Molecular materials, amorphous

T. Noda, H. Ogawa, N. Noma, and Y. Shirota, A novel family of amorphous molecular materials containing an oligothiophene moiety as color-tunable emitting materials for organic electroluminescent devices, Adv. Mater., 9 720-722, 1997. 

Usually, in amorphous molecular materials, charge transport is described by a disorder formalism that assumes a Gaussian distribution of energetic states of the molecules between which the charges jump [246]. The mobility is then given by... 

Recently, a novel series of amorphous molecular materials based on carbazole and methine dyes has been synthesized [89], These molecular materials exhibit a very interesting charge-transfer complex formation and large PR responses. 

Molecular Recognition and Chemistry in Restricted Reaction Spaces. Photophysics and Photoinduced Electron Transfer on the Surfaces of Micelles, Dendrimers and DNA [N. J. Turro, J. K. Barton, D. A. Tomalia, Acc. Chem. Res. 1991, 24, 332], Self-Assembly in Synthetic Routes to Molecular Devices. Biological Principles and Chemical Perspectives A Review [J. S. Lindsey, New J. Chem. 1991,15, 153], Amorphous molecular materials synthesis and properties of a novel starburst molecule, 4,4, 4 -tri(N-phenothiazinyl)triphenylamine [A. Higuchi, H. Inada, T. Kobata, Y. Shirota, Adv. Mat. (Weinheim, Ger.) 1991, 3(11), 549-550],... 

Shirota, Y, Moriwaki, K., Yoshikawa, S., Ujike, T., and Nakano, H. 4- [di(biphenyl-4-yl)amino]azobenzene and 4,4 -bisfbis(4 -rerr-butylbiphenyl-4-yl amino]azobenzene as a novel family of photochromic amorphous molecular materials. /. Mater. Chem. 8, 2579, 1998. 

Noda T., Ogawa H., and Shirota Y., "A Blue-Emitting Organic Electroluminescent Device Using a Novel Emitting Amorphous Molecular Material, 5,5 -Bis(dimesitylboryl)-2,2 -bithiophene", Adv, Mater, (Weinheim, Ger.), 11,1999, 283. 

Charge-transporting and Charge-blocking Amorphous Molecular Materials for Organic Light-emitting Diodes... 

Since the pioneering studies on OLEDs using small molecules and polymers [1, 2], both small molecules and polymers have been studied for use as materials in OLEDs. Small organic molecules that readily form stable amorphous glasses above room temperature, i. e., amorphous molecular materials [3], and polymers containing it-electron systems in the main chain, i.e., it-conjugated polymers, have been proven to be promising candidates for materials for OLEDs. 

This chapter describes first the general aspects of amorphous molecular materials and then hole-transporting, electron-transporting, and hole-blocking amorphous molecular materials for use in OLEDs. 

Generally, small organic molecules tend to crystallize readily, and hence, they usually exist as crystals below their melting temperatures. However, recent extensive studies have revealed that like polymers, small organic molecules can also readily form stable amorphous glasses above room temperature if their molecular structures are properly designed [3]. Such amorphous molecular materials have... 

Table 7.1 Hole-transporting amorphous molecular materials.

Table 7.2 Glass-transition temperatures (7"gs) and oxidation potentials (E°)2) °f hole-transporting amorphous molecular materials.

New classes of hole-blocking amorphous molecular materials have recently been developed, which include the families of triarylbenzenes and triarylboranes (Table 7.4). These compounds readily form amorphous glasses with well-defined Tgs and possess weakly electron-accepting properties. These hole-blocking materials enabled fabrication of high-performance blue- and blue-violet-emitting OLEDs using a-NPD, p-TTA and TPD as emitters. The performance of some devices is summarized in Table 7.5. 

Table 7.4 Hole-blocking amorphous molecular materials.

Charge carrier drift mobilities of a number of amorphous molecular materials have been determined by a time-of-fhght method, and their electric-field and temperature dependencies have been analyzed in terms of the disorder formalism [56, 57] ... 

Table 7.6 Hole drift mobilities of amorphous molecular materials [a].

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