Biphenyl Au(III) Complexes with Phosphine Ancillary Ligands: Synthesis, Optical Properties, and Electroluminescence in Light-Emitting Electrochemical Cells

Abstract

A series of ten cationic complexes of the general formula [(C^C)Au(P^P)]X, where C^C = 4,4′-di-tert-butyl-1,1′-biphenyl, P^P is a diphosphine ligand, and X is a noncoordinating counteranion, have been synthesized and fully characterized by means of chemical and X-ray structural methods. All the complexes display a remarkable switch-on of the emission properties when going from a fluid solution to a solid state. In the latter, long-lived emission with lifetime τ = 1.8–83.0 μs and maximum in the green-yellow region is achieved with moderate to high photoluminescence quantum yield (PLQY). This emission is ascribed to an excited state with a mainly triplet ligand-centered (3LC) nature. This effect strongly indicates that rigidification of the environment helps to suppress nonradiative decay, which is mainly attributed to the large molecular distortion in the excited state, as supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) computation. In addition, quenching intermolecular interactions of the emitter are avoided thanks to the steric hindrance of the substituents. Emissive properties are therefore restored efficiently. The influence of both diphosphine and anion has been investigated and rationalized as well. Using two complexes as examples and owing to their enhanced optical properties in the solid state, the first proof-of-concept of the use of gold(III) complexes as electroactive materials for the fabrication of light-emitting electrochemical cell (LEC) devices is herein demonstrated. The LECs achieve peak external quantum efficiency, current efficiency, and power efficiency up to ca. 1%, 2.6 cd A–1, and 1.1 lm W–1 for complex 1PF6 and 0.9%, 2.5 cd A–1, and 0.7 lm W–1 for complex 3, showing the potential use of these novel emitters as electroactive compounds in LEC devices.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

“…10 Compounds containing biphenyl underwent electrophilic substitution to aromatic substrates. Dihydro-6H-dibenzo [1,5] dioxonine 168 was produced by reuxing biphenyl-diol 167 with dibromopropane in acetone containing catalytic amount of anhydrous K 2 CO 3 . Whereas, under the same condition, reuxing of biphenyl-2,2′-diol (167) with dibromomethane afforded dibenzo [1,3]…”

“…The reactions of biphenyls are similar to benzene as they both undergo electrophilic substitution reaction. Biphenyl derivatives which are used to produce an extensive range of drugs, products for agriculture, uorescent layers in organic lightemitting diodes (OLEDs) 5,6 and building blocks for basic liquid crystals are signicant intermediates in organic chemistry besides being the structural moiety of an extensive range of compounds with pharmacological activities. [7][8][9][10] Whereas several biphenyl derivatives serve as versatile and multifaceted platforms in medicinal chemistry, as large number of biphenyl derivatives are patented and broadly used in medicine as the antiandrogenic, 11 immunosuppressant, antifungal, antibacterial, antimicrobial, anti-inammatory, anti-proliferative, osteoporosis, antihypertensive, antitumor, b-glucuronidase inhibition activity, anti-leukemia agent hypotensive, anticholinesterase, anti-diabetic and antimalaria drugs.…”

Luminescent Au(III)–M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions

“…28 In recent years, a series of biphenyl-derived C ∧ C gold(III) complexes with promising photoluminescence have been reported 29−31 and one cationic 4,4′-di-tert-butyl-1,1′-biphenyl Au(III) diphosphine complex has been already employed as electroactive complex in the first light-emitting electrochemical cell (LECs) device based on this element. 32 These ligands have proved their ability to stabilize gold(III) complexes by a combination of good electron-donor properties, and π-acceptor capability with steric rigidity. This provides excellent protection against reduction.…”

“…More recently, Mohr and co-workers prepared a series of t -butyl substituted 2,2′-biphenyl-diyl compounds, with improved solubility and potentially interesting photophysical properties . In recent years, a series of biphenyl-derived C ∧ C gold­(III) complexes with promising photoluminescence have been reported − and one cationic 4,4′-di-tert-butyl-1,1′-biphenyl Au­(III) diphosphine complex has been already employed as electroactive complex in the first light-emitting electrochemical cell (LECs) device based on this element …”

Bond-Dissociation Energies to Probe Pyridine Electronic Effects on Organogold(III) Complexes: From Methodological Developments to Application in π-Backdonation Investigation and Catalysis

“…Thirty-three gold­(III) complexes of the [(C^C)­Au­(NHC/PPh 3 )­L] + and [(C^N^C)­AuL] + type were designed with L being the pyridine ligand of interest (Scheme ). These (C^C) and (C^N^C) chelating ligands are known for their high stability − and a large panel of applications in fundamental organometallic chemistry, , photoluminescence, − and biology. ,, Three scaffolds were chosen in order to access a large range of electronic effects. Aryl ligands (complexes 1 and 2 ) are indeed known to have a higher trans influence compared to N -donor ligands (complexes 3 ) …”