Polyfulvenes: Polymers with 鈥淗andles鈥?That Enable Extensive Electronic Structure Tuning

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• 作者：Christian Dahlstrand ; Burkhard O. Jahn ; Anton Grigoriev ; S茅bastien Villaume ; Rajeev Ahuja ; Henrik Ottosson
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 19, 2015
• 年：2015
• 卷：119
• 期：46
• 页码：25726-25737
• 全文大小：671K
• ISSN：1932-7455

文摘

The fundamental electronic structure properties of substituted poly(penta)fulvenes and pentafulvene-based polymers are analyzed through qualitative molecular orbital (MO) theory combined with calculations at the B3LYP and HSE06 hybrid density functional theory (DFT) levels. We argue that the pentafulvene monomer unit has a unique character because electron density in the exocyclic C鈺怌 double bond can be polarized into and out of the five-membered ring, a feature that is not available to other more commonly used monomers. It is investigated how the energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively), as approximate band gaps, are influenced by exocyclic substitution, introduction of linker groups, benzannulation, and ring substitution. In particular, the exocyclic positions of the fulvene act as 鈥渉andles鈥?by which the electronic structure of the polymer can be tuned between the quinoid and fulvenoid valence bond isomers; electron-withdrawing exocyclic substituents lead to polyfulvenes in the quinoid form while those with electron-donating substituents prefer the fulvenoid. Taken together, the HOMO鈥揕UMO gaps of polyfulvenes can be tuned extensively, varying in ranges 0.77鈥?.44 eV (B3LYP) and 0.35鈥?.00 eV (HSE06) suggesting that they are a class of polymers with highly interesting, yet nearly unexplored, properties.