Enhancement of the Luminescent Efficiency in Carbene-Au(I)-Aryl Complexes by the Restriction of Renner–Teller Distortion and Bond Rotation

• Published in: Journal of the American Chemical Society Vol. 142; no. 13; pp. 6158 - 6172
• Main Authors: Li, Tian-yi, Muthiah Ravinson, Daniel Sylvinson, Haiges, Ralf, Djurovich, Peter I, Thompson, Mark E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.04.2020
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b13755

A series of (carbene)­Au(I)(aryl) complexes are reported. The nature of the lowest excited state in these complexes changes character from metal-to-ligand charge transfer (MLCT) to interligand charge transfer (ICT) with increasing electron-donating strength of the aryl ligand. Complexes that have the MLCT lowest excited state undergo a Renner–Teller bending distortion upon excitation. Such a distortion leads to a large rate of nonradiative decay, on the order of 108 s–1. Renner–Teller-based nonradiative decay does not occur in chromophores with an ICT emissive state. Introducing a julolidine moiety and ortho -methyl substituents to the aryl group makes the molecule rigid and hinders the rotation along the Au–Caryl-coordinate bond. Consequently, the nonradiative decay rates of these ICT emitters are decreased and become lower than the radiative decay rate constants (k r = 105 s–1). Thus, high-luminescent efficiencies (ΦPL = 0.61 and 0.77) along with short lifetimes (τ < 2 μs) are obtained for yellow and green emitters, respectively. Thermally assisted delayed fluorescence behavior is observed, owing to the small exchange energy (ΔE ST < 1600 cm–1) in these emitters.