Synthesis and Properties of Octithiophene Dication Sterically Segregated by Annelation with Bicyclo[2.2.2]octene Units

Abstract

Octithiophene sterically segregated by annelation with bicyclo[2.2.2]octene (BCO) units was synthesized to study the unimolecular properties of longer oligothiophene dications. For the preparation of such longer oligomers, a new route for the synthesis of the monomer annelated with BCO unit at the 3,4-positions of thiophene ring was developed. Attempted synthesis of octithiophene 1(8T) fully annelated with BCO units was hampered by low solubility of the product, and octithiophene 2(8T) having octyl groups instead of the BCO units at the second rings from the both ends of 1(8T) was synthesized to solve the solubility problem. Neutral 2(8T) has a lower planarity due to the steric repulsion between the octyl substituents and the neighboring thiophene units. However, dication 2(8T)2+, which was obtained as a stable salt by chemical two-electron oxidation with NO+SbF6–, has a planar quinoid structure, as judged from a linear correlation between the inverse chain length and the absorption energy for 1(nT)2+ (n = 3,4,6) and 2(8T)2+. Based on the comparison with the calculated absorption spectra and the result of ESR inactive properties, 2(8T)2+ appears to have a singlet ground state with open-shell biradical character rather than a closed-shell singlet structure.

Synthesis and Conductive Properties of Gold Nanoparticles Protected by Partially Bicyclo[2.2.2]octene-Annelated and Methylthio End-Capped Oligothiophene Thiolates

“…The longest wavelength absorption bands of the quaterthiophenes 2 The distortion in the π-systems of 1 and 2 caused by the steric repulsion between the bridgehead protons of the BCO units and the sulfur atoms of the neighboring thiophene rings is responsible for this phenomenon, as mentioned in our previous report. 27,31 To examine the redox behavior of 1c, 2c, and 4c, cyclic voltammetry was conducted in dichloromethane. The voltammograms are shown in Figure 2 and Figure S2, and the oxidation potentials are summarized in Table 1.…”

Electrochemistry and electrogenerated chemiluminescence of thiophene and fluorene oligomers. Benzoyl peroxide as a coreactant for oligomerization of thiophene dimers

“…The same trend was seen in other examples involving phenylvinylenes, thiophenes, and BODIPY oligomers. 11,19,75 The energetic separation for addition of the second electron relative to the first varies with the extent of conjugation and the size of the oligomer. For example the thiophene trimer shows a separation between first and second electron reduction waves (DE 1,2 ) of around 0.4 V, which is larger than the 0.2 V for the corresponding oligofluorenes and 0.1 V seen for typical BODIPY dyes.…”

“…11,38 This trend was also noticed for the bicyclo[2,2,2]octene segregated thiophene oligomers and 3,4-propylenedioxythiophene, where the appearance of a third wave was seen in the case of the hexamer. 75,76 The fact that adding a third electron is energetically much more difficult than adding either of the first two electrons can be understood in terms of repulsive coulombic forces. For example, upon addition of electrons to a hexamer, one can envision that addition of a second electron will result in increased electron densities at the extreme ends of the polymers (units 1 and 6).…”

Structural, Optical, and Electronic Properties of a Series of 3,4-Propylenedioxythiophene Oligomers in Neutral and Various Oxidation States

“…For one type, we reported on the preparation of oligothiophenes annelated with bicyclo[2.2.2]octene units. By virtue of the unusual stabilizing effect of bicyclo[2.2.2]octene annelation, we succeeded in the first systematic study of the X-ray structural analyses of the radical cation salts of the dimer and the trimer and the dication salts of the tetramer and the hexamer . For our second type of molecule, we prepared thiophene-pyrrole mixed oligomers end-capped with methylthio groups .…”