Synthesis, Structure, and Characterization of Dinuclear Copper(I) Halide Complexes with P^N Ligands Featuring Exciting Photoluminescence Properties

Abstract

A series of highly luminescent dinuclear copper(I) complexes has been synthesized in good yields using a modular ligand system of easily accessible diphenylphosphinopyridine-type P^N ligands. Characterization of these complexes via X-ray crystallographic studies and elemental analysis revealed a dinuclear complex structure with a butterfly-shaped metal-halide core. The complexes feature emission covering the visible spectrum from blue to red together with high quantum yields up to 96%. Density functional theory calculations show that the HOMO consists mainly of orbitals of both the metal core and the bridging halides, while the LUMO resides dominantly on the heterocyclic part of the P^N ligands. Therefore, modification of the heterocyclic moiety of the bridging ligand allows for systematic tuning of the luminescence wavelength. By increasing the aromatic system of the N-heterocycle or through functionalization of the pyridyl moiety, complexes with emission maxima from 481 to 713 nm are obtained. For a representative compound, it is shown that the ambient-temperature emission can be assigned as a thermally activated delayed fluorescence, featuring an attractively short emission decay time of only 6.5 μs at ϕPL = 0.8. It is proposed to apply these compounds for singlet harvesting in OLEDs.

Cuprophilic interactions in highly luminescent dicopper(i)–NHC–picolyl complexes – fast phosphorescence or TADF?

“…This is exemplified by comparison of the polymeric compound [CuCl(IDippPic)] N (5) with no Cu-Cu contacts and inefficient pure phosphorescence, and the TADF exhibiting dimers [Cu 2 Cl 2 (IMesPic R ) 2 ] (1: R = Cl, 2: R = H), which show formation of 1 (Cu 2 -py)CT and 3 (Cu -py)CT states. The frontier orbitals, which are involved in the transitions S 0 -S 1 of many of the previously reported efficient dicopper(I) TADF emitters, are located at the respective Cu 2 core, 4,8,19,[27][28][29] which corroborates our findings. The photophysical behaviour and the nature of the states involved for 1 and 2 are summarized in Fig.…”

“…[24][25][26] A few dicopper(I) complexes with short Cu-Cu contacts (o2.8 Å) have been reported to emit efficiently via TADF, but the influence of cuprophilic interactions in those has yet not been addressed. 4,8,19,[27][28][29] In this case study on a family of new bidentate copper(I) NHC-picolyl complexes we show that cuprophilic interactions can greatly enhance the radiative rate constants of the T 1 state by increasing spin-orbit coupling (SOC), giving emission lifetimes comparable to TADF, and can even be involved in the luminescence mechanisms when TADF is present. Thus, cuprophilic interactions provide a design methodology for highly efficient Cu I emitters.…”

“…This assignment is in agreement with other Cu I TADF emitters, of which the 3 MLCT states exhibit similar lifetimes as found for 1 and 2. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]28,29 However, the T 1 state of the highly efficient pure triplet emitter 4 (R = OMe) contains a significant Cu 2 -NHC/py contribution, allowing for very efficient SOC, coupling T 1 with the ground state S 0 . Consequently, we conclude that TADF and phosphorescence in the Janus compound 3 originate from two distinctly different triplet states, which are a 3 MLCT with a long lifetime (t 77K = 113 ms) similar to 1 and 2, and a 3 (Cu 2 )LCT state with a short lifetime (t 77K = 23 ms) similar to 4.…”

Luminescent Complexes Containing Halogeno-bridged Dicopper(I) Unit {Cu2(µ-X)2} (X = Cl, Br, and I)

“…The emissions of several other complexes with phosphine and Nheteroaromatic ligands are explained in the same schemes as the CT transition from {Cu 2 X 2 } unit to ³* orbitals of L. 16,17 Very recently, a systematic study of the discrete binuclear complexes [(Cu 2 X 2 )(¯-P^N)(P^N) 2 ] where P^N is a P,N-bridging ligand has been reported from Yersin's group. 18 The P^N ligands are a series of N-heteroaromatic compounds with a diphenylphosphino group which give butterfly-shaped {Cu 2 I 2 } units bridged by the P^N ligand (Figure 2b). The dinuclear complexes show strong phosphorescence in the solid state at room temperature, among which several complexes possess emission quantum yield close to 1.…”

“…As in the case above, emission wavelength is determined by the ³* orbital level of the ligand, and linear correlation between them has been observed. 18 …”