Ionic-pair effect on the phosphorescence of ionic iridium(III) complexes Loredana Ricciardi a , Teresa Fina Mastropietro b , Mauro Ghedini a , Massimo La Deda a , Elisabeta Ildyko Szerb a, * a Centro di Eccellenza CEMIF.CAL, LASCAMM e CR INSTM, Unit a INSTM della Calabria and CNR-IPCF-UOS di Cosenza e Laboratory Licryl, Dipartimento di Chimica e Technologie Chimiche, Universit a della Calabria, Arcavacata di Rende, CS 87036, Italy b Dipartimento di Ingegneria dell'Ambiente e del Territorio ed Ingegneria Chimica, Universit a della Calabria, Arcavacata di Rende, CS 87036, Italy article info Article history: Received 21 August 2014 Received in revised form 24 September 2014 Accepted 25 September 2014 Available online 7 October 2014 Keywords: Iridium(III) ionic complexes Photophysical properties Crystalline structures Water solubility abstract The synthesis and characterization of two water soluble ionic iridium(III) complexes containing hydro- philic acetate counterions is presented. The complexes exhibit one of the highest phosphorescence quantum yields reported up to now in water solution. The influence of the counterion position on the photophysical properties was highlighted through investigations in several polar solvents and in the crystalline solid state. © 2014 Elsevier B.V. All rights reserved. Introduction Phosphorescent complexes based on iridium(III) metal centers are attracting significant attention because of their high emission intensity, long living triplet excited states and color tunability [1]. Therefore, they promise improved performances when used as molecular-based materials for practical applications within a large variety of fields ranging from electrooptical devices to biomedical technologies. Indeed, although they were mainly researched as active materials in electrooptical devices [2], the solubility of the ionic species in ‘environmentally friendly’ solvents moved forward the attention to their use in sensing [3], biomedical applications [4] or photocatalytic water-splitting processes [5]. Hence, a huge li- brary of iridium(III) complexes were synthesized and reported to date, the research mainly focusing on tailoring the desired photo- physical properties by ‘smart’ molecular engineering of the ligands, whereas less attention was paid to the counterions [1e5]. Never- theless, this ‘neglected’ counterpart of charged iridium(III) metal complexes may be a tool to induce solubility in specific desired solvents, thus avoiding time spending and high cost synthetic procedures. Furthermore, some recent studies showed that the counterion may have a strong influence on the energy and orbital mix of the excited states [6]. Our group previously reported several highly phosphorescent ionic iridium(III) complexes with the general formula [(ppy) Ir(N^ N)]X, where ppy ¼ 2-phenylpyridine; as ancillary ligands N^ N were used ethylenediamine (en) or 2-picolylamine (pam) and as counterions X ¼ Cl, PF 6 , ClO 4 or BPh 4 [7]. The complexes having en as ancillary ligand exhibited in deoxygenated acetone solution brilliant blueegreen emissions, with the emission maximum cen- tred at 502 nm, luminescence quantum yield (F) of 0.68 and emission lifetime (t) of about 1.6 ms. By replacing the N^ N ligand with pam, the emission maximum shifted to 490 nm in dichloro- methane deoxygenated solution, while a slight decrease of both F and t to 0.39 and 0.80 ms respectively was observed. On this background, we decided further to introduce solubility in water for these complexes, by changing the counterion through a simple metathetical reaction. Acetate is a non-innocent hydrophilic counterion with a moderate coordinating strength and a great ability to offer proper intermolecular interaction for building su- pramolecular materials both in solvent media and solid state [8]. Therefore, herein we report the synthesis and characterization of two iridium(III) complexes Ir en and Ir pam having acetate as coun- terions, whose chemical structure is presented in Fig. 1 . The complexes showed exceptionally high phosphorescence quantum yields in water solution, with values which significantly * Corresponding author. E-mail address: elisabeta_ildyco.szerb@unical.it (E.I. Szerb). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.09.034 0022-328X/© 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 772-773 (2014) 307e313