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| - Zero Band-Gap Polymers: Quantum-Chemical Study ofElectronic Structures of Degenerate π-ConjugatedSystems
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| - In search of very small band-gap polymers, we have quantum-chemically investigated theelectronic structures of various polypentafulvalenes (PFVs) fused with six-membered rings.Geometrical parameters of the polymers were optimized through semiempirical Hartree−Fock band calculations at the Austin Model 1 (AM1) level. Electronic structures of thepolymers were obtained through modified extended Hückel band calculations by adoptingAM1-optimized geometries. It is predicted that poly(di-vinylenedioxy-pentafulvalene) andpoly(di-vinylenedithia-pentafulvalene) would possess nearly zero band gaps (correspondingto λmax) despite their large bond-length alternation of ∼0.1 Å. However, these polymers areexpected to be very susceptible to oxidation. Poly(di-2-butenylene-pentafulvalene) and poly(dipyrazinopentafulvalene) are estimated to possess band gaps comparable with that (1.13eV) of PFV. The calculated band gap of poly(di-ethylenedioxy-pentafulvalene) is 0.77 eV,smaller than that of PFV by 0.36 eV. We explained the evolution of the band gaps of thepolymers through molecular orbital arguments.
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