Heptacene derivative

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]... 

As with hexacenes, the i-Pr group (TIPS) was too small to stabilize the heptacene. Even the t-Bu group (TTBS) resulted in a heptacene derivative that was described as being only marginally stable. Heptacene 40b decomposed within a day in a rigorously oxygen-free solution, and even faster when the solution was... 

In agreement with the earlier observations at the pentacene core, the two (p-tert-butylphenyl)thiophenyl substituents in 57 increase the stability of the heptacene towards oxidation [58]. An even larger increase in stability is observed with the presence of four 0,0-dimethylphenyl groups as in 58 [58]. This heptacene derivative is stable for weeks in the solid state, for 1-2 days in solution in the dark, and for several hours under ambient conditions in the presence of laboratory light. The heptacene 58 could be fully characterized by NMR, UV/vis-NIR, fluorescence, and LDI-TOF-MS [58]. By the latter technique the absence of oxygenated derivatives... 

The Miller group also reported the synthesis of nonacene derivatives 75 and 76 using their thioaryl approach discussed above in the context of substituted heptacenes [62]. The synthesis is reminiscent of that of heptacene derivatives [58], with the key step being the Diels-Alder reaction between anthracenequinone 72 and the bis-ortho-quinodimethane precursor 73 (Fig. 35). The persistence of the less substituted derivative 76 is insufficient for characterization by solution phase methods. Derivative 75, however, could be investigated by NMR, UV/vis-NIR, and fluorescence spectroscopies as well as by LDI-TOF-MS [62]. 

Chrm et al. also investigated the electronic structure of their heptacene 44 by UV/vis-NlR spectroscopy and cyclic voltammetry [56]. The heptacene shows one reversible reduction and one reversible oxidation step. The electrochemically derived HOMO-LUMO gap is 1.38 eV, in good agreement with the gap derived... 

As expected, the 7,16-di(p-ferf-butylphenyl)heptacene 53 decomposed rapidly in solution in an ambient atmosphere in the presence of light, while the four additional o,o-dimethylphenyl substituents in 54 enhance the stability somewhat [58]. The half-life in the presence of light was not given, but appears to lie in the region of 10 min for this derivative from the displayed time dependence of acene absorption. The solids have significant lifetimes" [58] and could be studied by LDI-TOF-MS. In addition to the molecular ion M", the less substituted derivative 53 also showed the presence of the oxygen adduct (M" + 32) and its fragment (M-" + 16) [58]. 

The 1950s and 1960s also saw work on a number of linearly-annelated benze-noid derivatives of the highly reactive hexa- and heptacene as well as the first octa-cene derivative. One notable structural motif present in all of the analogs is a pyr-... 

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