Systematic Investigation of the Metal-Structure–Photophysics Relationship of Emissive d¹⁰-Complexes of Group 11 Elements: The Prospect of Application in Organic Light Emitting Devices

Abstract

A series of new emissive group 11 transition metal d(10)-complexes 1-8 bearing functionalized 2-pyridyl pyrrolide together with phosphine ancillary such as bis[2-(diphenylphosphino)phenyl] ether (POP) or PPh(3) are reported. The titled complexes are categorized into three classes, i.e. Cu(I) complexes (1-3), Ag(I) complexes (4 and 5), and Au(I) metal complexes (6-8). Via combination of experimental and theoretical approaches, the group 11 d(10)-metal ions versus their structural variation, stability, and corresponding photophysical properties have been investigated in a systematic and comprehensive manner. The results conclude that, along the same family, how much a metal d-orbital is involved in the electronic transition plays a more important role than how heavy the metal atom is, i.e. the atomic number, in enhancing the spin-orbit coupling. The metal ions with and without involvement of a d orbital in the lowest lying electronic transition are thus classified into internal and external heavy atoms, respectively. Cu(I) complexes 1-3 show an appreciable metal d contribution (i.e., MLCT) in the lowest lying transition, so that Cu(I) acts as an internal heavy atom. Despite its smallest atomic number among group 11 elements, Cu(I) complexes 1-3 exhibit a substantially larger rate of intersystem crossing (ISC) and phosphorescence radiative decay rate constant (k(r)(p)) than those of Ag(I) (4 and 5) and Au(I) (6-8) complexes possessing pure π → π* character in the lowest transition. Since Ag(I) and Au(I) act only as external heavy atoms in the titled complexes, the spin-orbit coupling is mainly governed by the atomic number, such that complexes associated with the heavier Au(I) (6-8) show faster ISC and larger k(r)(p) than the Ag(I) complexes (4 and 5). This trend of correlation should be universal and has been firmly supported by experimental data in combination with empirical derivation. Along this line, Cu(I) complex 1 exhibits intensive phosphorescence (Φ(p) = 0.35 in solid state) and has been successfully utilized for fabrication of OLEDs, attaining peak EL efficiencies of 6.6%, 20.0 cd/A, and 14.9 lm/W for the forward directions.

Synthesis, Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5‐a]quinolinol Scaffold

“…[7,17,30,31] Despite the high atomic number of gold, the spin-orbit coupling promoted by the gold atom is comparably low and leads to relatively long phosphorescence lifetimes at 77 K, but it is high enough to allow for efficient S 1 -T 1 intersystem crossing. This behaviour can be traced back to the low-lying d orbitals, which are not involved in low-energy electronic transitions.…”

“…[7] It should be mentioned that Gray and co-workers postulated a non-emissive excimer state to explain the concentration-dependent phosphorescence intensities of some aryl-gold(I) complexes. [31][32][33] For 5, IL fluorescence, excimer emission and IL phosphorescence can be observed at 77 K.…”

“…[4][5][6] Those bearing ligands with huge π systems and energetically low-lying excited ππ* states feature intense intraligand (IL) emissions. [7][8][9] However, Au III with its low-lying dd states causes effective quenching of the excited state, thus diminishing or even preventing luminescence. [10] Therefore Au III complexes are only emissive if strong ligands destabilize these dd states thereby hampering radiationless deactivation.…”

Substitution‐Controlled Excited State Processes in Heteroleptic Copper(I) Photosensitizers Used in Hydrogen Evolving Systems

“…[27][28][29] In contrast, much less is known about the synthetically more sophisticated heteroleptic complexes, which offer a great potential due to the multitude of possible variations of the involved ligands. [28,[32][33][34] In particular, this inhibition of the molecular distortion, that occurs in the metal-to-ligand charge transfer excited state, is suggested to positively influence their capability to catalyze the photoreduction of protons to hydrogen compared with traditional homoleptic CuPS. [15][16][17] Interestingly, these heteroleptic complexes possess longer lifetimes of the triplet excited state than the homoleptic analogs [Cu(N^N) 2 ] + , which is attributed to a weaker geometrical distortion of the former.…”

Crystal Multi‐Conformational Control Through Deformable Carbon‐Sulfur Bond for Singlet‐Triplet Emissive Tuning

“…Solid-state organic luminogens play as ignificant role in modern optoelectronics,light-emitting materials,luminescent displays and light sources. [1][2][3][4][5][6][7][8][9][10][11] In particular, luminogens that can work in the crystal phase have generated ac onsiderable interest due to their material anisotropy,s tability and the potential to construct perfect optoelectronic devices with low defect density. [12][13][14][15][16] Thep ast years witnessed substantial progress in developing crystal-state emissions,t he study and application of which have been principally focused on luminescent color tuning, brightness adjustment and device fabrication.…”