Heteroleptic Copper(I) Pseudorotaxanes Incorporating Macrocyclic Phenanthroline Ligands of Different Sizes

Abstract

A series of copper(I) pseudorotaxanes has been prepared from bis[2-(diphenylphosphino)phenyl] ether (POP) and macrocyclic phenanthroline ligands with different ring sizes (m30, m37, and m42). Variable-temperature studies carried out on the resulting [Cu(mXX)(POP)] (mXX = m30, m37, and m42) derivatives have revealed a dynamic conformational equilibrium due to the folding of the macrocyclic ligand. The absorption and luminescence properties of the pseudorotaxanes have been investigated in CHCl. They exhibit metal-to-ligand charge-transfer emission with photoluminescence quantum yields (PLQYs) in the range 20-30%. The smallest system [Cu(m30)(POP)] shows minimal differences in spectral shape and position compared to its analogues, suggesting a slightly distorted coordination environment. PLQY is substantially enhanced in poly(methyl methacrylate) films (∼40-45%). The study of emission spectra and excited-state lifetimes in powder samples as a function of temperature (78-338 K) reveals thermally activated delayed fluorescence, with sizable differences in the singlet-triplet energy gap compared to the reference compound [Cu(dmp)(POP)] (dmp = 2,9-dimethyl-1,10-phenanthroline) and within the pseudorotaxane series. The system with the largest ring ([Cu(m42)(POP)]) has been tested as emissive material in OLEDs and affords bright green devices with higher luminance and greater stability compared to [Cu(dmp)(POP)], which lacks the macrocyclic ring. This highlights the importance of structural factors in the stability of electroluminescent devices based on Cu(I) materials.

Topological and Steric Constraints to Stabilize Heteroleptic Copper(I) Complexes Combining Phenanthroline Ligands and Phosphines

“…The electronic properties of the copper(I)‐complexed pseudorotaxanes constructed following this principle have not been discussed in the present concept article, which is mainly focused on the coordination chemistry aspects. It must be however mentioned here that the pseudorotaxane structure positively impacts the excited‐state properties of [Cu(NN)(PP)] + complexes and enhances their stability in light emitting devices . This design principle has been therefore already successfully used to generate stable copper(I) complexes for optoelectronic applications.…”

“…In solution, the control of the heteroleptic coordination scenario is difficult and an equilibrium between the heteroleptic, [Cu(NN)(PP)] + , and the homoleptic, [Cu(NN) 2 ] + and [Cu(PP) 2 ] + , complexes is often observed. To drive the thermodynamic equilibrium towards the desired heteroleptic complex, we have applied a synthetic strategy based on topological constrains by using macrocyclic phenanthroline derivatives . Thus, stable heteroleptic copper(I)‐complexed pseudorotaxanes have been obtained when the macrocycle was large and flexible enough to allow for the threading of the diphenylphosphino groups of the PP ligands .…”

“…The strategy based on topological constraints initially developed by Sauvage and co‐workers has been widely exploited to generate pseudorotaxane building blocks allowing for the synthesis of sophisticated mechanically interlocked molecules and molecular machines . We have recently shown that this principle is also perfectly suited to stabilize heteroleptic complexes prepared from various PP ligands and macrocyclic phenanthroline derivatives . The preparation of the copper(I) pseudorotaxanes is depicted in Scheme .…”

“…Despite increased ring sizes, a similar conformational equilibrium has been also observed for [Cu(m37)(POP)] + and [Cu(m42)(POP)] + . In both cases, the dynamic conformational equilibrium is in favor of a C 1 ‐symmetrical conformer but the Δ G ≠ values estimated from the NMR data are smaller (m37: 9.3 kcal mol −1 , and m42: 8.6 kcal mol −1 ) …”

Mechanochromic Switching between Delayed Fluorescence and Phosphorescence of Luminescent Coordination Polymers Composed of Dinuclear Copper(I) Iodide Rhombic Cores

“…The metal‐to‐ligand charge‐transfer (MLCT) excited state is a well‐known emissive state of not only Cu I complexes but also of other noble metal complexes such as those of Ru II , Ir III , and Pt II . It is well known that in order for the Cu I complex to achieve high emission quantum yield, the Jahn–Teller flattening distortion of the MLCT excited state should be suppressed . The wide emission color tuning ranging from blue to red has been also achieved by the modification of the π* orbitals of the organic ligands .…”