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 H-1, C-13 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, pi-pi*) transitions and the weak one arises between 400 and 600 nm due to metal-to-ligand charge-transfer (MLCT, d-pi*) 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 (LC)-L-3 transitions. However longer emission lifetime (657 ns) for complex 5b confirms that the emission totally results from (MLCT)-M-3 transitions.