Oligoacene

Other donors very often used in combination with fullerenes comprise ferrocene, phthalocyanine, transition metal complexes, aniline derivatives, tetrathiafulvalene and oligoacenes, carotenoids, oligoarylene, and oligothiophene and many examples are collected in recent reviews and books dedicated to this subject.3a,7e 28... 

The degree of geometry relaxations calculated when going from the neutral to the cation or anion states in compounds 45, 111, and 112 is similar to those observed in the corresponding oligoacenes. 

As the size of the systems increases, when going from tricycle 45 to pentacycle 112, the Huang-Rhys factors (the electron- and hole-vibration constants) for high-frequency vibrations decrease as expected. In contrast, the vibronic interaction with low-energy vibrational modes shows an opposite trend for both electrons and holes. The electron-vibrational interaction with low-energy vibrations is much larger than the hole-vibrational interaction a similar pattern is also characteristic for oligoacenes. 

In this case, the conical volume of 1 cm is aligned with the cone axis along the a-direction. Similar to the oligoacenes, di-indenoperylene crystals prepared by sublimation under streaming hydrogen show platelet-hke morphologies with an [001] surface normal (d). The smooth terraces of 100 pm are a precondition for rehable FET measurements. 

Figure 25.1 Selected organic molecules discussed in the course of this chapter. Special attention is drawn to tetracene and diindenoperylene both representing different classes of PAHs, viz. oligoacenes and perylene-derivatives, which are of great interest for organic electronic applications.

As a representative example of the class of oligoacenes, tetracene crystals were grown by sublimation imder streaming H2 gas at a flow rate of 50 seem. The... 

Fig. 1. Cohesive energies of the oligoacene series from napthtalene (2A) to pentacene (5A). Theoretical values obtained within the van-der-Waals density functional (vdW-DF), the local densiy approximation (LDA), and the generalized gradient approximation (GGA) are compared to experimental data.

Fig. 2. Surface energies within the vdWDF for the oligoacene (nA), oligophenylene (nP), and the oligothiophene (nT) series. Values for the (100), (010), (001), and (110) planes are given and the corresponding surface terminations are depicted for tetracene (4A).

Coropceanu, V., Malagoli, M., da Silva, D.A., Gruhn, N.E., Bill, T.G., Bredas, J.L., Hole- and electron-vibrational couplings in oligoacene crystals Intramolecular contributions, Phys. Rev. Lett., 89, 275503, 2002. 

Deng, W.-Q., and Goddard, W. A., Predictions of hole mobilities in oligoacene organic semiconductors from quantum mechanical calculations, J. Phys. Chem. B, 108, 8614, 2004. 

Cheng, Y. C. et ah. Three-dimensional band structure and bandlike mobility in oligoacene single crystals A theoretical investigation, J. Chem. Phys., 118, 3764, 2003. 

FIGURE 3.1.2 Chemical structure of anthracene- and tetracene-based oligoacenes. 

While the longest commercially available oligoacene, pentacene, also exhibits the highest OTFT performance, very few longer acenes or derivatives thereof have been reported. Recently silylethynylated hexacene and heptacene derivatives were synthesized (Figure 3.1.3), but their transistor characteristics were not reported.[78]... 

Heteroarenes are an interesting but much less studied class of Jt-functional materials. Substitution of one of several carbon atoms in oligoacenes with a heteroatom such as nitrogen or sulphur in different valence state may induce unique properties in these Jt-electron systems. The generally decreased HOMO-LUMO gap is of particular interest for many applications. 

Comil, J., Calbert, J.P., and Bredas, J.L., Electronic stracture of the pentacene single crystal Relation to transport properties, J. Am. Chem. Soc, 123, 1250, 2001 Cheng, Y.C., Silbey, R.J., da Silva, D.A. et al.. Three-dimensional band structure and bandlike mobility in oligoacene single crystals A theoretical investigation J. Chem. Phys. 118, 3764, 2003. 

Cheng, Y.C., et al. 2003. Three-dimensional hand structure and handlike mobility in oligoacene single crystals A theoretical investigation. / Chem Phys 118 3764. 

Kim, B., Choi, S.FL, Zhu, X.Y., and Frisbie, C.D. (2011) Molecular tunnel junctions based on pi-conjugated oligoacene thiols and dithiols between Ag, Au, and Pt contacts effect of surface linking group and metal work function. J. Am. Chem. Soc., 133, 19864-19877. 

Various oligoacenes have been synthesized using quinone derivatives as the dienophile in Diels-Alder reactions. One example is the synthesis of a series of epoxypolyacenequinones 19-21 by Miller et al., via repetitive Diels-Alder/oxida-tion reactions with appropriate bis-dienes and quinones. The ether-bridge could be cleaved to give the desired acene 22 with up to 11 linearly aimulated rings (Scheme 6) [25]. The final aromatization, however, has not been reported. 

---