Steric hindrance at metal centre quenches green phosphorescence of cationic iridium(III) complexes with 1-(2-pyridyl)-pyrazoles

Cationic cyclometalated iridium(III) complexes (N,C-2'-2-phenylpyridyl)(2)Ir((NN)-N-boolean AND) with alkyl-substituted 1-(2'-pyridyl)-pyrazole (NN)-N-boolean AND ligands exhibit green phosphorescence from a cyclometalating-ligand-centered excited state with structured emission spectrum and with quantum yield and excited-state lifetime of up to 26% and 1.4 mu s in argon-saturated dichloromethane solution. The alkyl groups do not change the energy or the nature of the emissive state; however, those alkyl groups that hinder coordination of the (NN)-N-boolean AND ligand to iridium(III) strongly quench phosphorescence of the complex. (C) 2013 Elsevier B.V. All rights reserved.