Solid-State Conformation, Molecular Packing, and Electrical and Optical Properties of Processable β-Methylated Sexithiophenes

Newly synthesized sexithiophenes, di- and tetramethylated at the β-positions, are shown to be soluble
and processable compounds, giving single crystals suitable for X-ray structure determination. The molecular
packing was characterized in terms of crystal cohesion and short CH··· S and CH···π intermolecular
distances. In particular, the dimethylated sexithiophene displayed very compressed molecular packing and a
thin film field effect transistor, fabricated with this material, was characterized by high charge mobility [2 ×
10-2 cm2/(V s)]. The tetramethylated compound crystallizes at room temperature in two different systems and
with different conformations. The conformational polymorphs, which are easily interconverted at room
temperature, are characterized by different wavelengths of light emission and excitation decay rates.