Since the advent of the first practical organic light emitting diodes (or OLEDs) about three decades ago, they have attracted a great deal of attention as potential future lighting technology. In the construction of OLEDs, especially OLEDs whose working principles are based on phosphorescence phenomenon, noble metals such as Iridium or Platinum constitute the main component of the device.
However, due to their low natural abundance in the earth’s crust, noble metals can influence the economics of manufacturing such systems. This is an important point that one has to consider, in particular in large-scale production of OLEDs. In order to address this important issue in regards to OLEDs, scientists have been researching the development of light emitting devices based on cheaper and more abundant metals such as silver or copper.
It has been shown that luminescent silver and copper complexes and clusters are promising materials to replace OLEDs based on noble metals. With the progress made in the past decade on the development of structurally and thermally stable copper-based luminescent systems, especially those based on copper clusters, this old dream is getting closer to be a reality. Besides, some copper complexes show interesting thermally-activated delayed fluorescence (TADF) property, which has sown to be an interesting mechanism to increase metal-complex photoluminescence quantum yields up to 100 percent.
Recently, Neshat et al. have reported the synthesis and characterization of some copper dimer and clusters with interesting photoluminescent properties. In this report, they have thoroughly investigated the structural and luminescent properties of the metal complexes they have reported. First, in the characterization section of their report, Neshat el al have utilized X-ray diffraction and solid state 31P NMR techniques to properly characterize solid state structures of the reported structures. The latter technique, other than providing valuable information about the structure of the system under study, gives information about the symmetry of charge distribution around NMR active nuclei. Through analyzing splitting patterns from coupling between NMR active copper and phosphorous atoms, they have characterized all the present structural isomers in the solid states.
By careful assessment of the number of signals, splitting patterns as well as the magnitude of indirect Cu-P coupling constants measured for two of their reported structures by solid state NMR techniques reveal, they have corroborated the assignment of a number of structural isomers in the solid state. They have shown that true structures of these systems are highly dependent on the nature of the solvent used for the synthesis. Understanding this phenomenon, which greatly influences the photophysical and structural properties of these systems could assist in the preparation of copper based materials and clusters with tailored optical properties.
These findings are described in the article entitled Dinuclear and tetranuclear copper(I) iodide complexes with P and P^N donor ligands: Structural and photoluminescence studies, recently published in the journal Polyhedron. This work was conducted by Abdollah Neshat and Reza Babadi Aghakhanpour from the Institute for Advanced Studies in Basic Sciences, Piero Mastrorilli and Stefano Todisco from the Politecnico di Bari, Farzad Molani from the Islamic Azad University, and Andrzej Wojtczak from Nicolaus Copernicus University in Toruń.