, a strong ligand field and suitable LC excited states [2,4–25,31] . Combined experimental/theoretical studies on such complexes have previously related structural features with photoluminescence (PL) properties [11,18,19,23–31] . While structural effects on the emission energy can be rationally predicted via density functional theory (DFT) modelling, the PL efficiency, expressed as PL quantum yields, is less predictable [13,22,25–27] .…”

“…Herein, we report on a study beyond the two Pd(II) complexes [Pd(ph(py)tz)Cl] and [Pd(ph(tbppy)tz)Cl] by shifting the central pyridine to phenylpyridine and 3,5‐(bis‐ tert‐ butyl)phenylpyridine, which had turned out to be beneficial for efficient triplet emission, [13,26–28,32] as well as by exchanging the peripheral phenyl group for naphthyl or fluorenyl and the thiazole ring for benzothiazole (Scheme 1B).…”