Synthesis and Structure of Fused α-Oligothiophenes with up to Seven Rings

Abstract

To combine the stability of alpha-oligothiophenes with the planarity of acenes, fully fused oligothienoacenes were synthesized and their properties compared to the nonfused alpha-oligothiophenes. By employing removable solubilizing groups, our synthetic methodology made it possible to efficiently prepare and purify oligothienoacenes with up to seven fused rings. The key steps involved the halogen dance reaction and Pd-catalyzed coupling of Bu3SnSSnBu3 to introduce sulfur linkages. This approach eliminates alpha-beta anion equilibration, a significant improvement over the traditional method of introducing sulfur linkages via Li-Br exchange. X-ray diffraction data indicate that pentathienoacene and heptathienoacene adopt pi-stacked packing motifs in contrast to the herringbone packing of nonfused oligothiophenes. On the basis of the linear dependence of the longest lambdamax on the reciprocal number of double bonds of thienoacenes with three to seven rings, the band gap of polythienoacene is extrapolated to be 2.21 eV.

π-Conjugated molecules with fused rings for organic field-effect transistors: design, synthesis and applications

“…Recently an improved synthesis of pentathienoacene (5) and extension of the series to make heptathienoacene (7) has been reported by Zhang and co-workers. 6 These oligothienoacenes show molecular packing in the desired face-to-face π-stacking motif, rather than the herringbone packing typical of nonfused oligothiophenes or pentacene. Pentathienoacene octathienoacene, consisting of an even number of thiophene rings, have also been synthesized although somewhat later than pentathienoacene (5) and heptathienoacene (7), mainly due to their limited solubility during the synthetic steps.…”

Optical absorption and emission properties of end-capped oligothienoacenes: A joint theoretical and experimental study

“…Table 1 shows the wavelengths of the absorption and fluorescence emission maxima recorded at both temperatures. [6]. ss…”

“…[1][2][3][4] Among the many different molecular materials for organic electronic applications, oligothienoacenes (linearly fused thiophenes) are of particular interest because they combine the rigid planarity and extended conjugation of acenes with the chemical stability of oligothiophenes. [5,6] Unfortunately, the structural rigidity of these materials limits its solubility in common organic solvents, which in turn, restricts their use in the development of solution-processed organic semiconductors. To overcome this problem, oligothienoacenes are frequently functionalized with solubilizing trimethylsilyl (TMS) and triisopropylsilyl (TIPS) substituents, which aid in purification and solution processability.…”

“…To overcome this problem, oligothienoacenes are frequently functionalized with solubilizing trimethylsilyl (TMS) and triisopropylsilyl (TIPS) substituents, which aid in purification and solution processability. [5][6][7][8] However, despite the important role of the silyl groups in the solubility properties of molecular materials for organic electronic applications, only a few studies up to date have investigated the electronic and optical properties and electron transfer characteristics of silyl-functionalized -conjugated oligomers. [9][10][11] On the other hand, even though qualitative interpretations of the well-resolved absorption and emission spectra of oligoacenes can be found in the literature, [12,13] to the best of our knowledge, a detailed analysis of the vibronic features in silyl end-capped oligothienoacenes has not yet been conducted.…”

Determination of Trace Metals by Differential Pulse Voltammetry at Chitosan Modified Electrodes

“…However, their structural rigidity leads to reduced solubility with regard to their non-fused α-oligothiophene counterparts. To solve this problem, the most effective synthetic strategies incorporate trimethylsilyl (TMS) and triisopropylsilyl (TIPS) solubilizing substituents at the α-position of thienoacenes [11,12]. On one hand, this end-capping strategy enhances the solubility at the time that lowers the possibility of polymerization under oxidative conditions, which in any case does not occur in our oligothienoacenes because their corresponding radical cations are stabilized by the high degree of π-conjugation.…”