Β-Diketonate ancillary ligands in heteroleptic iridium complexes: a balance between synthetic advantages and photophysical troubles. Issue 9 (26th July 2018)

• Record Type: Journal Article
• Authors: Penconi, Marta; Cazzaniga, Marco; Kesarkar, Sagar; Baldoli, Clara; Mussini, Patrizia R.; Ceresoli, Davide; Bossi, Alberto
• Is Part Of: Photochemical & photobiological sciences. Volume 17:Issue 9(2018)
• Page Start: 1169
• Page End: 1178
• Publication Date: 2018-07-26
• Subjects: Photochemistry -- Periodicals; Photobiology -- Periodicals; 541.35
• DOI: 10.1039/c8pp00052b
• Languages: English
• ISSNs: 1474-905X

Abstract

Abstract : How the triplet energy of β-diketonate ancillary ligands in Ir(iii ) complexes affects the phosphorescence emission: photochemical and electrochemical investigations and DFT calculations shed light on the dark triplet excited states. Abstract : β-Diketones are an important class of bidentate cyclometalating compounds, used in organometallic chemistry as ancillary ligands because of their wide commercial availability and easy synthesis. They are employed to finely tune the electronic, spectroscopic and physical properties of metal complexes. Heteroleptic iridium complexes often benefit from the use of β-diketonate ligands, their properties being similar to those of the corresponding homoleptic tris-cyclometalated ones. Nevertheless, in some cases, their use results in a complete quenching of the phosphorescence. Aiming to understand the origin of this drawback, we designed a suitable class of heteroleptic complexes and studied their thermal stability (DSC/TGA). We explored the effect of the ancillary ligand in a series of Ir(iii ) complexes bearing 2-phenylpyridine ( ppy ) as a cyclometalated ligand and acac (acetylacetonate), tta (2-thienoyltrifluoroacetonate), dtdk (1, 3-di(thiophen-2-yl)propane-1, 3-dionate) and BPhen (4, 7-diphenyl-1, 10-phenanthroline) as ancillary ligands. Through photochemical and electrochemical investigations, whose results agree with and support our density functional theory calculations, we demonstrate that β-diketonate ligands with low triplet energy generate dark triplet excited states with negligible coupling to the ground state which indeed promote non-radiative relaxation through population of higher states.