Strongly Luminescent Cyclometalated Gold(III) Complexes Supported by Bidentate Ligands Displaying Intermolecular Interactions and Tunable Emission Energy

Abstract

A series of charge-neutral Au complexes, which comprise a dicarbanionic C-deprotonated biphenyl ligand and bidentate ancillary ligands ([Au(C^C)(L^X)]; L^X=β-diketonate and relatives (O^O), quinolinolate and relatives (N^O), and diphosphino (P^P) ligands), were prepared. All the complexes are emissive in degassed CH Cl solutions and in thin-film samples with Φ up to 18 and 35 %, respectively, except for 5 and 6, which bear (N^O)-type ancillary ligands. Variation of the electronic characteristics of the β-diketonate ancillary ligand was demonstrated to be a viable route for tuning the emission color from blue-green (peak λ at ca. 466 nm for 1 and 2; 501 nm for 4 a and 4 b) to orange (peak λ at 585 nm for 3), in contrast to the common observations that the ancillary ligand has a negligible effect on the excited-state energy of the Au complexes reported in the literature. DFT/time-dependent (TD) DFT calculations revealed that the energies of the ππ*(C^C) and the ILCT(O^O) excited states (ILCT=intraligand charge transfer) switch in order on going from O^O=acetylacetonate (acac) to aryl-substituted β-diketonate ligands. Solution-processed and vacuum-deposited organic light-emitting diode (OLED) devices of selected complexes were prepared. The vacuum-deposited OLED fabricated with 2 displays a sky-blue emission with a maximum external quantum efficiency (EQE) of 6.71 % and CIE coordinates of (0.22, 0.40). The crystal structures of 7 and 9 reveal short intermolecular Au ⋅⋅⋅Au contacts, with intermetal distances of 3.408 and 3.453 Å, respectively. DFT/TDDFT calculations were performed on 7 and 9 to account for the noncovalent interactions. Solid samples of 1, 3, and 9 exhibit excimeric emission at room temperature, which is rarely reported in Au complexes.

Thermally Stable Donor–Acceptor Type (Alkynyl)Gold(III) TADF Emitters Achieved EQEs and Luminance of up to 23.4% and 70 300 cd m−2 in Vacuum‐Deposited OLEDs

“…Thanks to a low turn‐on voltage of 2.4 V, high power efficiency of 99.4 lm W −2 was achieved in the 2 device at the dopant concentration of 8 wt%. To the best of our knowledge, this is the highest value among Au‐OLEDs . The device performance and operational lifetime of OLEDs based on 6 have been evaluated by Samsung with industry standard (see the Supporting Information for details).…”

“…However, contrary to iridium that has been extensively used in organic light‐emitting diode (OLED) technology, examples of gold OLED with practical interests are scarce. The first example of gold OLED was reported by Ma and Che in 1999 with inferior performance, and device performance has been improved in recent years exploiting luminescent cyclometalated Au(III) complexes . Due to the electrophilic nature/relatively high reduction potential of Au(III) ion, the luminescent excited states of Au(III) complexes are usually ligand centered with little metal character, resulting in long triplet emission lifetimes, thereby posing significant challenges to achieve high performance OLEDs with low efficiency roll‐off at high luminance and driving voltage.…”

Synthesis of New Donor‐Substituted Biphenyls: Pre‐ligands for Highly Luminescent (C^C^D) Gold(III) Pincer Complexes

“…Besides the findings of To ste, [35] Bourissou [36] and Bertrand [37] on the oxidative addition of biphenylenet os everalA u I species, the transmetalation of stannoles is the method of choice for the preparation of cyclometalated biphenyldiyl Au III complexes. [34,38] Thus, we anticipated the corresponding 4-substituted stannoles 5 would be equallyu seful for the preparation of non-palindromic (C^C^D)c omplexes of gold.…”

Non-palindromic (C^C^D) gold(iii) pincer complexes are not accessible by intramolecular oxidative addition of biphenylenes – an experimental and quantum chemical study

“…This approach was used by different groups for the preparation of luminescent gold(III) complexes. [30][31][32] In 2015, Nevado and co-workers 33 described the nonpalindromic 34 (C^C^N) analogue of the (C^N^C) pincer and proved the corresponding gold(III) complexes to outperform most palindromic congeners in regard of emission quantum yields. 35 In subsequent reports it was shown that the [(C^C^N)Au(III)] complexes differentiate from the palindromic counterparts with respect to chemical properties as well.…”