Triarylamine derivatives

The use of insoluble, highly cross-linked anisotropic networks created by the polymerisation of photoreactive monomers, eliminates the problem of crystallisation, at least for organic materials, since polymer networks are macromole-cular structures incapable of crystallising, see Chapter 6. Furthermore, the fabrication of multilayer devices would be facilitated by the use of a cross-linked stable HTL next to the anode on the solid substrate surface, onto which subsequent layers can be deposited by vapour deposition. Multilayer OLEDs are intrinsically more stable than monolayer devices due to a better balance of charge-carriers and concentration of the charged species away from the electrodes. The synthesis and cross-linking of a suitable aromatic triarylamine derivative with a polymerisable oxetane group at each end of the molecule for use as a HTL has been reported recently, ... 

Figure 6 The field dependencies of the photogeneration efficiencies for single- and dual-layer photoreceptors prepared with AZO-TPA. The transport layer contained a triarylamine derivative (MAPS).

Fig. 6.3 presents results obtained with a dual-layer system [8, 9]. Here, the CG layer consisted of a dispersion of the triphenylamine triazo pigment AZO-3 (see Chart 6.1) in poly (vinyl butyral) in a 4 10 weight ratio, while the CT layer consisted of a mixture of bisphenol A polycarbonate and the triarylamine derivative MAPS (see Chart 6.1) in a 10 9 weight ratio. 

Chart 6.1 Chemical structures of the triphenylamine triazo pigment AZO-3 and the triarylamine derivative MAPS. 

Due to the utility of the methods and the significance of the materials, the use of Pd-catalyzed fV-arylation reactions in oligoaniline and polyaniline synthesis has remained an active area of research [344, 345]. For example, in recent work Kulszewicz-Bajer and coworkers have employed Pd-catalyzed amination reactions for the synthesis of AT-aryl poly(w,-p-aniline) derivatives that can be oxidized to high-spin radical cations [346, 347]. The preparation of these materials was accomplished by coupling 1,3-dibromobenzene with A TV -diarylphenylenediamine derivatives (Eq. 65). Palladium-catalyzed A -arylation reactions have also been employed for the preparation of partially annulated poly(w-anilines) [348] and other triarylamine-derived polymers [349, 350]. 

Scheme 1-12. Synthesis of PPV derivatives incorporating triarylamines a) KOtBu, toluene.

Light emission occurs during the reaction of numerous radical anions of aromatic hydrocarbons with radical cations such as Wurster s red 103, Wurster s blue 104 or radical cations derived from triarylamines of the type 105, 106. 

Aromatic primary monoamine such as aniline serves as a difunctional monomer for Pd-catalyzed amination polycondensation to afford poly(triarylamine)s. For example, m-dibromobenzene [71] or 2,7-dibromo-fluorenes [72] reacted with aniline derivatives (Scheme 16). In these polymerizations, P(f-butyl)3 was an effective ligand of Pd2(dba)3 in a manner similar to the amination of aryl dibromides with secondary diamines. The Mw values were in the range of 9000-37 700. 

Cyclic voltammetry revealed that the N-atoms of 86a, 88a and 91a are oxidized at lower potentials than the trivalent P atoms. Comparison of these data with those observed with model compounds shows a very weak electronic delocalization via the P centers for copolymers 86a and 91a. In contrast, the low first oxidation potential observed for 88a (Table 4.5) is assumed to result from an electronic communication between the N moieties through the connecting P centers [59b]. The equivalence of the oxidation potentials for the oxidized polymers (Table 4.5) suggests the presence of electronically isolated triarylamine fragments in these derivatives. Note that the involvement of the P lone pair in jt-delocalization... 

The halogens were also used as oxidizing reagents bromine in particular has proved quite useful. It was employed in 1879 on di- and tetramethyl-p-phenylene-diamine, [49-51] and Wieland used it to generate numerous aminium salts derived from triarylamines and tetraarylhydrazines [52,53]. 

The current organic photoreceptors are triarylamines, triarylmethanes, hy-drazones, oxadiazoles, pyrazolines, oxazoles, and more recently, stilbene derivatives. The polymer matrix, on the other hand, is constituted by polyesters and polycarbonates (Fig. 5). The common presence of aromatic amines as substituents in all these materials contributes to efficient hole transport [44]. The nonbonding electron pair on the nitrogen atom, in fact, confers on these molecules a low oxidation potential, and consequently, the production of a chemically stable radical cation with the possibility of an effective overlap of nonbonding molecular orbitals between neighboring molecules. 

Nishiyama, and co-workers first reported that the catalyst derived from Pd(OAc)2 and (f-Bu)3P effects the C-N bond formation to produce triarylamines in excellent yield [65]. This system also is useful in the coupling of diarylamines and aryl chlorides. Hartwig and co-workers found this protocol optimal for the preparation of triarylamines. The (f-Bu)3P/Pd-catalyst was sufficiently active such that the coupfing of diarylamines and aryl bromides can be performed at room temperature,Eq. (34) [50]. The (f-Bu)3P/Pd-system has been used to produce new triarylamine-based polymers [ 64 a - d]. 

The arylation of aniline derivatives can be executed such that triarylamine products can be obtained from a one-pot procedure. Marder and co-workers coupled aniline with the first equivalent of aryl bromide using the DPPF/ Pd-based catalyst at 90 °C, Eq. (94) [100]. After the reaction was judged complete by TEC, the second aryl bromide was added to the reaction, along with an addition amount of base and catalyst. The resulting mixture was heated to 90 °C. After chromatography, the unsymmetrical triarylamine was obtained in 72 % yield. 

By electrochemical oxidation in alcoholic solution, e.g. in the presence of alkoxides, of aldehyde acetals or 1,3-dioxolanes derived from aldehydes orthoesters, e.g. (400 equation 185), can be obtained. " Orthobenzoates (401 equation 186) are accessible by electrolysis of substituted toluenes in the presence of triarylamines in solvents such as methanol/meAylene chloride. Decarboxylation and subsequent electrochemical oxidation of the dicarbonic acid (402 equation 187) in methanol affords cyclic orthoesters (403). ... 

Fig. 9.14 Chemical structures of oxetane-functionalized low-molecular-weight hole conductors a) derivatives ofTPD [34, 35, 36], b) hyperbranched triarylamine [35], and c) liquid-crystalline bisbenzthiazole derivative [64].

A variety of substituted parylene derivatives have been used as gate dielectrics for TFTs in a control study to investigate the effect of surface energy on channel characteristics and mobility [55]. It was found that the field effect mobility for an amorphous polymer semiconductor (MEH-PPV) increases with increasing surface hydrophobicity (a result that has been seen with amorphous poly(triarylamine)s [PTAAs] also) [5]. 

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