Browsing by Subject "Polythiophenes"
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Item Open Access Density functional theory investigation of substituent effects on building blocks of conducting polymers(Elsevier, 1999) Salzner, U.Substituted heterocyclic dimers were calculated employing density functional theory (DFT) and analyzed with the natural bond orbits method (NBO). Substitution in 3- and 4-positions leads to parallel shifting of HOMO and LUMO but does not reduce energy gaps. For bridge dimers, HOMO-LUMO gaps correlate with π-electron densities in the carbon backbone and energy gap reduction correlate with the strength of π-π* interactions from the backbone to the bridging group. Alternating donor-acceptor groups do not reduce energy gaps and lead to systems with average HOMO and LUMO levels compared to the parent molecules.Item Open Access Does the donor-acceptor concept work for designing synthetic metals? 1. theoretical investigation of poly(3-cyano-3′-hydroxybithiophene)(American Chemical Society, 2002) Salzner, U.Homo- and copolymers of hydroxythiophene and cyanothiophene have been investigated by employing density functional theory with the aim of determining the effect of donor-acceptor substitution on the electronic structure. The band gap of the copolymer is 0.11 eV smaller than that of polythiophene. Bandwidths of valence and conduction bands are reduced by 0.22 and 0.36 eV compared to polybithiophene. Conductivity after p- and n-doping could therefore be less than that of polythiophene. All properties of the copolymer are averages between those of the homopolymers. The charge separation between hydroxy- and cyano-substituted rings is 0.12 e in the neutral state and 0.13 e and the dication. The ionization potential and electron affinity of poly(hydroxythiophene) are 1.78 and 1.63 eV smaller than those of poly(cyanothiophene). According to the donor-acceptor concept, a decrease in band gap and an increase in bandwidths compared to the homopolymers should have resulted: We rationalize the absence of band broadening with reduced interaction between fragments with very different energies in agreement with perturbation theory.