Asymmetric Triaryldiamines as Thermally Stable Hole Transporting Layers for Organic Light-Emitting Devices

Abstract

The synthesis of a series of asymmetric triaryldiamines has provided a number of materials with a wide range of thermal, electrochemical, and spectroscopic properties. The asymmetric materials described herein have two different diarylamine groups bound to a 1,4-phenylene or 4,4‘-biphenylene core, i.e., Ar1Ar2N−C6H4−NAr1‘Ar3 or Ar1Ar2N-biphenyl-NAr1‘Ar3, respectively. The diarylamines studied include diphenylamine, phenyl-m-tolylamine, naphthylphenylamine, iminostilbene, iminodibenzyl, and carbazole. These materials were prepared by copper- and palladium-catalyzed coupling of aryl halides and diarylamines. The asymmetry inherent in these compounds prevents these low molecular mass compounds from crystallizing, thus yielding higher thermal stability over that of the symmetric derivatives. In all cases, the asymmetric diamines form stable glasses, with glass transition temperatures up to 125 °C. HOMO levels for these materials, estimated by cyclic voltammetry, show a broad range of values, with oxidation potentials both lower and higher than those of common hole transport materials used in organic light emitting devices.

Synthesis and Photophysical Properties of Pyrene-Based Multiply Conjugated Shaped Light-Emitting Architectures: Toward Efficient Organic-Light-Emitting Diodes

“…thermal and morphological stability). It is well demonstrated that the thermal stability or glass-state durability of organic compounds could be greatly improved upon incorporation of a carbazole or fused aromatic moiety in the core structure (Kuwabara et al, 1994;Koene et al, 1998;O'Brien et al, 1998). Furthermore, the carbazole moiety can be easily functionalized at its 3-, 6-, or 9-positions and covalently linked to other molecular moieties (Joule, 1984), such as alkyl, phenyl, diarylamine, pyrenyl, etc.…”

Improved Performance of Organic Light-emitting Diodes with a New Hole-transporting Material

“…[2][3][4] Recently, considerable efforts have been devoted to the development of new amorphous triarylamines possessing high morphologic stability. [5][6][7][8][9][10] Certain tetraaminobiphenyl derivatives are known to have photoconductive properties. They have been used for electrophotographic applications.…”

Properties of materials for organic light emitting diodes

“…The bulk thermal properties of CBP, BCP and TCTA are relatively well known. The glass transition temperature (T g ) of CBP is difficult to determine 130 although it has been reported to be as low as 62 °C 131 but up to 78 °C. 263 BCP, and the related 4,7-diphenyl-1,10-phenanthroline (BPhen), also have glass transition temperatures around 62 °C 255,264 although one report puts the T g of BCP at 83 °C.…”

“…protonated CBP. 130 In contrast the emission ( em = 516 nm) from both blend concentrations was entirely from the Ir(ppy) 3 indicating that the Ir(ppy) 3 was distributed such that it was within the diffusion length of an exciton formed on the d-CBP.…”

“…128,129 Many more examples of carbazole based materials exist in the literature. 128,130,131 While electron transport materials can also be used as phosphorescent hosts, compared to hole and bipolar hosts development has been limited. 25 This is due in part to the lower mobility of electrons than holes in organic materials.…”