Luminescent transition-metal complexes for lighting

The European Union set the ambitious target of reducing the final energy consumption by 20% within 2020. This goal demands a remarkable change in how we generate and consume energy and urgently calls for an aggressive policy on energy efficiency. Since almost 20% of the European electrical energy is used for lighting, considerable savings can be achieved with the development of novel and more efficient lighting concepts [1]. In the last decades, several outstanding goals have been achieved in this area, for instance with the invention of blue Light-Emitting Diodes (LED), which was awarded the Nobel Prize in Physics in 2014, and the commercialization of the first displays based on Organic Light-Emitting Diodes (OLEDs), allowing the fabrication of flexible and ultrathin luminescent surfaces. Within this framework, our research group has been involved in the development of a new concept for flat and flexible electroluminescent devices, i.e. the Light-Emitting Electrochemical Cells (LECs) [2a]. Such devices rely on a much simpler architecture compared to OLEDs and they are therefore expected to be a viable low-cost alternative to the technologies already on the market [2]. In this talk, some of the objectives we accomplished in the development and characterization of emitting materials for LECs will be presented. The first part of the presentation will be focused on cationic cyclometalated iridium(III) complexes, with a particular emphasis on deep-blue emitting materials since they turned out to be rather challenging due to emission red-shift in the solid state and instability under operative conditions [3]. In the second part, cationic copper(I) complexes as a potential alternative to iridium(III) counterparts will be discussed [4]. Iridium, in fact, is one of the rarest elements on the Earth crust and, therefore basing a largescale lighting industry on this metal might be unrealistic. Copper, on the other hand, is much more abundant and cheaper, but exhibits several drawbacks if used as metal center for luminescent complexes, such as limited color tunability and low stability in the devices. 1. (a) L. S. Brown, Plan B. Mobilizing to save the civilization, W. W. Norton & Company, New York, 2009. (b) Light's Labour's Lost - Policies for Energy-efficient Lighting, tech. rep., International Energy Agency, 2006. 2. (a) https://www.cello-project.eu/ (b) R. D. Costa et al., Angew. Chem., Int. Ed., 2012, 51, 8178. 3. (a) N. M. Shavaleev et al., Inorg. Chem., 2012, 51, 2263; (b) F. Monti et al., Inorg. Chem., 2013, 52, 10292; (c) F. Monti et al., Inorg. Chem., 2014, 53, 7709; (d) F. Monti et al., Inorg. Chem., 2015, 54, 3031; (e) F. Monti et al., Faraday Discuss., 2015, 185, 233. 4. (a) A. Kaeser et al., Inorg. Chem., 2013, 52, 12140; (b) M. Mohankumar et al., Chem. Eur. J., 2014, 20, 12083; (c) J.-J. Cid et al., Polyhedron, 2014, 82, 158.