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This work provides the synthesis, structural characterization, electrochemical and photophysical features, as well as the application in light-emitting electrochemical cells (LECs) of a novel small molecule belonging to the pyridilimidazo[1,5-a]pyridine family, namely 3-(2-methoxyphenyl)-5-methyl-1-(6-methylpyridin-2-yl)H-imidazo[1,5-a]pyridine (Me-impy). This compound shows a low-cost and facile synthesis, excellent redox properties, and a high photoluminescence quantum yield (Φ) of 0.4 associated to a blue emission (∼436 nm) in solution. Despite these appealing features, the emission in solid state is red-shifted to the yellow region, owing to its aggregation character. Additionally, the electroluminescence response shows a broader and red-shifted emission even upon dilution of Me-impy thin films with polymethyl methacrylate (PMMA). Herein, we report an in-depth study on the aggregation features and their impact on the electroluminescence response of Me-impy, providing relevant information to design small-molecule based LECs. [ABSTRACT FROM AUTHOR]

In contrast to mononuclear iridium(III) complexes, dinuclear iridium(III) complexes have been less well studied, especially as dopants in phosphorescent organic light-emitting devices (PhOLEDs). This is largely a consequence of the established view that dinuclear iridium(III) complexes are poorly emissive and give unsatisfactory device performance. However, this is not always the case. In this review, recent advances in dinuclear iridium(III) complexes and their applications in OLEDs are discussed. Systems with bridges comprising bis(µ-Cl), bis(µ-NCO), N^N, N^O and C^N structures are included. The relationships between chemical structures and luminescent properties are presented. Additionally, recent reports of good electroluminescence (EL) performance of dinuclear iridium(III) emitters demonstrate that rationally designed diiridium complexes present a feasible alternative to typical monoiridium systems in optoelectronic applications, with the bridging ligands providing additional structural versatility. [ABSTRACT FROM AUTHOR]

In this minireview, a state of the art of the NHC transition metal complexes applied in two different modern technologies for lightening applications, namely Organic Light Emitting Diodes (OLEDs) and Light-Emitting Electrochemical Cells (LECs), is presented. In each technology, the different transition metal centres studied are described and the advantages brought by the NHC ligands in terms of electronic and steric properties is discussed. Devices obtained with these complexes are also presented and the stability and their efficiencies are also highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Green and yellow light emitting phosphorescent iridium complexes with 5-methyl-1,10-phenanthroline as an ancillary ligand were synthesized and characterized for the fabrication of light-emitting electrochemical cells (LECs). The photophysical and electrochemical properties of the resulting complexes, [Ir(dfppy)2(Me-phen)]PF6 (1) and [Ir(ppz)2(Me-phen)]PF6 (2) (where dfppy=2-(2,4-difluorophenyl)pyridine; ppz=1-phenylpyrazole, Me-phen=5-methyl-1,10-phenanthroline) were investigated by means of UV–Vis absorption, fluorescence spectroscopy and cyclic voltammetry. Density functional theory (DFT) calculations were performed to gain insight into the photophysical and electrochemical behaviors and to determine the electronic energy levels for the complexes. LECs were fabricated based on these complexes and their electroluminescent properties were investigated, which resulted in a maximum luminance of 2430 and 1549cdm−2 for complexes 1 and 2 respectively. LECs incorporating these heteroleptic complexes effectively tuned the emission color through the meticulous selection of the cyclometallated ligands and they displayed highly luminescent green and yellow electroluminescence with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.25, 0.58) and (0.42, 0.54) for complexes 1 and 2 respectively. [Copyright &y& Elsevier]