Sexithiophene crystal structure

Y. Sakamoto, S. Komatsu and T. Suzuki, Properties and crystal structure of perfluoro-a-sexithiophene, Synth. Met., 133-134, 361-363 (2003). 

Yassar A, Gamier F, Deloffre F, Horowitz G, Ricard L (1994) Crystal structure of a,(0-bis(triisopropylsylyl)-sexithiophene unusual conjugated chain distoition induced by interchain steric effects. Adv Mater 6 660-663... 

The X-ray crystal structure of a-5T(/3-Bu)2 (Scheme 14) has been recently investigated by Liao et al. together with that of a /3-tetra-alkylated sexithiophene derivative [50], In both cases, the /8-alkyl chains induce structural and conformational deviations from the standard non-substituted homologs. First, the a-5T(/8-Bu)2 unit cell (Z = 8) contains four independent molecules, one of them having its two terminal thiophene rings in the syn conformation (see Fig. 10), similarly to the yellow monoclinic form of the a-4T(/8-SMe)4 crystal [89]. The syn conformation of this oligomer is reminiscent of the coil geometry claimed for poly thiophene. 

Before the elucidation of the crystal structure of non-substituted o-6T, a few alkylated sexithiophene a-6T derivatives have been studied. In particular, Herrema et al. [96] have synthesized two stereoregular dialkyl sexithiophenes and investigated their X-ray structure. Both 4, 3 ""-dibutyl-sexithiophene (Scheme 16) and bistri-methylsilyldioctyl-sexithiophene (Scheme 17) crystals are grown from solution. They crystallize with the monoclinic system in respectively the C2/c and P2i/n... 

Finally, Yassar et al. have determined the crystal structure of a,a>-bis(triisopro-pylsilyl)-sexithiophene (Scheme 19) [97]. This end-substituted compound crystallizes from a heptane solution as blade-shaped brownish crystals in the unusual triclinic system with only one molecule per unit cell (Z = 1). The most stricking feature of this compound is that, although the molecules have the anti-parallel conformation with no substituent on the /3-positions, all the rings are strongly twisted around the... 

Figure 12. Molecular and (a) and crystal (b) structure of a,ai-bis(triisopropylsilyl)-a-sexithiophene...

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