Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of Ir(III) are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn-on time, stability, efficiency, and color is presented.

Cu(I) complexes and clusters are the largest class of compounds of relevant photochemical and photophysical interest based on a relatively abundant metal element. Interestingly, Nature has given an essential role to copper compounds in some biological systems, relying on their kinetic lability and versatile coordination environment. Some basic properties of Cu(I) and Cu(II) such as their coordination geometries and electronic levels are compared, pointing out the limited significance of Cu(II) compounds (d 9 configuration) in terms of photophysical properties. Well-established synthetic protocols are available to build up a variety of molecular and supramolecular architectures 70 N. Armaroli et al.(e.g. catenanes, rotaxanes, knots, helices, dendrimers, cages, grids, racks, etc.) containing Cu(I)-based centers and exhibiting photo-and electroluminescence as well as light-induced intercomponent processes. By far the largest class of copper complexes investigated to date is that of Cu(I)-bisphenanthrolines ([Cu(NN) 2 ] + ) and recent progress in the rationalization of their metal-to-ligand charge-transfer (MLCT) absorption and luminescence properties are critically reviewed, pointing out the criteria by which it is now possible to successfully design highly emissive [Cu(NN) 2 ] + compounds, a rather elusive goal for a long time. To this end the development of spectroscopic techniques such as light-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS) and femtosecond transient absorption have been rather fruitful since they have allowed us to firmly ground the indirect proofs of the molecular rearrangements following light absorption that had accumulated in the past 20 years. A substantial breakthrough towards highly emissive Cu(I) coordination compounds is constituted by heteroleptic Cu(I) complexes containing both N-and P-coordinating ligands ([Cu(NN)(PP)] + ) which may exhibit luminescence quantum yields close to 30% in deaerated CH 2 Cl 2 solution and have been successfully employed as active materials in OLED and LEC optoelectronic devices. Also copper clusters may exhibit luminescence bands of halide-to-metal charge transfer (XMCT) and/or cluster centered (CC) character and they are briefly reviewed along with miscellaneous Cu(I) compounds that recently appeared in the literature, which show luminescence bands ranging from the blue to the red spectral region. An Overview of Copper Historical Notes, Current Use, Consumption TrendsCopper was known to some of the oldest civilizations on record, and has a history of use that is at least 10 000 years old. A copper pendant was found in what is now northern Iraq that dates to 8700 B.C. and by 5000 B.C. there are signs of copper smelting from simple copper compounds such as malachite or azurite. This process appears to have been developed independently in several parts of the world since several centuries B.C., including Anatolia, China, Central America and West Africa. The Egyptians found that, upon addition of small amounts of tin, copper becomes easier to...

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Luminescent metal complexes are key materials for several applications such as lighting, analytical probes, and lasers. In many cases compounds based on precious (i.e. platinum group) and rare earth metals are utilized, which are often rather expensive and environmentally problematic. In recent years, interest is growing in luminescent complexes based on less traditional but more abundant and cheaper metal elements. In this scenario compounds of metals with a d10 electronic configuration are playing a prominent role, also thanks to the versatility of their luminescent levels which can be of ligand centred, charge transfer or, in the case of polynuclear compounds, even metal-centred nature. Here we focus on some selected examples of Cu(I), Ag(I), Au(I), Zn(II) and Cd(II) luminescent complexes to suggest some possible routes towards promising and unprecedented emitting materials.

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