Synthesis of biscyclometalated iridium(III) acetylacetonate complexes via a 15 min bridge-splitting reaction, their characterisations and photophysical properties

Abstract

Chloro-bridged diiridium(III) complexes (4a and 4b) were subjected to a bridge-splitting reaction with acetylacetone and sodium carbonate in 2-ethoxyethanol. The reaction was complete within 15 min and two novel biscyclometalated iridium(III) acetylacetonate complexes (5a and 5b) were successfully obtained in 41% and 63%, respectively. Complexes (5a and 5b) were fully characterised by 1H, 13C NMR, FT-IR and elemental analysis. UV-Vis spectra of complexes (5a and 5b) showed two absorption bands: a strong one appears below 400 nm due to ligand-centered (LC, π-π*) transitions and the weak one arises between 400 and 600 nm due to metal-to-ligand charge-transfer (MLCT, d- π*) transitions. The emission of the complexes (5a and 5b) arises in the red region of the spectrum, emitting ca. 675 nm for 5a and ca. 625 nm for 5b. A short emission lifetime (62 ns) for complex 5a indicates emission originates from 3LC transitions. However longer emission lifetime (657 ns) for complex 5b confirms that the emission totally results from 3MLCT transitions.