Hexacene is not stable in air, and dimerises upon isolation. Heptacene (and larger acenes) is very reactive and has only been isolated in a matrix. However, bis(trialkylsilylethynylated) versions of heptacene have been isolated as crystalline solids.[3]
Larger acenes
Due to their increased conjugation length the larger acenes are also studied.[4] Theoretically, a number of reports are available on longer chains using density functional methods.[5][6] They are also building blocks for nanotubes and graphene. Unsubstituted octacene (n=8) and nonacene (n=9)[7] have been detected in matrix isolation. The first reports of stable nonacene derivatives claimed that due to the electronic effects of the thioaryl substituents the compound is not a diradical but a closed-shell compound with the lowest HOMO-LUMO gap reported for any acene,[8] an observation in violation of Kasha's rule. Subsequent work by others on different derivatives included crystal structures, with no such violations.[9] The on-surface synthesis and characterization of unsubstituted, parent nonacene (n=9)[10] and decacene (n=10)[11] have been reported. In 2020, scientists reported about the creation of dodecacene (n=12)[12] for the first time. Four years later, in the beginning of 2024, Ruan et al. succeeded in synthesizing unsubstitued tridecacene (n=13) on a (111)-gold surface. The acene was characterized by STM- and STS-measurements. [13]
Related compounds
The acene series have the consecutive rings linked in a linear chain, but other chain linkages are possible. The phenacenes have a zig-zag structure and the helicenes have a helical structure.
Macromolecular forms consisting of seven fused benzene rings
Heptacene
[7]Phenacene
M-heptahelicene
Benz[a]anthracene, an isomer of tetracene, has three rings connected in a line and one ring connected at an angle.
^Electronic structure of higher acenes and polyacene: The perspective developed by theoretical analyses Holger F. Bettinger Pure Appl. Chem., Vol. 82, No. 4, pp. 905–915, 2010.
doi:10.1351/PAC-CON-09-10-29
^Anthony, John E. (2008). "The Larger Acenes: Versatile Organic Semiconductors". Angewandte Chemie International Edition. 47 (3): 452–83. doi:10.1002/anie.200604045. PMID18046697.
^Zade, Sanjio S.; Bendikov, Michael (2010). "Heptacene and Beyond: the Longest Characterized Acenes". Angewandte Chemie International Edition. 49 (24): 4012–5. doi:10.1002/anie.200906002. PMID20468014.
^Tönshoff, Christina; Bettinger, Holger F. (2010). "Photogeneration of Octacene and Nonacene". Angewandte Chemie International Edition. 49 (24): 4125–8. doi:10.1002/anie.200906355. PMID20432492.
^Kaur, Irvinder; Jazdzyk, Mikael; Stein, Nathan N.; Prusevich, Polina; Miller, Glen P. (2010). "Design, Synthesis, and Characterization of a Persistent Nonacene Derivative". Journal of the American Chemical Society. 132 (4): 1261–3. doi:10.1021/ja9095472. PMID20055388.
^Purushothaman, Balaji; Bruzek, Matthew; Parkin, Sean; Miller, Anne-Frances; Anthony, John (2011). "Synthesis and Structural Characterization of Crystalline Nonacenes". Angew. Chem. Int. Ed. Engl. 50 (31): 7013–7017. doi:10.1002/anie.201102671. PMID21717552.
^Nonacene Generated by On-Surface Dehydrogenation Rafal Zuzak, Ruth Dorel, Mariusz Krawiec, Bartosz Such, Marek Kolmer, Marek Szymonski, Antonio M. Echavarren, Szymon Godlewski, ACS Nano, 2017, 11 (9), pp 9321–9329 doi:10.1021/acsnano.7b04728
^Decacene: On-Surface Generation J. Krüger, F. García, F. Eisenhut, D. Skidin, J. M. Alonso, E. Guitián, D. Pérez, G. Cuniberti, F. Moresco, D. Peña, Angew. Chem. Int. Ed. 2017, 56, 11945. doi:10.1002/anie.201706156