Browsing by Subject "Donor-acceptor concept"

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    Does the donor-acceptor concept work for designing synthetic metals? III. theoretical investigation of copolymers between quinoid acceptors and aromatic donors
    (2006) Salzner, U.; Karaltı, O.; Durdaǧi, S.
    Homopolymers of quinoxaline (QX), benzothiadiazole (BT), benzobisthiadiazole (BBT), thienopyrazine (TP), thienothiadiazole (TT), and thienopyrazinothiadiazole (TTP) and copolymers of these acceptors with thiophene (TH) and pyrrole (PY) were investigated with density functional theory. Theoretical band-gap predictions reproduce experimental data well. For all but six copolymers, band-gap reductions with respect to either homopolymer are obtained. Four of the acceptors, BBT, TP, TT, and TTP, give rise to copolymers with band gaps that are smaller than that of polyacetylene. BBT and TTP copolymers with PY in 1:2 stoichiometry are predicted to be synthetic metals. Band-gap reductions result from upshifts of HOMO energies and much smaller upshifts of LUMO values. The smallest band gaps are predicted with TTP, since changes in LUMO energies upon copolymerization are particularly small. The consequence of the small interactions between LUMO levels of donor and acceptor are vanishingly small conduction bandwidths. © Springer-Verlag 2006.
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    Investigation of the effect of donor-acceptor substitution on band gap, band width, and conductivity
    (Elsevier, 2001) Salzner, U.
    Polymers of two donor-acceptor systems, 3-cyano,3′-hydroxybithiophene 1 and 4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b′],3,4-ethylenedioxythiophene (CDM-EDOT) 2, were analyzed with density functional theory. As predicted by perturbation theory, interactions between donors and acceptors with very different energy levels are greatly reduced compared to those between fragments with similar energy levels. This leads to localized states and bands with little dispersion. For poly-1 these localized states lie below the valence band and above the conduction band. For 2 localized unoccupied levels lie within the band gap. These acceptor levels account for the high electron affinity of poly-2 and allow for self-doping. Self doping explains the increased intrinsic conductivity of poly-2, the localized nature of the low lying MOs rationalizes the low mobility of n-type carriers in poly-2.
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    Theoretical analysis of poly(difluoroacetylene) PDFA
    (Elsevier, 2003) Salzner, U.
    Due to the π-donating ability of fluorine, fluorosubstitution has a remarkable effect on the band structure of polyacetylene (PA). Valence and conduction band edges decrease in energy, leading to narrower valence and wider conduction bands. Ionization potential and electron affinity of PDFA are predicted to be about 1.5 eV higher than those of PA. This indicates that PDFA is an excellent candidate for an n-type conductor. PDFA tends to adopt non-planar structures but the energy of planarization is only 5.44 kcal/mol. Alternating difluoroethylene and ethylene units yield planar polymers with decreased band gaps. Ionization potential and electron affinity of the mixed polymer are between those of the homopolymers. © 2003 Elsevier Science B.V. All rights reserved.