Photophysical Properties of Simple Palladium(0) Complexes Bearing Triphenylphosphine Derivatives

Abstract

Pd­(0) complexes with monodentate phosphine ligands, [Pd­(P) n ] (n = 3, 4), are well-known catalysts. However, the nature of the Pd(0) complex, especially the basic photophysical properties of the Pd(0) complexes, has not been extensively explored. In this work, we measured the general photophysical properties and crystal structures of Pd(0)-bearing PPh3 derivatives in the solid state and in solution. In the solid state, four-coordinated Pd(0) complexes exhibited blue-yellow emission. On the other hand, three-coordinated Pd(0) complexes displayed yellow-orange emission. In solution, orange emission of three-coordinated complexes was observed, and prompt fluorescence was detected using time-resolved emission spectroscopy, which suggests a thermally activated delayed fluorescence mechanism. Density functional theory (DFT) and time-dependent DFT calculations show that the difference in the transition mechanism between the [Pd­(PPh3)4] and [Pd­(PPh3)3] complexes explains the different emission colors. The emitting states of both complexes have metal-to-ligand charge-transfer character, but the metal-centered d → p transition is considerably incorporated for emission of the tris complex.

Luminescence and Palladium: The Odd Couple

“…An interesting example of luminescent Pd(0) compounds with phosphine ligands was reported in 2021 by Tsubomura et al [ 94 ]. The obtained Pd(0) complexes, of stoichiometry Pd(PR 3 ) 3 90 and Pd(PR 3 ) 4 91 as shown in Figure 25 , show high quantum yields and long lifetimes.…”

“… Syntheses and abbreviations of the unusual fluorescent Pd(0) complexes 90 and 91 . Adapted from [ 94 ]. …”

Metal–Organic Frameworks with Zero and Low‐Valent Metal Nodes Connected by Tetratopic Phosphine Ligands

“…The photophysical properties of Pd(PPh 3 ) 4 and several substituted derivatives have been recently investigated. [20] These complexes display strong emission in the solid state, with the emission bands having metal-to-ligand charge transfer (MLCT) character. Emission spectra (λ ex = 360 nm) were collected for dried samples of Si1-Pd, Sn1-Pd, Si1-Pt, and Sn2-Pd, which displayed emission maxima at 586, 584, 594, and 667 nm, respectively (Figure S28).…”

“…The photophysical properties of Pd(PPh 3 ) 4 and several substituted derivatives have been recently investigated [20] . These complexes display strong emission in the solid state, with the emission bands having metal‐to‐ligand charge transfer (MLCT) character.…”