Pentacene, reactivity

The first photochemical reactions to be correlated with PMO theory were the dimerizations of anthracene, tetracene, pentacene, and acenaphthylene. 36> More detailed energy surfaces for the photodimerization reactions of butadiene have also been calculated. 30> In the category of simplified calculations lie studies of the regiospecificity of Diels-Alder reactions 37>, and reactivity in oxetane-forming reactions. 38,39) jn these... 

An ingenious route to the solubilization of pentacene involves addition of substituent groups that can be removed thermally after film formation is complete. The reactive nature of the central aromatic ring in pentacene makes it a good diene for Diels-Alder type reactions, and the reversibility of this reaction makes this approach ideal for such a functionalization strategy. 

Fig. 15.11. Pentacene TFT characteristic change after parylene passivation with PVA as a buffer layer. The small change in mobility (less than 14%) suggests the PVA layer acts as a buffer between pentacene and the reactive parylene.

With pentacene, the stabilization energy is less than that of the two naphthalene units formed by 1,4 addition across the central ring, and this corresponds to its high reactivity. On the other hand, the isomeric picene would have an energy change comparable to that of phenanthrene, thus accounting for its greater stability. 

Here again the reactivity increases as the number of rings increases. Thus, solutions of the violet-colored pentacene absorb oxygen when irradiated and solutions of the green hexacene are very sensitive to both air and light. Similarly their reactivity toward maleic anhydride increases in the same order and the condensation takes place as near the center of the chain as possible. But magnetic measurements have shown the pentacene to be diamagnetic, so that we have... 

A pentacene OFET process is shown in Fig. 4.13, based on the processes proposed by Kelley and Baude, et al. in [74], [75] and [40]. All four layers in the device are shadow masked, and a passivation layer is used to quench reactive sites on the e-beam thermally deposited AI2O3 layer, which has a high density of dangling bonds. 

The sextet formula for tetracene, for pentacene and for hexacene are respectively depicted in Fig.7 these structures correspond to the properties of the hydrocarbons. Anthracene is colourless but rather reactive and easily adds maleic anhydride tetracene is orange yellow and more reactive pentacene is violet and so reactive that it must be prepared under CO. ... 

Table 7.4 lists the thermal reactivity data for a number of polyacenes and it can be seen that the first three members all boil below 400°C, but do not react at their boiling point and atmospheric pressure, whilst tetracene and pentacene, although stable at 400°C, do react at the higher temperatures shown. The reactivity can also be related to the ionization potential, which is a measure of the ease of removal of an electron from the molecule. The lower the ionization potential the more readily a molecule will react and Table 7.5 lists the thermal reactivity of a number of polynuclear aromatic hydrocarbons. 

One way to increase the persistence of reactive molecules is the introduction of bulky groups that can exert kinetic stabilization by increasing the barriers for decomposition reactions. In the case of the acenes, the most important of these reactions are oxidation via endoperoxide formation and dimerization. The introduction of silylethynyl groups was shown to be advantageous in pentacene... 

The centrosymmetric dimer 24 formed by reaction between the two most reactive sites (C7 and C14) and in this sense resembles the photodimers of parent anthracene, tetracene, and pentacene [38]. The dimer 25 formed in the dark reaction resulted from reaction of the most reactive ring of one monomer with the next to terminal ring of the other molecule [33]. Another interesting dimer 26 was isolated as a by-product of the hexacene synthesis by the Anthony group [33]. It is formed by Diels-Alder reaction between the reactive ring containing the C7 and C14 atoms and the alkynyl group of another TIBS-hexacene. As one intact hexacene unit is... 

Nearly all polycyclic aromatic hycrocarbons form excimers and show typical excimer fluorescence. Exceptions occur only in the case of certain extremely reactive hydrocarbons such as pentacene, where chemical dimers are formed on exposure to light, e.g.,... 

Kipping [79] tried to protect the olefin bond in the diester (12) as the anthracene adduct but found that adduct formation was difficult. The cycloaddition was achieved with the more reactive hydrocarbon pentacene. 

FIGURE 3.13 The colors of the molecular paths v. are determined by the CFD hierarchy within the Wiener indexing framework. Examples of t(x j reactive members are computed here for pentacene. Entry Kx)n parameters are considered... 

TABLE 3.9 Electronegativity Values (in electron-Volts, eV) for the Pentacene Using Eq. (3.172) and the Numerical Schemes in Table 3.5, Aiming the Topo-Reactive Coloring As in Figure 3.12, and Further Used to Compute the Coloring Waits in the Figure 3.13 ... 

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