Softening the Donor-Set: From [Cu(P^P)(N^N)][PF6] to [Cu(P^P)(N^S)][PF6

Isaak Nohara,Edwin Constable,Catherine Housecroft,Alessandro Prescimone

doi:10.3390/inorganics7010011

Abstract

We report the synthesis and characterization of [Cu(P^P)(N^S)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl) ether (POP) or 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene (xantphos) and N^S = 2-(iso-propylthio)pyridine (iPrSpy) or 2-(tert-butylthio)pyridine (tBuSpy). The single crystal structures of [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] have been determined and confirm a distorted tetrahedral copper(I) centre and chelating P^P and N^S ligands in each complex. Variable temperature (VT) 1H and 31P{1H} NMR spectroscopy reveals dynamic behavior with motion of the POP backbone in [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] frozen out at 238 K. VT NMR spectroscopic data including EXSY peaks in the ROESY spectrum of [Cu(xantphos)(tBuSPy)][PF6] at 198 K reveal that two conformers exist in an approximate ratio of 5:1. Replacing bpy by the N^S ligands shifts the Cu+/Cu2+ oxidation to a higher potential. The copper(I) compounds are weak emitters in the solid state with PLQY values of <2%. These values are similar to those for [Cu(POP)(bpy)][PF6] and [Cu(xantphos)(bpy)][PF6] in the solid state.

Highlights

Around forty years ago, McMillin and co-workers reported the photoluminescence of the metal-to-ligand charge transfer (MLCT) state of copper(I) complexes containing both diimine
The highest occupied molecular orbital (HOMO) of [Cu(PP)(NN)]+ is largely centered on copper with small contributions from phosphorus, and structural variation within the PP domain is expected to affect steric rather than electronic properties [14], and the P–Cu–P bite angle is critical in understanding the detailed structure and properties of a [Cu(PP)(NN)]+ complex [15]
Suggested that the lowest unoccupied molecular orbital (LUMO) copper energy character with smaller contributions from the ligands. These results suggested of [Cu(PP)(NS)] complexes may be modified by structural modification of the NS domain.that the LUMO energy of [Cu(P^P)(N^S)]+ complexes may be modified by structural modification of the N^S

Summary

Introduction

Compounds exhibit thermally activated delayed fluorescence (TADF), meaning that the energy gap between the singlet and triplet excited states is small enough to permit repopulation of the singlet from the triplet state under ambient conditions. This leads to indirect harvesting of triplet-state fluorescence, thereby improving LEC performance [7,8,9,10,11,12]. In [Cu(PP)(NN)]+ cations, the lowest unoccupied molecular orbital (LUMO) is localized on the NN ligand and the emissive properties of these compounds are typically tuned by structural and electronic manipulation of the NN domain [3,4,13]. The most commonly encountered PP ligands are 4,5-bis(diphenylphosphino)-9, 9-dimethylxanthene (xantphos) and bis(2-(diphenylphosphino)phenyl)ether (POP) (Scheme 1), both of which are commercially available

Methods

Results

Conclusion