Exceptionally long-lived light-emitting electrochemical cells: multiple intra-cation π-stacking interactions in [Ir(C^N)2(N^N)][PF6] emitters† †Electronic supplementary information (ESI) available: Experimental details. Fig. S1–S10: additional structural and NMR spectroscopic figures; voltage vs. time plots for LEC devices and electroluminescence spectra. CCDC 1019226–1019229. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc03942d

1H and 13C NMR spectra were recorded on a Bruker Avance III-500 or III-600 NMR spectrometer (chemical shifts with respect to (TMS) = 0 ppm). Solution electronic absorption and emission spectra were recorded on an Agilent 8453 spectrophotometer and Shimadzu 5301PC spectrofluorophotometer, respectively; a Perkin Elmer Spectrum Two UATR instrument was used to record FT-IR spectra of solid samples. Electrospray ionization (ESI) mass spectra were measured using a Bruker esquire 3000plus mass spectrometer. Solution and solid-state quantum yields were measured using a Hamamatsu absolute PL quantum yield spectrometer C11347 Quantaurus_QY. Lifetimes and emission spectra of powdered samples were measured using a Hamamatsu Compact Fluorescence lifetime Spectrometer C11367 Quantaurus-Tau. Electrochemical measurements were performed using a CH Instruments 900B potentiostat using a glassy carbon working electrode, platinum-wire auxiliary electrode, and silver-wire pseudo-reference electrode. The redox potentials were determined by both cyclic voltammetry (CV) and square wave voltammetry. HPLC grade, argon degassed CH2Cl2 solutions (≈10–4 mol dm–3) of samples were used in the presence of 0.1 M [Bu4N][PF6] as supporting electrolyte; a scan rate of 0.1 V s–1 and ferrocene (Fc+/Fc) was used as an internal standard. The compounds HPhppy1 and HPh2ppy1 were made according to literature methods. Atom labelling for NMR assignments is shown in Scheme S1.