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 CH₂Cl₂. 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.