LAUSR

Abstract Five novel cationic cyclometalated Ir(III) complexes of type [(CˆC)IrX(PPh3)2(dmbpy)]A (X = halogen; dmbpy = 4,4′-dimethoxy-2,2′-bipyridine; A = counterion) were synthesised and characterised. Complexes 1–3 ([(CˆC)IrCl(PPh3)2(dmbpy)]A) have different anions (A = Cl−, CF3SO3−, PF6−) and complexes 4–5 ([(CˆC)IrX(PPh3)2(dmbpy)]PF6) have different halogen ligands (X = Br−, I−). Changing either the counter anion or halogen ligand altered the photophysical properties of the complexes. Interestingly, complex 1 (X = Cl, A = Cl−) did not exhibit mechanochromism, while the other four complexes all displayed mechanochromic properties. Crystal structures were determined for all compounds, and two types of single crystals are obtained for compounds 4 and 5. All complexes displayed bright solid-state phosphorescence, and reversible room-temperature mechanochromic luminescence was observed for complexes 2–5. The mechanism of the mechanochromic behaviour was investigated by combining powder and single-crystal X-ray diffraction analyses.