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.

中文翻译：

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杂多铱复合物中的β-二酮酸酯辅助配体：合成优势与光物理问题之间的平衡†

β-二酮是一类重要的双齿环金属化化合物，由于其广泛的商业应用范围和易于合成，因此在有机金属化学中用作辅助配体。它们用于微调金属配合物的电子，光谱和物理性质。异铱铱配合物通常受益于β-二酮酸酯配体的使用，其性质与相应的均三环金属化的均相类似。然而，在某些情况下，它们的使用导致磷光的完全淬灭。为了了解这一缺点的根源，我们设计了一类合适的杂合剂配合物，并研究了它们的热稳定性（DSC / TGA）。我们探索了辅助配体在一系列Ir（III）带有2-苯基吡啶（ppy）作为环金属化配体和acac（乙酰丙酮），tta（2-噻吩基三氟丙酮酸酯），dtdk（1,3-二（噻吩-2-基）丙烷-1,3-二酸酯）和BPhen的配合物（4,7-二苯基-1,10-菲咯啉）作为辅助配体。通过光化学和电化学研究，其结果与我们的密度泛函理论计算相符并支持我们的密度泛函理论计算，我们证明了具有低三重态能量的β-二酮酸酯配体产生了暗三重态激发态，与基态的耦合可忽略不计，这确实促进了种群的非辐射弛豫更高的州。