Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine Ligands: Rationalization of the Photophysical and Electrochemical Properties

Abstract

The electronic and structural properties of ten heteroleptic [Cu­(NN)­(PP)]+ complexes have been investigated. NN indicates 1,10-phenanthroline (phen) or 4,7-diphenyl-1,10-phenanthroline (Bphen); each of these ligands is combined with five PP bis-phosphine chelators, i.e., bis­(diphenylphosphino)­methane (dppm), 1,2-bis­(diphenylphosphino)­ethane (dppe), 1,3-bis­(diphenylphosphino)­propane (dppp), 1,2-bis­(diphenylphosphino)­benzene (dppb), and bis­[(2-diphenylphosphino)­phenyl] ether (POP). All complexes are mononuclear, apart from those based on dppm, which are dinuclear. Experimental dataalso taken from the literature and including electrochemical properties, X-ray crystal structures, UV–vis absorption spectra in CH2Cl2, luminescence spectra and lifetimes in solution, in PMMA, and as powdershave been rationalized with the support of density functional theory calculations. Temperature dependent studies (78–358 K) have been performed for selected complexes to assess thermally activated delayed fluorescence. The main findings are (i) dependence of the ground-state geometry on the crystallization conditions, with the same complex often yielding different crystal structures; (ii) simple model compounds with imposed C 2v symmetry ([Cu­(phen)­(PX3)2]+; X = H or CH3) are capable of modeling structural parameters as a function of the P–Cu–P bite angle, which plays a key role in dictating the overall structure of [Cu­(NN)­(PP)]+ complexes; (iii) as the P–Cu–P angle increases, the energy of the metal-to-ligand charge transfer absorption bands linearly increases; (iv) the former correlation does not hold for emission spectra, which are red-shifted for the weaker luminophores; (v) the larger the number of intramolecular π-interactions within the complex in the ground state, the higher the luminescence quantum yield, underpinning a geometry locking effect that limits the structural flattening of the excited state. This work provides a general framework to rationalize the structure–property relationships of [Cu­(NN)­(PP)]+, a class of compounds of increasing relevance for electroluminescent devices, photoredox catalysis, and solar-to-fuels conversion, which so far have been investigated in an unsystematic fashion, eluding a comprehensive understanding.

Dinuclear Copper(I) Complexes Combining Bis(diphenylphosphanyl)acetylene with 1,10‐Phenanthroline Ligands

“…The decomposition products are then observed in the backward scan giving rise to two broad waves around +0.6 and + 0.2 V vs. SCE. In the cathodic region, all the [Cu 2 (µ‐dppa) 2 (NN) 2 ](BF 4 ) 2 derivatives revealed the typical electrochemical response of [Cu(NN)(PP)] + derivatives, , and the first reduction process is likely centered on the phenanthroline ligands.…”

“…The absorption spectra of the whole series recorded from freshly prepared CH 2 Cl 2 solutions are in line with [Cu(NN)(PP)] + coordination compounds previously reported (Figure ) , . The strong bands observed in the UV region (260–290 nm) stem from both the PP and NN ligands.…”

“…This is a key factor for the preparation of [Cu(PP)(NN)] + materials with long excited state lifetimes and high emission quantum yields. Whereas mononuclear [Cu(PP)(NN)] + derivatives have been already intensively explored, related dinuclear copper(I) complexes with bridging PP ligands have been investigated to a lesser extent . For instance, dinuclear copper(I) complexes with two bridging bis(diphenylphosphanyl)methane (dppm) ligands have shown promising photophysical properties .…”

“…Whereas mononuclear [Cu(PP)(NN)] + derivatives have been already intensively explored, related dinuclear copper(I) complexes with bridging PP ligands have been investigated to a lesser extent . For instance, dinuclear copper(I) complexes with two bridging bis(diphenylphosphanyl)methane (dppm) ligands have shown promising photophysical properties . As part of this research, we became interested in using bis(diphenylphosphanyl)acetylene (dppa) as a non‐chelating PP ligand for the preparation of [Cu 2 (µ‐dppa) 2 (NN) 2 ](BF 4 ) 2 derivatives.…”

Copper(I) Phosphinooxazoline Complexes: Impact of the Ligand Substitution and Steric Demand on the Electrochemical and Photophysical Properties

“…This is mainly caused by the formation of thermodynamically more favored homoleptic bisdiimine complex [Cu(N^N) 2 ] + . Hence, this drawback drove the search and development of novel Cu I complexes with an increased stability, but also having other desired properties like a broad absorption in the visible and a reversible redoxchemistry …”