Stable and Tunable Phosphorescent Neutral Cyclometalated Au(III) Diaryl Complexes

Abstract

A series of novel luminescent cyclometalated Au(III) neutral complexes of the type cis-[(N(∧)C)AuL] [N(∧)C = 2-phenylpyridine (ppy), L = 1,1'-biphenyl (1)] and cis-[(N(∧)C)AuL(2)] [N(∧)C = 2-phenylpyridine (ppy), L = C(6)H(5) (2), C(6)F(5) (3), C(6)H(4)-CF(3)-p (4), 2-C(4)H(3)S (5)]; [N(∧)C = 2-(2-thienyl)pyridine (thpy), L = C(6)H(5) (6), C(6)F(5) (7)]; [N(∧)C = 2-(5-methyl-2-thienyl)pyridine (5 m-thpy), L = C(6)F(5) (8)] were successfully synthesized. The X-ray crystal structures of all compounds except 3 have been determined. These complexes were found to show long-lived emission in solution at room temperature. The emission origins of the complexes have been tentatively assigned to be derived from triplet states predominantly bearing intraligand (IL) character with some perturbation from the metal center. Density functional theory (DFT) calculations were performed to evaluate the stability associated with the complexes and TD-DFT calculations to ascertain the nature of the excited state. Variation of the cyclometalated ligands in the complexes readily leads to the tuning of the nature of the lower energy emissive states.

Thermally Robust and Tuneable Phosphorescent Gold(III) Complexes Bearing (N^N)‐Type Bidentate Ligands as Ancillary Chelates

“…No oxidation peaks were observed (see Figures S7–S14). The reduction peaks are similar to previously reported mono‐cyclometalated complexes and are ascribed to be a predominately cyclometalating ligand‐centred electrochemical event . Electrochemical data for all final complexes 1 a – 6 b are represented in Table .…”

“…The onset of degradation ( T d ) for the samples are provided in the Supporting Information (Table S1 and Figures S2–S6) and show similar temperature ranges between 340–365 °C for the complexes bearing 2 ‐ppy as the ligand. Compared with previously investigated mono‐cyclometalated gold(III) complexes bearing two perfluorinated aryls as ancillary ligands, the studied compounds exhibit a thermal stability that was significantly increased by about 70–100 °C.…”

“…We considered that this reduced stability could be overcome by utilising bidentate ancillary chelates. However, a previous work reported on a mono‐cyclometalated bis‐bidentate complex of the type [Au(C^N)(C^C)], in which (C^N)=2‐phenylpyridine (2‐ppy) and (C^C)=biphenyl, proved to be unstable . In this context, we sought to investigate new luminescent organogold(III) complexes with dianionic chelates as ancillary ligands where the possibility for reductive eliminations is suppressed.…”

Syntheses and Photophysical Properties of Luminescent Mono-cyclometalated Gold(III) cis-Dialkynyl Complexes

“…We chose to use fluorinated aryl acetylides in most of the complexes, with an anticipation they will improve the stability of the complexes on similar lines of thought as explained for gold(III) biaryl complexes presented in our previous study. 21 All complexes synthesized were found to be stable to air and moisture in the solid state under ambient conditions. Homocoupled products, namely, the butadiynes formed through reductive elimination, were observed as byproduct (confirmed by 1 H NMR and GC-MS studies) in some cases such as for 1a and 3a but were not observed in others, especially for the fluorinated analogues.…”

Stable and color tunable emission properties based on non-cyclometalated gold(iii) complexes

“…The majority of the strategies to obtain emissive Au(III) complexes so far have relied on a tridentate biscyclometalated or a bidentate monocyclometalated ligand scaffold appended to the gold(III) center. 1, 3 Despite the recent progress, very limited success has been achieved on luminescent Au(III) complexes devoid of cyclometalation and the only known ones are cationic in nature. 1a, 4 To the best of our knowledge, there are no luminescent neutral Au(III) complexes that are devoid of cyclometalation.…”