Diversity of Luminescent Metal Complexes in OLEDs: Beyond Traditional Precious Metals

Abstract

Organic light-emitting diodes (OLED) have attracted increasing attention due to their excellent properties, such as self-luminosity, high color gamut and flexibility, and potential applications in display, wearable devices and lighting. The emitters are the most important composition in OLEDs, mainly classified into fluorescent compounds (first generation), metal phosphorescent complexes (second generation), and thermally activated delayed fluorescence (TADF) materi-als (third generation). In this review, we summarize the advances of novel emitters of organic metal complexes in the last decade, focusing on coinage metals (Cu, Ag, and Au) and non-precious metals (Al, Zn, W, and alkali metal). Also, the design strategy of d 10 and Au(III) complexes was discussed. We aim to provide guidance for exploring efficient metal complexes beyond traditional phosphorescent complexes. Non-traditional phosphorescent complexes2.1. d 10 complexes (Cu(I), Ag(I), Au(I))Cu(I), Ag(I), Au(I) complexes with closed shell d 10 configuration have been researched extensively for the most promising alternative emitters to traditional precious metal complexes in OLEDs. [13] In this section, some typical research progress in the [a] X.

Spin-flip luminescence

“…Although all of these complexes feature a d 2 electronic configuration, their emission does not arise from an intraconfigurational spin-flip state but rather from an interconfigurational MC states. The complexes' D 4h symmetry and strong -bonds to the nitrido or oxido ligands give rise to a 1 A 1 ground state with (d xy ) 2 configuration and an emissive 3 E state with (d xy ) 1 (d yz , d xz ) 1 configuration [148][149][150][151][152][153][154], which is distinctly different from the 3 T 1 ground state and 1 T 2 / 1 E spin-flip states expected for octahedral d 2 complexes (Fig. 1a) [50].…”

“…Photoactive complexes are both fundamentally interesting and highly valuable in many applications, e.g., optical devices, catalysis and biomedicine [1][2][3][4]. Traditionally there is an excessive reliance on compounds containing precious transition metal ions like Ru II , Ir III , Os II or Pt II due to their favorably high intrinsic ligand field splitting and strong spin-orbit coupling (SOC) [5][6][7][8][9].…”

Tuning the luminescence of transition metal complexes with acyclic diaminocarbene ligands

“…Luminescent transition metal complexes underpin the development of OLEDs and other electroluminescent technologies (for the main reviews on the topic see ref. [1][2][3][4][5][6][7][8][9][10], and a broad range of applications in the fields of luminescence chemosensing, [11][12][13] photocatalysis, [14][15][16] sensitisation, [17][18][19] selfassembled materials, 20 and bioimaging. [20][21][22][23] Although pure organic light emitters are predominantly fluorescent (triplet excitons formed are deactivated by thermal processes), the presence of strong spin-orbit coupling in transition metal complexes upholds the intersystem crossing from the singlet to the triplet state enabling phosphorescent relaxation.…”

Visible-emitting Cu(i) complexes with N-functionalized benzotriazole-based ligands

“…Luminescent first-row transition metal complexes are viable alternatives to second-and third-row transition elements and trivalent lanthanide derivatives for advanced applications such as organic light-emitting diodes (OLEDs), light-emitting electrochemical cells (LECs), solar cells and sustainable photoactivated reactions. [1][2][3][4][5][6][7][8][9][10][11][12][13] In particular, d-block metals such as Ir(III) and Pt(II) are commonly exploited in photoluminescent dyes for OLEDs, [14][15][16][17][18] but their high cost, scarce abundance and toxicity determined a growing interest for cheaper and greener alternatives. Moreover, the employment of precious and rare-earth metals is geopolitically problematic because of the presence of only a few mining countries.…”