Low Work Function Reduced Metal Complexes as Cathodes in Organic Electroluminescent Devices

Abstract

Several electrochemically active polypyridine-metal complexes are isolated in the formally zero-charged state via reductive electrocrystallization, and are thermally evaporated to form conducting thin films with low work functions. Solution-phase cyclic voltammetry of the parent complexes is used to predict the work function of these materials. The reduced films are used as cathode materials in organic light-emitting devices, in place of the commonly used low work function metals such as calcium and aluminum. These reduced complexes represent a new class of materials available for use as electron-injecting contacts in organic electroluminescent devices.

Controlling Molecular Doping in Organic Semiconductors

“…These materials are unstable when exposed to air or water and are therefore unsuitable for commercial applications. Many n‐type molecular dopants have also been explored including tetrathiafulvalene derivatives such as BEDT‐TTF, organic dyes such as acridine orange base and Pyronin B, and organometallics such as [Ru(terpy) 2 ] 0 , W 2 (hpp) 4 , and Cr 2 (hpp) 4 . In particular, these last two compounds are good n‐type dopants for C 60 , yielding conductivities as high as 4 S cm −1 …”

Synthesis and Reactivity of Ru-, Os-, Rh-, and Ir-Halide−Sulfoxide Complexes

“…There are several reports concerning the reactivity of cis,fac-RuCl 2 (dmso-S) 3 -(dmso-O) (8) toward tridentate N ligands (Scheme 16). The reaction of 8 with 1 equiv of 2,2′:6′,2"-terpyridine (terpy), or of a 4′-substituted terpy analogue, in refluxing ethanol afforded cis,mer-RuCl 2 -(terpy)(dmso-S) complexes, which were further used for the preparation of heteroleptic bis-trischelate compounds [Ru(terpy)(L)] 2+ upon replacement of the dmso and Cl ligands with a further tridentate ligand L. 168,169 Treatment of 8 with 2 equiv of terpy, or modified terpy ligands (terpy-R, Chart 12), sometimes in conjunction with the addition of 2 equiv of a soluble Ag salt, produced a series of homoleptic [Ru(terpy-R) 2 ] 2+ complexes (substitution in 4′ position: R ) H, 170 4-anilino, 171 hydroquinones, 172 4-pyridyl, 173 ferrocenyl groups, 169,173,174 metal complexes with pendant terpy moieties; 175 substitution in 5 position: R ) thiourea 176 ). Heteroleptic complexes bearing two different modified terpy ligands were prepared from 8 either through a stepwise synthetic procedure involving RuCl 2 (terpy-R)(dmso-S) intermediates (see above) or through one-pot reactions followed by chromatographic purification of the product.…”

Solution‐Processed, Alkali Metal‐Salt‐Doped, Electron‐Transport Layers for High‐Performance Phosphorescent Organic Light‐Emitting Diodes

“…The use of strong reducing molecule such as cobaltocene (CoCp 2 ) was reported and investigated, showing that the Fermi level shifted toward the unoccupied states of the host ETM, which resulted in three orders of magnitude current increase 42. Other examples of n‐type dopants include electrochemically reduced form of the transition metal complex43 or salts of cationic dyes as strong molecular donors 44, 45…”