Geometrical and Electronic Structures of New π-Conjugated Pyrrole− and Furan−Nonheterocycle Copolymers

Abstract

The geometrical and electronic structures of new hypothetical pyrrole-and furannonheterocycle copolymers were theoretically investigated. Nonheterocycles include cyclopentadiene, silole, oxocyclopentadiene, and thiocyclopentadiene, whose homopolymers are of the quinoid forms in their ground states. AM1 band calculations show that in the ground states the aromatic forms of the copolymers containing cyclopentadiene or silole rings are more stable than the quinoid types, whereas the aromatic forms of the oxocyclopentadieneor thiocyclopentadiene-containing copolymers are less stable. Modified extended Hü ckel band calculations predict that bandgaps of the copolymers in the ground states are smaller than those of the corresponding homopolymers. The absorption peaks of π-π* band transitions are estimated to appear at 1.68 eV for poly(pyrrolylenesilolylene) and 1.67 eV for poly(furylenesilolylene). Small bandgaps of the copolymers come from the fact that the copolymers consist of different types of cyclic units. Decomposition of the bandgaps reveals that the electronic effect of the heteroatoms (NH and O) in the copolymers is less than half of the effect found in polypyrrole and polyfuran. The small electronic effect decreases bandgaps of the aromatic forms and increases bandgaps of the quinoid types, in comparison to the average of the gaps of the corresponding homopolymers.

Synthesis and Optical, Electrochemical, and Electron-Transporting Properties of Silicon-Bridged Bithiophenes

“…Tamao et al have previously reported similar results of MO calculations for some heterocycles, including silole, pyrrole, furan, and thiophene; of these silole has the smallest HOMO−LUMO gap, arising primarily from its lower-lying LUMO 2a…”

“…π-Conjugated systems containing silole rings are of current interest because of their unique optical and electrical properties. − Both experimental and theoretical studies have demonstrated that the silole ring system possesses a particularly low-lying LUMO, presumably due to the orbital interaction between the σ* orbital of the silole silicon atom and the π*-orbital of the butadiene fragment, namely σ*−π* conjugation …”

Polymeric Organosilicon Systems. 28. Preparation and Properties of Novel σ−π Conjugated Polymers with Alternating Disilanylene and 2,5-Diethynylenesilole Units in the Backbone

“…The remarkably red-shifted UV absorptions and high electron-transporting properties of the compounds containing the silole ring would result from their low-lying lowest unoccupied molecular orbital (LUMO) due to the σ*−π* interaction between the silole silicon atom and the π-orbitals . Although many papers concerning the synthesis of polymers and oligomers containing the silole ring have been published to date, , only a few refer to polymers bearing 2,5-linked silole rings in the backbone . In the course of studies concerning the synthesis of silole-containing conjugated polymers, , we have prepared polymers having repeating organosilicon-2,5-diethynylenesilole units in the backbone, by dehydrobromination of 2,5-dibromosilole and diethynyldi- and monosilanes in the presence of a CuI/Pd(PPh 3 ) 4 catalyst…”

“…Results and Discussion. The starting monomer 2,5-dibromo-1,1,3,4-tetraphenylsilole ( 1 ) was prepared as reported by Tamao et al6b Tamao et al have also reported the synthesis of 2,5-bis(phenylethynyl)-1,1,3,4-tetraphenylsilole from the reaction of 1 and phenylacetylene in the presence of a CuI/Pd(PPh 3 ) 4 catalyst in a mixed solvent of THF and triethylamine 6b. First, we examined a model reaction to confirm that CuI/Pd(PPh 3 ) 4 -catalyzed dehydrobromination is applicable to the synthesis of 2,5-bis(silylethynyl)silole.…”

Polymeric Organosilicon Systems. 30. Preparation and Properties of Polymers Containing Iron(0)-Complex-Coordinated Silole Units

“…Current interest has been focused on the chemistry of the silole ring system, which shows unique optical properties. The characteristic red-shifted UV absorptions of silole derivatives originate from their low-lying LUMO that is due to the σ*−π* interaction between the silole silicon atom and the π-orbitals . Highly electron transporting properties of cooligomers of silole-2,5-diyl and heteroaromatic systems and dithienosiloles having a silole ring fused with two thiophene rings also reflect the low-lying LUMO of the silole ring systems.…”